03 Cobra Dies At Random

LarsD

Founding Member
Jul 2, 2002
2,680
120
123
Texas
Been chasing this problem for a couple of months now and running out of ideas.

The first time I had been driving for a bit (15 minutes or so) and was headed back home, in third gear, A/C on, and rolled into the throttle (60% or so at about 60mph). The car was making boost (10ish psi) and then it stumbled pretty hard. I lost power, but when I backed out of it and blipped the throttle I could hear the SC whine, at this point all the gauges except the boost gauge were dead, odo was all dashes, speedo and tach at 0. I made sure it was in neutral, flipped the ignition off and tried to restart it while I was rolling. From the sound of it, it seemed like the engine was struggling to start (I traced this to the weak economy battery the previous owner had put in the car), but after a second or two of cranking, it fired up. It drove normal the last couple of miles home.

I removed the integrated radar detector that didn't work and all of it's associated wiring. I also re anchored the ECU (it wasn't secured in the plastic holder) and regrounded it.

Took the car out for a test drive, wasn't even a mile from my house and it died, all dashes on the odometer, and dead gauges just like before). I recranked it, it fired up easily, and I motored along. I noticed now however since the radar detector is gone (it was in the way of the light), the theft light was blinking a code at me. Code 16, which comes back as the PATS system can't see the ECU. I was informed by the previous owner that PATS was disabled, so this could be the source of the code, not sure at this point.

I drove around a bit more to get some heat in it, at one point when I was pushing it a little bit it did the thing that it does where it drops power so hard it feel like I jammed on the brakes. I suspect these are two different issues.

Anyway, I got it home and was laying down boards to get it in my shop (it drags the exhaust otherwise) and it died just sitting there. In fact, it died two more times before I was able to get it the last 15 feet into my shop. While trouble shooting it I had it running in my shop and it ran (idled) fine, no issues. Not sure what to make of this. The car has an SCT flip switch plugged into the service port of the ECU (which I noticed today is a reman unit). I don't really care for these type of programmers, however I don't know if this could be the source of my issues or not.
 
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Absolute first thing. Double check that the battery, battery cables, radiator core support grounds, and alternator are in tip top shape. Do yourself a favor and don't cut any corners here.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

Now that you are certain the charging system is solid some tests results are needed. Test for key on power in fuse F2.34, F2,2 and F2.8.

If no power in/out F2.34, suspect an ignition switch problem.

If no power in/out of fuse F2.2 and F2.8, suspect a CCRM problem.

1996+ Crank with no start check list

http://www.allfordmustangs.com/forums/4-6l-tech/336452-1997-mustang-wont-ignite.html#2984838

1999-2004 MY fuse panel schedule:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271
 
Absolute first thing. Double check that the battery, battery cables, radiator core support grounds, and alternator are in tip top shape. Do yourself a favor and don't cut any corners here.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

Now that you are certain the charging system is solid some tests results are needed. Test for key on power in fuse F2.34, F2,2 and F2.8.

If no power in/out F2.34, suspect an ignition switch problem.

If no power in/out of fuse F2.2 and F2.8, suspect a CCRM problem.

1996+ Crank with no start check list

http://www.allfordmustangs.com/forums/4-6l-tech/336452-1997-mustang-wont-ignite.html#2984838

1999-2004 MY fuse panel schedule:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271

I've check, cleaned, and retightened the grounds (core support grounds, the ECU ground, and that ground connector hidden next to the battery), replaced the cheap Walmart battery with a Yellow Top Optima, and verified my alt is charging 14.3-14.4 volts at idle and running down the road with my OBD2 BT scanner. Cables show no corrosion and are tight. I am thinking data logging might be useful at this point, but I can't do that with the old SCT flip switch. Fuses I can't check when rolling down the road dead. If I can get it to die while idling again I'll check them for sure. Also, car restarts every time when I crank on it, just keeping it running is the issue.
 
Fuses I can't check when rolling down the road dead. If I can get it to die while idling again I'll check them for sure. Also, car restarts every time when I crank on it, just keeping it running is the issue.
Yes it is possible to check the fuses going down the road. Look up "add a fuse" or "add a circuit". The pig tail from the "add a fuse" can easily be used to attach an volt-ohm meter (VOM). Use a KNOWN good ground.

The trick here is to find out WHY the cluster Odometer is going to all dashes. This is a huge clue. Which takes us back to fuse F2.34, F2,2, and F2.8 as a place to start.

Note, this could also be a bad ground from the CCRM and/or PCM. But if this were my car I would visually check the grounds and then monitor F2.34 first. Once it's known that the fuses have STABLE power, then go on to other possible problems.
 
Yes it is possible to check the fuses going down the road. Look up "add a fuse" or "add a circuit". The pig tail from the "add a fuse" can easily be used to attach an volt-ohm meter (VOM). Use a KNOWN good ground.

The trick here is to find out WHY the cluster Odometer is going to all dashes. This is a huge clue. Which takes us back to fuse F2.34, F2,2, and F2.8 as a place to start.

Note, this could also be a bad ground from the CCRM and/or PCM. But if this were my car I would visually check the grounds and then monitor F2.34 first. Once it's known that the fuses have STABLE power, then go on to other possible problems.

I checked the grounds on the core support, the plugs by the battery, and the one over by the ecu, any other that I might have missed?
 
Not sure what to make of this. The car has an SCT flip switch plugged into the service port of the ECU (which I noticed today is a reman unit). I don't really care for these type of programmers, however I don't know if this could be the source of my issues or not.
^^^YES^^^ Get rid of the "chip" or at the least CLEAN the leads/pins of the chip.
 
^^^YES^^^ Get rid of the "chip" or at the least CLEAN the leads/pins of the chip.

I pulled the ecu yesterday and took a look at it.

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I don't like the look of the gold fingers at all. I am thinking when I reseated the ECU and bolted it down that the bracket pushed on the chip which made the problem worse. I got my X4 in yesterday also and was letting it idle to warm up. I was data logging at the same time, about 10 minutes in the car died, I went over looked and saw the X4 said there was an error connecting to the ECU. I also noted when I pulled the ECU, the chip was secured with duct tape, once I pulled the tape it wiggled very easily on the gold fingers, even with the tape I could move the chip a bit.

EDIT: Here is a link to the data log file.

https://www.dropbox.com/s/30v063voygo2g07/datalog1.csv?dl=0
 
Some things I noticed.

The long term fuel trim (LTFT) is always 1.

Check out the battery voltage. It drops down to 12.6 which says to me that the alternator is cutting out.

It is a two week old yellow top Optima, it normally sits at 13.1V, but it had dropped to 12.6V cause it had been sitting all week. The voltage dropped out like that cause that is when the car died. What do you think the LTFT sitting at 1 all the time means?
 
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So I have test run the car in the garage a couple more times. I set the ECU on the floor of the car with the chip plugged in where it doen't contact anything, and it didn't die like it was before. I think it is the chip that is causing me problems.
 
It finally dried out enough I could take the car for a little drive. It didn't die on me, but twice when I pushed it kind of hard it did that thing where the power drops out really hard. You should probably be able to see it in the log when I push the throttle hard. Did it to me twice within a mile or two. I finally got one more clean pull right there towards the end (within 5 minutes or so before I stopped logging). However I could feel the car kind of stuttering a bit when I was winding it out, like it wanted to drop out again.

Oh, both times it dropped power on me, the SCT threw an error saying it lost communication with the ECU, however all the gauges were still responding and the car didn't die. I still have the ECU sitting on the floor of the car, and I lightly taped the chip in place, nothing was rubbing on it, and it didn't wiggle much at all. It seems fairly secure otherwise.

https://www.dropbox.com/s/5y5lpip78nkhf46/datalog4.csv?dl=0

I tried to interpret the log myself, but there is so much going on it still looks like Greek to me.
 
I still do not believe the alternator is keeping up or putting out enough at high RPM's. There are still large periods of time where the battery voltage is below 13.5. Many when the RPM's above 4,000.

Consider as the RPM's go up, the electrical demands of the ignition system go up as well.

As for what could "cause" this, one possibility is alternator brush bounce. At high RPM's the alternator is spinning very fast due to the small pulley. If the brushes and slip ring is worn, this increases the possibility of "brush bounce".

In one of my links is some information on how to rebuild an alternator yourself. Consider watching the rebuild video and look at the examples of extreme slip ring wear. IMO there's a possibility that you will find heavy brush and slip ring wear on the alternator.

As for other "possible" causes, consider a loose ground or other loose electrical connection.

Bottom line. IMO problems could arise anytime the system voltage drops much below 13.5 volts.
 
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Makes sense, it seems like two different problems, the chip being loose could be causing the dying, and the alternator is dropping voltage out when I am on it hard.