Just bought this 2006 4.2 Envoy,runs good and sounds good for the most part,at idle it throws a p0300 and after a bit p0301
Compression good,did tighten intake bolts.swapped coils and new plug.Here is a log at idle ,below 750 rpm it has low timing,with idle up timing is up.Long terms go lean near the end.Please help see what I am not seeing Thanks.
Have you tried swapping injectors yet or making sure fuel pressure is good?
2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.
If you don't post your tune and logs when you have questions you aren't helping yourself.
Originally Posted by 5FDP
fuel pressure good,have not swapped injectors.Would faulty injectors drive timing so low under 750 rpm?
Post your tune, even if stock please!
Timing below 750 rpms will be set in the tune, without a tune file we can't compare what the log says with what the PCM has programmed.
On my 02 (early coil design), I was getting P0300 and cyl 4 misfire (typical water coming off the cowl and landing on #4). Think #2 had an issue as well, ended up replacing both of them (and new plugs) in 2020 during the winter. Decided to just replace all 6 of them once it warmed up with fresh plugs all around.
Recommend clean the throttle body as well and pulling the negative cable for ~30min while doing it.
5FDP may be on to something, if it's new to you and previously sat for a while, the injectors could be partially gummed up/clogged.
~Erik~
2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned
I will post the stock tune,ive swapped 3 coils in on #1 plus it had 1 new one. 3 different plugs,it idles at 600 or so,thats when it will idle fine for a bit then the misfires climb to 100 and re set to zero,then idles smooth for a bit then starts missing and climbing again,if I hold the above 750 rpm it has not miss and timing is up, at idle timing is way low like 5*.THANKS for posting.
OEM tune and a log of today as it warms up then it starts the misfiring ,in earlier log holding rpm over 750-800 rpm it doesnt seem to misfire and timing is up.THANKS ! appreciate all help.
Base idle table at 400, 600, 800rpm cells is set to 8* spark.
ECT correction table has a few degrees that decrease as ECT increases.
Warm idle RPM is 595, you're getting close to that when ECT nears 176*. This log doesn't show engine going to full operating temperature (~203-207F).
I see misfire counts starting at the beginning of the log that occurs throughout, so I don't think it's directly tied to coolant/engine temp. I'm guessing that higher idle speed is masking the misfires a bit more, then when the rpms drop and ECT modifier gets pulled, the engine stumbles and it's more apparent.
If you get another log, could you include airmass (g/cyl) and start it from cold (low ECT) and let it fully warm up?
I think there's something mechanical happening here, can you swap spark plug+coils around to see if the misfire follows?
~Erik~
2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned
Thanks ScaraEpic22,,I will get that log in the morning when its cold,I just got done doing a injector swap and it didnt make any difference,,just as the coil and plug swap multiple times didnt change any.Side note this 4.2 runs as quiet as can be.
Last edited by Sierravgen; 10-26-2022 at 04:21 PM.
Here is a log from cold start and a log with HP tuners idle raise to 700 rpm.This does not stumble or stutter at all.Slight rough idle at when you see it missing.it revs up fine but these 4.2s kind of come on at upper RPM like cams is coming on or timing coming in,its just not as strong as others.Thanks
It gets more strange,raise the rpm to idle at 700rpm,in park it will mis and trip the light.In gear it will not mis or throw the light.I did check the crank for end play.seems tight.
Last edited by Sierravgen; 10-28-2022 at 04:51 PM.
Yea they're pretty quiet engines in factory form! And yes, lots of torque down low thanks to moving the exhaust cam around, but the HP doesnt come in until you rev it up a bit and let it breathe.
If it only does it under 700rpms and only when in P/N, that's a bit puzzling. Wonder if it has anything to do with load, when in D there'll be load on the engine as the transmission will be in gear vs not in gear.
I'm running out of ideas other than something mechanical that only shows up without load.
~Erik~
2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned
Thanks for taking the time to look at my info,it does make it quite odd that it wont miss in gear at 700 rpm.Crank end play was the only thing I could think of.But its tight.I see in all different forums 4.2 misfires and a lot not solved.Appreciate it Eric
These were notorious for failed valve seats. Gm even issued a software update that wouldn?t flag misfires at idle to weasel out of warranting the heads on the 5 and 6 cylinder engines of the day. They usually idle a bit rough but run mostly fine in the road.
I hate to give you bad news. But i think you have a worn thrust bearing or possibly the crankshaft area that rubs against the thrust bearing. In gear the driveline load will push the crank in place. in park the crank could be moving away from the crank sensor. Easy to check. With engine not running, using a prybar between lower pulley and the timing cover. Check for excessive movement front to back of the crankshaft endplay. Should be very little movement. If you can move it a 1\4 inch that is real bad.
Dave,that was my first thought when I discovered it didnt mis in gear at 700rpm.As earlier mentioned I checked for crank play and could not get it to move.
Misfire with a stock engine with a stock tune. Why don't you take it to a shop? Can't tune out real problems.
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