Electrical Calling all wiring guys - absolute head scratcher

rock4451

Active Member
Nov 30, 2004
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New Baden, IL
I have an 86 GT that out of the clear blue, has an inexplicable issue.
When I start the car, it starts up and dies 2 seconds later. Rinse and repeat, regardless of how many times I try.
I remove the chip in my A9L computer (it has been tuned) and it runs, roughly, but it runs.

I have dumped codes, I get 22 (BAP out of self test range), 63 (TP circuit below min voltage), and 66 (MAF circuit below min voltage). With KOEO, I checked the TPS sweep with an analog volt meter and it increases and decreases as normal when opening the throttle. Tested all 3 at their connector unplugged between tan/white and sig return and all were at 5.07v.

I noticed one time when it was started and running, that if I twisted the computer (and consequently the wires) the car died. I checked my wiring from my MAF conversion I did in 2015 and I had a bad solder to the MAF ground. Fixed that, issue did not go away. Found the connector to the MAF had some shoddy connections, replaced the connector, problem did not go away.

I have been testing for continuity on circuits that I believe should not have continuity and I am stuck on the fact that (with the computer unplugged, testing at the connector) pin 37/57 have continuity with 40/60, which tells me it should be a short, right? However I have no fires, smoke, or anything I would expect with a direct short to ground. I even unplugged every sensor/10pin connectors/relay that uses circuit 37/57 and there is still continuity between 37/57 and 40/60.

Has anybody had an issue similar before? I am hoping jrichker is still around!
 
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7991LXnSHO

wanna catch the space herp
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Definitely going through that tonight!

Off topic, how do I get a fancy 10yr member badge like you have??:cool:
I think it will take more messages on your account before it gets handled. Or if you are brave, ask @Noobz347 , but that is living dangerously. Bring cookies for the staff to share.
 

Noobz347

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Definitely going through that tonight!

Off topic, how do I get a fancy 10yr member badge like you have??:cool:

I think it will take more messages on your account before it gets handled. Or if you are brave, ask @Noobz347 , but that is living dangerously. Bring cookies for the staff to share.

This is correct. There are more criteria involved beyond just your join date. Active participation in the forums will have an effect.
 

rock4451

Active Member
Nov 30, 2004
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New Baden, IL
04D8EE4E-1F0B-4F73-9FE1-6C32DE546083.jpeg
Here’s one, before I dropped the engine in a couple months back. Has been running amazing until this most recent hair-puller.
Tomorrow I’m going to disconnect the ground that attaches to the body, pull the main ECU connector through and visually inspect for exposed wires or anything that may be causing this intermittent issue. Sometimes I also have to have the pedal on the floor to start it. When it starts and stays running (rarely) it idles roughly and then acts as if a switch was turned that kills all ignition and fuel.
I really need to find this issue for the sake of my sanity.

Hoping @jrichker can let me know if its normal to see continuity between pin 37 and pin 40 in the harness, my gut tells me no and there’s a short somewhere but I would see smoke or melted connections I would assume.
 
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rock4451

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Nov 30, 2004
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New Baden, IL
Okay, so I got it to start and idle (idled very low, throttle response was garbage) and when I turned the computer physically 90 degrees, the car killed. Retried this test 3 times and same results. Inspecting the harness, there are no bare wires and no loose terminals.

I am testing the capacitors in the computer, one of them starts with low resistance and then continues to 160,000 ohms. The other two are already at very high resistance with no change to the reading.
 

Mustang5L5

Put lubricant all over the balls
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I think the issue is in the wiring harness or 60-pin connectors. Physically moving the ECU and having a change points to a bad connection in the harness. A visual inspection may not be enough as it may be a bad pin in the ECU connector or in the ECU pins themselves.

in theory, if you have the ECU connector bolted in place, it should restrict movement of the connector to the ECU pin. You can still have a bad connection in the wire to terminal socket however. These are tricky to find.

testing capacitors can be tricky. They need to be discharged first with a resistor and then will start at 0 ohms and then move to infinity. Usually a visual of the capacitors can verify if they are bad. They tend to puff and looks corroded/green on the bottom.
 

Dan02gt

10 Year Member
Mar 2, 2003
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The female connectors in the 60 pin ECU connector spread out and get loose just like the salt and pepper shakers connections. I could touch the ground wire on the 60 pin connector on my car and it would make the engine die completely. I ended up buying a replacement 60 pin connector and tightening each wire when I moved them to the new connector.
 
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rock4451

Active Member
Nov 30, 2004
12
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New Baden, IL
@jrichker or anybody have advanced tests to do on my MAF? Testing at the MAF connector, disconnected, when I touch the blue wire and tan wire, I’m getting 5.83v, when I touch the tan wire and the black ground wire I’m getting 5.92v. Touching the red 12v and black ground gives me battery voltage so I’m all good on those two.
 

manicmechanic007

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Damn straight you wish you had a factory processor and a breakout box. I have a breakout box for EECIV You will get there eventually
 

manicmechanic007

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Yes you should swap out the TFI or use a bypass remote TFI module for test. The pip signal for the fuel injection timing is supplied by the TFI module. The super star EEC tester said what? You can make your own star tester with a light bulb
 

rock4451

Active Member
Nov 30, 2004
12
1
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New Baden, IL
New capacitors didn’t fix the issue. Good news is throughout this process I found several loose terminals and so forth that I’ve corrected. I went through the 60 pin connector and pinched the female ends together so there is a solid connection between harness and computer.

Good news is it starts and runs, but it starts, idles at about 1100 for a few seconds (like normal on a cold start) and then it idles down to about 600-650. Unplugging the MAF results in no change. Giving it throttle, it’s a little laggy but nothing near as bad as it was before tightening up the 60 pin harness. No longer have a change in behavior from physically moving the computer.

DVOM reading on the blue wire on MAF (ground lead touching battery negative) is very low at idle, bouncing between .09 and .11, giving it throttle does show a steady increase, voltage moves with the throttle.

Random test, testing for voltage between pin 46 sig return and battery neg, I’m getting .04v. Thought this should show 0 as both are grounds and pin 46 connects to power ground in the ECU.
 

Noobz347

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Returning to this for a second:

Physically moving the ECU and having a change points to a bad connection in the harness.

It can also mean a broken solder connection between the EEC connector and the board. If you haven't inspected them already, look closely and see if there are any broken solder connections where the pins enter the board.
 
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