Engine Dies while Driving

[Elvis]

The micro switch does NOT turn the idle ECU or the idle motor off !!!


there's thousands of infos about the idle system here in the forum...

Sounds to me like your idle speed microswitch isn't engaging. Loosen the lock nut on the upper post and dial it in one full rotation (360 deg) towards the microswitch tab. Tighten the nut and go take it for a test drive. Double check the electrical connections on the switch are ok too while you're there. There are only two, the black ground goes to the top and the black/green one goes to the lower tab. Make sure neither of those has fallen off or is loose.

[David T]

The micro switch does NOT turn the idle ECU or the idle motor off !!!


there's thousands of infos about the idle system here in the forum...

For all practical purposes you can say it "turns it off". Refer to the Workshop Manual D:05:02. The Idle Speed Control System is only "in operation" when the throttle plates are closed and the micro switch provides a ground path for the ECU via the B/LG wire. From a more technical point of view, the Idle ECU is always on, it is just not controlling the Idle Speed Regulator, aka idle air motor. The idle ECU is getting power whenever the key is in the RUN or Start position. For a more complete description of the Idle Speed Control System refer to Section D:05

[DMC5180]

This story may be long winded, but a Delorean Adventure with a Happy ending is GOOD THING and the found fault could be applicable to this thread topic.


I had a recent Failure to start a couple weeks ago. First time in my 22 years ownership. I had packed up the car for a 4 hr road trip and when I went to leave it would not start. My car has never failed to start before for no apparent reason. I checked the obvious things, resistor connections, Fuel pump, Etc. Nothing I tried worked. We were running behind our scheduled departure time, so I packed up the daily driver and left it to when I got back home. Once, I returned, I did more confirmation checks. On one of those checks I went into the ECU bay and wiggled the two connectors in the Idle ECU and followed that a crank attempt. Boom It fired right up. Thinking somehow the IDLE ECU may have lost connection to the ISM, I figured this may have been the plausible reason for the NO START.

Now Fast forward 2 weekends, Friday I go out to the garage and start the car up just to be sure I don't get Surprised when I need to take it on long drive to partake in a Midwest Tech day. The car fires up and I let it go through normal warmups and everything appears fine. Okay, so SATURDAY Morning at 3:30 AM, I get ready to leave on a 400 mile drive to the Tech day. The car fires right up and I leave, I stopped for fuel and fill up. Everything is hunky dory, UNTIL about 3 miles down the road the ENGINE SHUTS DOWN. I Let the car roll as far as I can until I see a side road I can pull off on. I come to a full stop Open the door and then try cranking a couple times, NOTHING. Less than 30 seconds later a vehicle pulls in behind me from off the Highway that had been traveling the opposite direction. AND the LIGHTS COME it was a county Sheriffs Deputy. I walked back to his car and explained what had just happened, I can only imagine what the guy was thinking at seeing a Delorean off the side of the road at 4 AM. Anyway, after the usually Plate run and DL check, He offered to call a tow truck If I needed it. I said, I would do that IF needed and that I could roll the car off the road into a Drive way just ahead of me that just happened to be Country Church. I told him I was going to call my wife to come get me since I was just barely out of town. He said, no problem and I thought I was going to need to leave the car unattended, to just call it into dispatch to let them know and then he went on his way. I called the wife and told her what had happened and to come get me. So while I was waiting for her to arrive. I did a few more diagnostics including jumping the RPM relay. (always carry a jumper in he car) I could here the pump running but It still would not start. So on a hunch I decided to go back into the ECU compartment and check the IDLE ECU Connection again. Wiggle,wiggle and Crank, NOTHING! Then, just for shits, I put my fingers on the IGNITION ECU connector, you can barely move it due to its difficult location. I crank the engine Engine again and SHE FIRES RIGHT UP. WOW I think, maybe it was not the Idle ECU connection I had previously thought it was. I must have disturbed the Ignition ECU connection under the Idle ECU connectors when I was checking those 2 weeks earlier. With the engine running, I did a verification of the Ignition ECU connector rocking it side to side until one side popped loose, just barely I might add, and the engine dies. I grab screwdriver and managed to pry the connector off the ECU to examine it. NOTHING appeared abnormal, so I just re-connected it and the engine fired right back up. Right about that time the phone rings and my wife is nearby but can't seem to find me. (misunderstanding in location details) I told her what I had found and told her the car was running and I would come back into town and meet her at a well lit location. After we met up, I told her I thought a had found the root cause to my NO START problem and decided I would proceed on my Tech DAY trip. The Car ran fine and I just returned from an 800 mile ROUND TRIP. It was a Saturday Event and probably one of the last times the car will get out this year save for some fall color touring.



The moral here is that we tend to overlook the remote causes for NO STARTS. It is largely Agreed that the Ignition ECU almost never fails, so it tends to get overlooked. But in this case the ECU connection developed light oxidization and lost connection. Hopefully, just pulling the connector off and reinstalling it scratched fresh points of contact on the terminals and it will be okay. At least if I have another NO START or Random SHUT DOWN , I'll know what not to overlook.

[Bitsyncmaster]

The micro switch does NOT turn the idle ECU or the idle motor off !!!


there's thousands of infos about the idle system here in the forum...

+1
When I was designing my idle ECU I tested the stock unit and never found the idle switch to do anything to the ECU. Now it may have changed a little timing but I never put much effort into analyzing it. The main purpose of the idle switch is to turn the ignition advance on or off.

Someone with the stock ECU should pull a wire off that diode near the idle ECU and see if anything changes with your idle.

[Jimmycxc]

Just ordered a new set of relays just for shits and giggles.

[David T]

That was a long-winded little story! The moral of the story should be if you have an intermittent you cannot be sure it is fixed unless you actually find the problem. You may have disturbed it and got the motor running again but until it is fixed you can't trust it. You can expect the problem to occur again. I would suspect the wire to the impulse coil, the coil itself, or the connections to the ballast resistor. I don't see how the idle ECU can prevent the motor from running or shut it down. The next time it happens you should immediately check for spark to verify an ignition problem.

[DMC5180]

David,

The Original No Start Happen in my Garage after previously parking a running car following my 2 week Vacation driving tour that coincided with DCS 16.

Imagine my surprise when I go to start the car two weeks ago. As I stated, the last item I touched was the Idle ECU prior to it starting up like nothing happened. This apparent coincidence led me to think the plausible cause was a poor connection at one of the idle ECU connectors. Btw, what usually happens when You pull the Connector off the ISM when the Engine is running? Not trick question. The engine has a tendency to stumble and or quit. The valve closes and starves the Engine of Idle control Air. So it's plausible that if the ISM lost partial signal it could be driven closed. This possibility led me to believe thats what had happened. Also, I never consciously heard the ISM hum. Of coarse I wouldn't if the key was Off While I was checking the usual suspects. iE resistor connections, ignition coil, coil wire both ends. And I had confirmed I had functioning Impulse coil, the RPM relay was running the FP And TACH needle was Bouncing while Cranking, but it did not fire till I after I had Wiggled the Idle ECU connection.

The engine shutting down on me after leaving the gas station made me ponder other possibilities. I recalled recently that someone else on the forum experienced a similar situation. He went through all the connections and found the Ignition ECU connector was not fully seated. He heard it Click after touching it. His engine started right up after that one. This is what made me go to that connector and see if that was a possibility. In my case it was kind of I'm very confident I found the Smoking Gun. I think my 800 mile trip gives me that reassurance. I'll look at the glass as half full, you can see it as half empty and continue to cast doubt.

I'm good with what I found. I'll agree with you that those items you mentioned are always a potential suspect.


Sent from my iPhone using Tapatalk

[Jimmycxc]

Update:

Received my new relays and put them in. Fuel pump will not turn on now. Tried jumping it and nothing. I removed the new Lambda relay and plugged the old one back in. Fuel pump turns on and car starts and idles. However, it will turn off after about 30 seconds. When it shuts off I can hear and feel the idle speed motor buzzing. Fuel pump, when running is getting 11.4 volts. When engine dies, so does the voltage to the fuel pump. I've tested the inertia switch and it works as it should...with it up, the fuel pump does not work, I push it down, fuel pump works.

[Bitsyncmaster]

The lambda relay should have no effect on the the fuel pump running. Maybe someone modified your wiring. The RPM relay powers the fuel pump and drives the lambda relay coil. Maybe that lambda relay coil is shorted but that would have blown the fuse.

[Jonathan]

Is this thing you mentioned about it shutting off after about 30 seconds repeatable? And is the duration exactly the same each time? (30 seconds, or 45 seconds, or 22 seconds, etc.) If you can get the car to keep doing what you've described consistently, it'll help you narrow down what the problem is.