2007 suburban 5.3L flex .
I was driving to work this morning and all of a sudden got warning chime and flashing ck. engine light, and stability trac service light came on(which it has done numerous times in past usually while stopped at a light. Truck felt ok but did notice oil pressure was around 32psi vs 40 which it typically is. Had replaced the oil sensor about 1 1/2 yr ago. It wasn't till I got to towm and rpm's lowered that I felt a miss. The tranny shifting wasn't as smooth but wasn't a hard shift. I didn't have time to look at it this weekend, so took to a mechanic I've used before. He got following codes:
PO306 #6 cylinder misfire
PO 121 Throttle position peddle sensor (range)
PO521 Oil press. sensor (range)
PO451 evap (that's been a code I've known about for a while that I never did fix)
He tried replacing plugs, and wires. I think he said he switched coils??? on adjacent cylinders? Pressure on #6 was 75 and about 100psi on other cylinders. So he's not for sure whats wrong at this point without removing head. Wondered if anyone had seen these sets of things happen all at once in a vehicle that's run like a top for years
Thanks,
Mike

 

Normally I'd clear the codes and see what returns but if 6 has 25psi lower compression than the other cylinders theres definitely an issue. He should be able to do a cylinder leakage test to narrow down where its leaking without pulling the head just yet.

 

Just for my info, could someone hook compressor to the cylinder at TDC and pressurize and listen for intake or exhaust noise to check for valve leaks, and oil in cylinder for rings? He said he thought the cylinder should fire with 75 psi? I'm taking it to another shop that has good rep.

 

that's the "old school" way to check for leakage yea, just make sure its regulated air or it might push the piston down and you'll have to start all over again. If all the other cylinders are pretty close and the 1 that's lower is the 1 throwing misfire codes I'd definitely say its worth looking into a little more

 

You could also remove the valve cover and visually inspect the springs, its not uncommon for a valve spring to fail.

 

Thanks for the info
Took it to another shop today, they looked at valve springs, and they are all right, and suspect lifter. He says hes seen it a several Chevys of this vintage. He won't know until they pull head. He's hoping that the cam is ok, says it's not making any noise so he's hopeful. Trying to decide if I want to spend $2200 to $2400 or not.

 

Unfortunately it is common enough problem that they sell an afm lifter kit on Amazon

http://www.amazon.com/gp/aw/d/B00LXBLTSW/ref=mp_s_a_1_1?qid=1450133162&sr=8-1&pi=SX200_QL40&keywords=5.3+valve+lifter+kit&dpPl =1&dpID=51KtxpDTx4L&ref=plSrch

I have a 2013 and the dealer just replace a valve spring in cylinder 7 after a bad misfire. I have 3 months of lease left to decide if I buy it (great buyout price in my contract) or if I give it back. Love the truck but afm has hurt reliabilility of the valves and lifters.

 

I'm really trying to decide if I want to sink $2300 into Burb, or take that and do down payment on new or used vehicle. Guy at shop can't say for sure cam is good or not, with my luck, they will get $2300 into it and find it's a $4000 repair. After $2300 you're pretty well committed to go that extra bit if the cam's bad. Guy said SUPPOSEDLY Chevy has fixed the lifter issue on newer vehicles?????

 

I can't say for sure if they fixed anything. Mine is a 2013 with 42k miles and I've already broken a valve spring. I've never had a broken valve
spring in any car I've owned in the past 40 years

 

I guess it depends on how many miles, what condition it is in, if it is paid for, and if you need the vehicle or not. At this point I'm think your the original owner or second owner and it is paid for. If that is the case, not sure how much you can get for a broken one on the secondary market, but it would be worth looking into given how much a new(er) burb is going to cost you.

I think they have AFM delete kits out there as well, so if you have to do the cam (maybe even if you don't? not sure how it works), you make want to look into it. You could also consider that a running vs not running burb might be worth more than the repair itself, so it might make more sense to fix it and then sell it or trade it in.