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ECM I Fuse blowing

FormulaGT

FormulaGT

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Hi,
Newbie here. I have an '88 Jimmy 4X4 350 that keeps blowing the ECM I fuse when you turn the key. Fuel pump does not prime thus vehicle does not start. I did get it to start with a 15A fuse rather than the stock 10A and shut it off right away. Any common remedy's to this problem? Thanks for the suggestions.
 
15A fuse is a BAD idea. Extra power through the ECM will burn it up fast.

No common ECM issues I know of. Start hunting for shorts to ground. Disconnect the ECM and see if the fuse still pops.
 
I agree abut the BAD idea but I was in a remote area and out of fuses and a little desperate. The truck is 2 hours away from home at my inlaws who live in the boonies. I need to do some homework before I return to it. Electrical issues are sooooo much fun!
 
I had the same problem with the ECM II fuse blowing, and shutting the truck off. I found there was a short were the wires come from the computer, out of the fire wall. They must have rubbed the fire wall. I just pulled them out some, and haven't had a problem. I didn't get to pick up my new harness my friend has for me, but soon as I do, I'll inspect the old one to find the exact problem.
 
There is prolly a short somewhere in the fuel pump circut. ECM1 controls the fuel pump. Check the FP wireing al the way back to the tank. Check the FP relay and the oil pressure switch. If all looks good. It may be a bad fuel pump or a short in the fuel pump wires inside the fuel tank. DO NOT PUT A BIGGER FUSE IN ! Unless you like gasoline fires.
 
my ecm fuse kept blowing and it ended up being the fuel pump pulling to many amps so we replaced the pump and problem solved.
 
Some history:
About a year and a half ago, I took off from a stop light with my foot into it a bit. Running along and BAM the engine just shuts down. I pull over and realize my fuel pump is not turning on or "priming" during ACC on ignition. I ASSume it is the fuel pump. The tank needed replacement anyway as it was just starting to show moisture seeping through. So I replaced the tank, fuel pump (AC Delco), filter, strainer and relay. Still did not fire up. No power to fuel pump. Went through the fuses and found ECM I dead. Replaced it and all was good untill now. I have wondered what the cause was for the fuse to blow originally as I replaced a lot of parts I did not need to. Oh well. I noticed in the wiring diagram that the coil / tachometer is running on that circuit. When I originally got the truck I put a tach in it and am wondering if some of my conections have gone south. I think I will have to go over a lot of wiring with a fine tooth comb. Too bad it is not sitting in my driveway to tackle this. It will be a few more weeks before I get a chance to tackle this project in person. Appreciate the suggestions so far.
 
As suggested, with a good supply of fuses, you can simply unplug things that are tied into the ECM1 fuse, until the fuse stops blowing.

There are other ways to do it (continuity tests) but that's about the fastest, especially if you've got handfulls of fuses from the wrecking yard. :)
 
I've seen the wires going to the injectors get pinched under the air cleaner. I just don't remember if it blew ecm 1 or 2.
 
same thing happened to me a while back. turned out to be a bad fuel pump relay. unplug it put in a new fuse turn the key if it dont pop replace the relay. if it still pops unplug the fuel pump put in a new fuse and turn the key if it pops rolly the pump. but check all the wiring to the relay, injectors, and pump first. doubt the ecm is bad though it is possible. and as stated before use only a 10 amp fuse. good luck.
 
As you stated The coil is also wired thru that circut but. It usually does not cause any trouble. But beings you have a tach wired in that may be the problem. Try disconnecting the Tac first and do a visual on the injector wires inside the aircleaner.
 
I appreciate the suggestions. Dear god I hope it is not the fuel pump. Been ther done that twice.
My factory manual has these items listed as ECM I:
ECM Ignition Feed, Vehicle Speed Sensor, TBI Spark Control Module, TBI Fuel Injectors, TBI A.I.R. Divert Solenoid, TBI E.G.R. Solenoid or E.V.R.V. Solenoid.
ECM B has the Fuel Pump, ECM Memory and TBI Auxiliary Fuel Tank Switching Valve.
Given that information I would assume it is not the pump itself as I am blowing the I fuse and not the B.
Thanks again for the suggestions. I am taking notes to take with me when I get a chance to tackle my project.
 
oohh ok. i got the ecm i and ecm b fuses mixed up. i guess i was blowing the ecm b fuse. wont be the pump or relay for sure. so like you said check all the wireing to the components and the components on that fuse. shouldnt be TOO hard to find.
 
now that i think about it i beleive i had a prob blowin the ecm i fuse a seperate time and it ended up being the coil or one of the injector wires pinched. cant remember which. its been a while. might want to try borrow a known good coil and just plug it up and set it on the intake manifold. and see if it works. also make sure the injector wires are not pinched. and as it happens i have two spare tbi coils.
 
Try unplugging the oil pressure sending unit and see if it stops blowing fuses.
Pretty common for the sender to short out internally and blow fuses.
The sender is behind the distributor and has a 3 wire connector.
 
Finally got some time to do a visual on the Jimmy at the in-laws today. Pulled the air cleaner off and didn't notice anything obvious at first. Then I started moving the injector wires a little and one of them was pressed against a bent tab on the TB riser plate. It had vibrated through the insulation and the wire was in constant contact with the metal tab. Thank you all for the input. Your suggestions got her home where I can do some long overdue tlc. Cheers!
 
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