Possessed Truck

[JoeX87000031]

Hello to Everyone,

I am new to the forum and new to the honor of GM diesel Ownership. I purchased a 1994 6.5L and I love it so far. I got a real good deal on it, at a cost. I think it may be possessed. I think I may be confronted with multiple problems. I want to blame the ECM but they hardly ever go bad in my experience. To get to the point, she runs rough with white smoke anywhere from 2200 to 3000. Smoothe all other RPM. Here's the kicker. It will only run that good with the coolant temperature sensor disconnected. Once you plug that back in it on like donkey kong. Pulled 9 codes after running it with the sensor back in. 5 for the Throttle Circiuts, 1 for the Wastegate Solenoid, and 3 for Cylinder Misbalances. Unlpluged the Sensor and reset the codes, only 1 comes up, that being for the coolant temperature sensor. Its got a new Injector pump. I have already changed the fuel filter and have began to closely inspect the wiring harness. I found what I think was the AC compressor clutch cannon Plug all fried and burnt. Maybe that wasted the ECM? I dont know, but I cant find anything wrong with the wires headed to the coolant temp sensor and the sensor ohms good? Computer should only cost me about 300, anyone else ever ran into something like this, or do I need to find a priest?

[JohnC]

Could the sensor be shorted? Or the wrong sensor? I don't see how the ECT sensor could cause all those codes. If it ran off the 5 volt supply, maybe, but it doesn't. (How many wires on the sensor in question?)

Check closely the ground point on the rear of the intake manifold on the passenger's side head.

[JoeX87000031]

Said Sensor lead has 2 wires and you are right about it getting a 5 volt "feeler" signal from the ECM. I was wondering if you know how many sources the ECM uses to determine Coolant Temp. I ask because even with the coolant temp sensor unplugged I still get indication in the cab although it never gets past what I would guess to be about 150. If it only gets signal from the one Coolant Temp Sensor than I suspect that someone may have swapped the Inlet Air Temp sensor with the coolant temp sensor. Will troubleshoot further and re-post.

[JoeX87000031]

I disconnected the Inlet Air Temp Sensor to see if my coolant temperature gauge would stop reading, it kept on reading a temp even with both the Coolant temp sensor and the Inlet air temp sensor disconnected. I am going to gain access to the ECM and check the wire from the ECM cannon plug to the Coolant Temp Sensor to see if it has stray voltage and if it ohms good. If that wire checks good the only thing I could think of it being is the ECM itself. I think I said earlier that when I inspected the wiring harness I found that the plug that I suspect goes for the AC pump Clutch was burnt out and badly damaged. There is nothing but a threaded hole on the AC pump where the female end of the cannon plug should be. I think that when that AC Pump failed with sparks and flames it may have sent a damaging power spike to the ECM. I dont know though, wouldn't fuses and fusable links stop that? Whatever the cause may be I will keep posting in this thread so you all can enjoy my hipshot troubleguessing as if you were here to laugh at me in person. Also, ANY help or suggestions would greatly help me at this point. If you know of someone particularly electrically savvy in here that may have been turned off by the title "possessed Truck" send them this way. Take care and sure appreciate the input I have already recieved from you.

P.S. I ohmed the the Coolant Temp sensor and it was right on the money for what it should have been at ambient temperature.

[JohnC]

The dash gauge circuit is completely independent of the PCM. IIRC the sensor is on the outside of the driver's side head near the front.

[JoeX87000031]

Well this weekend I plan to pull my truck into to garage and do a good number of repairs over time so that I won't have to pull everything apart more than needed. My goals for improvement and repair are as follows;

1. Take off whatever fenders, wheelhouses, and interior panels as required to gain access for a complete inspection of my wiring harness and also to replace all the grounds with new better ones.

2. Replace all injectors with new Staynadine ones and also have the old ones testested to confirm any problems

3. Replace both batteries with new Optima yellow 720 CCA ones. I guess the yellow means that they are a mix between deep cycle and Cold Cranking. I figure that 1400 CCA should be more that enough?

4. Get new battery cables made, maybe even top post ones if there is clearance, if not enought clearance I will get new side posts and use that nice mod with the bolt and the nut I saw on here. My compliments to whomever cam up with that one, I dont have the post in front of me now.

5. Replace the turbo wastegate vacuum controller. Getting a code for that every now and then and its only 30 bucks, I mean why not. Also run new soft vaccuum lines from the pump to the controller and over to the actuator even though they already leak ckecked pretty good with my little pump guage.

Thats all that I figure would be a good solid choice to tackle at this point. The previous owner said the Glow Plugs were new, but I am going to try and see if all 8 look new. If any of you have a chance to read this and have any input, I would greatly appreciate it. I am new to this and could be going in the wrong direction. I also have other codes occaisionally for the throttle system, but nothing that those codes lead to are cheap so I figure I better verify proper ECM operation first. Take care all, and I am going to put a picture on this post of what my truck looks like now with all the broken light lenses replaced and the tint gone and interior cleaned.