Possible missfire
Thread Starter
Safety Car
Joined: Jul 2010
Posts: 3,965
Likes: 386
From: Chandler AZ
Possible missfire
Been working on a friend’s 2004 C5 since December 2025, lots of stuff torque tube rear main seal, oil sender new intake gasket, valve cover gaskets, new rear cv axles, rear tie rod ends, lots more I can’t remember at moment.
It runs but kinda crappy, no check engine light but idling sounds decent but in park if I gently Rev the engine from idle up to say 1500-2000 rpm, it just feels/sounds sluggish.
If you hit the accelerator pedal quick it revs fine.
Could be weak/stale gasoline from Thanksgiving time, car shows 3/4 tank.
Was thinking of buying a temp laser gun to measure each header primary pipe to compare temps.
The spark plugs all looked good and he said they were about 2 years old, I just put new ac Delco plug wires.
Did tell him his upstream o2 sensors look like crap, the plastic ends are cooked pretty good from headers, asked him to get some new o2 sensors.
Or could it be it just needs to get out of garage and driven some before looking for issues?
It runs but kinda crappy, no check engine light but idling sounds decent but in park if I gently Rev the engine from idle up to say 1500-2000 rpm, it just feels/sounds sluggish.
If you hit the accelerator pedal quick it revs fine.
Could be weak/stale gasoline from Thanksgiving time, car shows 3/4 tank.
Was thinking of buying a temp laser gun to measure each header primary pipe to compare temps.
The spark plugs all looked good and he said they were about 2 years old, I just put new ac Delco plug wires.
Did tell him his upstream o2 sensors look like crap, the plastic ends are cooked pretty good from headers, asked him to get some new o2 sensors.
Or could it be it just needs to get out of garage and driven some before looking for issues?
Tech Contributor
Joined: Jan 2007
Posts: 19,401
Likes: 1,141
From: Dyer, IN
Been working on a friend’s 2004 C5 since December 2025, lots of stuff torque tube rear main seal, oil sender new intake gasket, valve cover gaskets, new rear cv axles, rear tie rod ends, lots more I can’t remember at moment.
It runs but kinda crappy, no check engine light but idling sounds decent but in park if I gently Rev the engine from idle up to say 1500-2000 rpm, it just feels/sounds sluggish.
If you hit the accelerator pedal quick it revs fine.
Could be weak/stale gasoline from Thanksgiving time, car shows 3/4 tank.
Was thinking of buying a temp laser gun to measure each header primary pipe to compare temps.
The spark plugs all looked good and he said they were about 2 years old, I just put new ac Delco plug wires.
Did tell him his upstream o2 sensors look like crap, the plastic ends are cooked pretty good from headers, asked him to get some new o2 sensors.
Or could it be it just needs to get out of garage and driven some before looking for issues?
It runs but kinda crappy, no check engine light but idling sounds decent but in park if I gently Rev the engine from idle up to say 1500-2000 rpm, it just feels/sounds sluggish.
If you hit the accelerator pedal quick it revs fine.
Could be weak/stale gasoline from Thanksgiving time, car shows 3/4 tank.
Was thinking of buying a temp laser gun to measure each header primary pipe to compare temps.
The spark plugs all looked good and he said they were about 2 years old, I just put new ac Delco plug wires.
Did tell him his upstream o2 sensors look like crap, the plastic ends are cooked pretty good from headers, asked him to get some new o2 sensors.
Or could it be it just needs to get out of garage and driven some before looking for issues?
While it's always good to have an IR thermometer at your disposal, I do not see how you are assessing the engine operation without examining live data. It's good that you are astute enough to sense an issue, but you have to confirm with a scanner. Pull your codes from the DIC and write them down. Reset all codes and see what comes back.
