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Hi Eric, love your YouTube videos, they are the best out there, period.
I own a 2010 GMC Sierra 5.3L Z71 SLT Crew-Cab (LC9 engine) I recently had an event with flashing check engine light and rough running engine. Codes came up P0307 and P0451 (with existing known code P0442). The #7 misfire was my focus and I have done nothing about the evap codes. I swapped coil, plug, wire, and injector with another cylinder with no luck. After research, I suspected collapsed lifter. I pulled the valve cover and found #7 intake rocker loose (I could rock it up and down a 1/4″). I pulled the heads and replaced all AFM lifters (1, 4, 6, 7 – intake & exhaust). Everything else looked good. No wear on lifter rollers, no visible damage to crankshaft. Still #7 misfire. I then replaced oil pressure sensor and the filter underneath, and I replaced the entire VLOM. Still have #7 misfire.
I could really use some advice on how to proceed. I just watched your video on compression testing and I just borrowed a compression tester so I will try that next and provide the results. Anything else I could try?
Thanks in advance,
Ryan Hottot
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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.
Thanks for the replies. I will try to get to the compression test tomorrow. I’ll update with the results.
Ok, finally got time to do the compression test.
Results (dry):
1: 167lbs
3: 186lbs
5: 190lbs
7: 167lbsI didn’t do the other side because it seems like it’s good. 1 & 7 are the AFM cylinders.
Any thoughts?
You show a high of 190 and a low of 167, That is beyond the considered “normal” tolerances when doing compression testing.
Along with that, you show a low (relative) compression on cylinder 7 which happens to be the cylinder that is misfiring.
BTW … what is the vehicles mileage???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.
Suggest doing a leak down test on all cylinders and pinpoint exactly where the pressure is going if it is dumping into the crank case then your looking at worn rings, if you hear it coming from the intake or exhaust then your looking at a valve or valve seat issue.
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 HottotQuestion:
Are the valves moving at all at the initial crank/start up say the first second or two or are they dead still.
GM dealers have the special tools to test the VLOM so I’d say next step would be the dealer either with the truck, or to see if they can test the VLOM for you. The GM test equipment has a solenoid control box and shop air supply. They pump 30psi to the VLOM and then use the control box to run each solenoid to test their function.When in V8 mode, the VLOM solenoids are in the closed position thus not letting oil flow to the lifter locking pins. When the solenoids are turned on, oil is sent to the lifter locking pins and disengage the pins to allow the lifter to “collapse.” If you have a VLOM solenoid sticking ON, that would explain why it is collapsing the lifters thinking it is in V4 mode.
If you aren’t worried about testing the existing VLOM, its ~$300 – 500 at a local dealer p/n 12571609. You will need intake gaskets as well ~$120.00 p/n 89060413.
Me? It wouldn’t hurt to have the VLOM tested if you already have the truck apart yourself.
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.
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