Looking for some help with phantom misfires... i have run out of ideas.
First some background - in early 2024 i took my 2002 LC w/375k mi on 2 long roadtrips 1) NY to FL, 2) NY to Montreal.
A couple months after these roadtrips, the truck developed a flashing CEL. Sometimes it would go away on its own, other times it would throw a Random Misfire code, accompanied by misfire codes for every cylinder. Occasionally it would throw the Random Misfire code and only Cylinders 5 & 8 would throw misfire codes. The catch is, there is no misfire that i can feel... truck drives normally. I drove it for a while hoping i would feel a misfire and replace a coilpack on that cylinder.
A short while later, the fuel pump went out on me. I replaced the fuel pump thinking that was also the reason for the codes. But, that didnt solve it. Since then i have replaced the following:
- all coil packs
- all spark plugs
- all injectors
- fuel filter
- gas cap
- several rounds of fuel system cleaner
- tested and cleaned MAF
- smoke tested EVAP and vacuum lines (replaced a couple lines and the solenoid that bolts to the intake manifold
- intake manifold gaskets
* The timing belt was done 2 years ago, less than 50k miles since
The intake manifold gaskets were the most recent. I am noticing that post, i am no longer getting just the cylinder 5&8 misfires, so i think that is resolved. But, i am still getting random misfire codes accompanied by all cylinder misfire codes.
The codes come up intermittently. I've narrowed it down to mostly cruising in 4th gear between 1-1.5k rpms. This is when i occasionally get a flashing CEL. Sometimes i can accelerate out of the flashing CEL by getting rpms up to 2k+. But, sometimes i get the codes at startup. And this is all intermittent. I cannot cause the codes to happen consistently
i have a replacement throttle body gasket on order but only for completeness on my intake manifold gasket replacement job.
Looking for suggestions on how to diagnose and next steps..... TIA
First some background - in early 2024 i took my 2002 LC w/375k mi on 2 long roadtrips 1) NY to FL, 2) NY to Montreal.
A couple months after these roadtrips, the truck developed a flashing CEL. Sometimes it would go away on its own, other times it would throw a Random Misfire code, accompanied by misfire codes for every cylinder. Occasionally it would throw the Random Misfire code and only Cylinders 5 & 8 would throw misfire codes. The catch is, there is no misfire that i can feel... truck drives normally. I drove it for a while hoping i would feel a misfire and replace a coilpack on that cylinder.
A short while later, the fuel pump went out on me. I replaced the fuel pump thinking that was also the reason for the codes. But, that didnt solve it. Since then i have replaced the following:
- all coil packs
- all spark plugs
- all injectors
- fuel filter
- gas cap
- several rounds of fuel system cleaner
- tested and cleaned MAF
- smoke tested EVAP and vacuum lines (replaced a couple lines and the solenoid that bolts to the intake manifold
- intake manifold gaskets
* The timing belt was done 2 years ago, less than 50k miles since
The intake manifold gaskets were the most recent. I am noticing that post, i am no longer getting just the cylinder 5&8 misfires, so i think that is resolved. But, i am still getting random misfire codes accompanied by all cylinder misfire codes.
The codes come up intermittently. I've narrowed it down to mostly cruising in 4th gear between 1-1.5k rpms. This is when i occasionally get a flashing CEL. Sometimes i can accelerate out of the flashing CEL by getting rpms up to 2k+. But, sometimes i get the codes at startup. And this is all intermittent. I cannot cause the codes to happen consistently
i have a replacement throttle body gasket on order but only for completeness on my intake manifold gasket replacement job.
Looking for suggestions on how to diagnose and next steps..... TIA
