Time for another "car won't start" thread

[AgentDL]

Drove car for 10 minutes. Parked. Walked into store for 6 minutes. Came out, noticed I had left headlights on (it's raining). Car started no problem, then died after 5 seconds, then wouldn't start again. Wants to turn over but can't. Coincidentally, I was at an auto parts store and asked for a jump. After using a booster pack the volt meter was up around 10-11 but still no start. Had a friend come over to try jumping using his car for additional juice. Volt meter now up to 12-13 but still no dice.

Hagerty Roadside Assistance is on its way to get me to a friend's warehouse where I can take a closer look and have tools.

Where to start with diagnosis?

Thanks in advance.
~
Doug

[AgentDL]

Also FYI car has a new fuel accumulator as it was having hot start issues during final testing at DMC-FL before I took delivery.

[David T]

Also FYI car has a new fuel accumulator as it was having hot start issues during final testing at DMC-FL before I took delivery.

My first thought would be to fully charge and test the battery. If the battery voltage is too low the ignition ECU won't work. Jumping a dead battery with a battery pack may not be enough to get it going, especially of the battery pack is not fully charged and the battery is very dead.

[AgentDL]

My first thought would be to fully charge and test the battery. If the battery voltage is too low the ignition ECU won't work. Jumping a dead battery with a battery pack may not be enough to get it going, especially of the battery pack is not fully charged and the battery is very dead.

We did try jumping with another vehicle after no success with the battery pack.

[DMCMW Dave]

What do you mean by "wants to turn over"?

Typically "turn over" means the starter engages and turns the engine.

"Does not fire" means that the engine turns over but never starts. This could be ignition or fuel.

"Does not turn over" means that the starter clicks but the engine does not turn at all. OR the starter may be dead quiet. This is typically the starter, battery, ignition switch, or an automatic that's not quite all the way in park.

If it's "turns over but does not fire" you should check the RPM relay and the connections to the ballast resistors and the small wires on the ignition coil. Those are the most common things that make an engine not run.

[AgentDL]

What do you mean by "wants to turn over"?

Typically "turn over" means the starter engages and turns the engine.

"Does not fire" means that the engine turns over but never starts. This could be ignition or fuel.

"Does not turn over" means that the starter clicks but the engine does not turn at all. OR the starter may be dead quiet. This is typically the starter, battery, ignition switch, or an automatic that's not quite all the way in park.

If it's "turns over but does not fire" you should check the RPM relay and the connections to the ballast resistors and the small wires on the ignition coil. Those are the most common things that make an engine not run.

Dave, my bad. I'm still learning "car stuff" and cutting my teeth on this new DMC of mine! To clarify, the car turns over but does not fire.

Once I got the car flat-bedded to where I could work on it (thank you Hagerty), I did quite a bit of rooting around while referring to the workshop and technical manuals, as well as your advice.


Ballast resistor connectors look good.
I didn't open up the RPM relay, but can confirm that it does *click* when I attempt to start the car. Does this mean it's functioning?
Wires on the ignition coil look good. Furthermore, we popped a spark plug into the lead to test it and and confirmed that it *does spark*.


If I'm not mistaken, this means that I need to start looking at other components of the fuel system. Can someone confirm and give me an idea of what to look at next? If whatever comes next requires some serious mechanical know-how, I'm going to need to get a mechanic involved.

Thanks as always.

[David T]

Dave, my bad. I'm still learning "car stuff" and cutting my teeth on this new DMC of mine! To clarify, the car turns over but does not fire.

Once I got the car flat-bedded to where I could work on it (thank you Hagerty), I did quite a bit of rooting around while referring to the workshop and technical manuals, as well as your advice.


Ballast resistor connectors look good.
I didn't open up the RPM relay, but can confirm that it does *click* when I attempt to start the car. Does this mean it's functioning?
Wires on the ignition coil look good. Furthermore, we popped a spark plug into the lead to test it and and confirmed that it *does spark*.


If I'm not mistaken, this means that I need to start looking at other components of the fuel system. Can someone confirm and give me an idea of what to look at next? If whatever comes next requires some serious mechanical know-how, I'm going to need to get a mechanic involved.

Thanks as always.

What you are describing can be caused by an ignition problem or a fuel problem. Make sure the fuel pump is running. A quick and "dirty" way to check is to squirt a LITTLE bit of Ether into the intake. If it fires at all you have a fuel problem. If it won't fire at all it is an ignition problem. If you think you have spark on the plugs the most common fuel system problem is the fuel pump not running. Some of the more common reasons the fuel pump won't run are:

Blown or melted fuse #7
Bad connection on the fuel pump or the plug right by the fuel pump
Bad connection at the harness plug up in the washer fluid bucket
Bad inertia switch (make sure it has a white splotch of paint on it and it is mounted to the side NOT on the Lambda counter).
"Creative" wiring in the fuel pump circuit to bypass the inertia switch or sometimes an engine kill circuit for a car alarm.
Bad RPM relay (the solder joints are notorious for cracking, ask Elvis).

The fuel pump can also be running but the motor won't run. You could be low on fuel or the pick-up hose can be kinked, collapsed, or cut. A good place to start is to get to the fuel pump and see if you have 12 volts at the terminals. You may have to jumper the RPM relay to make it easier to test.

[Rich]

Dave, my bad. I'm still learning "car stuff" and cutting my teeth on this new DMC of mine! To clarify, the car turns over but does not fire.

Once I got the car flat-bedded to where I could work on it (thank you Hagerty), I did quite a bit of rooting around while referring to the workshop and technical manuals, as well as your advice.

If I'm not mistaken, this means that I need to start looking at other components of the fuel system. Can someone confirm and give me an idea of what to look at next? If whatever comes next requires some serious mechanical know-how, I'm going to need to get a mechanic involved.

You are correct to be aiming at fuel given the symptoms.

There are two quick ways to check that, both needing no tools or gauges. Or mechanics.

1. Quickie fuel pressure check: With air cleaner off and after a failed attempt at starting push down lightly on the air meter/flap in the middle of the fuel injection body, the big silver disk on a pivot. If it falls away with light pressure then you need to sort out why fuel pressure is low. Normal behavior after a start attempt is firm pressure. You can move the flap but you have to push.
2. Quickie fuel-sub test: With a helper at the wheel - and again with the air box off - attempt to start the car while giving a couple of puffs of starting fluid sprayed down past that same air flap after the cranking begins (the flap valve will open bit). Follow directions on the can. If the engine starts then it's another clue that something needs attention fuel system-wise.

You do not need to do Test 2 if Test 1 fails. But if unsure then do both.

Now seeing I wrote this while David T wrote as well. Agreeing on all his points.

[djdogbone]

Sounds like an Ignition coil issue.

[AgentDL]

Thanks guys. As I mentioned, we attached a spark plug to the ignition coil and it did spark when trying to start the car. Isn't that conclusive evidence that it's NOT an ignition problem, and thus most likely a fuel problem?

Also, if the RPM relay *clicks* when trying to start the car, does this mean that it's functioning?

Seems the most reasonable next move is to get at the fuel pump and check on the items David T mentioned.

[nullset]

If you can find the RPM relay in the electrical compartment, you can try removing and jumping across it. Connect a wire from the brown wire in that connector to the one diagonal from it. You'll hear the fuel pump running. If you don't, then there is a problem with the wiring to the fuel pump.

With the RPM relay jumped, the car should start. If it starts with the relay jumped, then that could indicate a bad RPM relay.

[AgentDL]

Got into the fuel pump compartment. Confirmed that there is no activity from the fuel pump when the engine is cranked - no hum, no vibration, no nothing. Put a test lamp on the fuel pump terminals and it is getting juice when the engine is cranked.

Does this conclusively eliminate any problems leading up to the fuel pump, meaning that the RPM relay, fuses, inertia switch, and electrical connections are all in good order, and the most likely culprit is that the fuel pump itself took a sh*t?

EDIT: I got this car two and a half weeks ago from DMC-FL, and I just noticed that the multiple-page restoration work order does include fuel pump work, and everything in there looks pretty good and shiny... So next step is a call over to them to see if they have any insight.

[djdogbone]

No noise from the pump for sure confirms your problem. A lamp on the terminals should be ok...just watch out for fumes- I'd rathere check the relay side myself. Potential Sparks and all would be a concern to me.

[DMC5180]

You barely drove it off the lot, surely they have a 30 day warranty for this kind of thing. I understand it's a used car which is typically sold AS-IS. these aren't your average used car though. If it looks as clean inside the tank as you say they must have at least checked the tank for contamination. Fuel pumps are electric motors it either works or it doesn't. I'm sure it was operating fine when they gave it their blessing. Unfortunately they can fail at any time without notice.

[AgentDL]

You barely drove it off the lot, surely they have a 30 day warranty for this kind of thing. I understand it's a used car which is typically sold AS-IS. these aren't your average used car though. If it looks as clean inside the tank as you say they must have at least checked the tank for contamination. Fuel pumps are electric motors it either works or it doesn't. I'm sure it was operating fine when they gave it their blessing. Unfortunately they can fail at any time without notice.

Where did you put the test light probe to check for power? The two terminals on the pump or at the connector just before the pump? DO you have the OE pump or the NEW DMCH modular pump (white top).

I didn't look inside the tank but I'm positive they checked it. I meant that the fuel pump compartment looks good and sorted - nice shiny brackets, brand new rubber boot, etc. The test light probes were put ON the pump itself. I don't know which pump it has. The top is like a gold/bronze color, not white.

DMC-FL opens in a few minutes and I'll be calling them to get their input.

[DMC5180]

Great, you have the OE fuel pump. Good luck. DMC-FL is open on a Saturday?

[AgentDL]

Great, you have the OE fuel pump. Good luck. DMC-FL is open on a Saturday?
Thank you. Yes, they're open 10am-3pm. :nana2:

[DMC5180]

Thank you. Yes, they're open 10am-3pm. :nana2:


How far away are they from you?

[AgentDL]

How far away are they from you?

100 miles, +/- 2 hour drive.

[DMC5180]

100 miles, +/- 2 hour drive.

HMM, let us know how they deal with it? Not like you can just hop in and drive over there to kit it fixed:bang:.

[AgentDL]

HMM, let us know how they deal with it? Not like you can just hop in and drive over there to kit it fixed:bang:.

Can't pop over there, but if I ever have serious trouble, I can quickly/easily/cheaply get it flat-bedded over there, which is good. Will keep you posted. About to call them.

[AgentDL]

DMC-FL service department is closed today. I forgot that my first visit over there was on a Saturday to see Tony, and my second visit, when the shop was open, was on a Tuesday. For some reason I had it mixed up in my mind.

Car's staying put until Monday, I guess. Shame too, because I'm wearing my Doc Brown costume for an event tonight and would've loved to roll up in the car. :thumbdown:

[David T]

DMC-FL service department is closed today. I forgot that my first visit over there was on a Saturday to see Tony, and my second visit, when the shop was open, was on a Tuesday. For some reason I had it mixed up in my mind.

Car's staying put until Monday, I guess. Shame too, because I'm wearing my Doc Brown costume for an event tonight and would've loved to roll up in the car. :thumbdown:

If you have power and ground on the fuel pump and it isn't running that is pretty conclusive evidence that the pump is bad. If you can get your hands on a pump and put it in you should be able to drive the car.

[nullset]

If you want to do an experiment, and have a 12V battery (or a spare car battery ) handy, you can try disconnecting the fuel pump's power, and powering it directly from a battery.

That will determine wether the pump is the problem or not.

It could also be a bad ground, or a failure of the inertia switch ( if your car still has that)

--buddy

[SS Spoiler]

I've heard that by quickly reversing the wires to the pump several times you can sometimes
dislodge a jam. Seen it done.

[DMC5180]

If the test light was used across fuel pump terminals and it lights up that would confirm the ground side circuit (inertia switch).

[nullset]

If the test light was used across fuel pump terminals and it lights up that would confirm the ground side circuit (inertia switch).

Not necessarily - it could have enough current to run the test light, but not enough current to run the pump. A bad ground is like having a small resistor between the negative wire and the battery.

I'd also look at the voltage across the pump with a multimeter.

Alternatively, you could add an extra ground connection, but it's best to diagnose first.

[AgentDL]

Found out that DMC-FL didn't replace the fuel pump. They replaced the upper boot and CPR, and the pump passed pressure and rest tests. So it looks like this likely fuel pump failure was just an unlucky coincidence.

I am going to do the "quickie fuel pressure test" recommended by Rich above, and if there's no pressure, I will need to order a new fuel pump. Will search the site for chatter about those, and maybe start a new thread. :biggrin:

[David T]

I've heard that by quickly reversing the wires to the pump several times you can sometimes
dislodge a jam. Seen it done.

Even if this works and you are lucky enough to get the pump running I would replace it as soon as I could.

[AgentDL]

Resurrecting this thread as I am having issues again.

RECAP:
Car wouldn't start about 6 weeks ago - would turn over but not fire. In diagnosing the issue, I confirmed:
- Battery was functioning and charged
- Ignition system working - sparks getting to the cylinders
- RPM relay functioning
- Inertia switch functioning
- Power coming to the fuel pump
- Gas in the tank (hurrr durrr)
- Fuel pump NOT FUNCTIONING

So.... I replaced the fuel pump. By the grace of all the gods, the replacement went smoothly in 1hr45m, and the car started up and ran beautifully... for two weeks.

Now, it's not starting again, and experiencing the same symptoms as before - turns over but doesn't fire.

This time, I have confirmed so far:
- Battery charged
- Gas in tank
- Power coming to the fuel pump
- Fuel pump IS FUNCTIONING (used a battery charger on the electrical terminals and it started whirring)

Any suggestions on further diagnosis given that I've already replaced the fuel pump, and it's working now? Should I go back and check the ignition system, RPM relay, and inertia switch again, or should I be looking for something else that might be more specifically related to the fact that I just swapped out the fuel pump and it was working for a few weeks?

TIA.

[Bitsyncmaster]

Try the RPM relay jumper to see if it starts. Testing the fuel pump via external power does not verify it runs when your trying to start the engine.

[AgentDL]

Try the RPM relay jumper to see if it starts. Testing the fuel pump via external power does not verify it runs when your trying to start the engine.
We also used a test light to test the power going TO the fuel pump... So if there's power going TO the fuel pump when I try to start the engine, and the fuel pump fires up from external power, can we then conclude that the fuel pump is running when we try to start the engine? If not, why not?

[Bitsyncmaster]

We also used a test light to test the power going TO the fuel pump... So if there's power going TO the fuel pump when I try to start the engine, and the fuel pump fires up from external power, can we then conclude that the fuel pump is running when we try to start the engine? If not, why not?

Just that the RPM relays have been known to get broken solder joints. That could be an intermittent that could work fine for weeks and then show up randomly. The RPM relay jumper test would just prove that you have other problems.

[David T]

Just that the RPM relays have been known to get broken solder joints. That could be an intermittent that could work fine for weeks and then show up randomly. The RPM relay jumper test would just prove that you have other problems.

It is also quite possible that the old pump was drawing a lot of current, more than it should. That would overheat the RPM relay (and everything else in the circuit) and cause other, future problems such as you are now having. Since it can't hurt and is pretty easy to do, jumping the RPM relay to see of the car starts is no big deal. Just remember, if you do jumper the RPM relay you are probably not hooking up the wire to the CPR heater so the car won't warm up quite the way it should. Again, no big deal if you are only checking to see if the car starts. Refer to D:04:06 to see what you are doing. Jumper G (green) to WP (white/purple) terminal 30 to terminal 87. Not a good idea to drive around that way but OK for testing purposes. Using the G wire the pump won't run when the key is off. If you use the N wire (brown) the pump will run ALL the time (or at least till the battery goes dead).

[Bitsyncmaster]

It is also quite possible that the old pump was drawing a lot of current, more than it should. That would overheat the RPM relay (and everything else in the circuit) and cause other, future problems such as you are now having. Since it can't hurt and is pretty easy to do, jumping the RPM relay to see of the car starts is no big deal. Just remember, if you do jumper the RPM relay you are probably not hooking up the wire to the CPR heater so the car won't warm up quite the way it should. Again, no big deal if you are only checking to see if the car starts. Refer to D:04:06 to see what you are doing. Jumper G (green) to WP (white/purple) terminal 30 to terminal 87. Not a good idea to drive around that way but OK for testing purposes. Using the G wire the pump won't run when the key is off. If you use the N wire (brown) the pump will run ALL the time (or at least till the battery goes dead).

I would not run the fuel pump on that 19 AWG wire even for testing. Use the brown wire jumpered to the white/purple wire with a jumper and remove it when your done.

[Horsebox]

Does the fuel pump prime when you turn the ignition to the second stop? You should be able to hear it.

Sorry if you've already stated this but I didn't read it that you had.

[DMC5180]

Does the fuel pump prime when you turn the ignition to the second stop? You should be able to hear it.

Sorry if you've already stated this but I didn't read it that you had.

It does IF you have the RPM relay with that feature. The problem is both types (priming & non-priming) relays were used in Production.

[AgentDL]

Did some more testing today and kind of at a loss.

With the RPM relay in place, the car does not start.

With the RPM relay jumped W/P to brown, the car still does not start, and the fuel pump does not hum... BUT when the electrical connection at the fuel pump is disconnected and a test light is used on the incoming electrical connector near the fuel pump, the test light DOES light up.

When applying a power source directly to the fuel pump, it DOES come to life.

I'm REALLY confused, and it might be because I haven't been as systematic as possible with my testing even though I've messed with the fuel pump, RPM relay, and ignition systems.

So... (a) does anyone have any ideas as to what it could be based on this info, or (b) can you recommend a step-by-step testing procedure (i.e. try this, then this, then this, then this, then this) that might help me make better sense of the information?

P.S. Could it possibly have to do with my battery not having enough juice, or possibly the electrical connectors at the fuel pump being faulty or dirty?

[David T]

Test for ground at the pump. It could be where you get 12 volts at the pump BUT there is no ground to complete the circuit. The ground is completed through the wiring harness, the inertia switch and then to ground. You may have a bad connection or a bad inertia switch. You can temporarily run a wire from the ground connection on the pump directly to the negative terminal on the battery.

[AgentDL]

Test for ground at the pump. It could be where you get 12 volts at the pump BUT there is no ground to complete the circuit. The ground is completed through the wiring harness, the inertia switch and then to ground. You may have a bad connection or a bad inertia switch. You can temporarily run a wire from the ground connection on the pump directly to the negative terminal on the battery.

OK, that makes sense as a missing piece that goes with my results so far. So if I understand you correctly (I'm new to all this car stuff), to test this theory, I want to run a wire from the ground connection on the fuel pump all the way to the black terminal on the battery, and then see if the car starts? If it does, then what do I need to do? And if it doesn't?

Thanks for all your help in this thread btw. :thumbup:

[David T]

OK, that makes sense as a missing piece that goes with my results so far. So if I understand you correctly (I'm new to all this car stuff), to test this theory, I want to run a wire from the ground connection on the fuel pump all the way to the black terminal on the battery, and then see if the car starts? If it does, then what do I need to do? And if it doesn't?

Thanks for all your help in this thread btw. :thumbup:

If, by hooking up the temporary wire, the pump runs and the motor starts, it means there is no continuity from the pump to ground. Make sure you ground the - ground terminal on the pump to the battery - terminal. Making a mistake can cause damage. If this gets the pump running the next place to look is the inertia switch. It should be on the side of the foot well (not on the Lambda counter) and it should have a splotch of white paint on it. The plunger should be down. At some point you may need to get some help from someone who is familiar with a multi-meter and would be better able to trouble-shoot this.

[AgentDL]

Test for ground at the pump. It could be where you get 12 volts at the pump BUT there is no ground to complete the circuit. The ground is completed through the wiring harness, the inertia switch and then to ground. You may have a bad connection or a bad inertia switch. You can temporarily run a wire from the ground connection on the pump directly to the negative terminal on the battery.

Just did this. No action at the fuel pump.

...Now what? Argh!

[DMC5180]

How did you ground the negative side of the pump?

Do you have DVM? If yes, you need to confirm the ground wire has continuity to the frame. Disconnect the fuel pump harness connector. Set your DVM to the audible / diode check position. Place one probe In the black wire terminal socket of the chassis harness. Touch the other probe to a bolt head threaded into the frame. Theoretically the top of the body hold down bolt should work or you can remove the access panel over the brake fluid reservoir to gain access to easy ground points on the frame. You should get an audible beep if you have continuity.

[AgentDL]

How did you ground the negative side of the pump?

Do you have DVM? If yes, you need to confirm the ground wire has continuity to the frame. Disconnect the fuel pump harness connector. Set your DVM to the audible / diode check position. Place one probe In the black wire terminal socket of the chassis harness. Touch the other probe to a bolt head threaded into the frame. Theoretically the top of the body hold down bolt should work or you can remove the access panel over the brake fluid reservoir to gain access to easy ground points on the frame. You should get an audible beep if you have continuity.

Per my previous post, I followed David T's instructions and ran a ground wire directly from the negative side of the pump to the negative terminal on the battery, and the pump still didn't kick on when I tried to start the car. Wouldn't this unsuccessful bypass test suggest that the ground wire is NOT the issue?

[Horsebox]

I agree with you that your ground is OK. Here's a couple of things you can do quickly.

Pull fuse 7 and clean the terminals with sand paper or a small modelling file. Do the same for the RPM relay terminals. Then see if your pump runs.

I've just been through the whole wiring of my fuel pump circuit and found many losses due to bad connections. With engine running and system voltage 14V I was only getting 10V across the pump. It could be your car is similar, but the voltage at the pump as shown by your test lamp simply collapses under the load of the pump when it tries to run.

I would also get hold of a separate 12V source to prove that the pump runs in situ. Then you know you have a problem on the power side, and you will have to systematically go through the connectors.

Don't panic about it. When you eventually find the problem it will be staring you in the face!

[Bitsyncmaster]

Per my previous post, I followed David T's instructions and ran a ground wire directly from the negative side of the pump to the negative terminal on the battery, and the pump still didn't kick on when I tried to start the car. Wouldn't this unsuccessful bypass test suggest that the ground wire is NOT the issue?

Yes that would verify the ground side is not the only issue (if your wire was 16 AWG or larger). So you have proven the pump will run with +12 volts on the + terminal and ground on the - terminal with your early power test.

You also tried the jumper (RPM relay) and did not get the pump to run.

So either you have two bad connections (ground and power) or you still have not found the connection break of the +12 volts.

Jumper the RPM relay again and run your wire (- side of pump) to ground side of the battery. You don't even need the key on to test. If the pump does not run, you have a bad connection on the + circuit of the pump. Verify that and we can suggest testing from there.

[DMC5180]

Not if you verified the you had 12 v at the connector earlier and you confirmed the pump ran with external power in a previous post. By all accounts your pump should have run. I'd go back and check your connections again.

[Rich]

Not if you verified the you had 12 v at the connector earlier and you confirmed the pump ran with external power in a previous post. By all accounts your pump should have run. I'd go back and check your connections again.

+1

This is the situation?
1. Pump runs with direct 12V+ to it. Voltage not measured but likely >11V+ (proves pump is not dead and proves ground circuit OK)
2. Test lamp glows when trying to start. (proves that there is not a complete open circuit on the positive feed)
3. Pump does not run when trying to start.

Verify and correct any part of this summary.

If all true then the combo suggests low voltage at pump. Low voltage is <11V, let's say. Somebody can correct that.

Low voltage to pump can be due to several causes. Get a meter on the connection closest to pump and check voltage both with key-on and also during engine cranking. If low then work your way back upstream on components/connections til you find the problem.

If not low then other things come to mind....

[DMC5180]

I'd skip the engine cranking part for now and use the rpm relay jumper again. Once the circuit is confirmed or corrected you can go back to the crank test.

[AgentDL]

OK everyone, time for another update. I STILL can't make heads or tails of this...

- The fuel pump comes to life and hums when connected with a 12V+ external power source.

When testing voltage in this fashion: (http://i.imgur.com/BgDAqhm.jpg)
- 0.00 volts with RPM relay connected and key in ON position or when cranking the engine
- 0.00 volts with RPM relay jumped W/P to green and key in ON position or when cranking the engine
- 11.98 volts with RPM relay jumped W/P to brown and no key

So I only get power at the connection AT ALL with the RPM relay jumped W/P to brown, so I did more voltage tests around the fuel pump with the RPM relay jumped W/P to brown.

Putting the probe here (http://i.imgur.com/BgDAqhm.jpg) gave me a 11.98V reading. (Yes, same picture as above.)

With the connection plugged together (presumably with 12V coming in), the fuel pump does not make any noise at all, and...
Putting the probe here (http://i.imgur.com/0B1hdCF.jpg) gave me a 9.5V reading.
Putting the probe here (http://i.imgur.com/9FxnUsQ.jpg) gave me a 9.0V reading.
Putting the probe here (http://i.imgur.com/Z6L1ADS.jpg) gave me a 9.0V reading.

Is it possible I have a bad connection there AND a bad RPM relay? What can I do about the connection? Also, how am I getting a 12V reading from the wiring harness when unplugged, but only a 9.5V reading when it's plugged in and I put the probe in the back end? (hehe)

[Bitsyncmaster]

With the connector "pulled" you don't have any load so even a bad connection will show full voltage.

When connected, the pump is loading the circuit so your seeing all the voltage drops. Your pump should run even at 9.0 volts as a rule. But you are not testing the voltage drop on the ground side which may bring the pump voltage down to 7 or 8 volts which may not run the pump.

Leave the pump connected and the RPM relay jumpered and test the voltage back on that RPM relay jumper. If it reads 9 volts, your bad connection is before the RPM relay or your battery is bad.

[AgentDL]

With the connector "pulled" you don't have any load so even a bad connection will show full voltage.

When connected, the pump is loading the circuit so your seeing all the voltage drops. Your pump should run even at 9.0 volts as a rule. But you are not testing the voltage drop on the ground side which may bring the pump voltage down to 7 or 8 volts which may not run the pump.

Leave the pump connected and the RPM relay jumpered and test the voltage back on that RPM relay jumper. If it reads 9 volts, your bad connection is before the RPM relay or your battery is bad.

Thanks Dave. I read your post and then did the following:

1. Replaced the battery with another known fresh battery. Tried to start the car, no dice.
2. Put in RPM relay jumper W/P to brown. No hum at the fuel pump, tried to start the car, no dice. Got a 12.30V reading testing like this (http://i.imgur.com/BgDAqhm.jpg) and a 9.5V reading testing like this. (http://i.imgur.com/Z6L1ADS.jpg)
3. Removed the jumper wire, turned key to ON position. Got a 12.30V reading at terminal 30 of the RPM relay connector. Put the voltmeter at terminal 87 of the RPM relay connector, cranked the engine, and got a 0.00V reading.

[Bitsyncmaster]

Since you replaced the battery, it looks like you have one or more bad (marginal) connections in the fuel pump circuit.

Test one:
With fuel pump connector plugged in and jumper (brown to white/purple) in the RPM relay connector, read the voltage on that brown wire at the RPM connector (meter ground on battery -). If that reading is low then a bad connection exits between the battery + and that brown wire (brown is always connected to battery plus).

Remove that RPM relay jumper and report back with your reading and I will suggest the next thing to do.

I assume you have made a jumper for the RPM relay with the 1/4" (male) pins that you can buy at most auto parts stores and using at least 16 AWG wire. Every DeLorean owner should carry one or more of those jumpers with him in the car. Some people say use a paper clip for the jumper but that will just waste time and maybe damage pins in the connector.

[AgentDL]

Test one:
With fuel pump connector plugged in and jumper (brown to white/purple) in the RPM relay connector, read the voltage on that brown wire at the RPM connector (meter ground on battery -). If that reading is low then a bad connection exits between the battery + and that brown wire (brown is always connected to battery plus).
I did test the brown wire terminal (30) with the relay jumper in and got 12.30V.


I assume you have made a jumper for the RPM relay with the 1/4" (male) pins that you can buy at most auto parts stores and using at least 16 AWG wire.
That is correct. :-)

[Bitsyncmaster]

I did test the brown wire terminal (30) with the relay jumper in and got 12.30V.

But you did that test without the pump connected (loading the circuit), hence you read the battery voltage without any voltage drops.

[AgentDL]

But you did that test without the pump connected (loading the circuit), hence you read the battery voltage without any voltage drops.

Put my other battery back in (since that wasn't the issue). Plugged the fuel pump in and jumped the relay connector W/P to brown. Got almost 10.5V both at the brown wire and at the fuel pump.

[Bitsyncmaster]

Put my other battery back in (since that wasn't the issue). Plugged the fuel pump in and jumped the relay connector W/P to brown. Got almost 10.5V both at the brown wire and at the fuel pump.

Now you have verified the connections from the RPM relay to the fuel pump are good. We need to read the voltage on the two pump terminals or read the "ground" side referenced to the battery -.

If that ground side is not dropping much voltage, I would say your fuel pump needs replacement. I seem to remember testing my fuel pump would work down to 7 volts (pump + to pump -) but that does not say all pumps would work at that low voltage.

FYI
Even though my pump ran with 7 volts, I still did all the voltage drop testing to fix marginal connections. I was loosing about 1.0 volts at a fuse crimp, another 0.5 volts at one pin of that two pin connector and about 0.3 volts at the inertia switch ground. After fixing all those connections, I drop less than 1 volt over the stock wire harness.

[AgentDL]

Hi folks, back with another update on this.

Once my diagnostics got upstream to the RPM relay, I reached out to DMC-FL and spoke with technician Matt over there. We discussed what I had already done. He asked me to turn the key in the ignition and report back to him with the behavior of the tachometer needle. On cranking, the needle barely moved (up to maybe 100rpm) and just stayed there during the crank. Matt said that it should go up to 300-400rpm and bounce a little bit, and surmised that maybe the tach signal wasn't coming through from the distributor, thereby not engaging the entire works from the RPM relay downward in order to kick the fuel pump on. I checked the tach signal plug with a volt meter, got no reading, and ultimately decided to send the car over to DMC-FL as the issue had now officially gone above my pay grade.

While trying to find a transport option to get the car over to DMC-FL 115 miles away, I got lucky in that one of their employees was at a car auction with a trailer here on the east coast of FL, and being that I'm on his way back to Bonita Springs, we arranged for him to come pick my car up and bring it back across for a very reasonable price.

Anyway, got the car over there, and lo and behold, the culprit was the $#^$@#$@#&$@ FUEL PUMP! I guess the damn thing was defective, and when they replaced it, they got the car running. I don't want to think about it too much on a technical level for fear of my head exploding. It is what it is, and it all adds up because I didn't find any other real faults all the way upstream.

Took advantage of having the car over there to have them address a few other minor issues, and will be driving over to Bonita Springs on Saturday to pick up my car with a relatively clean slate... for now! Crossing my fingers to get some good use out of it and hope that it doesn't become inoperable for any other silly reason anytime soon.

[David T]

Hi folks, back with another update on this.

Once my diagnostics got upstream to the RPM relay, I reached out to DMC-FL and spoke with technician Matt over there. We discussed what I had already done. He asked me to turn the key in the ignition and report back to him with the behavior of the tachometer needle. On cranking, the needle barely moved (up to maybe 100rpm) and just stayed there during the crank. Matt said that it should go up to 300-400rpm and bounce a little bit, and surmised that maybe the tach signal wasn't coming through from the distributor, thereby not engaging the entire works from the RPM relay downward in order to kick the fuel pump on. I checked the tach signal plug with a volt meter, got no reading, and ultimately decided to send the car over to DMC-FL as the issue had now officially gone above my pay grade.

While trying to find a transport option to get the car over to DMC-FL 115 miles away, I got lucky in that one of their employees was at a car auction with a trailer here on the east coast of FL, and being that I'm on his way back to Bonita Springs, we arranged for him to come pick my car up and bring it back across for a very reasonable price.

Anyway, got the car over there, and lo and behold, the culprit was the $#^$@#$@#&$@ FUEL PUMP! I guess the damn thing was defective, and when they replaced it, they got the car running. I don't want to think about it too much on a technical level for fear of my head exploding. It is what it is, and it all adds up because I didn't find any other real faults all the way upstream.

Took advantage of having the car over there to have them address a few other minor issues, and will be driving over to Bonita Springs on Saturday to pick up my car with a relatively clean slate... for now! Crossing my fingers to get some good use out of it and hope that it doesn't become inoperable for any other silly reason anytime soon.

Go back and reread post #50. At that point you said the pump ran. If it was bad how did it run then? I hope they got the problem fixed but right now I have my doubts. Drive it a while and see what happens.