C7 plug misfire issue
Thread Starter
Intermediate
Joined: Jan 2016
Posts: 38
Likes: 64
From: Port Orchard WA
C7 plug misfire issue
My 2016 Corvette has something wrong and after two days at Jet Chevrolet in Federal Way, no smoking gun.
Currently, the car is not running smoothly, slight hesitations (not all the time) while cruising at a steady speed and rpm. Seems to be present at any speed.
History:
3/11/19 13,455 miles The car started shuddering like driving over a railroad track. Speedo displayed the following: Service Rear Axle also Service Stabiltrak. It must go into a limp mode as the shuddering does not stop.
Limped home, then flatbed wrecker to local Chevrolet Dealer. Scanned Codes: PO300--Engine Misfires and PO50D--Cold Start Rough Idle
They found Engine misfire on cylinder #2. They changed the spark plug, cleared the codes.
They also found codes in history: UA42B and U0401."Both relate to rear diff invalid data codes"
5/20/19 13,765 miles The car started shuddering. Dealer suspected Torq converter. There was a warrenty bulletin that required complete transmission fluid exchange.
4/25/22 21,834 miles The car started shuddering and had same speedo display: Service Rear Axle also Service Stabiltrak.
Took it back to local dealer. Scanned code PO300 and U042B. Found misfire on cylinder #5 and changed out that spark plug.
Regarding Service Rear Axle, they charged me $165 for "3602 Repair electrical 390CCC. Not sure what that they did here.
"Code U042B would not clear, followed SI to reprogram Chassis control module."
They could not tell me why this was happening.
So, I took it to Jet Chevrolet hoping they might be able to help figure out why it was fouling plugs. After talking to them, first step was to replace all the plugs and plug coils, thought was maybe a bad batch of plugs. Also, do a GDI, fuel induction service.
Then they contacted GM and opened a case regarding random misfire issue. When I brought them the car, no codes were displaying. GM "walked through checking and verifying proper fuel injection system spec such as long term trim and short term trim to verify vehicle is not leaning out causing misfire. Checked ignition timing and crank/cam sensor function, inspected relative engine comp to be in spec across all 8 cylinders, test drove and tested vehicle for 20 miles to verify proper engine operation. No misfire codes found or symptoms to be duplicated. Vehicle is functioning as designed."
I took the car and I'm still feeling the slight hesitation and shuddering (nothing like the railroad shudder though), it certainly is not running smoothly. I'm not very confident in the car right now, worrying the problem will reoccur when I'm a ways from a dealer and stuck in limp mode...
Any thoughts?
Thanks
Currently, the car is not running smoothly, slight hesitations (not all the time) while cruising at a steady speed and rpm. Seems to be present at any speed.
History:
3/11/19 13,455 miles The car started shuddering like driving over a railroad track. Speedo displayed the following: Service Rear Axle also Service Stabiltrak. It must go into a limp mode as the shuddering does not stop.
Limped home, then flatbed wrecker to local Chevrolet Dealer. Scanned Codes: PO300--Engine Misfires and PO50D--Cold Start Rough Idle
They found Engine misfire on cylinder #2. They changed the spark plug, cleared the codes.
They also found codes in history: UA42B and U0401."Both relate to rear diff invalid data codes"
5/20/19 13,765 miles The car started shuddering. Dealer suspected Torq converter. There was a warrenty bulletin that required complete transmission fluid exchange.
4/25/22 21,834 miles The car started shuddering and had same speedo display: Service Rear Axle also Service Stabiltrak.
Took it back to local dealer. Scanned code PO300 and U042B. Found misfire on cylinder #5 and changed out that spark plug.
Regarding Service Rear Axle, they charged me $165 for "3602 Repair electrical 390CCC. Not sure what that they did here.
"Code U042B would not clear, followed SI to reprogram Chassis control module."
They could not tell me why this was happening.
So, I took it to Jet Chevrolet hoping they might be able to help figure out why it was fouling plugs. After talking to them, first step was to replace all the plugs and plug coils, thought was maybe a bad batch of plugs. Also, do a GDI, fuel induction service.
Then they contacted GM and opened a case regarding random misfire issue. When I brought them the car, no codes were displaying. GM "walked through checking and verifying proper fuel injection system spec such as long term trim and short term trim to verify vehicle is not leaning out causing misfire. Checked ignition timing and crank/cam sensor function, inspected relative engine comp to be in spec across all 8 cylinders, test drove and tested vehicle for 20 miles to verify proper engine operation. No misfire codes found or symptoms to be duplicated. Vehicle is functioning as designed."
I took the car and I'm still feeling the slight hesitation and shuddering (nothing like the railroad shudder though), it certainly is not running smoothly. I'm not very confident in the car right now, worrying the problem will reoccur when I'm a ways from a dealer and stuck in limp mode...
Any thoughts?
Thanks
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,621
Likes: 4,066
From: Cape Coral, Florida
Well first thing is bringing the car to a dealership for diagnostics…they are clueless !!…I’m surprised they did a relative compression test…most dealerships don’t use a scope…your hesitation can be a number of things and without scoping the car as the hesitation is occurring will be difficult to find…find yourself a diagnostic shop in your area that uses a scope daily…they will find out what’s wrong !!
Melting Slicks
Joined: Dec 2007
Posts: 2,902
Likes: 668
From: North Fulton Georgia
Well first thing is bringing the car to a dealership for diagnostics…they are clueless !!…I’m surprised they did a relative compression test…most dealerships don’t use a scope…your hesitation can be a number of things and without scoping the car as the hesitation is occurring will be difficult to find…find yourself a diagnostic shop in your area that uses a scope daily…they will find out what’s wrong !!
