mountainmanjoe

You need to keep all your misfire troubleshooting together in one topic please.

MitchM

should I now delete this post and re - post this new information under my original p0300 thread, which is really long ?

Pierregirard

Just saw your post. If you're still looking for info, here's my take. The P0300 random misfire code on your '07 Express 3500 can be tough to pin down, especially with all the work you and your mechanics have already done. Since it mostly happens when you're maintaining or increasing speed uphill, there are a few things you might still need to check. Besides the throttle position sensor, you should look at the throttle body for carbon buildup and make sure the MAF sensor is clean and working properly. Both can mess with the air-fuel mixture, especially when the engine is under load.

mountainmanjoe

@MitchM just keep it in mind for the future

MitchM

thanks for your observations. the TPS was serviced and all freeze frames show normal operation. my OBDII routinely records various engine data. the TPS data recordings from the OBDII all show as normal . 4 different mechanics and one chevy dealer have all thrown various parts at this 07 chevy, trying to fix this recurring problem, without success. I do not recall any mechanic running the wire integrity test for CKP signal that Schroedinger suggests. Schroedinger's solution is to look for a deteriorated or loose signal wire for the CKP instead of throwing a new CKP on for $300. checking for a deteriorated CKP or CPS wire seems a lot more efficient and time saving than throwing yet another new Crank Position sensor on.
By now this vehicle has had : 3 visits to mechanic #1 from nov. 2021 through June 2022 :new fuel cap, smoke test, , each injector cleaned and individually tested, complete tuneup done w/ new coil packs. MAF cleaned then replaced , throttle body position sensor checked, fuel pressure of pump tested as normal . #1 installed first new 'ac delco' CKP. (none of this work cured the P0300. ) #2 Aug 2022 mechanic cleaned main ground wire and installed CKP #2, (claiming that CKP #1 s 'was not ac delco. ) 4 months later, went to Chevy dealer , ( van waiting 3 weeks on the Chevy dealer lot, 'waiting for the transmission lift to free up'. came back in Dec. , chevy dealer installed new Cam Position Sensor and inspected charcoal canister and hoses saying all 'looked good' . mechanic #4 in July 2023 found weak and variable signals in the signal wire from the fuel pump, recommended fuel tank sender unit and its wire were replaced. ( which requires dropping the fuel tank which is an additional $200 of labor . ) Still no joy. 2 1/2 years and over $3,000 in mechanic bills.

Pierregirard

If your current mechanics can't find the problem, I'd suggest taking your car to an electrical specialist for a fresh look.

MitchM

thanks, Joe!