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Corvette Ghost Misfire
Posted to Technical Tips Forum on 7/28/2017 22 Replies

A 2011 Corvette came in yesterday. It had been to another dealer, a Corvette specialty shop, and a general repair shop to repair a continuing SES complaint. The customer stated that the SES light came on every day with no driveability complaints. The other shops have already replaced the spark plugs and wires, the fuel injectors, fuel pump and crank and cam sensors without repairing the complaint.

The SES light was on when I drove the car in the shop. Scanning the control module system, I saw p0300 set as current in the PCM and no other codes set in any module. Looking at the history misfire counters, each was reading in the thousands without too much variance between cylinders. The car idled normally and no misfires were set yet the active counters kept increasing.

I cleared the counters and let the car idle in park for two minutes and recorded this.....

[2011 Chevrolet Corvette, ECM/Inputs/Outputs Scan Data]

During this test, the vehicle idled normally and no misfires were felt. I have always called this condition where misfire counters increment but no actual misfires occur as "ghost misfires." Next, I cleared all the counters again and put the car in drive and idled for 2 minutes and saw this...

[2011 Chevrolet Corvette, ECM/Inputs/Outputs Scan Data]

Any ideas? This is a seldom seen failure on Corvettes. Inside the torque tube where they cannot be seen without disassembly, front and rear phenolic type couplers are used on the actual driveshaft. These couplers can wear and develop play or actually start to come apart. In park or neutral when just the drive shaft and torque converter are spinning, back and forth movement can occur that the PCM sees with the crank sensor and can interpret as misfire on all cylinders. Putting the vehicle in drive or reverse loads the driveshaft and stops this motion and the ghost misfires cease. If you look at the misfire graph, you can almost see the cycling occurring.

If you remove the torque tube and tear it down, the couplers can be visualized. In this case, the vehicle had a GMPP extended warranty so the entire torque tube was replaced and after idling in park for 20 minutes showed no abnormal counters incrementing.

Something to remember in case you run into this scenario as many shops have their shorts handed to them when faced with this type of failure.

James from Florida

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car Vehicle Data

2011 Chevrolet Corvette 6.2L

Engine6.2 L
Trans6-speed Automatic (Electronic)

car Vehicle Data

2011 Chevrolet Corvette 6.2L

Engine6.2 L
Trans6-speed Automatic (Electronic)