Misfires higher than normal LTFT 2010 V6

[Davval]

Ok guys and gals I have a weird issue I have been tearing my hair out trying to figure out. Back in May of this year I had to redo my timing chains for the second time, I got the timing chain codes and an intermittent misfire on cylinder 3 bank 1 plus a really bad idle. Replaced timing chains hoping that would fix the misfire on cylinder 3 as well but it didn't. Car ran noticeably better, I was able to accelerate alot faster with no vibrations from the motor. After the timing chain fix I proceeded to get a P2097, I replaced all the coil packs with cheapo ones from amazon and had the same issue. Decided to replace the injectors as I was on lockdown and had nothing better to do. Purchased a set of cheap injectors from amazon, installed, had horrible misfires and tons of unburnt fuel exiting the tailpipes. Shut car off and primed the fuel pump a couple of times, proceeded to turn on engine and it wouldn’t turn over. Just a click, took off all the coil packs and spark plugs and cylinder number 5 practically threw fuel in my face. I was pissed at this point, took the intake and fuel rails off and took off injectors. Purchased a new set from amazon, this time the brand was GERMBAN and they looked just like the original ac delco injectors. The first set from amazon looked authentic until you look at the terminal tabs which were silver tinned and square, the ac delco ones were brass colored thin and with the corners rounded. Installed the new set, fired up the car and it idled somewhat ok took it for a test drive and now cylinder 1 was throwing a code P2146, open circuit. I head home, took everything apart again, and replaced cylinder 1 injector with one of the original ones I took off, put everything back together and took it out 1 last time. Everything worked, no misfires accelerated way better than before and I thought I fixed it. Next day it was colder than normal, car misfired on start up during the cold start procedure and continued to misfire until the cold start procedure was over. cylinder 2 registered 25 misfires and the other cylinders were only registering 1 or 2 max, problem is the cylinder 2 misfire saved on the cylinder 1 history which is weird. It has been doing the same ever since for about a month. Now my LTFT is around 12.5 on bank 1 and .78 on bank 2, checked for vacuum leaks which I did find, the air was leaking from the VVT solenoid oil seals. I replaced those with no difference. Rechecked for vacuum leaks using a homemade smoke machine, found none after fixing the oil seals. Walnut blasted the intake valves, checked the valve train on both sides for broken springs, rollers anything out of the ordinary. checked compression, preformed leak down test, replaced maf, replaced CPS, replaced pcv valve, checked fuel pressure both high and low, replaced spark plugs, replaced coils again, replaced engine coolant sensor, ran crc intake cleaner, pulled fuses for ecm, checked all grounds for coils, replaced main ground battery cable, replaced engine to chassis ground strap. Still have the same misfire at startup, driving has no issues, starting the car after 8 hours, no issues. The only problem is overnight cool down with a rough morning misfire. Current codes are P0420 and P0301, nothing else. Need some advice as to where to go next

Attached is a screenshot of my scanner after startup, registered misfires on cylinder 2 but recorded the misfires to cylinder 1.

[Davval]

Slight update:

spoke with amazon and they are sending me a new set of injectors, I am unsure if im going to replace all 6 injectors or just the three in bank 1. What annoys me is the misifiring on cylinder 2 when it reaches the 1k revolutions in the sample data but it puts that misfire data on cylinder 1's history. Not a huge deal as im pretty sure that cylinder 1 is the bad injector and the only one that is different from the others plus the LTFT being so high. I can confirm that clearing the codes resets the LTFT percentages, when I clear codes cylinder 2 misfires like crazy until it goes into closed loop and the STFT starts to rise it evens itself out.

[Davval]

Update 2:

Recieved new set of injectors from amazon, they resent the same order but these were in a completly different package. I then looked up the seller and its a chinese company, not a name brand so I was disappointed. These weren't the cheapest ones on amazon they were double the price so I was a little pissed off but I got cheap and got what I got. Installed and 2 injectors were bad and misfiring but this time it was on bank 2 cylinder 2 and 6 as it was late so I called it a night. Next day I salvaged 3 "good" injectors from the last batch I removed and took off bank 2's injectors. I reinstalled and no more misfires at all, well I had 1 or 2 on cylinder 2 and 6 but I had to clean the plugs as they were fouled. After that It was all good, LTFT's went opposite and running negative 12'ish on both banks during idle, they drop to +- 8 total fuel trim at highway speed. I believe that the oil is contaminated with fuel and was boiling off into the pcv system plus the crapload of chevron fuel injector cleaner I put in the tank has something to do with it so ill watch the fuel trims over the coming weeks and see if it changes. Best thing is no misfires and no morning rough idle which is what I was really worried about

[Davval]

Originally Posted by Davval

Update 2:

Recieved new set of injectors from amazon, they resent the same order but these were in a completly different package. I then looked up the seller and its a chinese company, not a name brand so I was disappointed. These weren't the cheapest ones on amazon they were double the price so I was a little pissed off but I got cheap and got what I got. Installed and 2 injectors were bad and misfiring but this time it was on bank 2 cylinder 2 and 6 as it was late so I called it a night. Next day I salvaged 3 "good" injectors from the last batch I removed and took off bank 2's injectors. I reinstalled and no more misfires at all, well I had 1 or 2 on cylinder 2 and 6 but I had to clean the plugs as they were fouled. After that It was all good, LTFT's went opposite and running negative 12'ish on both banks during idle, they drop to +- 8 total fuel trim at highway speed. I believe that the oil is contaminated with fuel and was boiling off into the pcv system plus the crapload of chevron fuel injector cleaner I put in the tank has something to do with it so ill watch the fuel trims over the coming weeks and see if it changes. Best thing is no misfires and no morning rough idle which is what I was really worried about

Update 3:

Ok that didn't fix it, I still get a several misfires on bank 2 cylinder 2,4,6 on morning start up but the LTFT at start up are -17 so I think that has something to do with it. No misfires at all on bank 1. I picked up a set of Platinum spark plugs to try out, bank 2 spark plugs were fouled out to begin with but i cleaned them with carb cleaner and a plastic bristle brush but ill just replace them and see if that makes a difference. I am able to make the LTFT go back down to around 0 on both banks. I tried introducing a vacuum leak by removing the oil cap and my STFT ramped up to +25 on both banks so I dont think I still have a vacuum leak. I disconnected the Evap purge solenoid and capped the end going into the intake and the other end of the valve thinking that its intoducing more fuel vapors when its not supposed to. I saw a slight difference but nothing major. I ended up capping the PCV orfice tube and hose, this corrected my Long Term Fuel Trims to -.78 % on bank 2 and -1.56% on bank 1 at idle. So my question is am I getting fuel blow by vapors on either some cylinders or through the intake valve seals? compression tests were within spec but I did test while at operating temp. Capping the PCV tube did correct my issues but I know its not a fix. anyone got any ideas as to what is causing the fuel vapors coming out of the pcv system?

[KillboyPowerhead]

Haven't read through your whole thread here (just about to leave for work), but maybe this is related?

[Davval]

Originally Posted by KillboyPowerhead

Haven't read through your whole thread here (just about to leave for work), but maybe this is related?

I did replace the PCV orifice nipple when I replaced the timing chains back in May. I also used the updated valve cover gaskets, I believe this is where I damaged the VVT solenoid oil seals. I replaced them but the solenoids were not going in easily so I had to oil them up and twist them in. The inside of my engine also did not look like that, there was some yellowing on bank 1 but bank 2 squeaky clean with no sludge build-up. I'm going to be changing out the oil again this weekend and see if there is a difference and maybe its contaminated. I didn't do it this past time myself as I was running late so I took it to a local shop. I'm hoping they actually did it and didn't give me the runaround, looks kinda dirty for only have 700 miles on it. I'm changing plugs and coils this weekend as well as replacing the vvt solenoids on bank 2. I already had the parts purchased and the ones on the car are original with 176k miles on them so I don't think it would hurt to switch them out. Also going to check the cam phasers on the weekend as well. I also ordered a catch can, the throttle body was dripping with oil when I was inspecting the seal. It was only a week and about 100 miles since I last took the plenum off to clean it out and for it to have that much oil is baffling. The oil could be fouling the spark plugs? car runs perfectly fine after 5 mins of warming up, no misfires at idle or at highway speeds. Its only in the morning that I'm having issues.

[Machh5]

Could be valve seals.

[Elite Engineering]

Read through and did not see you address the most obvious, unless I missed it. All you describe are the symptoms of intake valve coking issues. As the intake valves build deposits, the incoming air charge is disrupted, and as this never occurs equally on all valves, some will run too rich, some too lean, and a few will be close. The entire bank is read by the upstream O2's as an aggregate of all cylinders, so that data is what the ECU is using to determine fueling. As this builds, the misfires get more common. Rarely does more than one injector fail on these. Same with coils. Plugs should be changed at 50k miles and not 100k like the owners manual states.


And NEVER do a solvent based engine running cleaning on a GDI engine as we have yet to see that NOT damage pistons when the hard crystalline chunks come loose unlike old port injection engines that you could Seafoam/BG safely.


Do a manual intake valve cleaning. Some good threads on here to see step by step. You will be surprised.


Good Luck!!

[Davval]

Originally Posted by Elite Engineering

Read through and did not see you address the most obvious, unless I missed it. All you describe are the symptoms of intake valve coking issues. As the intake valves build deposits, the incoming air charge is disrupted, and as this never occurs equally on all valves, some will run too rich, some too lean, and a few will be close. The entire bank is read by the upstream O2's as an aggregate of all cylinders, so that data is what the ECU is using to determine fueling. As this builds, the misfires get more common. Rarely does more than one injector fail on these. Same with coils. Plugs should be changed at 50k miles and not 100k like the owners manual states.


And NEVER do a solvent based engine running cleaning on a GDI engine as we have yet to see that NOT damage pistons when the hard crystalline chunks come loose unlike old port injection engines that you could Seafoam/BG safely.


Do a manual intake valve cleaning. Some good threads on here to see step by step. You will be surprised.


Good Luck!!

Update 4:

I did the manual valve cleaning as a process of elimination when they issue first started, I walnut blasted all intake valves and I did see a difference in performance but nothing else. Currently only issue is misfire at cold start on bank 2 cylinder 2,4,6 cylinder 2 has the most misfires at 14 the others hang around 6-8 before the counter cycles. After the first 1k RPM I get no more misfires on any cylinder on either bank at any RPM, the problem is after a couple of morning starts the check engine light turns on P300,302,304,306. the one thing im chasing at this point is fuel delivery. I did find that my purge solenoid was faulty and would start leaking at 13in vacuum. Replaced it but it actually made my idle LTFT way worse with both banks running at an average of -19 at idle, when I accelerate to 2500 and 3500 my LTFT goes pretty close to 0 or slightly positive. Removed gas cap and that also made my fuel trims go way negative to more than -25 total on both banks then bank 2 started misfiring like it does in the morning so I think Im on the right track. I ordered and recieved a vxDiag device so im going to play with that during the week and weekend. There are also several updates from my ECU to address misfiring, change the OLM, and reporogram the p0008 trip code. So i might update as well depending on how comfortable I feel doing it. The dealership was going to change me 285 bucks to flash the ecu not including any diagnostics so I wont do that unless im real desperate. Car just has to last me 3 more years until my student loans are paid off. Thank you all for the pointers they keep me from going crazy and running around in circles.

[Davval]

Update 5:

The problems have been fixed, Turns out the LTFT issues, and misfire issues were related. I had 2 of the 6 injectors completely blow in the basket filter, I am unsure if this is something I didn't notice when first installing them or it happened when they were installed. I have a feeling the basket filters are shallow and not the correct ones for this injector. The filter failures occurred on cylinders 2 and 6 which would explain the misfires. The issue with the LTFT being negative has also been resolved. The replacement injectors from amazon have a different spray pattern and more flow than an OEM Bosch injector. The Bosch injector has a 6 hole spray pattern but the holes are more in an oval pattern with different spacing. The spray pattern also shoots at an angle when inside the cylinder head in order to avoid spraying the intake valve with fuel. The amazon injectors have a hole pattern that is circular and evenly spaced, the holes also look bigger and look to be drilled instead of laser cut like the authentic bosch injector. I'm unsure if the amazon injectors are counterfeit bosch or they just screwed up and used an incorrect spray cap as they look like they are removable. Posting some pictures in case anyone has the same issues and used shit injectors from amazon. I had to compile a list of what vehicles took the OEM injectors I was looking for and scoured the junkyard. I was able to get a set from a 2011 traverse that only had 23k miles on it. I took them to work, had them ultrasonic cleaned and replaced all the seals and filter baskets, and installed. Haven’t had a cold start issue and my fuel trims are running 0% total on both banks and -+.78% while driving. So I am confident that was my issue, just got to fix that p0420 code, and I’ll be gravy.
1st pic is oem bosch
2nd is amazon germban
3rd is a bad filter
4th is a good filter

[Machh5]

Good work, lots of interesting info in your quest. I have some misfires cold and always have. Not every time though, not enough to turn the mil on but when I scan it I get p302 pending. Mines a 15 so I'm sure they updated the programming so you don't get a mil until its really misfiring bad. All my old LS1 cars had terrible misfires until they warmed up and plenty of oil in the intakes. As long as it doesn't effect warm drive ability long term I can live with it. Of course now that I posted about it something will happen.

[Davval]

you might want to look into that as soon as possible, the last thing you want is to fry your cats. I looked at mine with a borescope I bought and they are melted on bank 1 so I will be gutting them once it starts to warm up weather-wise. If you don't have to funds to spend on new injectors I would just order the o-ring kits. I got mine on ebay for 20 bucks each bank, new micro basket filters, and a small ultrasonic cleaner to clean the carbon deposits on the jets. But of course, do the research first get a cheap scanner that shows live data, and look at your fuel trims, those are key. Then you can swap around your spark plugs and coils and see if the issue moves. I never replaced the high-pressure fuel crossover tubes and I have taken them on and off at least 10 times, just use a torque wrench to torque them down the same each time.