91 bonneville 3800 vin c not starting

[Pepcfreak]

Hello all,

This is my first post here.

Im having an issue with my 91 bonneville. I was driving it and it cut off in mid drive. Had it towed to a shop and they said it was the ECM. I then had it towed back to my house since i know how to change ecms with no issues.

I then changed the ecm and still it did not start.

I had my fiancee sit in the drivers seat and turn the car over as i sprayed starter fluid into the throttle body and i got ignition but it wouldnt start. This lead me to thinking the fuel pump was out.

I turned the key on and can hear the pump pump gas into the engine. I also removed the fuel line and place a cup to catch the fuel and i have determined the pump is indeed working fine. I also pressed the presure release on the black fuel line that carries the fuel to all the injectors and it shoots the gas up high enough to hit the hood so i assume the gas pressure is fine as well.

This leaves me completly stumped as to what the issue may be. /do any of you have an idea as to what i should do next. To recap the car wants to start when spraying starter fluid meaning it is getting spark/ignition, there is gas in the lines under pressure from the pump so it is recieving gas. I check my receipt from my last gas visit to make sure it wasnt desiel fuel (i know it would be awfuly dumb to do that but hey never hurts to make sure right )

Please help!


No cpdes from using the paper clip method. thought id add that.

[crash93ssei]

Did you use a new ECM or a old one?

Years ago, I had a '89 SE that had a bad miss, and I took it to my Uncle who is a GM master tech. He used light tester on the injector harness and found that the ECM was bad as it wasn't firing one injector. He also told me that you can take a 194 bulb, straighten the tabs on it and plug that into your injector plug when it is running or cranking to see if the injector is getting power.

You can try that, if the bulb flashes your ECM is firing the injector.

It is odd to me though that you would encounter the same problem with two different ECMs, used or new. I would do the bulb test to make sure the injectors are or are not firing and go from there. Check your battery connections, remove and clean all of your grounds.

I know that the '92+ cars have a ground buss that can cause a lot of issues, but I am not sure about the '87 - '91. I am sure someone will chime in on that one as something to look at if your car has one.

[Pepcfreak]

It was a brand new ECM. Weird thing is i tried starting it without the ecm and everything acted the same as if the ecm was installed.

Isnt the bulb test only good if you think only 1 of your injectors arent getting power? Like i said its not starting at all. Engine turns over fine. My battery connections are fine everything is grounded. It just doesnt seem the engine is getting any fuel since starting fluid wants to make it start.

Ill continue to look around anyone else have any ideas??

[2000Silverbullet]

Check all your fuses and relays.

You could have fuel pressure but if your injectors are not firing then you won't get fuel.

[Pepcfreak]

in looking at my user manual i see where the injection fuse should be... however i am unable to locate that fuse. I see my 25 fuse panel but not the other one. The ones under my hood are all good as well.

[Pepcfreak]

Found the fuse it was blown. I replaced it and now it keeps blowing fuses. I cant pinpoint the short. Is there anywhere is hould be looking in particular or up the amps a bit on the fuse see if that helps?

[2000Silverbullet]

Don't up the amps. You must have a short somewhere. It you up it, you could promote a fire! Track down the short. Use a multimeter and test your circuits.

[Pepcfreak]

I was joking about uping the amps

How ever i have no idea where to start looking for the short. I have no idea where to start. Any ideas?

[crash93ssei]

It is not going to be easy or fun, I had short issue on my old '93 (I have had many Bonnevilles and a lot of problems over the years LOL) that took me three months to track down because I didn't want to take it to a shop to figure out and pay $300. I could have been quicker, but I could only work on it a little here and a little there.

Start at your injector harness and look for any obvious signs of wear in the wires and wire loom and work your way down the harness to the firewall. Go under the dash and do the same thing where that set of wires goes in. If you don't find anything obvious, then it is time to start pulling wires out of the loom and trace the injector harness down to look for any bad spots. This may become difficult as you go into the loom as you may find factory splices in the wires that will lead you all over the engine compartment trying to track it down.

No need to do the bulb test now

[Pepcfreak]

i tested the wires and here are the ohms on all of them.

Harnesses by cylinder -

1 - 11.8
2 - 11.8
3 - 11.91
4 - 11.78 (bounced to 11.8 but stayed more on 11.78)
5 - 11.8
6 - 11.8

Injectors were all at 0 ohms.


As u can see cylinder 3 is higher then the rest. Is that an indicator of the problem or normal?

[Mechanical Mike]

Disconnect the ICM (ignition control module) & see if the fuse blows.

[Pepcfreak]

Icm is under the coil pack right?

Also, i can start the car multiple times and i actualy drove it around for about 20 or so miles (had extra fuses) and it didnt blow a fuse. Went to drive away again 1 hour or so later it blew as i was backing out my driveway. Replaced it and drove to dinner and came back and it blew right as we pulled into our neiborhood. Its the weirdest thing.

[Mechanical Mike]

Yes the ICM is under the coils but try unplugging the oil pressure sending unit instead of the ICM.

[Pepcfreak]

what all sensors and components are actualy on the circuit labled injectors? The icm and oil pressure sending unit is on this same fuse?

[2000Silverbullet]

Try replacing your oil pressure sending unit. It is a common failure. There is a circuit that shuts down the ignition if your oil pressure drops to dangerous levels.

[Pepcfreak]

Its kinda odd you say that because for the past 2 years its been showing around 80 amd above 80 as my oil pressure and if im not mistaken it should be round 40. Ill try disconnecting it and see if it stops blowing the fuse, but i just dont see how the oil pressure sensor will blow the ingnition fuse.

-Edit update - I decided before i did any to put a new fuse in it and check the wires under the dash by shaking them and tapping hard on the fuse box the fuse is in and see if it would short out. It did not. Also i shook the wires to each injector and tapped on each injector as the car was running and nothing happend. Took it for a ride around the club here and ran fine, we have alot of speed bumps and a brick paved road which causes alot of vibrations and nothing shorted out. That fuse is still going strong. When i got back to my garage i restarted my car about 13 times and no fuse blown. What ever is causing this issue is driving me nuts. Either that or the other fuse i used was bad. For the record the car has only blown 2 fuses. The one that was in tha injector slot since manufacture, and the one in the spare 10amp slot since manfacture. Since i put this new new fuse in it it hasnt blown. Is it possible that the fuses were just old?

Also i dont know if this is part of the issue, but since about 6 months after i got the car (with 40k on it) the headlight warning light has been on. Headlights work fine and never have had an issue. Could this be showing its ugly head finally causing problems?

[Mechanical Mike]

The fuel injectors, ICM, oil pressure sending unit and I believe the fuel pump relay are all on that circuit. Since the oil pressure gauge is showing high it seems like the most likely suspect.

[clm2112]

Its kinda odd you say that because for the past 2 years its been showing around 80 amd above 80 as my oil pressure and if im not mistaken it should be round 40.

Same sensor, but on different curcuits (the oil pressure sender is also an oil pressure switch.) One wire provides the variable resistance to the instrument panel to make the oil pressure gauge move, a seperate wire on the same sender operates the fuel pump relay to keep the pump running so long as the motor is developing oil pressure. The funky gauge readings are not a reflection of the circuit that operates the pump. Also, I've notice the instrument panel gauge is not a finely calibrated instrument By all means check it, along with the wiring harness leading up the back of the motor. A pinch point for the harness is right about where it passes behind the power steering pump and the valve cover.

Meanwhile... blowing fuses is never a good sign and the fact that it's not blowing the fuse every time indicates something that is intermitantly touching ground...like a chafed wire in the injector harness. Check the harness over very carefully. Remove the plastic looms (that black corregated plastic tubing that is wrapped around the wiring) and visually check every inch of the harness wiring.... yeah, it sucks, I just did the same thing this weekend... but if you are getting a intermittent fuse blowing then somewhere in that wiring is a bare piece of wire that touches steel when the engine is running, popping the fuse.

If you haven't realized it yet, there's a black plastic cover on the firewall just above and behind the motor on the passenger side. It's held on with two 10mm nuts and there's a lot of wiring hiding behind it... including the power distribution terminal, a pair of relays, and where the main harness comes through the firewall and jumps from the body to the engine. Take a peek under that cover while checking the harness. If you need them, I'll shoot some pictures of mine tonight while I'm working on my own issue.

[Pepcfreak]

Just spent the last hour checking the wires all the way to the firewall (Very dirty hands before typing this ) and i didnt see anything. The wires were also taped all the way down too. i started to look under the dash but keep losing track of the wires.

Im begining to think it my not be the wires or injectors.

The fuel injectors, ICM, oil pressure sending unit and I believe the fuel pump relay are all on that circuit. Since the oil pressure gauge is showing high it seems like the most likely suspect.

Now would this cause intermitant blown fuses? like i said ive only blown 2 fuses that are as old as the car, the new 10amp fuses are holding strong. Could it simply be they were old and time for them to just go poof?

[clm2112]

Now would this cause intermitant blown fuses? like i said ive only blown 2 fuses that are as old as the car, the new 10amp fuses are holding strong. Could it simply be they were old and time for them to just go poof?

Fuses don't wear out.... then melt when the current going through them goes beyond the rating. They could be 50 years old and still work like a charm.

If you blew just the fuel injector fuse, then you will probably find the problem in the pink & black wires that go to all six injectors. Short in the other colors leading from the fuel injectors back to the ECM would not cause a fuse to blow, they would just cause an injector to lock open. The ECM is switching these wires to ground to turn on the injectors, the pink & black wires are powered by the fuse all the time the key is in run, so a short on any of the pink & black wires would blow the fuse.