Misfire at Idle
When i first fire up intermittently it will miss really bad on cylinders 2 and 7. I checked plugs wires and coils, compression all came back good. I did a intake valve cleaning with a BG product and put injector cleaner in. No change at all after all of this. I did a injector balance test with manual gauge and didnt see any drop below 5 psi in all eight injectors. The pcm is up to date and there is no service bulletins that relate to this in my state. I check for a vacuum leak but that came back negative. Just wondering if you guys have any ideas on this?
Try scopeing the cam and the crank and do an in cylinder pressure waveform if you can for those two cylinders. These engines are known for valve spring and lifter issues
I don't have a really good in cylinder transducer. But I did an intake pulse with relative compression and the intake pulls looked really good.
I would check for excessive carbon deposits. you can pull the intake and have a look. if you find excessive carbon I use walnut shell media and clean up the deposits.
I was wondering if I should just take off the intake next and check it out
hi there, did you take the valve covers out, if I not mistake this engine has a cylinder deactivation system, it may be an valve pusher stock, the cylinders that have deactivation are 1-7 (left bank) and 2-4 (right hand), hope this helps you!
The intake pulses looked good but not sure about exhaust I may have to take it off and check it out.
How do you get it to stop missing or what is the scenario? Rev it up, warm up, does it disopate on its own regardless of your inputs? Did you verify injectors aren't leaking in those cylinders? Oil level and condition. As others have alluded to, the afm lifters may be too blame bleeding down overnight.
You can rev it up or wait till it goes into closed loop and it will stop missing after a little bit. I don't hear ticking until going into closed loop. I cant see any injector leaks into the cylinder. Oil level is good and condition is good.
I find balance testing to be inconclusive with these injectors (and GM GDI injectors in general). The test can pass, but your spray pattern can still suck. Does the miss go away once the engine goes into closed loop? I've had great success using a secondary ignition probe on the plug wires during cold start. One on a good cylinder, one on a suspect. Snap the throttle when cold. A lean cylinder…
Yes it goes away when it idles down and goes into closed loop. That's a really good idea about using secondary clamp on good and bad cylinder. What is a good injector balance tester out there?
Not my idea - Search Ray Yergeau around here. ;) He's got some fantastic scope captures using that technique.
Unfortunately the AFIT is the only gm accepted flow tester for gdi injectors. These can be difficult diagnose as they require the engine to be cranked so the hpfp can build the correct pressure. Can you use an amp probe on the injector‘s power for a current ramp with a trace? Then use the firing order to play one (or 2 in your case) of these is not like the other...
Also these are known for injector issues. GM has an internal memo about it. Also I found this interesting “During a cold start, the engine control module (ECM) commands dual-pulse mode during Open Loop operation to improve cold start emissions. In dual-pulse mode, the fuel injectors are energized twice during each injection event. As with misfire diagnosis, in dual-pulse mode the ECM monitors…
Using GDS there is a test to check the injector balance rates. There are bulletins for those three codes. One states to check for coolant intrusion. The other has you checking for excessive injector variance. States if they are out of spec then to replace the faulty injectors. I can find the bulletin numbers tomorrow, but I found them in alldata. Had a 17 sierra in today with these codes. Edit…
Yes I had the dealer confirm the injectors were the problem
Have you ever used napa injectors and had any luck with them or is it just best to go to oem and get dealer parts
does it only misfire when its cold? Seen coolant in the intake runners . SI information
I checked it and it had no coolant but it was confirmed I had injector issues
Does a good old fashioned vacuum gauge bounce while it's misfiring? Will the miss subside if you enrich with propane?
Look at misfires at cold start then any misfires on cylinders the injectors are bad GM has a cold start problem with injectors
Yes that is what it was I had injector problems
I did not check that but I was leaning on the injectors and had the dealer check it and I had a couple injectors that failed
I did not check that I had already taken it in to check and injector balance test but I will make sure I check that next time around
Fuel injectors are known problems, afit tool is only tool to catch it but can be inconclusive! 9.9 out of 10 it’s the injectors with the p050d- do them all at once,or it will be back !
Yes I took it the dealer and they confirmed it, I had 1, 2, 3, and 7 that failed the test thank you for the help
Yes I talked to the customer and that is exactly what they want to do is all of them like you said very good point thank you
Check these documents: 20-na-098, 3136475, pip5498L, N…
Yes i did check those but none of them work in my situation
A j2534 pass through device and a gm subscription is cheap. (In comparison to others). With that you could have confirmed it yourself. Look into to tooling up! Those documents are all the info you needed to confirm.
i know what your saying and you are right on the money. i need to do that i just have not got that deep yet. Thanks for your input brother i appreciate all the help.
Dont i also need to a injector balance tool tester in order to do this or is this all done through the subscription? Sorry i am very new at this.
You can use the GDS2 injector balance test, it is not precise tho. I have had many injectors that pass On GDS2 but fail on the AFIT. Only the AFIT can identify a bad GDI injector correctly by flow rate.
Very good info thank you very much. So more or less a guy needs to go out and spend a couple grand and buy this afit system.
Np. Yea GM is making it difficult for the aftermarket. Side note, the reason you change the whole bank is the piezoelectric injectors are easily damaged and most of the time they are damaged on removal and you don’t know it, then a few months down the line they fail. The correct tool uses a slide hammer and special pulling tool, but even then they break too.
Very good information so a guy cant just take them out by hand like other gdi injectors and install them by hand? Have you had any luck with using a quality napa injectors in a situation like this or is just best to always going oem? The reason i asked because the customer was very interested why i cant use a aftermarket injectors. I explained to them the injectors have different flow rates and…
The injectors for the truck I was working on are on backorder and who knows when they're coming... I wouldn't chance aftermarket.
Thats what i was thinking but i just wondering what you thought thank you for you input.
I would suggest. with out knowing mileage, fuel quality, how often is it driven, cold start misfire is something I c quite often on loaner vehicles, maybe u can reset fuel volatility, and road test