Cylinder seven misfire

2007 GMC C1500

200,000 MILES • 5.3L • V8 • 4WD • AUTOMATIC

SSHARPE

MEMBER
1 POST

I have a repeated issue with cylinder seven misfiring. To begin with I changed the plug, it worked fine for a day or two and ended up having to change again, no change. At this point I have changed the plugs and wires, the ignition coil, and had a new head gasket done. I have not changed injector yet. Any suggestions?

Apr 22, 2022 at 5:46 AM

BORIS K

✓ASE Certified Mechanic
836 POSTS

Hello,

Is the engine misfiring at idle or under load? Is the misfire constant or intermitted?

How to check for misfire.
https://www.2carpros.com/articles/engine-misfires-or-runs-rough

When doing a CAN scan what fault codes are set?

How to do a CAN scan.
https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Why was the head gasket replaced?
When you replaced the head gasket were the valves and rocker arms checked?
Have you checked the compression?

How to check compression.
https://www.2carpros.com/articles/how-to-test-engine-compression
and
https://youtu.be/J3j85hg0d-4

Symptoms and causes for low compression.
https://www.2carpros.com/articles/symptoms-of-low-compression
and
https://www.2carpros.com/articles/the-reasons-for-low-compression

The fuel injectors can be tested by using a suitable scan tool and fuel pressure tester and carrying out an injector balance test. Alternatively, injector testers and fuel pressure gauges can be purchased online, see images below. No expensive diagnostic tool is required.

See a good video.
https://youtu.be/I2IgGenAX0Q
and
https://youtu.be/QuknZ7KYBqs

Please let us know how you get along.

Cheers, Boris

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Apr 22, 2022 at 8:34 AM

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