Truck died about a month ago. See post started on 3/18. Shop replaced the distributor and it worked. However it happened again a couple of weeks ago. The same blown fuse ECM B indicated it was the same problem. In assessing the situation. the distributor was new and mostly mechanical with the only solid state part the Ignition Control Module. So I took a chance without really knowing and replaced the ICM. It worked. A commenter on my first post had the same problem and it was in his case caused by the air cleaner box shorting wires with worn insulation. I checked and it looked like there may be worn insulation on the plug wires to the ignition coil. So as part of last fix I wrapped them is electrical tape and hoped I was good. Not so. It died again today. How do I track down this intermittant problem? Could it be the Ignition Coil? More lost work. this thing is killin me. Thanks.
CK5
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1991 Chev V2500 5.7L ICM Keeps Blowing
- Thread starter GaBnn3
- Start date
If the plug wires are bad, replace them. Electrical tape isn't going to stop them from arcing.
IIRC people talked about the injector wiring being pinched under the air cleaner. Have you inspected those well? As a temporary fix electrical tape would likely be ok there, to see if that fixes it.
Hopefully this link works to show what wires people meant: https://www.gmfullsize.com/threads/the-tbi-thread-305-and-350.63198/post-6107683
IIRC people talked about the injector wiring being pinched under the air cleaner. Have you inspected those well? As a temporary fix electrical tape would likely be ok there, to see if that fixes it.
Hopefully this link works to show what wires people meant: https://www.gmfullsize.com/threads/the-tbi-thread-305-and-350.63198/post-6107683
The ECM B fuse is part of the fuel pump circuit in a TBI injected truck. I had an ECM B fuse blow in my truck, and it was a dead fuel pump in my crew cabs left side tank that caused it.
My case was a little different but my ‘91 Blazer was popping the ecm b fuse also.
Here’s where mine was different. I had a 5.3 swapped in at the time and we used the stock Tbi fuel pump wiring and relay to run the pump. I experienced a couple of occasions where the ecmB fuse popped and killed the truck.
If I remember right it was a 20 amp fuse. I ended up putting a fuse buddy device in the ecm b position so I could monitor the current load on the fuse.
The thing I had noticed is the fuses didn’t snap like a dead short. They were actually melted slightly where the fuse would normally pop.
Watching the fuse buddy as I drove it the display showed 19 amps most of the time. 20 minutes into my drive with the display never going over 19 amps the fuse failed.
Nothing was inherently wrong other than the higher pressure pump was pulling a little more current than the lower pressure Tbi pump.
I put a 25 amp fuse in it and continued to drive with the fuse buddy in place. I never saw the display go over 19 amps and it never killed the fuse again.
I would not recommend just throwing a bigger fuse in without checking what’s going on first. If it’s snapping the fuse right away there is a dead short somewhere. But if it takes a little while worth of driving before the fuse fails it may be worth the effort to get a fuse buddy and watch what it is doing. In my case the bump of 5amps was within the safe range for the factory fuel pump circuit.
Here’s where mine was different. I had a 5.3 swapped in at the time and we used the stock Tbi fuel pump wiring and relay to run the pump. I experienced a couple of occasions where the ecmB fuse popped and killed the truck.
If I remember right it was a 20 amp fuse. I ended up putting a fuse buddy device in the ecm b position so I could monitor the current load on the fuse.
The thing I had noticed is the fuses didn’t snap like a dead short. They were actually melted slightly where the fuse would normally pop.
Watching the fuse buddy as I drove it the display showed 19 amps most of the time. 20 minutes into my drive with the display never going over 19 amps the fuse failed.
Nothing was inherently wrong other than the higher pressure pump was pulling a little more current than the lower pressure Tbi pump.
I put a 25 amp fuse in it and continued to drive with the fuse buddy in place. I never saw the display go over 19 amps and it never killed the fuse again.
I would not recommend just throwing a bigger fuse in without checking what’s going on first. If it’s snapping the fuse right away there is a dead short somewhere. But if it takes a little while worth of driving before the fuse fails it may be worth the effort to get a fuse buddy and watch what it is doing. In my case the bump of 5amps was within the safe range for the factory fuel pump circuit.
Poor insulation on spark plug wires, won't pop the ecm b fuse. You would have a miss fire and poor performance.
If the insulation is damaged they need to be replaced.
The wiring to the injectors, enters at front through a rubber block in a notch. The air cleaner assembly sits on rim the notch is in. With normal service over time the wires that pass through can be pinched and shorted to ground, by the air cleaner assembly.
With age the wire insulation gets hard and cracks, exposing the conductor to possible shorting.
I would love to see a picture of the blown fuse.
It is possible the fuel pump is failing, or the wiring has high resistance.
I don't believe the distributor is the cause of ecm b fuse failing.
The pick up coil in the distributor does rotate and the wires do move, but if they went open or short the engine would die or run poorly, I do not believe it pop ecm b fuse
If the insulation is damaged they need to be replaced.
The wiring to the injectors, enters at front through a rubber block in a notch. The air cleaner assembly sits on rim the notch is in. With normal service over time the wires that pass through can be pinched and shorted to ground, by the air cleaner assembly.
With age the wire insulation gets hard and cracks, exposing the conductor to possible shorting.
I would love to see a picture of the blown fuse.
It is possible the fuel pump is failing, or the wiring has high resistance.
I don't believe the distributor is the cause of ecm b fuse failing.
The pick up coil in the distributor does rotate and the wires do move, but if they went open or short the engine would die or run poorly, I do not believe it pop ecm b fuse
I've also seen a number of fuses that no longer pop when they reach their supposed rating.
I'd make sure anymore I was buying fuses that were brand name, from a legitimate store.
My fuse block melted before the fuse popped, I assume that was most likely a "fake" fuse as well.
I'd make sure anymore I was buying fuses that were brand name, from a legitimate store.
My fuse block melted before the fuse popped, I assume that was most likely a "fake" fuse as well.
Thank you all for the replies. This thing is now the biggest paper weight in the world. It has new: fuel sending unit, distributor, ignition coil, spark plugs and spark plug wires. It has died 5 times within the last month. Each time a new ICM got it going temporarily. A couple of times the ECM B fuse did not blow but the ICM was still bad. This last time the fuse did blow and there was no "SERVICE ENGINE SOON" light showing on the dash. No trouble codes show when it dies on those occasions when the SES light is visible. I do not see any worn insulation on the fuel injector or coil wiring. I am at my wits end. I trace it back to that hard bang from a large pothole the first time it died. What could it be? Thanks.
All I can recommend at this point is to download the wiring manual for the '91 here: http://67-72chevytrucks.com/vboard/showpost.php?p=5621043&postcount=1 and fully understand everything tied into the ECM B fuse. Then you need to find every one of those wires (that carries voltage, not ground) and inspect them thoroughly.
The ICM's are very sensitive to heat, I'm assuming with this many changes the heat conducting paste is used every time under the ICM...
I'm totally speculating here, but I'm wondering if the ICM is acting as the weakest link in that circuit. Something is shorting out, but the fuse isn't blowing before the ICM does. Not going to hurt anything to run a lower and lower rated fuse until you find one that it runs on, but consistently pops before the ICM fails. If that will even happen.
But regardless, unfortunately an intermittent short is going to be tough to find, or you would have already. Start with every component that connects to that ECM B fuse, and work backwards from those. Connectors are always suspect, and usually that section of wiring is easier to inspect. Once those wires enter the harness is when it gets tough, but NORMALLY if there is a short inside the harness, you will see where the wire wrap has been abraded/pinched/whatever
The ICM's are very sensitive to heat, I'm assuming with this many changes the heat conducting paste is used every time under the ICM...
I'm totally speculating here, but I'm wondering if the ICM is acting as the weakest link in that circuit. Something is shorting out, but the fuse isn't blowing before the ICM does. Not going to hurt anything to run a lower and lower rated fuse until you find one that it runs on, but consistently pops before the ICM fails. If that will even happen.
But regardless, unfortunately an intermittent short is going to be tough to find, or you would have already. Start with every component that connects to that ECM B fuse, and work backwards from those. Connectors are always suspect, and usually that section of wiring is easier to inspect. Once those wires enter the harness is when it gets tough, but NORMALLY if there is a short inside the harness, you will see where the wire wrap has been abraded/pinched/whatever
Thanks for the reply. I did download the manuals. However, I fear this may be over my head. My attention is now on getting my other car running. I had more than one paperweight in the driveway and need a working vehicle.
Check the wires running along the outside of the frame on the drivers side. The wire loom likes to rub through, and ground onto the frame at that location.
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In my shop, an ignition module replacement always gets a coil as well. A coil can take out a module and vice-versa. Cheap insurance
The blowing fuses make you think there is wire touching somewhere, but that kind of problem shouldn't destroy the ignition module. The recurring dead module points to some shorted windings in the coil. It's been a while since I had an HEI, but I think you could place an inline fuse holder right by the coil. It should only need 5-10A. If that blows you've found the culprit. It's also possible these are off-brand modules which are failure-prone or not properly installed and they tend to pop a fuse on their way out.
I'm also curious if you have a condensor at the distributor, how it's grounded and how the distributor is grounded.
I'm also curious if you have a condensor at the distributor, how it's grounded and how the distributor is grounded.
Did you find a solution to this? I am fighting an ECMB fuse issue on a buddy's '89 suburban.
Yes, in my case I found the solution. The problem was that the ECM-B circuit wiring under the hood was shorting out due to worn insulation. The truck would immediately die. This happened several times before I figured it out after much cursing. Most, but not all, of the time the Ignition Control Module blew also. I have the manual and when this fuse blows it says to find the short in the wiring. This circuit is the orange wire that runs under the hood from the fuse box to the oil pressure switch and fuel pump relay then through the firewall to the computer. The temporary fix for me was to inspect that circuit and cut out a bad piece of wire with worn insulation. I just bought a used wiring harness but haven't received it yet. So I fixed the ECM-B issue for now but I'm struggling with another similar issue. The computer is not receiving the distributor reference signal so it runs like crap. The distributor and, of course, the Ignition Control Module are new. So another probable wiring issue indicated. I suggest that your buddy plan on a new or used wiring harness because if you have one problem there could be others. FYI Ron Francis Wiring has a new engine harness available at a steep price. Ebay seeks several hundred for an engine wiring harness. I lucked out and got a used one for $220 shipping included thanks to a tip from someone on this site. I posted under parts wanted. Good luck.
Thanks. Pretty sure we have the same issue. ECMB fuse blew. Put in a new one and it worked for a while and then blew again. Now its a dead short, blows every new fuse. That should be easier to find, just haven't had time to check it again. He was just throwing parts at it despite being told he was diagnosing things wrong. Already did a new fuel pump and he was about to do an ECM too. His harness isn't too bad but the loom is starting to fall apart in places.
I feel better now. I did the new fuel pump also, a big deal on a suburban. The shame of it, for us shade tree mechanics, is that, with an electrical issue, the symptoms resemble those of mechanical issues we've seen before. So, we think we know what the problem is. In the long run I feel like I'm ahead of the game, not having any formal training, even if I did one or two needless repairs. This site is a tremendous resource.
Yep. Most of my real automotive knowledge has come from doing things wrong or the hard way. Those lessons tend to be the ones you remember.
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A little late to the party here but I must be missing your point. A wire with higher resistance will have lower current passing through it.
For future reference, don’t go replacing a fuse with a higher rated one without knowing the current that the circuit draws and the acceptable current the wire gauge is able to handle. That’s a good way to start a fire.
The pick up coil is what generates the signal the the ECM. The signal comes from the pick up coil, through the control module, then out to the ECM. The problem could be the pick up coil, or sometimes the wire that connects the pick up coil to the control module goes bad. Also, the wire that connects the pick up coil to the control module can get pinched under the control module.
