96 Lumina Blowing ECM fuse

I just bought a 96 Lumina with the 3.1L engine. Shortly after buying the car it quit while sitting at a red light as if it was out of gas and would not restart. After towing it home I checked the fuses and found the ECM bat fuse that was supposed to be a 20amp fuse had been replaced by the previous owner with a 30amp and had blown. I replaced the fuse with a 20amp and the car started right up. I left the car idling and after 5 or 10 minutes it stalled again. I checked the fuse and it had blown again. Does this indicate the ECM is bad or going bad? Is there something else that would cause this to happen? Any help would be greatly appreciated.

After doing some more research it appears that the oil pressure switch could be a cause. The Low Oil light does come on and the oil level is right where it should be. Could this be the problem, maybe?

I just bought a 96 Lumina with the 3.1L engine. Shortly after buying the car it quit while sitting at a red light as if it was out of gas and would not restart. After towing it home I checked the fuses and found the ECM bat fuse that was supposed to be a 20amp fuse had been replaced by the previous owner with a 30amp and had blown. I replaced the fuse with a 20amp and the car started right up. I left the car idling and after 5 or 10 minutes it stalled again. I checked the fuse and it had blown again. Does this indicate the ECM is bad or going bad? Is there something else that would cause this to happen? Any help would be greatly appreciated.

After doing some more research it appears that the oil pressure switch could be a cause. The Low Oil light does come on and the oil level is right where it should be. Could this be the problem, maybe?

maybe something else is piggybacked onto the same fuse, (original or not). Sometimes stereo people hook up onto things for extra power.

Sounds like somebody modded something and subbed a borderline fuse in there.

The stereo is the factory original and there doesn't appear to have or previously had any type of aftermarket alarm or other electronics installed so I don't think there is anything piggy-backed but I will check that out.

I do have new information with a couple of theories. This afternoon I put a new 25amp fuse in and the car started right up and idled for a few minutes before blowing the fuse again. I immediately replaced the fuse and it would not start so I decided to try to reset the ECM by taking the fuse out. I left the fuse out for a few hours while I took the family to the beach. When we came home I put the fuse in and the car started right up. This time I messed with the throttle a bit. When I hold the pedal to the floor the engine misses like it is starving for fuel. It ran for about 10 minutes before blowing the fuse again. So my theories are that either the ECM is going bad and resetting it between fuses allows the car to run for a few minutes. My other theory is that the fuel filter is partially plugged causing the car to basically run out of fuel when the fuel in the system is used up and causing the fuel pump to overwork and blow the fuses. Letting it sit for awhile is allowing the system to refill with fuel through the plugged filter. Or I may just not have a clue as I am grasping at straws. Any ideas with the added information, ie the engine missing at full throttle? Thanks again for any help.

First...NEVER hold it to the floor unloaded (if that's what you did)...if so that was the rev limiter cutting it back around 4000 rpm so you don't grenade your motor...so it cutting out doesn't surprise me if that's what you were doing...it's supposed to do that...

I had this weird thought based on what you described that maybe the eCM ground is bad, it's trying to ground through the oil sensor, and causing both problems, sounds plausible, but I'm not sure if it's possible...I have seen ones that wouldn't start until you hooked a scanner to them, the ECM was grounding through the scanner...

I'd look at that sensor wiring and the ECM grounds and connectors real carefully...

Disconnect the sensor, see if it will run, and if so does it still blow the fuse?

The 20A ECM/BAT fuse also protects the fuel pump circuit from the relay to the tank. Perhaps that would get you pointed in the right direction.

You may have discovered the reason the previous owner sold the vehicle. They already installed a larger fuse in the circuit in an attempt to "fix" the problem. Now you get to perform a proper repair.

The 20A ECM/BAT fuse also protects the fuel pump circuit from the relay to the tank. Perhaps that would get you pointed in the right direction.

You may have discovered the reason the previous owner sold the vehicle. They already installed a larger fuse in the circuit in an attempt to "fix" the problem. Now you get to perform a proper repair.

Ahh.


So my patented "Defeat the fuse with a piece of metal, and fix whatever catches on fire" advice might have resulted in a fuel tank fire...

Good thing I didn't go that route :uhoh:

:runaround:

The 20A ECM/BAT fuse also protects the fuel pump circuit from the relay to the tank. Perhaps that would get you pointed in the right direction.

You may have discovered the reason the previous owner sold the vehicle. They already installed a larger fuse in the circuit in an attempt to "fix" the problem. Now you get to perform a proper repair.

Do these have the low oil shutdiown where fuel pump power is denied if it doesn't see minimal oil pressure after start?

I remember ones that did, but lost track of if that was still incorporated..

Just trying to think of how the false warning light could be involved...

Ok, so I had to work all day today and only had a chance after dark to try some things. First the 30 amp fuse that I started it on last night had not blown, so it stalled for a different reason last night. I looked at the sensors the best I could in the front of the engine. It looks like there are three. The one on the driver's side of the filter and closest to the filter was already unplugged. (oil pressure switch?) The one on the passenger side of the oil filter seemed to move around an awful lot. I was unable with a flashlight and my big hands to unplug the wire but it wouldn't pull out but seemed like the whole thing moved an awful lot. Shouldn't that be rigid? Also the third sensor further away from the filter on the driver's side looked ok but I am pretty sure only has one wire coming from it. Should there be two? I will double check that tomorrow. I had looked at wires yesterday in the light. Both of the driver side sensors have tape wrapped around them where they leave the harness. So after looking at those wires the best I could I attempted to start the car. It started right up, ran for about 10 minutes and sputtered a little before stalling. I immediately pulled the fuse and to my surprise it was not blown again. This is leading me back to the fuel theory. I will try to check the ground wires from the battery and ECM tomorrow before work and change the fuel filter if I have time. Thanks for you guys help so far. This sure is getting frustrating. I wish I had a couple hundred dollars to pay someone to fix this but being new to the area and not knowing alot of people I am also a little leary of having someone throw parts at it at my expense.

Test the fuel pressure while running. When it dies and does not restart, verify there is spark from the coil packs.

Also, the oil pressure switch does not cut power to the fuel pump. It is not a low oil pressure shutoff. The switch is used as a redundant path for power to the fuel pump in the event of relay failure. Look closely at the schematics in the service manual and you can see this clearly. No domestic GM vehicle has EVER had an oil pressure switch used as a safety shutoff for the fuel pump, despite the misinformation proliferated across the interwebs:

http://72.19.213.157/files/1996CorvetteFuelPump.jpg


http://72.19.213.157/files/C4FuelPumpCircuit.jpg


http://72.19.213.157/files/1991-92F-CarTBIFuelPump.jpg


http://72.19.213.157/files/S-TruckFPump.jpg


http://72.19.213.157/files/MAFpower.gif


You can usually win a bar bet with that one, so long as those betting aren't too drunk to understand the diagrams. Ford used a fuel shutoff switch, and those drivers think that since Henry did it, everyone did it. As usual, they are sadly mistaken.

Also, the oil pressure switch does not cut power to the fuel pump. It is not a low oil pressure shutoff.
You can usually win a bar bet with that one, so long as those betting aren't too drunk to understand the diagrams. Ford used a fuel shutoff switch, and those drivers think that since Henry did it, everyone did it. As usual, they are sadly mistaken.

My '78 Monza would cut the pump when it got about 3 qts low and the light came on....seems like my Vegas would too...

I trust you, but are sure on NEVER? :wink:

Ok so I started the car this morning and got down by the fuel filter and could hear the fuel pump running. It didn’t seem to chatter or sound real noisy but I could definitely hear it. While it was running the fuel pump stopped for a second or two and the car kind of sputtered, but the pump started again and it picked back up. It ran for 5 or 10 minutes before the pump stopped and the engine sputtered for a few seconds and shut off. I checked the ECM fuse and it hadn’t blown (but I do have a 30amp instead of the 20amp fuse in it) but it wouldn’t start or fire other than when it first rolled over it kind of sputtered like it was using up a little bit of gas left in the system. Then it just rolled over. Does the fuel pump have a resistor or anything in it that if it gets hot it kicks out or is it just the fuses? What I do know is it always seems to run for the same 5 to 10 minutes before shutting off. With the 20 amp fuse in there it blows that and shuts off, otherwise it acts like it runs out of gas and shuts off. I am going to try to change the fuel filter today and see what happens but I am thinking it is the fuel pump which is beyond what I know how to do. It seems like if it were a bad ground or a loose or broken wire it would run more erratic but it runs good while it runs minus the sputter when the pump stopped for a second. I did check the battery cable ground and the other grounds I could find in the front of the engine compartment and all seemed clean and tight. Thanks for all of your help so far.

Ok, so I changed the fuel filter and that didn't fix it. So it was concluded it was probably the fuel pump which is beyond my ability to fix on my own. So I dropped it off last night to a mechanic. They found the fuel pump was bad and some of the wiring going to it had to be fixed (from the oversized fuse I would guess). So I am told it is fixed now, though they closed before I left work so I am crossing my fingers that when I pick it up tomorrow that the fuel pump fixed it. Thanks again for everyone's help.