07 GMC Acadia 3.6l - Engine backfires and stalls after warm up.

Hello, I just purchased this vehicle so I don't know alot about it other then it starts when cold and idles and runs great until a minute or so goes by and warms up, then it will rough idle and backfire and sometimes I will smell raw fuel. I have Gioto or autoenginuity but not skilled with gas engines, mainly diesel. So I would appreciate some help as to what to look for and test to run. The person I purchased it from had just replaced timing chains and fuel pump and drove it a couple hundred miles before this started and couldn't figure it out,
I am kinda thinking maybe a bad injector?
I appreciate any help.

Sounds like an issue that only happens when the fuel system goes into closed loop. Possibly a bad input, be it an O2 sensor or MAF. Any codes? What are your trim and MAF readings (Idle and 3K RPM) after the system goes into closed loop?

I'd like to see fuel trims, all four O2's and the MAF reading, as Donut suggested. It sure sounds like it's running out of fuel, but the data will tell the story.

Unfortunately codes were cleared before I got it and only code that pops up now is P0300 (Random misfire). Also MAF sensor has been replaced. I am kinda new to using Gioto with gas engines but I will see if I can figure it out and get fuel trims and Maf for you.
Thanks

This is best I could do. It wouldn't start and run so couldn't record info with Giotto. But had this from friends code reader from couple days ago. Car has new MAF sensor, Fuel pump, timing chains and plugs. And only code that has came up for me is the P0300 random misfire. Sometimes it will act like it wants to start if I hold throttle to floor.

Here is 2000 rpm's -

Are you in mountains or at sea level? Baro pressure being 13.9 has me curious as it is part of map sensor which reads 6.8. Also maf is reading 9 g/s which is a little high for a 3.6 liter.

My elevation is 1,300 above sea level. One problem I have noticed is lots of crankcase pressure but I have checked all the cylinders with a scope and no cracked pistons that I can see. Only a slight bit of cylinder wall scuffing in cylinders 2 and 4. Havent done a compression check yet but it runs so good when it does start for a bit that i have a hard time believing cylinders are that bad. I just don't know what to think.

Positive pressure or excessive vacuum?

positive pressure unfortunately. Could a head gasket leaking from cylinder to cylinder cause excessive blow by?

Check the pcv valve pull it out and shake it up and down. Does it rattle? If not replace it. If it does then you will need a cylinder leak down tester, air compressor, air hose and fittings. Turn each cylinder to tdc compression stroke. Thread in leak down tester and hook up air hose. Adjust knobs per their instructions and listen in intake and exhaust pipe and in oil cap opening.

Can only hope you didnt crack a valve.

Why would it run so good for a little while before going wonky? No smoke from exhaust either?

There is a few things that can cause it.

Incorrect base timing/ jumped timing belt
Vvt solinoid issue
Knock sensor or knock sensor wire pinched somewhere grounding the circuit.

Its basically something that is used during closed loop. Or timing from whats going on.

Thank you for the data captures. Can you use the AutoEnginuity to look at the misfire counts on the OEM data? I'm willing to bet you'll find high counts on just a few cylinders. I know that the code description for P0300 is 'Random Misfire', but it's rarely random. GM's will set a P0300 for a dead misfire on one cylinder.

Looking at your data, my first instinct is exhaust restriction. It'd match your symptoms, and it's a pretty common problem with this platform. But it's also not the easiest thing to check for. :silly: Since it's not starting right now, have you tried adding some carb cleaner to the intake during cranking?

Okay, I kept trying to start it and it took forever and started rough but then it smoothed out after 30 seconds or so and ran good but lost communications with autoenginuity but random misfires popped up on cylinders 1,3 and 5 when it was running rough. ECM issue? I recorded a video but apparently cant upload it here.

I figured out the main problem thanks to your help. Bank 1 was misfire so I went through all the wires and found loose ground to coil wires on bank one. Runs good now. Thanks
Unfortunately I still have some problems with lots of blow by and after having front bank 2 breather line connected to snorkel I am getting lean codes bank 1 and 2. If I disconnect it from snorkel it doesnt pop up with codes. My question is can clogged up cats cause excessive blow by?
On bank 2 I tried unscrewing O2 sensor on exhaust manifold and just let it set in the hole to see if back pressure would blow it out of the hole while running and it didnt.

I hope you don't have 0 psi oil pressure.

Yes it is possible for plugged up cats to stall a motor as the pressure has to go some where. An easy test to do is thread in a fitting to pre cat o2 hole and use a 20 psi gauge with hose. Idle car and do snap throttles record highest reading at snap throttle then rev to 1500 record reading and 2000 rpm. 0-2 psi is normal 3-4 is partial blockage 5 and up you will want to clean or replace cat. If its really blocked you will see high pressures 14-18 psi which would stall engine.