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Gary, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1117
Experience:  Senior Technician
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Chevrolet Tahoe LT: I have a 07 Tahoe with AFM I all of a sudden

Customer Question

I have a 07 Tahoe with AFM I all of a sudden got a misfire one night and & I took it in to the dealership and was told #4 lifter had failed, so I took it back home and repaired at myself replaceing all the lifters on that side and when we first started the truck it was smooth and then all of a sudden it went to misfiring real bad, the only code I'm getting is p0300 but I have a misfire now on #4 and #6
Submitted: 2 years ago.
Category: Chevy
Expert:  Gary replied 2 years ago.

Hi there, The AFM cylinders are 1, 4, 6, 7. Did you fit AFM lifters in cylinders 4 and 6? Did you fit the lifters the correct way round, they only go in one way? You have be so careful and thorough on assembly of one of these, no room for error. Gary

Customer: replied 2 years ago.
Yes we installed them correctly
Expert:  Gary replied 2 years ago.
Hi again,
I've seen many AFM engine failures.
My best advice to you after seeing many techs pull their hair out, is to remove the rocker cover and observe the valve operation for cylinders 4 and 6, with the engine running.
If the cylinder is misfiring form no valves operating, the PCM deactivates the injector as well.
The valves will work while doing a compression test, but they won't work if the AFM function is activated.
The function of AFM will be activated if the lifter is fitted the wrong way round, or it has rotated in the guide.
It is no effort to prove the mechanical is ok before moving onto further diagnosis if needed.
Hope this helps.