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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1660
Experience:  GM Grand Master Technician 2007. 14 year experience.
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2008 5.3 J code, misfire cyl 6, changed coil, plugs, &

Customer Question

2008 5.3 J code, misfire cyl 6, changed coil, plugs, & injector. Changed TB Position sensor. Still have problem. Intermittent now, sometimes a misfire, sometimes high idle (3K) then back to mis.
JA: Have you seen the misfire code before? Has the car been stalling?
Customer: No stalling, code just stated Sunday. Clear code, mis goes away
JA: What is the model of your '08 Chevy?
Customer: GMC Sierra SLE
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Yes, depending on level needed. At a local shop now. Swapped out Coil pack, spark plug & Injector with another cylinder. No change.
JA: Anything else you think the mechanic should know?
Customer: Power windows act up at random times, after turning truck off and back on they work.\
Submitted: 2 months ago.
Category: GMC
Expert:  Ryan Schott replied 2 months ago.

Does your truck have active fuel management?

Customer: replied 2 months ago.
Customer: replied 2 months ago.
It isn't making any "noise" like a collapsed or stuck lifter. It acts like the timing is shifting. It is an oil burner.
Expert:  Ryan Schott replied 2 months ago.

a non working afm lifter does not make noise. I would pull the valve cover and bungee up your coil packs then start it up and watch the rockers on cyl 6 while watching the scan tool and see if they stop moving when the miss is occuring.

Customer: replied 2 months ago.
if there is no change?
Expert:  Ryan Schott replied 2 months ago.

they stop or they don't? sorry i didn't understand what you mean.

Customer: replied 2 months ago.
With cover off and misfire happening, the lifter is working perfectly. Compression in cylinder is at 150psi. Could this be electrical? In the ECM?
Expert:  Ryan Schott replied 2 months ago.

if its electrical it would more likely be a bad connection or wire than an ecm. I would do a cylinder leak down test on it next. Once the is starts is is consistent like a dead hole or still very intermittent?

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