Runs fine on cold start up, cylinder misfires on warm start up

FUNKYMOONCHEESE

MEMBER
2008 JEEP WRANGLER
3.8L
V6
4WD
MANUAL
120,000 MILES

I got a check engine light on my way to work one day. The engine was misfiring, I assumed it was a blown spark plug so I had them all replaced. Didn't fix the problem, the folks at Sears said it was a fuel injection problem on the first cylinder.

Mechanic said I should run a few tanks of Seafoam or Lucas through it to see if there is any improvement.

I've done that, here's what's weird:

- If I start the engine up after it's been sitting for awhile, it runs great. No power loss, no misfires. I can generally make it to work and back without any issues.

But,

- If I drive awhile and stop to get gas or something, I shut the engine off and when I start it back up, the 1st cylinder misfires.

This happens reliably every single time, I noticed that one of my spark plug cables was arcing electricity where it rests close to the header so I replaced it and thought it would fix the problem, but it did not.

Any thoughts on what the issue might be?

4 Replies

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello,

This sounds like you could have a failing fuel injector. What usually happens with an electrical component like a fuel injector that is starting to fail is they will run perfectly when they are cold, but when they heat up the internal coils that run the solenoid[a fuel injector is basically just an on/off solenoid] expand as they heat up and short out. This will happen the same for other electrical components like Crankshaft Position Sensors, Camshaft Position Sensors, Engine Coolant Temperature Sensors, etc. Please check into this and get back to us with what you find out. We can go from there, if needed. I hope that this helps.

Thanks,
Alex
2CarPros