5.3L no compression cylinder #6

[D_middlestead]

I have a 2007 GMC Yukon that has 108000 miles. Have had issues in the past with oil sending unit this I have replaced 2 times in the last 2 years. Not an expensive fix but a difficult one. Oil pressure has been consistently lower than usual lately but is around 25 psi at idle and normal 40 while driving. Now driving home from store my " service traction control" warning and "service stibiltrax" warning popped up on screen. Car began shifting very hard out of 1 gear into 2 and motor would shake badly while at idle. When driving at about 1500 rpm motor seemed to not shake so bad. A few miles down the road my chech engine light came on solid and then would flash at times. when I got home I read the codes and 3 popped up. 1. P0701 confirmed. 2. P0306 confirmed. 3. P0306 pending. My question to this is why is the second 0306 pending. What does that mean. So. What I have done is a compression test. I had already taken out plugs and all plugs were worn but #6 (problem cylinder) had a little oil on it. I know basic trouble shoot for misfire is change plugs and wires. Possible coil pack if that does not work and last usually a compression test. I did compression check first since already there and had equipment just to make sure. All cylinders accept #6 are between 160 and 170 psi. #6 has 0. I did the check a few time on tgis cylinder just to make sure and once out of 4 it came to 85 psi. My question is. What's next. Am I screwed. Is it shop time or it there something simple that could be happening. Any thoughts would've great. Thanks.

 

[OR VietVet]

You may have a valve stuck or lifter bad or really bad rings or...etc.

If you can get a cylinder leak down tester or have the rig towed where a qualified shop can do it then you can pin point where. The shop/tech will put air in that cylinder and listen for the source of escape. Out the oil fill means rings or hole in piston. Out the exhaust means exhaust valve, out the throttle body means intake valve and if is valves will need to remove valve cover and check for bent valve or broken spring or collapsed lifter. Lots of possibilities. Get it checked correctly before stressing out completely. May be small or large expense but unknown as of now.

 

[D_middlestead]

Thanks. I'll take to shop and keep updating. I'm stuck because I haveca 72 month 100000 mile warranty. Now at 108000 it takes a dive. I think gmc knows something we don't about their cars. Or what we find out just after warenty laps. Thanks and I'll keep u up to date.

 

[OR VietVet]

Right now you are guessing and I would want to blame GM too but unless you owned since new then you don't know how was treated before you got the rig. Make sure you tow it to a shop and do not drive it. You can put the good plugs back in the other holes because the shop will charge you for that and make sure you tell them everything that has happened. Do not hold back any info you know. When they give you the results of the testing then get estimates only for repairs and then post all of their info here for us to advise about. Good luck.

 

[D_middlestead]

Your right. Can't blame anyone yet. And I bought the car at 65000 miles and since then have kept up on it since. I usually do all my own work until something like this pops up so I know it's been taken care of by me. Thanks for the help and defiantly towing it.

 

[OR VietVet]

Make sure you don't just tow it anywhere. You want to go to a shop that will commit to doing a leak down test and that will share the "details" with you so you can make an "informed decision." Lots of shops say sure and then they spend 5 minutes on it and say whole engine. I say ********. Ask them to do the test. Ask them to explain to you how they will do the test or tests. They will certainly do a dry and wet compression test first themselves and likely a compression test on each cylinder next to #6. If that compression comes up with a wet test then is likely bad rings. But if stays the same then can be a hole in the piston or valve/lifter/valve spring problems and then they need to go further with the leak down test. Then they need to be very "detailed" with their estimate(s) as far as parts and labor and warranty. If is smaller type work and you are mechanically inclined then we can help you through it and remember, you tube is your friend.

 

[OR VietVet]

I have done some research about this and it may be something that will be less expensive than I thought. Do you have an AFM 5.3 engine? The 07-09 AFM 5.3 engines had a problem and was causing lifters to collapse. Under warranty the dealer was replacing the sets of lifters referencing what I believe to be a Technical Service Bulletin labeled PIP4568L. Yours may not be covered by the dealer but if the shop finds a collapsed lifter and they do some research they may find that all the needed parts are listed in that bulletin and then go in after the repairs and shut the AFM off/disable it in your PCM. It is supposed to be a fuel management system to help you save fuel but has caused major headaches for people with AFM 5.3 engines in the years 2007-2009. I may be barking up the wrong tree but if it is the same engine then it could save you some money. I also seem to remember that the thing that caused some of the AFM 5.3 engine problems was a poorly working pcv system and they did an update to a different design valve cover for the pcv system on that engine. Check in to this. I hope I am right and that this helps.

Also have the tech look up PIP4568H bulletin. Google those numbers, PIP4568h and PIP4568L and read up on this.

 

[D_middlestead]

How can I tell if AFM engine or not? I know it's a 5.3 vortex.

 

[OR VietVet]

The fact that it is a 5.3 2007 leads me to believe it is.

Like I said, google the PIP4568L and PIP4568H and you will see the descriptions of problems and vehicles effected. Or call your dealer and give the VIN and see what they say.

 

[50Chevy]

Speaking from experience here. My father-in-laws 2007 Suburban with 5.3L AFM had lifter issues and low oil pressure at idle (and still has low oil pressure, for my preferences). I pulled the motor when one of the AFM lifters for cylinder #7 failed at 173K. It made a terrible knocking sound. I replaced all the lifters and all engine gaskets/seals due to oil leaks. The engine does not have to be pulled to replace the lifters, just the cylinder heads. AFM cylinders are 1, 4, 6, 7. I reinstalled the engine, and it ran perfectly for a week then the AFM solenoid manifold failed and "Service Stabilitrak" and other traction control warnings displayed on the dashboard. I replaced the AFM assembly and all has worked perfectly since then (about 40K ago). Still has 20 psi oil pressure at a hot idle. So, it could be bad lifters causing the compression issue or a fault in the AFM assembly causing an internal oil leak/bypass to the AFM lifters to clyinder 6 and causing them to partially collapse and drop compression. If it's bad rings on cylinder 6, then there are bigger issues here. Suggestions to look at.