95 Jimmy start problems

I have a 1995 Jimmy and about a year ago, the fuel pump and relays went out. I had them replaced and hoped that would be the end of it, but the truck has had intermitent no-start problems ever since.

Both the fuel pump and relays have been replaced -- again (still under warranty), the ignition switch has been replaced, in fact, pretty much everything having to do with the fuel system has been either checked and/or replaced.

And it's still having no-start problems.

Basically, it doesn't do this all the time. There doesn't seem to be any repeatable sequence of events to trigger it -- sometimes it will not start after it's been sitting, sometimes it'll do it after it's been running for awhile, and sometimes it will fire right up, run for about 30 seconds and then die and refuse to start. Whenever it refuses to start, you can clearly hear that the fuel pump is not starting.

The one thing every instance has in common is that continuing to try to start it will do no good whatsoever, no matter how long you try. However, if you leave it sit (don't crank it or anything) for anywhere from 5 minutes to a half hour, it will fire right back up and not have any problems again for awhile.

Without knowing much about how the computer systems work (so bear with me if this theory is stupid), it's almost as if the computer "thinks" it's already started the fuel pump, so continuing to try to crank it does no good, but if you leave it set for awhile, the computer resets and comes to its senses. Is this possible? If so, any ideas what replacing this might cost (I already have well over $1000 invested in replacing everything else in the fuel system)?

Any help or further insight into what might be going on would be greatly appreciated.

-- Robert

CPI injector and nut kit

Open up your upper plenum and check for washing.

Search for CPI injector in the blazer section of this forum.

CPI injector and nut kit

Open up your upper plenum and check for washing.

Search for CPI injector in the blazer section of this forum.


Thanks for the tip. However, I double-checked with my mechanic and this is something that has been replaced recently (I've put so much into trying to solve this problem over the last year that I honestly can't remember what's been replaced -- or how many times it's been replaced...I love my Jimmy, but I'm about ready to drive it off a cliff!).

The problem is that this issue is very intermittent -- it happens just often enough that I generally get stranded somewhere and have to sit and wait for it to decide it's ready to run again. My mechanic has had it for over a week and have not been able to reproduce the problem (the one time it failed to start for them, by the time they got their diagnostic computer hooked up to it, it was starting again).

Any other ideas about what we might look at?

-- Robert

Did you mechanic replace the cpi injector and nut kit, or is he just speculating that it was done?

I'm with you, Blazer. I had one in my shop that dang near drove me nuts. Replaced everything but the CPI unit with no luck. Sometimes it would run fine, others...well, you know. Tried rebuilding CPI with no luck. Break down & put in a new one. It'll set you back about $300, but it worked for me.

Yea, shady mechaics like to string you along replacing everything else when on a 1995, this is the problem most of the time.

Did you mechanic replace the cpi injector and nut kit, or is he just speculating that it was done?

They say they've replaced it. The receipts for all the work done are in the glove box of the Jimmy (which is currently at the mechanic), so I can't verify for sure at the moment.

However, the mechanic really has no reason to jerk me around on this -- they are the in-house mechanics for a family-owned (Uncle's) dealership. So it's not like we're just people they can tell to get lost and hope we never figure out what was and wasn't done. ;)

But they are at a complete loss for how to fix the problem because the damn thing just won't not start for them (the GMC gods are toying with me -- I just know it), so they are having a hell of a time trying to diagnose anything.

-- Robert

REmove the upper plenum and check for washing from the nut kit and the CPI injector again. The new one could have been defective, it happens.

Also, have the ignition switch checked.

REmove the upper plenum and check for washing from the nut kit and the CPI injector again. The new one could have been defective, it happens.

Also, have the ignition switch checked.

I'll make sure they look at the CPI injector again. The ignition switch was fairly recently replaced.

Thanks for your help so far. I'll keep you posted -- particularly if the CPI injector doesn't pan out to be the culprit and I need to make another cry for help! :)

-- Robert

I would look at it yourself. Check for washing on the passenger and driver's sides.

Don't just blindly take his word for it.