Strange problem I can't pinpoint

[jharrison]

Occasionally, my Sy acts like the timing wire below the dash is disconnected. Check gauges light and engine light come on, timing drops to 0 degrees, and I can't connect to the PCM with my laptop (it says there's no sync and cannot find PCM). Here's the catch, I have traced the timing wire from the PCM to the ignition module, and it's fine. It isn't broken or shorted, and I have connectivity from the PCM connector to the ignition module connector no matter how I jostle the wire, loom or cable bundle.

What I don't understand is that magically without doing anything the problem just goes away, timing comes back, and I can connect with my laptop. I can't associate the problem with temperature or drive cycle, it happens randomly, and when it happens nothing I do makes it go away.

Mike Lee thought it might be PROM related, like the chip not being seated correctly, but I have swapped from an RPM 16 bin chip with carrier, to a Hood chip without a carrier, and the problem still comes and goes.

I'm leaning toward a bad PCM or ESC module, but I have been told that if either of those were bad the truck would be totally dead, no start, nothing. Everything in this truck has less than 20 miles on it, motor, turbo, and all sensors. My sig has all the info for my truck.

Any ideas? :banghead:

 

[QWERTYphoon]

Re: Strange problem I can't pinpoint

The truck will still run (like crap) with a bad esc module. I would check the brown wire ecm b fuse connector, and what codes is it throwing up at you?

 

[jharrison]

Re: Strange problem I can't pinpoint

When the problem is occurring I cant connect with Datamaster, and I haven't tried to pull a code using the ALDL "key" and counting flashes, also I don't have an OBDI code reader. I think it's time to buy one.

As for the ECM B connector, the way I have it there is a dedicated power wire seperately fused coming directly from the battery and plugging in where the fuse would be in the fuse panel. (I relocated it to the bed, and added an IHRA approved kill switch) This allows the truck to shut down when needed without the ECM having to relearn when power is restored. I'll check the brown wire and see if there's anything causing intermittent connectivity.

Thanks. Hopefully I can get rid of this gremlin.

 

[MikeRenz]

Re: Strange problem I can't pinpoint

i'd check the pin connectors at the ecm also. the solders don't hold up too well to us violently installing and uninstalling the thing over the years. easily checked if your ecm isn't tucked back up behind the dash.

 

[johnboy89]

Re: Strange problem I can't pinpoint

I had a similar problem and it was the timing connector under the dash. Connector looked fine, but had some corrosion in it. Replaced it and was good to go. The thing is I was able to get connectivity with datamaster to reveal a code 42. Your root cause is most likely something different!!!!

 

[ed hess]

Re: Strange problem I can't pinpoint

When the problem is occurring I cant connect with Datamaster, and I haven't tried to pull a code using the ALDL "key" and counting flashes, also I don't have an OBDI code reader. I think it's time to buy one.

As for the ECM B connector, the way I have it there is a dedicated power wire seperately fused coming directly from the battery and plugging in where the fuse would be in the fuse panel. (I relocated it to the bed, and added an IHRA approved kill switch) This allows the truck to shut down when needed without the ECM having to relearn when power is restored. I'll check the brown wire and see if there's anything causing intermittent connectivity.

Thanks. Hopefully I can get rid of this gremlin.

In case you are using the round knob style flaming river kill switch for a shutdown this may be your issue. If so get in touch, otherwise ignore this.

 

[0966Sy]

Re: Strange problem I can't pinpoint

I would ohm the connector, shouldnt be more than .02ohm across while it plugged in. Dont back probe each side of the black connector, hit it at the wire about 1-2" from each side of the connector. Have someone wiggle it while your doing the test to see if it becomes open. What is the condition of the distributer?

 

[jharrison]

Re: Strange problem I can't pinpoint

In case you are using the round knob style flaming river kill switch for a shutdown this may be your issue. If so get in touch, otherwise ignore this.

I'm running a Jegs 300A push/pull switch kit with the ECM b side wired to stay hot despite the switch position, and fused with I believe a 10A. IIRC

I would ohm the connector, shouldnt be more than .02ohm across while it plugged in. Dont back probe each side of the black connector, hit it at the wire about 1-2" from each side of the connector. Have someone wiggle it while your doing the test to see if it becomes open. What is the condition of the distributer?

I did a continuity check, but didn't actually ohm it out. I set the meter to continuously beep and punctured the wire about where you said then ended up going from the ECM connector to the distributor connector and no bending or shaking of the wire or bundle caused the meter to stop beeping, aside from disconnecting the timing conector.

The distributor is an MSD #8367 pro billet, cap, rotor, and ignition module are all what it came with. They have less than 20 miles on them.

i'd check the pin connectors at the ecm also. the solders don't hold up too well to us violently installing and uninstalling the thing over the years. easily checked if your ecm isn't tucked back up behind the dash.

That's definitely something I didn't even think of, and a good point. I will pull the ECM and check for any cold solder joints.

 

[jharrison]

Re: Strange problem I can't pinpoint

I just bought both the "key" type code retriever and the small plug in module that also reads the ABS codes earlier this morning before work, i'll see if there are any stored codes.

 

[Don W.]

Re: Strange problem I can't pinpoint

The ECM connectors are not soldered. Just crimped. Doesn't mean one isn't bad but I doubt it. Looked at the manual there is a bunch of stuff but a couple of off the wall things for you. Check the TPS. With engine off and key on watch DM and it should show throttle volts going up smoothly. Does the tach jump when attempting restart? On pin B1 on the 24 pin ECM connector and its neighbor Black 32 pin C15 there are (on each) an orange wire. Those wires should have 12volts. Exactly how they get that I don't know. It's described in the big S15 PU wireing manual which is at the shop. but it comes off the firewall pass-through connector. ECM fuse? Someone holler and LMK.

Hope this helps a bit. That code reader will be the key though.

 

[jharrison]

Re: Strange problem I can't pinpoint

Well no codes are in the ECM, I guess i'll have to wait until it does it again and try to pull codes while it's acting up.