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Ask Gm Tech (Cam) Your Own Question
Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29457
Experience:  GM Grand Master Technician 2007. 14 year experience.
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2005 GMC ENVOY 5.3. ENGINE CODE P0300... CYLINDER NUMBER 5

Customer Question

2005 GMC ENVOY 5.3. ENGINE CODE P0300... CYLINDER NUMBER 5 IS MISFIRING. SWAPPED COILS, INJECTORS, SPARK PLUGS,WIRES, SMOKED TESTED FOUND NO LEAKS, REPLACED INTAKE MANIFOLD GASKET. CHECKED INJECTOR PULSE, ITS FINE, CHECKED IGNITION/COIL PULSE IS OK.RAN VEHICLE WITHOUT VALVE COVER GASKET TO INSPECT ROCKER ARMS/PUSH RODS AND LIFTERS... SEEM TO BE WORKING FINE COMPARED TO OTHER CYLINDER. MISFIRE WILL NOT GO AWAY.. SENT CYLINDER TO MACHINE SHOP TO HAVE INSPECTED... FOUND NO DEFECT, HAD VALVES GRINDED ANY WAY. COMPRESSION BEFORE AND AFTER ALL THE WORK IS/WAS 154PSI.ALL OTHER CLINDER ARE AROUND 150PSI... ONLY THROWS ENGINE CODE P0300... BUT ITS ONLY CYLINDER NUMBER 5.... DONT KNOW IF ITS RELATED, BUT OIL PRESSURE IS ALWAYS AT 80
Submitted: 4 years ago.
Category: GMC
Expert:  Gm Tech (Cam) replied 4 years ago.
Hello, I'm Cam.

Wow you have done a great deal on this.

Have you only been looking at the code that sets or a misfire graphic?
Customer: replied 4 years ago.


misfire graph... with a tech 2... only cylinder number 5 is missing

Expert:  Gm Tech (Cam) replied 4 years ago.
Wow, sorry to ask this, but I need to know. You are checking third cylinder back on the drivers side?
Customer: replied 4 years ago.

lol! yes im sure... 3rd cylinder on drivers side

Expert:  Gm Tech (Cam) replied 4 years ago.
Ok, just brain storming, did you also swap the entire wire harness for the coils from passengers to drivers side?

Is it a dead miss or intermittent miss at idle?
Customer: replied 4 years ago.

dead miss... yes i swapped the harness with a know working one

Expert:  Gm Tech (Cam) replied 4 years ago.
How is the spark on the coil with a spark tester?
Customer: replied 4 years ago.

strong

Expert:  Gm Tech (Cam) replied 4 years ago.
Same as the #3?


Thanks for putting up with this, I just need to catch no fully.
Customer: replied 4 years ago.


yes

Expert:  Gm Tech (Cam) replied 4 years ago.
Ok, do you still have the valve cover off?

Did you measure the rocker are travel?

Customer: replied 4 years ago.

no.. how would i measure the travel?

Expert:  Gm Tech (Cam) replied 4 years ago.
Dial indicator. I am wondering if the lifter is pumping up and keeping the valve open.

Otherwise do a dynamic compression test which is with the engine running and the gauge in.