Low Compression

Chevylife88 · January 16, 2017

First time user bare with me, I have a 2011 chevy Silverado 5.3 engine has the 243 heads and I have low compression on cylinder 7 I removed my intake manifold and discovered quite a lot of gas in my cyl 7 port? Running a leak test tomorrow but has anyone had this problem I mean truck is 6 years old with 104k miles I'm 2nd owner but I'm hoping for a bad exhaust or intake valve I don't wanna replace piston rings anyways any ideas as what to also do or look for ? ( also when pulled valve cover cylinder 7 had a loose rocker pulled all rockers and pushrods seem to be all fine)

muddkatt · January 16, 2017

AFM lifter failure.

Chances are that the rings are fine.

Edited January 16, 2017 by muddkatt

carnau · January 18, 2017

The AFM lifters are 1,7,2,4. Chances are you could have a Lifter that is holding the valve open especially if it has come apart. Remove the 2 rocker arms on cylinder 7 and do a compression check again. If the compression returns to normal you have a faulty lifter. If it doesn't return to normal then do the leak down test.

Chevylife88 · January 18, 2017

Hey guys thanks for the reply your both right the lifter is bad and will be replacing all with original GM lifters now about this AFM I see a lot about it well a lot of bad and from what I see I can delete or turn off AFM ?

Chevylife88 · January 18, 2017

One more thing can I squirt WD 40 in cylinder bores and hold rag over and spray them out with air ? I don't wanna remove the pistons ?

muddkatt · January 18, 2017

http://www.rangetechnology.com/pages/v8

Edited January 18, 2017 by muddkatt

muddkatt · January 18, 2017

One more thing can I squirt WD 40 in cylinder bores and hold rag over and spray them out with air ? I don't wanna remove the pistons ?

Not understanding exactly what you are saying/asking.....

Chevylife88 · January 18, 2017

There is some grit in the cylinder bores above pistons they are all still in and I don't wanna force the grit down into the ring gaps but I don't wanna take pistons out what's a good way to clean them out without taking the pistons out

muddkatt · January 18, 2017

Wipe them out with a clean rag, then hit them with compressed air, then wipe them out again.

carnau · January 18, 2017

Yeah you can program the AFM out of it or you can replace the lifters with older model lifters but I believe you need to replace the valves and springs as well. I really dont remember it has been so long since I have done that,

slimjim2525 · January 18, 2017

OP, how did you know you had a problem? What was the truck doing?

Edited January 18, 2017 by txab

Chevylife88 · January 19, 2017

Slimjim2525 i was just going to park as I pulled into work and it started shaking in steering wheel and just missing out like it wasn't getting spark idling at 500 rpm like it was about to do finally check engine light started flashing and stabilitrak/service traction control was coming up on dash once I checked fuel injectors, new spark plugs put in, took a new coil pack around to all cylinders all of it never did a thing did compression test and it was very low cylinder 7 which is an AFM lifter and did leak down and then tore head off checked lifters sure enough 7 on intake side was collapsed

slimjim2525 · January 19, 2017

Slimjim2525 i was just going to park as I pulled into work and it started shaking in steering wheel and just missing out like it wasn't getting spark idling at 500 rpm like it was about to do finally check engine light started flashing and stabilitrak/service traction control was coming up on dash once I checked fuel injectors, new spark plugs put in, took a new coil pack around to all cylinders all of it never did a thing did compression test and it was very low cylinder 7 which is an AFM lifter and did leak down and then tore head off checked lifters sure enough 7 on intake side was collapsed

OK thanks. Mine has 132k miles on it and noticed recently when it goes into V4, there is a very slight vibration in the motor, then when I step on the gas and goes to V8 the vibration goes away. I just ordered the range disabler.

Chevylife88 · January 20, 2017

Well started assembly and the retainer bolt for the lifter tray is not tightening down I screwed it back out and had small thread shards spiraled on the bolt anyone know what tap size I should use obviously I'm going to have to go oversized, really don't know what to do ??

guygodwin · February 13, 2017

THIS POST IS FOR FUTURE VISITORS HERE THAT MAY HAVE THE SAME ISSUE.

I have this exact issue. My Sierra is a 2009 with 301,000 miles.

Started with a mis-fire in #7 and puffing some smoke. I did all the simple test to make sure I was getting spark. Did a compression check and 1,3&5 all had 160lbs and #7 was 0.

The needle didn't budge in the compression gauge which I thought was very odd. I pulled my valve cover off and redid the compression test. I was hoping to see air blow oil around the valve seats. However, what i saw was #7 Rocker wasn't moving. But what threw me was I could see the rod was actuating up and down. But, then I could see a good 3/8" of play between the rod and the rocker seat. These lifter have compression springs. I'm assuming my #7 intake has compressed and not returned.

I'm considering my options now. With 301K miles should I just replace the engine? I read some place that the kit to fix all of this may be $1100. (Crazy) the Ram dealer told me to buy that rocker, gaskets and a for sale sign. Then come trade it in.

If you think you have this same issue. Do your self a favor and take ten minutes and pull the valve cover. Look at the rockers. With the exhaust valve never opening there is NO air coming it to compress. Which is why the needle doesn't move.

"I assume that #7 has a serious vacuum on it and is sucking oil into the cylinder which is why I had oil on my #7 plug and puffing the smoke.

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