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[Ryan Hottot]

I thought about checking to see if the rockers move for the first second or two on start up but I didn’t have a helper. When I have started I did notice that I thought it was firing on all 8 for a second but then I notice the misfire as soon as it starts to idle down a little. I would say the rockers probably move briefly on start up.

I have a brand new VLOM on hand now. I’m working on putting it in this afternoon. I’ll let you know how it goes.

Thanks for the help.

[Ryan Hottot]

Ok, new info. I pulled the valve cover back off and ran the engine briefly. Both intake and exhaust rockers for #7 aren’t moving. They both moved nicely when I rolled the engine manually after replacing the lifters. I’m thinking this is VLOM or VLOM wiring related as the AFM system stops both intake and exhaust lifters from opening the valves when activated. Make sense? Any other suggestions?

Thanks in advance,
Ryan Hottot

[Ryan Hottot]

The milage is 327000km. I thought that because #1 was the same as #7 that it was not indicating an issue. Do you think the pressure test illustrates a problem? Rings? Or whatever?

Thanks again for your help.

[Ryan Hottot]

Ok, finally got time to do the compression test.

Results (dry):
1: 167lbs
3: 186lbs
5: 190lbs
7: 167lbs

I didn’t do the other side because it seems like it’s good. 1 & 7 are the AFM cylinders.

Any thoughts?

[Ryan Hottot]

Thanks for the replies. I will try to get to the compression test tomorrow. I’ll update with the results.

[Ryan Hottot]

Hey Catherine, I just wanted to second your thank you to Eric. I’ve been repairing my vehicles since I bought a Jeep YJ about 20 years ago. I’ve been all over YouTube for help with all kinds of repairs. There is nothing better than seeing an ericthecarguy video in my search results! Thank you Eric! You have helped me many times and saved me countless dollars!

[Ryan Hottot]

Ugh, I just noticed my typo in the title.

[Ryan Hottot]

Yes, I rolled the engine over manually after repairs with the valve cover off. The #7 rockers moved just like all the rest. A little info I didn’t mention in the first post: I checked the push rods during the repair, and they were all straight. I also followed the Haynes manual for all torque values and sequences. This was my first time removing the heads on a motor so I took my time, read the manual and followed all the directions. I took extra care cleaning mating surfaces with all new gaskets (no leaks that I can see). New head bolts. New exhaust manifold bolts.

I understand that AFM lifter failure is a pretty common issue on GMC 5.3L engines from 2007-2014 or thereabouts. I had code P0451 (Evaporative Emission Control System Pressure Sensor Range/Performance) show up at (or around) the same time, as well as my persistent P0442 (small EVAP leak) but I didn’t think they were related to my #7 misfire.

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