Random misfire and ticking 2008 5.3

[Tbrown312]

A week or so ago I noticed a ticking after my truck was warmed up at idle. Well a few days went by and my truck started to misfire as I accelerated from a stop clearing up once i got up to speed. Along with a flashing check engine light I had the codes P0300, P0455, P0306. The next day I bought a new evap solenoid canister hoping to get rid of the evap code. After installing, I still had a misfire and a ticking coming from the passenger side bank. I plugged in my code reading and watched cylinder 6 consistantly misfire at idle. After replacing the plugs, checking the injectors, coils, and wires I thought i may be having lifter problems as cylinder 6 is an AFM cylinder. I pulled the valve cover off to check for a loose or stuck rocker, everything seemed fine. I fired up the truck and the rocker arms all looked to be operating fine. The truck also didnt seem to have a rough idle and wasn't ticking. I put everything back together backed it out of the garage and it went right back to its old ways. I cant seem to figure out the problem and was wondering if anyone else has heard of this or experienced it? Seems to be worst when I put the truck in drive or reverse and hold the brake(rough idle along with a misfire.) Any help or guidence would be appriciated!

[anumber1]

Do a compression test.

 

Just guessing but I would imagine with the tick, isolated missfire on #6 only as described, ya got a failed AFM lifter.

[Tbrown312]

Compression in cylinder #6 is 70 psi, 125 psi in #4, and 90 psi in #2. Checked them again after pouring a little oil in the cylinders and the number didnt change.

[Tbrown312]

Truck has 88k, doesnt use any oil. All the plugs looked good.

[anumber1]

With the oil check seems to be valve related. #2 ain't great. #6 is bad. #4 is ok.

[Tbrown312]

Is it possible that its a lifter problem even with compression?

[anumber1]

By performing the compression test once, dry, then with a squirt of oil in the cylinder, you rule out a compression ring problem. The added oil should temporary aid in ring sealing during the test. Since the number didn't change wet or dry, the compression rings are sealing fine.

 

This leaves the valve train, heads and headgasket as the source of the loss of compression.

 

Since you have a tick, the next logical conclusion to draw is that there is excessive slack in the valve train somewhere.

 

That tick, is a gap between a lifter, pushrod, rocker arm and valve stem. The point if a hydraulic lifter is to automatically take up the slack in the valve train.

 

So, something is not right. You have a noisy valvetrain, low compression, no history of coolant loss (right?) No recent overheating (right?) And now a misfire (due to low compression). I'm ruling out the probability of a cracked head, failed headgasket here. The fact that # 4 is better than #2 and #6 aids this opinion.

 

Add in the fact that it is a GM, AFM motor (with a well documented history of lifter failure).

 

Walks like a duck, quacks like a duck, from the internet, I'm calling it a duck.

 

Failure of a couple lifters. More common than GM would like to admit.

[Tbrown312]

I've had no coolant loss, no pressure in the system or overheating. I've started the teardown today and have decided to do the full afm delete as well as an upgraded cam. Will update when i get the lifters out. Thank you for the help!

[Tbrown312]

Update: I tore down the motor to find 9 out of the 16 pushrods worn on the rocker arm side. I believe this is because of plugged/faulty lifters causing little to no oil flow up the pushrods. The noise I was hearing was chatter in the valve-train due to 9 pushrods being slightly shorter than the others. The lifters and cam didn't appear to have any wear but they are being replaced anyways. I decided to install ls7 lifters with a full afm delete and a texas speed and performance camshaft, along with chromoly pushrods, new rocker arms, and ls6 valve springs.

[arctictwist]

I have the typical tick like yours. If i keep my truck (will find out this weekend what kind of deal they get me on a new one) then i plan on rebuilding the heads. Is that a package you got or did you piece all of that together?

[Tbrown312]

I got the Afm delete kit and cam through texas speed and performance who I highly recommend!! They have great customer service and will answer any question you have. I upgraded to the 212/218 cam with ls6 valve springs which they sell as a kit as well as upgrading to all arp bolts. The only thing I didn't order from texas speed was my pushrods and rocker arms which I got from Brian tooley racing. All together I have about $1600 in parts. I did all the work myself and honestly it wasn't that bad at all.

[arctictwist]

Thanks for the info. Is there anything really technical to doing it? I usually do my own work but ive never torn into the engine before. I do plan on doing some informational searching before i do it, if i do it. Theres actually a good part of me that hopes they dont make the offer too tempting this weekend, but its labor day so well see. Lol

[Tbrown312]

It's a pretty straight forward job. Just make sure you have a clean work area and keep the engine clean while doing any work around it. I labeled every part I took off which made it super easy when it was time to put it back together. If you decide to do it and have any questions ill help you the best I can. Good luck!

[Sforrey]

I have the same thing going on with my 2007 Yukon 5.3 , but the only difference is that I recently had to replace my water pump and thermostat and it did overheat and went in to reduce engine mode. So I replaced those items and everything was fine for a week and then one morning I go to start it up and it’s ticking and idle is off, so I plug up my code reader to it and # 6 misfire. So since then I’ve changed out plugs, and wires, and did a compression test and all had compression of 145-150. So any ideas as to what I I’m not seeing?