Discussion in 'Chevy Truck Forum' started by Smallfry32, Apr 28, 2010.
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Go to an auto parts store and get a book on your truck their is some in their.
As I recall, that ECM fuse is a 10A and runs to two points on PCM connector.
As you noted it does run to oil pressure switch and fuel relay.
Suggest you do a little isolating, does this blow with key to run
but not starting? Then likely shorting in engine area or bad PCM.
Bad PCM does not seem likely to me.
Pull the fuel pump relay and see if fuse still blows. Leave out.
If so, disconnect oil switch (may not be same as oil sensor)
and use a 10A fused jumper from battery Pos to Grey wire
in either the relay socket or pressure switch (not Orange wire).
What this does is isolate the draw of fuel pump from rest.
I suspect that since the blow is not instantanious but delayed,
that the fuel pump is going bad on you or is being overloaded.
If the fuse in jumper blows, you are down to one wire or
the fuel flow is being restricted at pump, filter or pressure valve.
Hope that makes sense, let us know what you find.
OK guys this is what I found out. Went and checked all of the wires that have been mentioned, and double checked. Nothing, so with the permission of my father in law (his truck) he said put a bigger fuse in it and see. Well it started up an ran great until the smoke from under the dash..I cut it off, went to the passenger side, under the dash there is a bundle of wires, taped to the outside of the bundle is something I have never seen. Here are pics of it...there is a purple and white and just a plain purple wire running to it...the truck runs fine without it...just not sure what it is....
Have not figured what it is connected to, but looks like a diode.
If partly shorted by internal failure, it what will do what is called "leaking"
and that will lead to blown fuses. What was the clip hooked to ?
A connector that has a purple wire on one side and a purple and white on the other...no clue where the wires go to, they are in the bundle of wires...I dont have a good wiring diagram...
You did not say but I'm guessing this is 2wd not 4wd or there could be two diodes.
That would make this the "Diode Module"
(hype = higher parts prices and tech rep)
Diode can actually be had at radio shack for $1-2, even GM says so.
Believe it's a 1N4001 or 1N4004. A physical size comparison will likely do.
Difference between the parts is amp handling, don't think this requires much.
Can't find at the moment my copy of GM's notice on diode selection.
My best guess is this diode is used to prevent RWAL/brake circuit
from wrongly effecting TCC solenoid operation.
I'd suggest replacing, not leaving out the diode.
Look closely for a single circle stripe on it, that's the polarity - critical.
Backwards it will act as a short at times and open at others.
Look for a reason for this being cooked.
A likely cause would be a TCC solenoid shorted to ground in trans.
Or maybe the wires running to trans, check harness underneath.
I don't have good drawings and there are differences between the
C/K and R/V trucks in 1989. Chiltons/Haynes not been much help for wiring.
Might try getting a part print from dealership.
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