ecm ignition fuse

[bradleypa]

I am working to troubleshoot why the fuse on the ECM ignition keeps blowing out. My 97 blazer has been long faithfull. When the fuse blows there is no fuel pump, and the fuel gauge needle is all the way to the right. I can get the fuse to blow under normal acceleration. I have replaced the pump and trust it's working fine. I have looked at the harnesses as best as I can but find no bare wires. Any ideas?

[b1lk1]

97 was a bad year for ignition switches going bad causing all kinds of electrical gremlins.

[MT-2500]

Originally Posted by bradleypa

I am working to troubleshoot why the fuse on the ECM ignition keeps blowing out. My 97 blazer has been long faithfull. When the fuse blows there is no fuel pump, and the fuel gauge needle is all the way to the right. I can get the fuse to blow under normal acceleration. I have replaced the pump and trust it's working fine. I have looked at the harnesses as best as I can but find no bare wires. Any ideas?

EMC B fuse 9 feeds fuel pump relay and fuel pump switch /oil pressure fuel pump switch and VCM computer.

Hook a fuse jumper with a fuse 10-15 amp to fuel pump and see if it blows and also check amp draw on fuel fump under load.

Post back amp draw.

Check wiring at oil pressure switch real close to.

[bradleypa]

I had a long day of testing to no avail. I have a new problem now. the #10 fuse will blow when the ignition is turned on. I disconected the fuel pump at the harness and tried again still blew the fuse. I am starting to wonder about the ignition switch. We did have small issues about a year ago you would turn the ignition on slowly and there would be a long pause before the system would come on.
Could you tell the location of the oil pressure switch?

Thanks for the info.

In Christ,
Bradleypa

[MT-2500]

Fuse 9 and 10 both feed the computer.

Fuse 10 feeds crankshaft sensor and fuel injectors and computer.

Oil pressure switch is top rear of engine by dist.

If it is popping fuses it has something shorted.
Start disconnecting circuits one at a time untill you find it also inspect wiring and give them a wiggle test.

With fuse 9 and 10 both popping check the computer and wiring real good for shorts.

Some parts places and tool dealer sell a short finder tool that helps pinpoint shorts.
Good Luck and
Let us know how it goes.

[bradleypa]

Just #10 fuse is blowing. I tried the test of running the jumper wire with a 15 amp fuse to the pump and got nothing. No pump at all I checked the connections to the pump and tried again, nothing. This was very interesting since that line is supposed be direct. Did I miss something? I am working on getting an digital meterw/ OHMs on it to do the other test. I'm going to start looking at the ignition switch area first to find shorts. I hate moving old wire I sometimes wonder if I cause more shorts that way.

Thank to all

In Christ,
Bradleypa

[MT-2500]

Originally Posted by bradleypa

Just #10 fuse is blowing. I tried the test of running the jumper wire with a 15 amp fuse to the pump and got nothing. No pump at all I checked the connections to the pump and tried again, nothing. This was very interesting since that line is supposed be direct. Did I miss something? I am working on getting an digital meterw/ OHMs on it to do the other test. I'm going to start looking at the ignition switch area first to find shorts. I hate moving old wire I sometimes wonder if I cause more shorts that way.

Thank to all

In Christ,
Bradleypa

The gray wire from relay feeds fuel pump.

If it is only blowing fuse 10 get a good wiring diagraqm on it now work on that circuit.

[bradleypa]

Ok started with the ignition switch. Noticed there was some high heat warping in the harness lines were not melted but might be one cause. I can see why GM has had lots of problems with the switch. tooooooooooooo many connections. That little black box on the steering wheel that's the contact box. A cam on the inside rotates and makes the connections to run and start the motor. Some of these connections have burn marks from repeated use. I would say there normal but it creates contact loss in the system.

[bradleypa]

I replaced the ignition switch and the fuse #10 still blew. I have disconnected every line and have isolated the pink wire from the fuse box to the PCM so far all has checked. It's hard to get a good test though when the system is so intertwind with circuts. I think i'm getting close.

[MT-2500]

Originally Posted by bradleypa

I replaced the ignition switch and the fuse #10 still blew. I have disconnected every line and have isolated the pink wire from the fuse box to the PCM so far all has checked. It's hard to get a good test though when the system is so intertwind with circuts. I think i'm getting close.

Keep unpluging untill you find it.
Some times a short finder tester helps.
Good Luck

[bradleypa]

Found it!!!!! Crankcase wire was rubbed bare on a transmission return line. I did do what you had said by unplugging everything that was in that fuse line when I went to unplug the crankcase connector I saw the wire. Took the truck for test drive and all went well.

In Christ
BradleyPA

[MT-2500]

Originally Posted by bradleypa

Found it!!!!! Crankcase wire was rubbed bare on a transmission return line. I did do what you had said by unplugging everything that was in that fuse line when I went to unplug the crankcase connector I saw the wire. Took the truck for test drive and all went well.

In Christ
BradleyPA

Good Find.
Glad you found it.
And thanks for posting back how it went and what you found.
Good Luck