Wiring Disaster and bad pin 31 ECU ground

Hello DeLorean fans,

I recently inherited a DeLorean and I'm trying to get it running but there appears to be an electrical problem with it. Unfortunately, it looks like there has been quite a few electrical modifications behind both seats near the ECU and by the fuses. I'll probably be asking some other questions about the electrical system once I get the car into a running state.

The car turns over but it sounds like it's having a hard time getting enough juice to turn over. So I looked in the Technical Information Manual and saw that it has a troubleshooting section, I found C1 - IGNITION SYSTEM DIAGNOSTIC CHART (pg 122/137). On #2, it had me probe pin #15 at the coil against ground and said it should be 6-8 with the key on. However, I see more like 10.5V and the troubleshooter suggested that the system has a bad ground. To dig in, it says:

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Check resistance of primary coil winding (0.95 - 1.4 Ohms)
Check for battery voltage at contact pin #15 of ignition ECU module, using voltmeter with ignition in Run' position" I started to dig out the ECU and I am left with lots of questions.

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I got into the compartment behind the driver's seat and found the three boxes that are all apparently called the ECU :hmm:. Anyway, I see that they are all attached to a metal plate, I pulled the bolts from the metal plate so I could see how everything was mounted and probe the correct pin. When I probe it, pin 31 appears to be just grounded to this metal plate. What worries me is that the place where this plate mounts is wood/fiberglass/rubber (insulated) so that plate grounding wire is probably not the same "ground" as the engine will see.

Attachment 44051

How is this supposed to work? Seems to me like there should be a fat ground wire running from the engine back to this plate so they have the same 0V reference voltage. What is this ground system supposed to look like when stock?

Thanks,
-Greg

Welcome,

The thing about manuals is they don't account for previous owner mods and hack jobs. Before diving into the repair, you need to figure out what all those extra wires are for, if they are even hooked up, and where they go. Chances are it's some kind of stereo or alarm but you need to know for sure because those mods could be part of the problem. Once all that is sorted out (removed) then start diagnosing.

From the factory: ECU's are grounded to a junction under the console, thence to a junction in the relay compartment, thence the rear bulkhead bolt (main grounding point for the entire car body):

Attachment 44054
Attachment 44055

PO mods can of course change factory configuration.

Bill Robertson
#5939

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Originally Posted by content22207_2

From the factory: ECU's are grounded to a junction under the console, thence to a junction in the relay compartment, thence the rear bulkhead bolt (main grounding point for the entire car body):

Attachment 44054
Attachment 44055

PO mods can of course change factory configuration.

Bill Robertson
#5939

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AWESOME, Bill! I just found a long thread of yours called Ground-Location-List and it has a lot of really good detail. I printed out a few pages already. If you have any photos of that rear bulkhead bolt so I know exactly where to find it? I'll likely do the 4ga grounding reinforcement you posted found in this thread: voltage-gauge-quot-health-quot-assessment.

If you pull the carpeted bulkhead off you can't miss the bolt. It's right next to the ignition coil (that's the other side of the bolt).

Speaking of which: ignition circuit is totally unprotected (no fuse, fuse link, or circuit breaker), despite the coil being mounted to a metal plate that grounds pretty much the entire car. I added a fuse link into the resistor grid.

Bill Robertson
#5939

Please note: my ground bus does not depend upon the original bulkhead bolt to frame wire (attached under the coolant expansion tank), nor the frame to battery wire (community wisdom is that terminal can come loose). Bulkhead bolt is tied into the bus, but the bus has its own wire directly to the battery. Being located inside the car, this direct connection is weather protected.

Bill Robertson
#5939

ECU is short for "electronic control unit".

The metal plate behind the drivers seat is normally grounded with one or two black wires with ring terminals (can't remember how many is stock). The lambda ECU (metal case) has electrical ground connection inside the ECU to it's case. So normally there is no current flowing with the metal case ground circuit. It's more of a electrical noise shield.

The meal plate behind the passenger seat is not grounded with stock wiring.

That ring terminal is ganged into the ignition ECU ground (pull back the rubber boot and Pin 1 has two ground wires -- one to the tray and one to the junction under the console).

Bill Robertson
#5939

The wiring jumble and that little clear topped box on the right side appear to be related to the power antenna located in the rear, driver's side quarter vent. And generally they would be for the power up and down feature of the antenna. One of those thicker black wires is also the radio antenna wire. The little clear topped box is not factory, and as Michael mentioned, it could be tied into some sort of alarm or ignition shut-off switch. The speaker and antenna wiring from the factory was not normally the prettiest thing you've ever seen, but it usually wasn't quite that messy. Those wiring colours also aren't factory and indicate some PO hack-job.

Here's a schematic of just that Lambda ECU (the black one lying flat on top of the metal bracket there) and the two connectors on the back of it. All of these schematics are included in the forum resources section along with the master wiring diagram. I would also recommend you taking some time to sort out wiring that isn't right. I know you would like to get the car running and then sort it out, but you may never get the car running depending on how messed up the wiring is. And it could be as simple as an extra fuse that got unnecessarily added but is now blown that stops you.

Attachment 44056

Clear case relay is factory OEM for the power antenna (factory antenna didn't have an integrated relay as aftermarket units do).

To be brutally honest OP's ECU compartment looks stock.

Bill Robertson
#5939

I agree, there is nothing out of the ordinary in that picture; it looks stock to me.

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Originally Posted by content22207_2

Clear case relay is factory OEM for the power antenna (factory antenna didn't have an integrated relay as aftermarket units do).

To be brutally honest OP's ECU compartment looks stock.

Bill Robertson
#5939

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Originally Posted by dn010

I agree, there is nothing out of the ordinary in that picture; it looks stock to me.

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Thanks for clarifying. I stand corrected. My own car has the fender antenna so this area behind my driver's seat is a little cleaner without the power antenna wiring. Good to know.

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Originally Posted by dn010

I agree, there is nothing out of the ordinary in that picture; it looks stock to me.

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If it is having trouble cranking over you should go over all of the "big" connections between the battery and the motor. Don't know your VIN but if it applies check out service bulletin ST-05-2/82. If it hasn't been running for a long time you should inspect the fuel tank, cleaning it out and replacing any deteriorated parts before trying to start it. Getting a Delorean that hasn't been running for a long time means going over each system and rebuilding them as necessary, especially the brakes, clutch, cooling and fuel. Replace all of the fluids and filters. Tires over 7 years (check the date codes). If you are not getting spark 2 of the more common causes are 1) rusty/dirty connections on the ballast resistor, a bad impulse coil inside the distributor.

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Originally Posted by David T

a bad impulse coil inside the distributor.

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Has anybody ever actually seen one of these go bad? It's an electromagnet. Unless something physically damages the wires, there's nothing to go bad.

Bill Robertson
#5939

Changing the distributor windings is not an easy task, especially if screws that hold the distributor together are seized (removing the trigger wheel without bending it is no walk in the park).

Put an ice pick light on the negative terminal of the coil and watch for the light bulb to flash on & off as you crank the engine. If it does, not only are the distributor windings/pickup OK, but the ignition module most likely is OK as well.

If the ice pick light doesn't flash on & off, use a multimeter to pass voltage through the distributor pickup (resistance setting) and watch for digital display numbers to jump around/analog needle to swing back & forth as you crank the engine. If they do, the pickup most likely is OK.

Bill Robertson
#5939

Quote:

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Originally Posted by content22207_2

Changing the distributor windings is not an easy task, especially if screws that hold the distributor together are seized (removing the trigger wheel without bending it is no walk in the park).

Put an ice pick light on the negative terminal of the coil and watch for the light bulb to flash on & off as you crank the engine. If it does, not only are the distributor windings/pickup OK, but the ignition module most likely is OK as well.

If the ice pick light doesn't flash on & off, use a multimeter to pass voltage through the distributor pickup (resistance setting) and watch for digital display numbers to jump around/analog needle to swing back & forth as you crank the engine. If they do, the pickup most likely is OK.

Bill Robertson
#5939

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The impulse coils do fail. I think it is the wire from the coil to the plug where the failure actually occurs. When they fail they seem to fail temperature sensitive. The classic symptom is the car starts fine cold but within about 20 minutes it dies and won't restart till it is cold again. It is a PITA to change it, you must remove the distributer, disassemble it, reassemble it and then reinstall it and retime the motor. A lot of work. Do a simple resistance measurement. An open circuit (a very high to infinity resistance) would tell you the coil is bad.

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Originally Posted by Bitsyncmaster

The meal plate behind the passenger seat is not grounded with stock wiring.

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It probably should be though, right?

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Originally Posted by spikeygg

It probably should be though, right?

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Probably would reduce some radio noise when a relay switches but otherwise I don't think you need to ground it. Mine is still floating. One guy had an AUX relay short to the metal case and his metal plate was grounded and he found that relay fault quickly. I also put some cut silicone tubing on the edges of my metal plate where wires touch to prevent it cutting into the wire insulation.

I'm disassembling the center console in my car to determine where the electrical shortcomings are and discover all the botch-jobs that I need to repair. One of the irst things I noticed was a Green/White and Black wire exiting the driver's side wiring bundle and taped up with electrical tape. I'm wondering if you guys know where this pair of wires was headed before someone chopped it up and wrapped the ends in electrical tape.

See picture for detail:
Attachment 44815

Quote:

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Originally Posted by spikeygg

I'm disassembling the center console in my car to determine where the electrical shortcomings are and discover all the botch-jobs that I need to repair. One of the irst things I noticed was a Green/White and Black wire exiting the driver's side wiring bundle and taped up with electrical tape. I'm wondering if you guys know where this pair of wires was headed before someone chopped it up and wrapped the ends in electrical tape.

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Can somebody confirm the wire pair in the photo is the OE wiring pair that would've hooked up to the lamp in the 3-spd shifter?

From the wiring diagram there's a Light Green/White wire and a ground wire to that lamp, something your 5-spd D doesn't need or have. If the ID is confirmed this is factory wiring, not PO mayhem.

For any new owner dealing with PO hacks order a poster-size color wiring diagram to save yourself headaches and eyestrain. Also useful for troubleshooting at connections.

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Originally Posted by Rich

Can somebody confirm the wire pair in the photo is the OE wiring pair that would've hooked up to the lamp in the 3-spd shifter?

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yes it is!

Quote:

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Originally Posted by Rich

Can somebody confirm the wire pair in the photo is the OE wiring pair that would've hooked up to the lamp in the 3-spd shifter?

From the wiring diagram there's a Light Green/White wire and a ground wire to that lamp, something your 5-spd D doesn't need or have. If the ID is confirmed this is factory wiring, not PO mayhem.

For any new owner dealing with PO hacks order a poster-size color wiring diagram to save yourself headaches and eyestrain. Also useful for troubleshooting at connections.

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Originally Posted by BABIS

yes it is!

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Thanks guys, just after I posted this I was staring at the schematic and I found the light you're referring to... I'm still in disbelief that this was acceptable wiring practice in the 80s. :) Thanks for the help.

Attachment 44818

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Originally Posted by spikeygg

Thanks guys, just after I posted this I was staring at the schematic and I found the light you're referring to... I'm still in disbelief that this was acceptable wiring practice in the 80s. :) Thanks for the help.

Attachment 44818

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Here's a photo of the light bulb from an automatic: http://dmctalk.org/showthread.php?10...l=1#post165448

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Originally Posted by spikeygg

Thanks guys, just after I posted this I was staring at the schematic and I found the light you're referring to... I'm still in disbelief that this was acceptable wiring practice in the 80s. :)

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Doing it that way simplified production. The factory didn't need to keep track of and buy more than one harness style at a time. Cars are still made this way...sometimes there are seat-motor-control or seat-heat connectors under front seats that are manual-adjust or aren't heated.

The transmission selector lamp wire isn't the only unused circuit in your car. I can think of at least 2 others.

The bottom line: When you find more color-coded wiring it's probably factory, not a PO hack.