Mechanics

INTERMITTENT FAILURE TO START

1997 GMC Sierra • 192,000 miles

I've had intermittent problems with this truck for a couple of years now, but have usually been able to get it running reliably for a period of time. I've replaced cap and rotor, plug wires and plugs in the past. More recently, it failed to start winter of 2010. I let it sit until the spring then diagnosed that the fuel pump was failing. I dropped the tank and replaced the fuel pump and it seemed to run fine through the summer/fall. It refused to start again in the winter, so it sat until this spring. I replaced the fuel filter (had to cut/splice the lines) and got it running again, but now at my current issue.

Randomly, the truck will fail to start. When it does start, it runs a little rough, but it accelerates and idles without significant issue. There doesn't seem to be any consistent set of conditions when it fails to start - it could be morning, noon, night, wet, dry, hot or cold (weather) or hot or cold (engine).

When this occurs, I do notice that I can't hear the fuel pump "priming" when the key is turned to the start position, but before attempting to crank the engine. I thought it might be a short or bad connection to the fuel pump, but haven't been able to trace it down.

Also, without any understanding of why, the truck will frequently start and run OK again for awhile after it sits for a few hours after trying to start it. To reiterate again though, it doesn't seem to be tied to the engine temperature.

Any thoughts/troubleshooting tips?

Best regards,

Mark
Avatar
Mark_harris
June 26, 2012.




Get a spark tester ST-125 and a fuel pressure gauge-hook it-don't wait for nothing-attempt to start -this will tell you something what's missing make sure you have a helper to observe
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Tiny
Rasmataz
Jun 26, 2012.
I think I discovered the issue (and a new problem?). Before I dropped the tank to replace the fuel pump last year, I replaced the fuel relay (in the fuse box under the hood). On a hunch, I pulled it out to reseat it and noticed some "scorching" on one of the terminals (#30 pin). One I cleaned it off, the fuel pump kicked in on the first try and the engine fired up.

When I got the truck home, I pulled the relay again to clean it up better and noticed that it was very warm and smelled of ozone. I plan to get another replacement, but am now concerned that something else may be going on to cause this relay to fail so quickly (probably ran less than 20-40 hours with this relay).

Thoughts?

Tiny
Mark_harris
Jun 26, 2012.
Relay getting hot to the touch-could be short circuit somewhere

Tiny
Rasmataz
Jun 26, 2012.

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