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Thread: Car died in parking lot after running, now won't start, will crank

  1. #11
    Delorean Guru
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    You really have to narrow it down to either the fuel or electrical system. Either check for spark or squirt some Ether into the motor and see what happens. It may not be an electrical problem at all but if you keep pulling and bending the wires on the ballast resistor you WILL have a bad connection there. A wire could have come off the ignition coil, the coil could have failed, the impulse coil could be bad, it *could* be a lot of things.
    David Teitelbaum

  2. #12
    Senior Member SBL's Avatar
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    Agree with David. Fuel, ignition, or "electrical" (which I put in a third category). The starter fluid spray is an excellent test. Temporary plug swap between WUR and ISM also helpful, just don't flood it. I have seen a hole in the fuel pickup line do this, although usually preceded with some erratic running.

    For ignition, attach a plug wire to a spare pug, ground it, and look for spark, or push the wire through to see the metal connector and place it 1/4 inch from ground an look for spark, or, attach a timing light to a plug wire.

    For electrical, I am referring to fuses, relays, and now that you have been cranking it a lot, battery capacity (would start putting it on a charger or jump it). The fact that you had no fuel pump action indicates that electrical is an issue that you will need to tackle at some point anyway. While you are jumping the fuel pump, also jump the frequency valve (same relay socket), which brings it closer to reality.
    Steve Liggett
    Treasure Island, FL
    1982 automatic, VIN 10342, grey int

    Previous: VIN 5983, VIN 3670
    Who knows where my previous 1981 with 6 cylinder Chevy engine is these days (cannot find that VIN) ?

  3. #13
    Junior Member
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    Quote Originally Posted by dmcnc View Post
    Now that you have it home, what's your battery voltage on a multimeter?
    First thing I did when I brought it to the house was hook it up to my battery charger/starter. It can supply 120A continuous and 225A for start peaks as it has huge capacitors in the bottom. The thing has 2 wheels to move it around, not just a hobby charger. Hooked it up, charged it for a bit then put it to START mode which will give it up to 225A peak and 120A continuous and the car did the same thing. Crank but no turn over. I turned it back down to a maintenance mode and left it there which is how that SLA is treated normally. Voltage reads 15.2v-ish which is normal for that starter.

    Quote Originally Posted by David T View Post
    You really have to narrow it down to either the fuel or electrical system. Either check for spark or squirt some Ether into the motor and see what happens. It may not be an electrical problem at all but if you keep pulling and bending the wires on the ballast resistor you WILL have a bad connection there. A wire could have come off the ignition coil, the coil could have failed, the impulse coil could be bad, it *could* be a lot of things.
    Yes indeed. I am first trying to do the easy things hoping it is something like a loose connection that can be repaired properly once found.

    Quote Originally Posted by SBL View Post
    Agree with David. Fuel, ignition, or "electrical" (which I put in a third category). The starter fluid spray is an excellent test. Temporary plug swap between WUR and ISM also helpful, just don't flood it. I have seen a hole in the fuel pickup line do this, although usually preceded with some erratic running.

    For ignition, attach a plug wire to a spare pug, ground it, and look for spark, or push the wire through to see the metal connector and place it 1/4 inch from ground an look for spark, or, attach a timing light to a plug wire.

    For electrical, I am referring to fuses, relays, and now that you have been cranking it a lot, battery capacity (would start putting it on a charger or jump it). The fact that you had no fuel pump action indicates that electrical is an issue that you will need to tackle at some point anyway. While you are jumping the fuel pump, also jump the frequency valve (same relay socket), which brings it closer to reality.
    No erratic running at all when it was running until it suddenly quit while stopped.

    I have since jumped both the frequency valve and the fuel pump off the RPM Relay socket and still no turn over. After an unsuccessful crank the faint smell of fuel at the rear engine is there.

    But thismorning I did some diagnosis by the chart and I am stopped at checking the ignition ECU. I incorrectly assumed the black box behind the drivers seat was the ignition ECU. I had no idea there were 3 ECUs in there. My understanding is the big vertical one is the lambda ECU, the small black one is the idle ECU and then the ignition ECU is hidden below the idle ECU? I only came to realize this when the flow chart said to check Pin-15 of the ignition ECU and there was no pin-15 on the box I was looking at.

    So what I did today:

    (1) Battery is charging via the wall. Resting voltage is 14-15v.

    DeLoreanDebug001___103.jpg

    (2) Cleaned and tested ignition ballast resistor terminals. Measured 0.85R and 0.92R between each side which seems reasonably well matched for using the leads I was.

    DeLoreanDebug001___100.jpg

    DeLoreanDebug001___101.jpg

    DeLoreanDebug001___102.jpg

    (3) Tested the jump point for battery voltage just in case, measured the same 15.2v

    (4) Tested Coil Terminal 15 to ground with ignition OFF and got 0v as expected.
    (5) Put car in RUN and tested coil terminal 15 to ground and got 14.281v. Troubleshooting chart says for a reading of 12v there is a break in the primary coil winding or ECU module not conducting.

    DeLoreanDebug001___105.jpg

    (6) Turned car OFF again. Unplugged terminals from coil. Main plug and slave plugs look to be in poor condition. I cleaned off the coil terminals a bit and the connectors. Will most likely need to replace main coil wire.

    DeLoreanDebug001___106.jpg

    DeLoreanDebug001___107.jpg

    (7) Measured between coil terminal 1 and coil tower, got 8.706Kohm. Measured between terminal 1 and terminal 15 of coil and got 0.92R which seems to be in-spec with what to expect.

    DeLoreanDebug001___108.jpg

    DeLoreanDebug001___109.jpg

    ( Measured 0v between terminal 1 and ground when the car is OFF. Measured 14.2v between coil terminal 1 and ground with the car in RUN. I believe the checklist says that means that the ECU Module is not conducting...

    At this point before I tear apart the insides more to get to the ECU, just hoping someone can confirm this is logical and as of now points to the ECU being the no start culprit at least when the RPM relay is jumpered. I suppose it is also possible it has something to do with that relay as well or improbable but possible both failed simultaneously...

    Thankyou all again for the help.

  4. #14
    Senior Member Bitsyncmaster's Avatar
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    The stock ignition ECU will ground the coil so with the engine not running and key on you should be getting a low voltage (less than 1 volt) on the coil white/slate wire and the coil white/yellow wire will be about 6 volts.

    If your tach does not move when cranking the engine that usually shows you the ECU has died.

    Note: the GM ignition unit turns coil current of when the engine is not running so you would get full voltage on both terminal of the coil with that unit.

    A dead ignition ECU will also cause the RPM relay to not work.
    Last edited by Bitsyncmaster; 08-01-2019 at 04:33 PM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #15
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    Quote Originally Posted by Bitsyncmaster View Post
    The stock ignition ECU will ground the coil so with the engine not running and key on you should be getting a low voltage (less than 1 volt) on the coil white/slate wire and the coil white/yellow wire will be about 6 volts.

    If your tach does not move when cranking the engine that usually shows you the ECU has died.

    Note: the GM ignition unit turns coil current of when the engine is not running so you would get full voltage on both terminal of the coil with that unit.

    A dead ignition ECU will also cause the RPM relay to not work.
    Well that sounds logical and explains the improbable double failure. Single source failure of the ECU. As far as I know, it's the original ECU. Obviously I am not the first owner and don't know if it is original or not.

    Is the best replacement still NOS ECUs? Or is this replacement GM considered superior? Any more "modern" ECUs that exist that would be a good upgrade while in there? I think while I have it opened up I will replace the remaining relays in the back (already did all the fuses a couple years ago) and probably replace the coil and wire just because I don't like the way they look.

    Is there any documentation on what the 3 ECUs actually do, must be relatively simple, and if there has been any work to make an open source or replacement microcontroller based equivalent?

    I will look around to see if I can answer these questions myself as well, but I am sure the more knowledgeable than I gurus have this information on hand easily.

    Bummer the ECU died. I guess it is verified that either the ECU is dead, or a wire between the ECU and various points in the car is not connected properly. I guess the next step is to find more ECU attached points and probe them to see signs of life. But the RPM relay failure is almost a give away of at least part of it being bad. Perhaps the connector fell off? I dunno yet...

    Thankyou again

  6. #16
    Senior Member Bitsyncmaster's Avatar
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    Pull the ECU, it is a grey plastic cover over a metal mounting plate. Just remove the idle ECU and you can remove the two screws holding the ignition ECU out. I think you can then get the ignition ECU out (I can on my car but the bracket is loose).

    I don't think they are high priced at DMCH. There is no plug an play alternative as far as I know. The GM unit is a module that you can wire up inside a stripped OE box.

    I do keep a stock spare and an extra GM modified spare in my car mostly to help other owners stranded on the road.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #17
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    Quote Originally Posted by Bitsyncmaster View Post
    Pull the ECU, it is a grey plastic cover over a metal mounting plate. Just remove the idle ECU and you can remove the two screws holding the ignition ECU out. I think you can then get the ignition ECU out (I can on my car but the bracket is loose).

    I don't think they are high priced at DMCH. There is no plug an play alternative as far as I know. The GM unit is a module that you can wire up inside a stripped OE box.

    I do keep a stock spare and an extra GM modified spare in my car mostly to help other owners stranded on the road.
    I will take a look at it.

    I just found the trusty giant schematic of the DeLorean.

    Looks like the Ignition ECU is a black box that takes the:
    • WS wire from the coil and tachometer and RPM relay
    • G wire which looks like a fused W wire which looks like the IGN wire, hot +12v when the car is on only
    • 2 mystery wires on pin-15 and pin-16 that go to the distributor... I am guessing a hall sensor AC signal that corresponds to the dwell angle?
    • Grounds


    I am guessing it drives the WS wire and then uses the 2 mystery wires from the distributor as feedback? When it has power, only when ignition on, it drives that WS wire low by pulling it down at some duty cycle which in turn makes a spark which makes the engine go controlled boom. Since there is no pedal input or feedback on the throttle position, it's purpose seems limited to extracting the RPMs that the engine is currently running at which is controlled completely independently by only the throttle valve itself, and then calculating the best time to make a spark so that everything is in alignment.

    To me this sounds like a zero cross detector on the hall input lines that drives a big 'ol transistor to ground. Is it truly that simple?

    I am sorry but I come from the world of working on next-next generation vehicles. Everything is by wire and thousands of sensors. The last BMS system I worked on isn't due to be put into production until 2028 on some big name vehicles. I am just not used to everything being so non-dependent.

  8. #18
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    The ignition ecu is gray and mounted underneath that.

    Dave B.
    Last edited by WHO1DMC; 08-01-2019 at 06:17 PM.

  9. #19
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    Most of what you described early on had me saying ballast resistor/ignition coil connection problem. Your mention of wiggling the RPM relay when trying to jumper the fuel pump to had your door locks trying to lock makes me think it could be your inertia switch.

    The inertia switch is supposed to shut off the fuel pump if you're in an accident (and upside down or worse). The other thing it is supposed to do is unlock your doors for you.

    Those two things combined make me suspect a problem with the inertia switch.

    ...the times I have had ignition coil connection issues or ones on the ballast resistor give me grief, I have been able to crank the engine, but not get it to start... AND there's never any fuel that you can smell. Each time a wiring issue has come up, it has meant the fuel pump isn't pumping. Perhaps a small piece of troubleshooting advice for anyone with a no-start issue. If you can get it to crank and can't already smell fuel, lean towards the issue being electrical first, then check other stuff.


    Sept. 81, auto, black interior

  10. #20
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    Quote Originally Posted by WHO1DMC View Post
    The ignition ecu is gray and mounted underneath that.

    Dave B.
    Sorry I meant "black box" in the geeky sense. "Black Box" is an unknown block. It has inputs and outputs and magic happens inside.

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