Faulty PCM?

[mrsolo2000]

All, I wanted to get a sanity check with my 94 MTX.

Over the last year, I have replaced the timing belt, CPS, CID, water pump, 02 sensors, y-pipe, exhaust, suspension, plugs, cables, alternator, etc. It drove great. Recently, the charging light began to flash intermittently upon downshifting and then the engine began to run extremely rough and kept stalling out when trying to give it gas. I pulled the codes (KOEO) and only 212 was showing up. I began testing the ICM. I used a test light and probed the VBAT IGN pin (left harness, top pin) and turned the ignition to run. The test light lit up indicating the ICM was receiving power. Next I tried the PIP pin and cranked the engine, no voltage was showing. I plugged the ICM back in and tried to start the engine. It barely starts and when it does, it immediately stalls.

I went back to probing the ICM wiring, suddenly there is no voltage present at the ICM on the VBAT IGN pin and the fuel pump will no longer prime when the ignition is turned to the on position. Additionally, I can no longer run the KOEO test.

This smells like a dying/dead PCM to me. My 92 Mustang GT did this to me. Apparently the alternator fried the PCM which caused the fuel pump not to prime and of course a no start condition.

Autozone tested the alternator and they said it checks out. It was a supposed new Bosch alternator when I bought it.

Any advice/hints? Thanks.

 

[Devin]

Is there any activity from the car when turning the key from off to on?

 

[mrsolo2000]

The starter turns but the engine does not start.

 

[Devin]

Do you get status lights in the cluster?

 

[mrsolo2000]

The CEL does not immediately come on, very noticeable delay and also a lot dimmer than I recall too.

 

[Off Road SHO]

Dead battery.

Tom

 

[mrsolo2000]

I'll investigate the battery but the engine cranks strong.

 

[Off Road SHO]

Maybe the good voltage is not getting to ALL the components the same. Maybe check the connection points for feed into the the PCM and the grounding points (return path).

Tom

 

[shomethe$$$]

PCM's rarely fail. Follows what Off Road said, I would check the CCRM and the FP relay in the engine fuse box location, they also have a fuse. So does the indicator light. A blown fuse will make the instrument lights come on slow because its getting the voltage from somewhere else.

Also, put your test light on the negative terminal of the battery, disconnect the terminal, put the other on the test light. Open a door make sure the test light comes on. Close it. If it doesn't go off, then your drawing power somewhere. Start pulling fuses until it goes away.

Check your grounds. Going back to your original problem, if the light came on I would obviously start with the grounds and the draw test I described above since I'll assume the alternator is charging, since its new, but check it anyway. What brand alternator?

BTW, never downshift in a manual car, its not good for it, in an emergency or hard braking fine but all the time? very bad for the clutch. Its not a brake. But it does sound cool.

 

[mrsolo2000]

Thanks for the tips. I did find the IGN COIL 10A fuse blown in the engine compartment fuse box. That partly fixed the no start condition. The first time starting the engine after replacing the fuse went great. The engine started immediately and ran/idled perfectly. I did not drive it, it was late and kids needed to get to bed.....

This morning, I started it again. However, this time it started immediately but ran horribly for 10 seconds and then died. It did this a few more times. I checked the PIP signal coming into the ICM during cranking. No signal with a test light. I did unplug the wire harness from the ICM to test the PIP (pin 4 according to the OEM wiring/vacuum manual). Is this correct or does it need to be plugged into the ICM to properly assess the PIP signal? Additionally, the CPS is getting power but I tried to test the PIP signal out of it during cranking but no signal there either. For this test I back probed the CPS PIP signal at the harness. However, I was alone and I am not sure if the test light was actually making contact inside the harness.

I have seen a few posts here regarding faulty "new" CPS sensors. Hopefully I can convince the parts store to replace this one if it is the cause of the issue. When I installed the CPS, I did ensure there was a gap between the sensor and the timing vane on the crank sprocket. Is there a specific gap that needs to be set or just enough clearance to not have the sensor impact the vanes?

Tonight, I will start chasing grounds with the assistance with the OEM electrical manual and do shomethe$$$'s approach stated above.

Thanks again.

 

[rubydist]

The gap on the crank sensor is specified at .030" but the common mistake is to make that gap too large - the sensor has a magnet on the bottom part, which wants to stick to the shutter wheel, and that causes destructive failure of the crank sensor. So, the trick is to keep the gap from being much larger than .030 when you are tightening down the sensor.

However, if it starts at all, or if it fires at all, then the crank sensor has not been destroyed in the way I described. I had one that failed within a couple of weeks of being installed new, so I personally know that infant failures in the crank sensor do occur. That infant failure could provide the symptoms you describe, but I think that the situation where you have good cranking but the alternator light flickers, points to some situation other than the crank sensor.

 

[mrsolo2000]

Forgot to add, the alternator that was installed ~14 months ago was a new Bosch.

 

[shomethe$$$]

Forgot to add, the alternator that was installed ~14 months ago was a new Bosch.

Yes, it needs to be connected to test the signal but I don't think the module is the issue, it seems like a short somewhere, probably blown the fuse again. Check the fuses again, check the instrument lights (still coming on slow?), do the parasitic drain test like I described above. Just to rule out the fuel pump, just direct it from the CCRM while you sort the other issues unless you're sure the relay is engaging during cranking and once it tries to start.

Just to be sure its not a mechanical issue, check all vacuum and inlet hoses, make sure you have no leak after the MAF.

 

[mrsolo2000]

All, I haven't forgotten about all the support. I am having to make some international travel for work and will have to put this troubleshooting aside for a while. I will follow-up once I get her running again. Thanks.

 

[mrsolo2000]

It was eating at me and I may have fixed it. I was fooling around with the ICM and it seemed that was where the issue was. I took it apart, cleaned up the grounding connections and she now fires right up and runs fine. I have not driven it out of my neighborhood. I fixed it late last night and don't trust it enough to drive to work yet. I will take her for a short drive soon and see what happens. The ground connections seemed to be tight and in good condition before I took everything apart. However, after I put everything back, no problems or starting issues.

On the ICM pigtail that has the CID, PIP, VBAT, IGND, etc. It was damaged by a rodent when I bought it but I repaired the damage. I noticed last night that the CID and PIP wires are wrapped in a shielding and has a bare, stranded wire wrapped around it. This stranded wire is not connected to anything. Is this normal? Should it be grounded somewhere or is this part of the shielding? I do not recall anything in the OEM wiring diagrams about it.

 

[rubydist]

iirc, that shield should be grounded

 

[kevinspann]

Yes, the shielding goes to a connector that leads to a ground in the harness.

Where are you at in VA?

 

[mrsolo2000]

I'm in Chesapeake.

 

[luigisho]

What color is your car? Maybe I'll give you a wave when I pass you in my green one. Not many still on the road locally.

 

[mrsolo2000]

Mine is green too. I am in the Hickory area now. I used to be in Western Branch.