Hello all! New member here and I am hoping you can help me resolve my problem.

The vehicle is a 2000 GMC Jimmy 4wd, 4.3, auto trans, 115k miles.

I recently purchased this vehicle for cheap due to a mechanical problem under the assumption it would be something I could resolve myself.

1.The motor starts right up and idles fine.

2. The vehicle will accelerate and get up to speed as long as you use very little throttle and are patient.

3. If you floor the vehicle from a dead stop it jerks, misfires, backfires through the intake, and will not shift up.

4. I scanned the vehicle and received zero codes. (with a snapon

 

The following items were already replaced for tune up purposes.

1. Delco plugs, wires, cap, and rotor.

2. Napa fuel, oil, and air filters.

I performed the following tests with results as follows:

1. I tested the TPS performing a sweep scan with a knowningly good multimeter. It started with a baseline voltage of 0.5V to a wide open throttle voltage of 4.1v. Upon further investigation I should be achieving a higher baseline and WOT voltage of 0.9v-4.7v respectively. I also tried adjusting the sensor to achieve a higher voltage range with zero results. It also swept smoothly through the entire range with no dead spots. Any thoughts?

2. I verified the catalytic converter was not plugged by performing a back pressure test and a hand heat test. While I have encountered plugged converters before, the issue with this vehicle does not seem caused by an exhaust restriction.

3. Fuel pressure checked out in its specified range with no sudden surges or drops.

4. I verified there were no vacuum leaks and achieved 18" at idle.

5. I cleaned the mass air flow sensor with its specific cleaner as well.

The battery has always been fully charged as well.

When the vehicle is acting up, it wreaks of gas almost like it would be loading up.

Could the MAP sensor be a culprit? How about the cam or crank sensors? Would the lower voltage of my TPS be a concern?

I am honestly stumped but am certainly open to new tests or suggestions. I am well stocked on tools and specialty equipment.

Thank you again for any help!

Brad

 

have you checked your o2 sensors to make sure there not getting lazy? I would lean more to faulty o2,cam or crank sensors. As it sounds like the computer is pumping in too much gas.

 

check ignition timing. Someone set mine to 7 degrees advanced like a sbc and when the dist advanced the timing during load it backfired thru the intake. It's supposed to be at 0 degrees in base timing mode. Unsure how to do that on the newer blazers but my 94 has a wire to unplug under the dash.

 

^^+1, get your timeing checked, i have a 2000 GMC Jimmy and had the smae problem, and did bascily all the same things as you, and finly broke down and took it to a mechanic, and turns out my timeing was -13 degrees!!!! he couldnt belive i was even able to drive it! all i needed was a new distributor, and my mass air flow was starting to go, but timeing was my problem. MAF didnt help anyhtough.

 

I have a 00 blazer 4.3 doing Exactly the same thing. Did it seem to do it at a lower rpm when engine was cold than when it was at op temp? I don't want to throw anymore parts at this thing till I'm certain. Thanks!! So glad to see this thread!!

 

Wouldnt the engine not start up if these sensors were bad?
I say this based on my experience I had an engine with fault crank sensor and wouldnt start till I replaced.
Im going with timing problem.

 

Did you get this solved I'm still chasing mine

 

This may not be the cause of your "engine issues" but I ran into something similar on my 2001 TrailBlazer.

If you exhaust all the "typical engine diagnostic" solutions without any success, think about what I've encountered.

I'm working on a 4WD issue and replaced the TCCM with a refurbed unit.
Much to my suprise I had loss of power above 2,000 RPM, shfiting from 1st to second took forever, the engine stumbled no matter how much throttle was given. Getting on a highway was almost a suicide mission.

I did all the "battery tricks" to no avail. Worked on the problems for 2 days and still had the engine and 4WD issues.

Once I put my original TCCM back in, every "new engine problem" went away.

I love my Blazer - I just wish it could talk and tell me "where it hurts".

 

I just wanted to thank you, efr3 - I have been dealing with this stumbling issue for weeks and removing the fuse for the TCCM allowed me to pinpoint the problem - it runs great with it disabled. It was a really strange issue that the normal diagnostics did not uncover. You're a credit to this community.