For those who like to fix things, keep reading. For those who think the answer is " take it to the dealer", turn back now!

I picked up a 2009 GMC Acadia AWD at an auction with 142K miles on it, that was flagged as "non-running". It started, but ran rough. Drove it out of the gate, and found it was too wide for the trailer I brought, so I drove it a couple miles to a friends house, until I could come back in a couple days with a wider trailer (didn't realize this thing is wider than a full size 1/2 ton Chevy truck, which does fit on that trailer!). It ran very rough, but made it there. When I picked it up a couple days later, it barely started to drive it into the trailer. The low fuel light was on, so I stopped at a station on the way home and filled the fuel tank.

When I got it home, the battery was too low to start it, so charged the battery for several hours. After that, it started right up, and ran smooth. I backed it out of the trailer, parked it in front of the shop, and let it run for a good 15 minutes while I put the truck and trailer away. It was still idling smooth when I shut it off. The next morning, it wouldn't start again. I eventually got it into the shop, checked the codes, and there were 19 of them (all fuel pressure, misfire, and timing related). After clearing them, and some additional troubleshooting, I found there was low fuel pressure from the in tank pump to the test port at the engine. The pressure read 4psi, then I bumped the bottom of the tank with a dead blow, it came up to 20psi, bumped it again, got it to 48psi. So, I bought a new pump and replaced it.

Now the fun begins, as it still wouldn't start. Checking codes again only shows even bank misfires, and P0191, fuel pressure performance. The new in tank pump was putting out 60psi, right within spec. I checked the high pressure pump output with a ODB-II scanner, and it was reporting 78psi while cranking. Odd thing was that after trying to start it, just leaving the key on, the pressure would slowly creep up, all the way to 480+psi, repeatedly. I wasn't sure if this is just the computer playing games with the numbers, or if a cylinder under compression was bleeding back through an injector. I've read fuel in the rail can heat up and cause the pressure to rise, but since the engine was cold, that seemed unlikely. Either way, with no high pressure from the pump, knowing it had been starved for fuel, I replaced the pump (it'* easy to get to, and not very expensive). Still no change to the high pressure reading, and it still won't start.

Now I'm thinking an injector might be stuck open, and preventing the pump from building pressure. I pulled intake manifold, so I could pull the coils and plugs, to see if any plugs are overly wet, and #5 is very wet (the rest are dry). Also, the top of the #6 piston is shiny clean, while the rest have a light carbon coating. I'm suspecting 2 injectors have been leaking, so I replaced all 6 of them with new ones. I was initially planning to clean and test them, but the odd bank gave me such a fight removing them, I was concerned I may have damaged a couple.

After I put it all back together, it still won't start, still sounds the same (like one cylinder is missing from the pulse sequence sound while cranking). Now I'm starting to scratch my head, because all the symptoms and diagnosis to this point made sense. However, now not so much, as it was running smooth after filling the fuel tank with the bad pump. My next step is to run a compression check. Now it gets interesting. With all the plugs out, when I put the compression gauge on the even bank cylinders, the cylinder with the gauge will pop back through the intake runner, and the compression numbers are lower than the odd bank. It appears the timing is off on the even bank, so now I'm suspecting the timing chain has jumped a tooth (possible because of the pump starving the motor for gas, making it run rough?). Thoughts? Could the VVT system explain the popping back through the intake?

I looked up the history for this vehicle on Carfax, and it shows a very complete maintenance history, including the timing chains being replaced at 75K miles. It now has 142K miles on it. Also, the report shows regular oil changes every 3K to 5K miles before and after the chains were replaced. From what I've read, the timing chains had issues early on, but were later fixed. Since the chains were replaced in December of 2014, does it seem likely that they're already in need of being changed again?

I looked down into the cylinders with a borescope camera, and don't see any signs of contact or damage to the tops of the pistons. At this point, I'm suspecting the even bank cam(*) jumped timing, which means removing the timing cover. Since this is a transverse mounted engine, with no real clearance, it means pulling the engine. If I go that far, I'll definitely install new chains. Before I go to that extreme, I'm open to any other suggestions of things to consider, since this is my first adventure digging into the LLT motor, and I'd hate to pull the engine if I don't have to.

Can boil this down to a question?

The questions are there, followed by question marks.

Not likely. Running rough wouldn't make any of the timing chains skip.

Why do you think timing is off on the even bank? Measurement or a stored code or . . . ?

Maybe, I'd have to know more about the popping sound.

Unlikely with regular maintenance like you've described. I have an LY7 that got chains at about 80,000 miles and it has almost 200,000 miles on it now with no timing chain issues.

google 16-na-383. Its a GM TSB for possible sticking valves causing no start, rough idle, misfires. Hope this is helpful

Where is the VVT located in a 2012 GMC Acadia?

The last post in this thread is over eight months old. Please do not post in threads that have no entries less than six months old. Please refer to https://www.gmforum.com/introduction...-first-304557/ for more details. If you have a question related to this thread'* subject, please start a new thread with a reference to this thread.

I also see a thread from dawsotr regarding the same issue at: https://www.gmforum.com/gmc-chevrole...-acadia-314518

Please refer to that thread for future activity on this issue. I have replied over there.

Thread closed.