PCM problem please help

[skeeter72]

I'm running the new EEC. I have the diagram of the EEC system, thanks to this thread, but I need a diagram of the other circuit on this fuse. Completely blanking what is at the moment all the info is the truck and the weather is turning and I'm in bed so it will wait but I'm glad to see you got your short fixed. I'll keep yal posted. Once again if anyone could please post a pic of a 90-94 power distribution box and the wiring around it would be appreciated. I would like to plumb the wires correctly and maybe fix my problem.


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[LCAM-01XA]

Once again if anyone could please post a pic of a 90-94 power distribution box and the wiring around it would be appreciated. I would like to plumb the wires correctly and maybe fix my problem.

Actually you need the diagrams for a '92-'94 truck, '91 and older didn't have these nice power distribution centers at all so wiring for them is done quite differently from what you're working with. Unfortunately I don't have said diagrams, but have you searched to buy and EVTM (electrical and vacuum troubleshooting manual) online? They pop up from time to time and can be had for quite reasonable cost.

 

[skeeter72]

Well I fond the evtm online as well as a full electrical diagram for a 94. They should be here in a couple days. So till then I'll just keep replacing fuses. I do want to mention that I do not think the fuse blows on hitting a bump. I have noticed it is generally in the mornings on the first start up of the day. I'm wondering if it has to do with the starter working hard or the cold advance. Tomorrow I'm going leave a bad fuse in and start and let her warm up then put the good one in. I'll do this on all my cold starts. Let see if that isolates the problem.


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[LCAM-01XA]

Starter would be a doubtful suspect there, it's power feed circuit (which is what handles the load) is all heavy gauge cables and all are on the passenger side, and its trigger circuit (from ignition switch to relay behind passenger side battery) sees the same load regardless of ambient temperatures.

Really any guessing at this point is just that, guessing, better wait till the EVTMs arrive then dig into it more. In the mean time try to clean those loose wires real good, you'll need to be able to see their colors clearly when reading the diagrams.

 

[yARIC008]

You may have already said, but have you done any work on the truck recently, like right before or recently before this problem started happening? I managed to find mine by checking everything I could think that I had worked on recently.

I picked up a fox and hound the other day but didn't use it. In your case, it may still be handy to trace out some wiring.

 

[ifrythings]

I think I know what your problem is, Fuse U (20A maxi) goes to the TCM and.... the fuel heater, I bet ya its shorted and taking out your fuse, also the fuel heater only works when its below a certain temperature (when I tested mine I had to put it into the fridge before it would work) hence why its killing the fuse in the mornings or if the wire is shorting to ground on bumps.

I also wouldn't worry about extra plugs laying about, there probably for the trailer wiring or extra option.

P.S. Fuse I is the main TCM power feed.

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