SureTrack Community Fix: Misfire On My Mind

Real Fixes from the SureTrack® expert information resource are documented issues from actual shop repair records and community discussions. Read on to see how SureTrack can help you correct issues that are not easily diagnosed using OEM information alone. SureTrack is currently available free with the purchase of a current Snap-on® diagnostic software version or in our ShopKey Pro product.


Replacing a vehicle’s engine with a used one has its risks as you’re going to be counting on it working as it should. SureTrack community member MobleMech had a 2015 Camaro in their shop that came in with a misfire on cylinder one due to engine damage. They replaced it with a used engine and again had a misfire on cylinder one. They posed the question to the community, and with the help of fellow community member Jamesbellam and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

Vehicle
2015 Chevrolet Camaro LS 3.6L

Title
Cylinder one misfire, replaced injector.

Complaint
Misfire on cylinder one.

Diagnostic Steps Performed/Parts Replaced
Originally came in for misfiring, after ruling out the obvious causes it was discovered to have a scratch on the cylinder wall. Replaced the engine with a used one. Replacement engine had a misfire on cylinder one that was caused by a broken fuel injector. Replaced the fuel injector and test drove the vehicle and issue was resolved. Customer picked the vehicle up and drove a block away and returned with the MIL on. Pulled codes for misfiring on cylinder one again. Takes a while to register as a DTC. Checked electrode and gap on spark plug, tested and swapped coils with another cylinder, pressure tested cylinders 1 and 2; cylinder 1 was at 145 psi, cylinder 2 at 150 psi. Reset fuel trim, did Idle Relearn, test drove and it is still misfiring. Fuel trim after reset is: ST 1 at -0.7%, LT 1 at -15.5%, ST 2 at 0.8%, LT 2 at -6.9%. Is the misfire due to an injector imbalance or is there another cause that I have not considered?

Best Answer from Community Member Jamesbellam
Install vacuum gauge on the engine. Is it steady or does it fluctuate? If it is steady then proceed with a smoke test of the intake air system.
Perform running compression test pressure should not be more than 5 to 6 PSI between cylinders. If greater than that, remove valve covers for inspection of rocker arms, valve springs, camshaft lobes, stuck valves, or other valve train issues.

Cause
Thank you both jamesbellam and DAG1365. I smoke tested the intake manifold, removed the valve cover and visually inspected the valve train and found no issues. I unplugged the main connector to the odd side injectors and pulsed the injectors individually only to find that they too where working fine. After being at a total loss I test drove it roughly 10-20 drive cycles and monitored the live misfire data, the count came down from about 180/255 to 6/255 and did not set off the MIL nor did it request for a DTC/MIL.

Correction
After repairing injector, many drive cycles were required to clear up misfire.


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About the Author

Nick Taylor

Nick Taylor is the SureTrack Community Administrator and a Senior Applications Specialist at Mitchell 1 with over 25 years of experience with electronic repair data systems. Nick previously worked in the automotive dismantling and engine rebuilding industries.