Fuel Pressure Loss

[Ricker]

The long my car sits without running, the more time I have to keep turning the key to get the fuel pump to get fuel to the engine and build up the pressure (the fuel pump only runs for a second or two before it stops). Once the fuel is there and pressure is up the car starts perfectly hot or cold. Question number 1 - I had the fuel injectors checked and cleaned, the fuel is not leaking there. Where else should I look? (I do have the new modern fuel pump installed for some time) Question number 2 - Is there a way the jumper something out so when the key is turned on the fuel pump runs continuously? Question number 3 - Is this bad for the fuel pump then?

[Bitsyncmaster]

I ran a test to when control pressure would reach 40 PSI (warmed up engine) and it was less than one second running the OEM pump and OEM (large) accumulator. If you find yours takes longer to reach that pressure first thing I would check if the accumulator is leaking. Also check the voltage at the fuel pump (jumper the RPM relay).

[Ricker]

I ran a test to when control pressure would reach 40 PSI (warmed up engine) and it was less than one second running the OEM pump and OEM (large) accumulator. If you find yours takes longer to reach that pressure first thing I would check if the accumulator is leaking. Also check the voltage at the fuel pump (jumper the RPM relay).

When you say the fuel accumulator is leaking do you mean externally?

[Bitsyncmaster]

When you say the fuel accumulator is leaking do you mean externally?

It would leak into the return line to the tank if the bellows inside were leaking.

You can pull that return hose off and run the pump to see if fuel is flowing from the return.

[Rich]

It would leak into the return line to the tank if the bellows inside were leaking.

You can pull that return hose off and run the pump to see if fuel is flowing from the return.

Note to those wondering which of the 3 accumulator connections is the "safety fuel return line", the one that should be pulled to check for a busted accumulator diaphragm, it's the single hose on the end of the accumulator closest to the engine.

That hose is normally dry. Its only function is to direct any fuel that leaks past the internal diaphragm safely forward into the fuel tank. Until the accumulator is replaced.

[Ricker]

It would leak into the return line to the tank if the bellows inside were leaking.

You can pull that return hose off and run the pump to see if fuel is flowing from the return.

Understand. Will do so when I can get under there. Kinda tough place to get to.

[82DMC12]

Understand. Will do so when I can get under there. Kinda tough place to get to.

This problem could also be caused by a failed check valve at the fuel pump. There's supposed to be a check valve either integrated in the neck of the pump (long neck style) or it screws into the neck (short style).

[Jonathan]

Try this instead: confirm the adjustment of your idle speed motor microswitch. This is the one that gets actuated when the throttle spool and arm are at rest. There are two adjustment pegs on the lever arm. Lower one corresponds to the rest position of the butterfly valves inside the manifold (you can't see them when everything is assembled). The upper adjustment peg engages the idle speed motor microswitch. You want that microswitch to click just prior to the arm and throttle spool coming to rest. You can listen while the engine is off and you are moving the throttle spool with your hand. Get it so the microswitch clicks at the exact moment the arm stops at rest, then turn it in a half turn more (so it's engaged at rest versus not engaged). Your lack of apparent fuel pressure (while not actually measuring the fuel pressure) might be a lack of air and not fuel. Give it a try and report back. It's easy to put it back the way it was if you're in doubt. Just make note of where it was when you started.

[David T]

When you are checking the accumulator you must remove the hose from it and block it off. Otherwise fuel returning to the tank from the PPR will come out. If fuel comes out of the accumulator with the "safety" hose removed it means the diaphragm inside is bad and the accumulator should be replaced otherwise you will have problems restarting the car when it is hot. The temporary "fix" is to do the "plug swap" to get the motor started till you can replace the accumulator.

[Helirich]

The long my car sits without running, the more time I have to keep turning the key to get the fuel pump to get fuel to the engine and build up the pressure (the fuel pump only runs for a second or two before it stops). Once the fuel is there and pressure is up the car starts perfectly hot or cold. Question number 1 - I had the fuel injectors checked and cleaned, the fuel is not leaking there. Where else should I look? (I do have the new modern fuel pump installed for some time) Question number 2 - Is there a way the jumper something out so when the key is turned on the fuel pump runs continuously? Question number 3 - Is this bad for the fuel pump then?

When you say “the longer it sits” , how long are we talking? If you are talking hours, look at the accumulator, but if you are talking weeks, I don’t think that’s your problem. It may be a weak pump or somewhat clogged fuel filter.

When you say “I have to keep turning the key”, do you mean cranking the engine? If so, try just turning the key on and off (without cranking). Every time you turn it on, it should run the pump for a few seconds. That way the pressure comes up without heating up your starter and straining your battery.

There is a way to jumper the rpm relay and turn the pump on, but you shouldn’t have to resort to that. (It’s mainly used for trouble shooting)

[Ricker]

Thinking it was definitely the Fuel Accumulator I replaced it. Well, nothing changed. Still when it sits for a few days I still need to hit the key 20 - 30 times (not starting the starter motor) to get fuel to the motor and build up pressure. I think my next step is to replace the check valve at the fuel pump. I have a modern DMC one that is a few years old.

I also have been thinking about get a new RPM Relay and Hot Start Relay from DM-Engineering. They are solid state and do a few more things than the originals in there now.

Any comments?

[Ron]

How do you know that there is no pressure at the engine?

[Ricker]

How do you know that there is no pressure at the engine?

I really don't. I've not placed a gauge on it. I assumed that because even when you finally get fuel to the engine, and it starts it doesn't fire on all cylinder for 3 seconds or so. I may be wrong, but I am sure the engine is not get getting fuel until I keep cycling the fuel pump.

If the pressure is there but the fuel doesn't get to the engine for a while, what does that indicate? Thanks for the comments!

[Ron]

I really don't. I've not placed a gauge on it. I assumed that because even when you finally get fuel to the engine, and it starts it doesn't fire on all cylinder for 3 seconds or so. I may be wrong, but I am sure the engine is not get getting fuel until I keep cycling the fuel pump.

If the pressure is there but the fuel doesn't get to the engine for a while, what does that indicate? Thanks for the comments!I was thinking that your cold start valve might not be priming the engine.
Next time it's fully cooled off, see if the air metering plate has pressure against it after you first try to start it. If it does, press the plate down fully and quickly release it to prime the engine...(Pumping the pedal does nothing.)

Not firing on all cylinders at first could mean that some of the plugs were fuel fowled.

I suggest you put a fuel gauge set at the top of your want list.

[Ricker]

Well, I think I finally got it by trial and error. I replaced the Fuel Accumulator, a new DMC Check Valve at the fuel pump and a new DM-Engineering solid state RPM Relay. So far so good. Starts right up hot and cold. Stay tuned.

[Ricker]

Well still not fixed. However, I could not get the car to start and ran down the battery. Jumped it and it started immediately. So, I checked the battery, and it was bad, so I replaced it. Still the same thing. If I let it set for a week it takes a lot of fuel pump running to get it started. Then I let it sit and the new battery went completely dead. I'm sure I had everything off. The only thing I can think of is those stupid door plunger switches did not cut out the door lights. What does everyone use on them to extend their length? Stupid car. Eventually something will finally break and then I will know what it was.

[82DMC12]

Well still not fixed. However, I could not get the car to start and ran down the battery. Jumped it and it started immediately. So, I checked the battery, and it was bad, so I replaced it. Still the same thing. If I let it set for a week it takes a lot of fuel pump running to get it started. Then I let it sit and the new battery went completely dead. I'm sure I had everything off. The only thing I can think of is those stupid door plunger switches did not cut out the door lights. What does everyone use on them to extend their length? Stupid car. Eventually something will finally break and then I will know what it was.

You can just cut a bit of vacuum tube or something and place it in the rubber cap first before slipping it over the switch.

Regarding battery drains, you should start by taking an amp draw reading between the positive cable and the battery connection with your multimeter. Then remove fuses one at a time until the draw becomes essentially zero. Then you know what circuit to look at to find the phantom draw.

Do you have an alarm system, subwoofers, aftermarket stereo, the original door lock solenoids, or any other extra "stuff"?

I have a toggle switch wired up to fuse 12 so I can turn off the interior lights and door lights when I'm working on the car with the doors open. Or at a car show.

[Bitsyncmaster]

The stock door lock ECU draws 10 ma. and the stock clock about 5 ma. So a week should not affect battery much but if my car sits for a week or longer then it needs the CSV to fire since some of the injector lines get some air in them.

You should do as suggested to measure battery draw with the doors closed to see if it if greater than 25 ma. If your drawing above 250 ma then that would drain your battery in a week.

[todd1561]

As for the fuel pressure issue, since that still seems to be a problem(?) check the little oring on the primary pressure regulator in the fuel distributor. If it?s bad it?ll let fuel drain back to the tank too quickly.

[Ricker]

Thanks guys! Alot to check and will probably take some time but at least a direction

[Ricker]

Can someone recommend a volt/amp meter (make & model) to check the milliamps from the battery to try and locate what is causing the battery to die after 2 days? I'm just a dumb mechanical engineer and electrical is not easy for me. Any comments on how to use or be careful of is greatly appreciated. Don't want to burn it up the first try.

[todd1561]

Doesn't require anything too special, just put it in ammeter mode (with the leads in the correct sockets as well) and disconnect the + lead going to the battery. Connect one test lead to the battery + terminal and the other to the loose + battery cable. This will cause all current to go through the meter so it can be read. Most meters are fused to something around 10 amps. If you're pulling more than that with the car off something is terribly wrong. But even if you are you won't hurt the meter, just the internal fuse will blow.

Edit: as for a specific suggestions on a multi-meter. The one I use is probably over 20 years old and I'm sure not sold anymore. But I just found this on Amazon (https://www.amazon.com/AstroAI-Digital-Multimeter-Voltage-Tester/dp/B01ISAMUA6/ref=sr_1_1_sspa?keywords=digital+multimeter&qid=1669845468&s=hi&sprefix=digital+m%2Ctools%2C88&sr=1-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyVFJaSEMyNkZBRUhSJ mVuY3J5cHRlZElkPUEwMjgwMzQ2MlZWME44VUQ1M1hZMyZlbmN yeXB0ZWRBZElkPUEwMDM3NzkxM00xTTlPV1dFWFYwRCZ3aWRnZ XROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05 vdExvZ0NsaWNrPXRydWU=) and seems to have decent reviews, but I don't have any experience with it. In the case of this one you'd put the test leads in the leftmost and rightmost ports and set the dial to the yellow "10" setting just past the 3 o'clock position.

One more edit: After you test directly at the battery and confirm if there's too much drain on the whole system you can reconnect the battery as normal. Then start pulling fuses one by one and put the test leads in the fuse socket (leave the meter on the same settings as before). This will cause just that one circuit to be read for current so you can narrow down your problem.

[Ron]

An ice pick probe or taillight bulb in line with one of the battery cables should work...

[82DMC12]

I don't have one yet, but I'm going to get one shortly - a clamp amp meter is super convenient for checking amperage. Extech MA120 is a pretty good value but only has resolution down to 0.1 DC amps. Good for finding large to medium amp draws but not quite sensitive enough for the tiny trickles.

Sent from my Pixel 6a using Tapatalk

[DMC-Ron]

I"m very pleased with this one. It's small and reads DC down to milliamps.
Ron

https://www.amazon.com/gp/product/B00O1Q2HOQ/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&th=1

69262

[82DMC12]

I"m very pleased with this one. It's small and reads DC down to milliamps.
Ron

https://www.amazon.com/gp/product/B00O1Q2HOQ/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&th=1

69262

Oh nice, thanks for the heads up! It's on the Christmas list :-)

[Ricker]

I went out and bought the UNI-T UT210E multimeter.

Zeroed the unit and clipped it on the positive cable wire near the battery. With only the passenger door open on the 2A scale it read 1.105. With the door closed it read 0.042. Pulling each fuse, the only change was with fuse #11. It then read 0.011 (I believe this is the radio clock disconnected) (Note: I have all the original equipment, no adds). Therefore, I see that something is drawing 0.011 amps? What else is there to check? Do I need to place the meter with the probes to each fuse position for a more accurate reading?

On another note: I disconnected the battery after it was fully charged. With that in mind I, when reconnected it started right up after sitting for over a week. I think the issues with starting has been a weak battery? Is there something in the fuel injection system that is that sensitive to voltage/amps?

[Bitsyncmaster]

I went out and bought the UNI-T UT210E multimeter.

Zeroed the unit and clipped it on the positive cable wire near the battery. With only the passenger door open on the 2A scale it read 1.105. With the door closed it read 0.042. Pulling each fuse, the only change was with fuse #11. It then read 0.011 (I believe this is the radio clock disconnected) (Note: I have all the original equipment, no adds). Therefore, I see that something is drawing 0.011 amps? What else is there to check? Do I need to place the meter with the probes to each fuse position for a more accurate reading?

On another note: I disconnected the battery after it was fully charged. With that in mind I, when reconnected it started right up after sitting for over a week. I think the issues with starting has been a weak battery? Is there something in the fuel injection system that is that sensitive to voltage/amps?

A stock door lock unit will draw about 0.012 amps standby. The stock console clock about 0.005 ma. A radio clock another small load. So your 0.042 standby is not that bad.

It takes a long drive to charge up a low battery fully. So many short drives will not do it. You may just need to charge it once a month or use a battery tender.

By the way, I ordered one of those meters because it has such a good low scale reading for a clamp on unit.

[Ricker]

A stock door lock unit will draw about 0.012 amps standby. The stock console clock about 0.005 ma. A radio clock another small load. So your 0.042 standby is not that bad.

It takes a long drive to charge up a low battery fully. So many short drives will not do it. You may just need to charge it once a month or use a battery tender.

By the way, I ordered one of those meters because it has such a good low scale reading for a clamp on unit.

So, you don't think this amp load as measured above would drain the brand-new battery in 2 days? That's my thoughts but it did happen. I wouldn't think the battery is somehow bad? I keep thinking back to the issue I have with the dome lights - the low (4) volt on the one, 12 on the other.

Oh well, always something with this car. I'm told that's the fun of own it.

[Bitsyncmaster]

So, you don't think this amp load as measured above would drain the brand-new battery in 2 days? That's my thoughts but it did happen. I wouldn't think the battery is somehow bad? I keep thinking back to the issue I have with the dome lights - the low (4) volt on the one, 12 on the other.

Oh well, always something with this car. I'm told that's the fun of own it.

No that small drain would not kill it in two days. You must have an intermittent larger drain sometimes. Do your dome lights go on when the doors are open? Next time you stop it overnight, look to see that the dome lights are off. I remember another owner had a bad radio draining 0.2 amps but that was constant. Can't think of much else that would be an intermittent load.

You can pull fuse #12 which should kill the door, dome, glove box, trunk and engine bay lights.

[Ricker]

Ok. So, I took the new battery back to the store to be tested. It tested ok. However, I had them give me a new battery as I still think there was something wrong with it. Told them it would not hold a charge. I got a different one that is "glass packed" designed for car that sits a lot, so I was told? When putting it back in the car I checked the wire for the trickle charger. The fuse in it was blown so I didn't put it back in. The car sat for a week. Battery was still good and started up the first time. Strange machine this Delorean is! The fun never ends.

In an automatic, when in gear the idle RPM is +/-820. Place it in neutral and it jumps to +/-1200. Is this right or should they be the same despite what gear? Seems right but just checking.

[Bitsyncmaster]

In an automatic, when in gear the idle RPM is +/-820. Place it in neutral and it jumps to +/-1200. Is this right or should they be the same despite what gear? Seems right but just checking.

It should hold 775 RPM both in gear or in neutral if your stock idle system is working and your curb idle is not open to far.

If your curb idle is set to far open you would see a lower RPM with the cold engine and higher as the engine warms up. A curb idle open to far makes the idle system exceed it's control limits (idle motor is closed as far as it can go).

[David T]

If you found the fuse blown for the trickle charger it usually means the trickle charger is going bad. Yes, if the car isn't holding 775 RPM's + - 50 in park or in drive, (it doesn't matter) something needs to be fixed. The idle system, when it is working right, is supposed to be able to adjust for varying loads and hold the idle at a near constant speed.