Difficult Ignition Cutout Problem

[Aries_Turbo]

i used to have a large blanket that i didnt care about that spread on the floor of the living room to stretch out, disassemble, repair and re-wrap harnesses.

fire up some fun videos and work on old wiring.

Brian

[cordes]

i used to have a large blanket that i didnt care about that spread on the floor of the living room to stretch out, disassemble, repair and re-wrap harnesses.

fire up some fun videos and work on old wiring.

Brian

I think that might be the way to go. This thing is completely out of hand.

[cordes]

I'm still going strong with this. Can anyone tell me if this is a factory connection coming off of the j1 wire on the 10 way connector at the power module? It is the ignition feed.

I don't show it in the manual, and while it certainly looks like it should most likely get the job done, it leaves a lot to be desired when ruling out an intermittent problem in what could presumably be power to the lm or pm.

The heat shrink on it is what tells me this might have been a repair. It was a plastic that just doesn't seem to fit with anything else on the harness. Of course, the use of a bullet type connector doesn't seem very factory either, but I also don't see why it would have been put there by someone as a repair. The tape on the harness over top of it looked very factory. It's all so confusing to me.

[Dr. Johny Dodge]

I've seen odd job splices like that one before
I think it's where they ran out of wire on the roll and started a new roll of wire while creating the harness

more cost effective than throwing away 4-6 feet of not quite long enough wire

[Dr. Johny Dodge]

ment to ask before ..you mentioned the water temp sensor sometimes throws a code when your issue happens..
what about checking the splice at the firewall for the sensor grounds ?

all the black sensor grounds splice together about halfway across the firewall

[cordes]

ment to ask before ..you mentioned the water temp sensor sometimes throws a code when your issue happens..
what about checking the splice at the firewall for the sensor grounds ?

all the black sensor grounds splice together about halfway across the firewall

I believe I checked that one, and it looked great.

It makes sense that they would splice the wires sometimes. At the same time, I'm surprised they used the bullet connector like that. I would have thought a butt splice or similar would be used instead.

[135sohc]

Those bullet splices are OEM. I have seen them used on front end lighting where the turn signal and side marker circuits come together and covered with friction tape. Total junk way of doing things but it was good enough to last awhile.

[cordes]

Those bullet splices are OEM. I have seen them used on front end lighting where the turn signal and side marker circuits come together and covered with friction tape. Total junk way of doing things but it was good enough to last awhile.

Thanks for the clarification. I guess the question becomes whether or not I just fix that and then throw the harness back in there. It looks really great otherwise.
ETA: even this looks good. None of it makes sense so far.

[Dr. Johny Dodge]

have you tried changing the power module?

a glitch..is how I would describe my 87 shelby z..or a ghost as I later swapped the known "glitchy" 87 lm/pm TII deal into my turbo z
and yep the glitch carried over to the new car

thinking now..that glitch might have been in the power module

as that's the car/wiring set up I had when I dropped the hood shut in the garage one night .. and got lucky because I didn't go in the house in the moment

the power module started to smoke heavily out from behind the headlight in the moment

so there might be something going on in your pm (???)

[cordes]

I've tried two lms and three pms. The lm ans pm in the car ran joys daytona flawlessly before and during this ordeal.

[cordes]

I now have the harness on a 4ftx6ft table in my basement. I'm going through it inch by inch. After 1 hour I'm up to where the map sensor is, and being that I started at the right side turn signal, I'm guessing there will be many hours into this phase.

Eta: I've gone through almost the whole harness, and it looks great. The only exception is the barrel terminal I Posted earlier. There was another one in the harness which I also eliminated. The other I found was significantly tighter than the one coming off of that power feed. To the PM, but I doubt it was an issue.

I've also gotten rid of the factory neutral connector behind the battery in favor of another Deutsch connector. Some of the harness was also cleaned up with dr-25 and a new connector at the charge temperature sensor.


I'm guessing the 8 hours today won't make a bit of difference, but I might be lucky.

[cordes]

I'm trying to install the harness today. The only section left to go through was the portion which goes to the speed sensor and starter etc. The one rough looking spot in the harness is where the park neutral switch wiring is. It was clearly a manual trans section which has been modified to have the auto trans switch. I'm wondering if Shelby did this, or if it was done at some point as a modification or repair. It's not horrible, but not very professional either. I'm going to rebuild the section and set it up for auto trans wiring. From there, who knows?

[cordes]

Of course, all of that work made no difference. I'm at a loss and can only imagine that one of the wires has a break in it, or there is some sort of incidental problem which has begun.

This is ridiculous at this point, and I'm not sure that I have much of an option other than to use the rougher looking harness I bought.

[chromguy]

Hi Brian,
Have you tried a current test on the wires? See what the voltage drop for a constant current such as two amp.

[cordes]

No. I will have to do that with this harness at some point. I think my father might be going back into business soon, so a fully equipped electronics lab may be available to me in the near future.

That said, this other harness isn't quite as bad as I had originally thought. I'll change the connectors at the battery to Deutch style and be done with it. There are a couple wires which will need to be repaired at the tb, but that's not a huge deal to me at this point.

[Aries_Turbo]

i used to poo poo it as i was concerned about the current through small wires (20 ga) but simon's method of using a headlight bulb to test wiring for good, solid, low resistance connections but it will probably help in this case.

if you have the harness laid out and you check circuits with a low beam (55w, 4.58a) headlight (or high beam or high wattage if you wanna get a little wild) and if you let it run for a while and see a spot start to smoke, then it has a bad connection and should be addressed.

Brian

[cordes]

i used to poo poo it as i was concerned about the current through small wires (20 ga) but simon's method of using a headlight bulb to test wiring for good, solid, low resistance connections but it will probably help in this case.

if you have the harness laid out and you check circuits with a low beam (55w, 4.58a) headlight (or high beam or high wattage if you wanna get a little wild) and if you let it run for a while and see a spot start to smoke, then it has a bad connection and should be addressed.

Brian

I might give that a try. I have the harness in the basement next to my large bench. It would be easy enough to do.
Eta: I finished off repairing and modifying the other harness today. It is loosely in the car and still needs another repair ot two. I bet it will run the car with no issues.

[RattFink]

So... Idea.
Most wiring failures happen at the end of the wire, aka the connector. Connectors are mechanical and fail more often than the wire itself. It sounds like your wiring is in great shape.
I wonder if you are getting interference from the ignition system which is inducing voltages in the HEP circuit. I had this happen once on a Ford truck. A faulty coil was the culprit. Very very difficult to diagnose. In your case, maybe it's not the coil or ignition system with issues, but more so you may need some shielding around the wire harness, or maybe the capacitor coming off the coil is no good?

I've seen this on certain GMC trucks too. The transmission harness would cross the engine and lay right on one of the ignition coils. The truck would throw a random output shaft speed sensor code. You could test all the wires, replace the speed sensor, replace the transmission control module, and the code would still randomly come back. Moving the wiring harness a couple inches off the coil would fix it... I caught it on a scope once. Instead of the normal 0-5v OSS signal, it spiked up off the scale of the scope... right as the code threw... I trips the module out long enough to throw a code and/or cause an issue.

[dodgeman87]

Brian, the wiring harness was bought from a guy with a SL in Wyoming. It was for a manual but we changed it to an automatic.

[cordes]

So... Idea.
Most wiring failures happen at the end of the wire, aka the connector. Connectors are mechanical and fail more often than the wire itself. It sounds like your wiring is in great shape.
I wonder if you are getting interference from the ignition system which is inducing voltages in the HEP circuit. I had this happen once on a Ford truck. A faulty coil was the culprit. Very very difficult to diagnose. In your case, maybe it's not the coil or ignition system with issues, but more so you may need some shielding around the wire harness, or maybe the capacitor coming off the coil is no good?

I've seen this on certain GMC trucks too. The transmission harness would cross the engine and lay right on one of the ignition coils. The truck would throw a random output shaft speed sensor code. You could test all the wires, replace the speed sensor, replace the transmission control module, and the code would still randomly come back. Moving the wiring harness a couple inches off the coil would fix it... I caught it on a scope once. Instead of the normal 0-5v OSS signal, it spiked up off the scale of the scope... right as the code threw... I trips the module out long enough to throw a code and/or cause an issue.

Thanks for that tip. I'll look at that, and it certainly seems like it is time for a scope, as the second harness is doing the same thing. I'm going to put a new hep in it after testing it on another car. I guess it wouldn't be the first time that two old heps failed at the same time, but this is getting ridiculous to diagnose.

Brian, the wiring harness was bought from a guy with a SL in Wyoming. It was for a manual but we changed it to an automatic.

Thanks for that info Jim. It really helps. I can't track this down for anything.

ETA: The generic heps have really gone up in price. Looks like the days of getting them for 20 bucks are long gone.