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blowing ecm i fuse

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k5floyd

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Feb 6, 2004
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Friendswood, Tx
*still having problems

well, i fixed my truck yesterday. the msd didnt like being dunked:doah: so i got a new one and it started right up. and now, last night coming home, right as i entered my neighborhood, it died. too tired, and lazy to do anything with it then, i just pushed it to the side of the road. got it home this morning, and discovered it was a blown ecm i fuse. put another in and it blew. so now i have a short or something somewhere in the ignition stuff i dont know how to find. any ideas?? all the wires look good, ive got a new msd box, and a new coil.
 
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Give it some time my friend. Most people are at work and haven't had a chance to read or respond yet. After a day or so there should be some help. My only ideas as of now are maybe one of the power wired could be a little chafed and is shorting out to the dash. You need to unplug the ECM and check the wires for shorts and the like.
 
Had the same thing happen to my 87 TBI several months ago. Had to put in a new ECM. I also looked for shorts but I had another truck that ran and tried the ECM from it before I purchased one. It cost around $75 from Auto Zone. Good luck!
 
i just disconnected the msd wires to the distributor, turned the key, and the fuse didnt blow. connected the back up. then i disconnected teh msd wires to the coil, turned the key, and the fuse didnt blow. connected them back up, and turned the key, and it started right up. let it run for a min. and **** it off the put the air cleaner back on and make sure every was like it should be. then i turned the key, and the fuse blew. ARG! anyone else here have an msd box with their tbi? or anyone with experience with the msd box and tbi? i think this is happening because of my wiring, but i dont see anything that could cause this. how about some pictures of someones wiring on their tbi motor with msd at the distributor and coil? thanks guys
 
My plastic tub within the fuel tank came loose breaking the sending unit. This cause the ECM to blow whenever the tub hit it just right. Never knew there was such a thing within the fuel tank, so it was very difficult for me to find.
 
there are 2 different ecm fuses, ecm i and ecm b. from my understanding ecm b is fuel related, and ecm i is ignition related. my ecm i fuse is whats blowing.
 
ohh, and i think my air cleaner box thing is causing my problem because when ever i have it off to get access the the wiring and such and i turn the key it starts fine and the fuse holds. but when i shut it off to put it all back on, and turn the key, the fuse pops. but now i dont see any exposed wires or anything that could be touchting it and causing it to short. any more ideas??
 
When I had my 89 I had this problem, it turned out to be the fuel pump(in tank).
The way I figured it out was I isolated the wire to the pump (+) and tried a fuse and turned the ignition and the fuse never blew, this after someone told me it could be the pump. By isolating I mean I cut the wire at a point before it went to the tank/pump.
Hope this helps.
 
ughh, this is not fuel related, otherwise it'd be blowing ecm b fuses. i already had problems with my ecm b fuses blowing a while ago, which turned out to be a bad fuel pump relay.
 
i had a similar problem with a TBI s10 p/u.. turned out the wires going to the injectors were being pinched between the ring that holds up the air cleaner and the throttle body, easy fix but a PITA to find!!! something for you to check out good luck!
 
yeah, thats the first thing i looked at when i first thought it was the air cleaner, but it looks ok. thanks
 
ok, so i did end up finding a wire to the injector pinched between the ring on top of the throttle body and the throttle body. it had just a small bare spot, so i wrapped a bit of electrical tape around in, and made sure it wasnt touching another wires or the throttle body or being pinched. so now this whole problems gets even gayer when i now try to start it, im not blowing the ecm i fuse anymore, but now the ecm b fuse. so im not sure if solved my problem and now having another, or the previous problem just stopped by itself, and i now have a different problem. i unplugged the connecter at the fuel pump to try and see if something on that circut was causing my short, but im still blowing the ecm b fuse. tried unplugging the fuel pump relay, and still the ecm b fuse is blowing. i keep searching and searching for any bare wires or anything that looks like it would cause a short, im not seeing anything. i need more help. thanks
 
im thinking one of two things, 1. you fried the box when you dunked it check the backside of it the rubber part and see if its black instead of yellow like its supposed to be, 2. when you get out of the truck after its working and you go back to put it together do you leave the key on "ignition on" position and listen to the radio by any chance?
 
that will fry some fuses. I just blew fuel pump fuse or ecm b putting in cps sensor when two wires with current touched. always good idea to kill ingnition. could be metal touching your ignition or shorted wires if its not the wires you might have fried something in the ecu.
 
Whats on the ECM B fuse?

Guessing you don't have a wiring manual around, but all you need to do is test each wire on that fuse with a voltmeter for short to ground, then just trace the wire.
 
not too sure where the actual circuit is but it controls power to the fuel pump. Sits to the left of the ecm i fuse on the box. If you blow the ecm b fuse your fuel pump will not come on.
 
smokedout said:
im thinking one of two things, 1. you fried the box when you dunked it check the backside of it the rubber part and see if its black instead of yellow like its supposed to be, 2. when you get out of the truck after its working and you go back to put it together do you leave the key on "ignition on" position and listen to the radio by any chance?
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1. i dont know what rubber part you're talking about. the msd box is an all metal case. and ive got a new box now.

2. ive had the radio off so i can hear anything that might be important, and i always turned the key all the way back

that will fry some fuses. I just blew fuel pump fuse or ecm b putting in cps sensor when two wires with current touched. always good idea to kill ingnition. could be metal touching your ignition or shorted wires if its not the wires you might have fried something in the ecu.
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ive looked and looked for bare wires, wires touching another wire or something metal. i doubt any part of the ecm fried, because the couple times the fuse didnt blow, the engine started right up, idled and reved up just fine.

Whats on the ECM B fuse?

Guessing you don't have a wiring manual around, but all you need to do is test each wire on that fuse with a voltmeter for short to ground, then just trace the wire.
Click to expand...
fuel pump i know for sure, not positive if injectors or whatever else is. how do i find what wires are on that fuse? and how do i test the wires with a voltmeter? what will it tell me? ive used a voltmeter before, but i dont have much experience with them. my dad, does have one and hes an electrical engineer so he may be able to help me with this.

not too sure where the actual circuit is but it controls power to the fuel pump. Sits to the left of the ecm i fuse on the box. If you blow the ecm b fuse your fuel pump will not come on.
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actually my ecm b fuse is to the right one and down one, but thats not important. and i know that when the ecm b fuse blows my fuel pump doesnt come on, as i had my fuel pump relay crap out a while back, causing a short, which was blowing the ecm b fuse.
 
bump. any more suggestions, help, or answers to my above questions? i know i need to be patient, but really need some more help.
 
You need to get a wiring manual for your year (although any TBI '87-91 is going to be close enough likely) and that will tell you everything that is tied into the ECM B fuse.

Say you find out that the wire on pin B of the fuel pump relay (just making up locations here) is tied into ECM B. You would just set the voltmeter to check continuity, plug one end of the probe into pin B, and the other end to ground. If the wire is cut somewhere, and shorting to ground, you'll know.

I've never looked at a troubleshooting manual to see if fuse blowing is in there for the flowcharts, but that would be your BEST bet if it is, since the component itself could be faulty, and the manual will tell you which components/wires to test, and how to test them.

Electrical problems can be extremely frustrating, but the factory flow charts make it all come together, and really relieve the frustration, at least for me.
 
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