2003 Trail Blazer 4.2 2WD Will Not Rev Past 2100 RPM - Hard Stumble - P0341

Hello Everyone,

First time posting on here and hopefully get some direction with this trail blazer.

I purchased the vehicle for my wife with an issue from a guy who already had it at a garage for 2 weeks and they gave up. So here we go...

Vehicle will not rev past 2100 Rpm whether in park or while driving so vehicle speed is limited to about 30 to 35 mph. I can describe the event as a hard bucking/rapid misfiring more of the sound of good anti lag on a turbo.

From the garage, they already loaded the parts cannon, there was a new VVT solenoid, Cam position Sensor, Crank Position Sensor, Ignition Coils, Spark Plugs, Knock Sensors, ECT sensor, oxygen sensors, fuel filter Timing Chain kit with new sprockets and VVT actuator, oil pump and pickup tube and harmonic balancer, along with a several fresh oil changes and air filter, all the parts were GM parts by the way.

So now here is where i come in, I checked over there work including pulling the valve cover to verify timing marks which are spot on, fuel pressure remains constant 53 to 58 key on prime and about 50 running including a throttle snap, pressure never drops. Engine produces 21 to 22 inhg of vacuum and the needle is steady. Compression on all 6 cylinders is about 205 to 210. Lastly, I even dropped the converter to rule out plugged cat.

So what i am seeing on the scan tool is steady fuel trims + or - 6, oxygen sensor respond quickly to extra air, map reading remains accurate to load. Now the kicker, at the 2100 rpm when the engine bucks the RPM pid on the scan tool drops off and the Cam sync counter starts climbing till the ECM fails out the sensor, even with that failed out it still will not rev. So i can not attempt the crank variation relearn. Even on the freeze frame data it shows Zero rpm.

I have checked for the wiring from the sensor to the ecm for rub through which resulted in nothing, i have tested power and grounds to the pcm during the stumble and all values are good, no drop outs Also Oil pressure remains constant in the vehicle in the middle of dash gauge. Lastly, i have scoped the cam and crank sensor directly at the pcm, both have solid waveforms which never drop out.

I am starting to think this is a p0341 by proxy from another issue such as fuel volume perhaps?

Really need some directions with this guys.

wow that's a tough one I guess a fuel volume test wouldn't hurt i am fairly new at this just trying to get better in diagnosing engine performance problems

Would you be able to post the cam and crank waveforms? I'd love to compare to a known good. The CMP Sync counter going off when the symptom happens is a big red flag for me.

While we're talking scan data, I'd be interested to know what the commanded and actual timing advance PIDs are doing at 2100 RPM. Maybe try power braking it and see if the PCM is getting the advance it's looking for?

FWIW, I'd stay with the P0341. It seems like the PCM is definitely pissed off about what the CMP/CKP are reporting, and doesn't really know what to do about it. :silly: