Misfire while cold

jeremesh · **Posted:** Fri Feb 26, 2010 11:21 am

Last week I had to replace the cam position sensor, did that and things ran fine. Yesterday, jeep ran fine in the morning. Ran fine when I went to a meeting in the afternoon but when I left to go home, it was running very rough, lack of power and the check engine light was flashing. So I drove the 5 miles taking it very easy... about 1.2 mile from home, starts running fine. I pulled the codes and it had a misfire on cylinder 2.

This morning, I went out and started the jeep and let it warm up, although not fully warm. Started driving and same symptoms... about 1 mile from work, starts running fine.

What would cause a misfire when the engine is not fully warmed up but would run fine when the engine is fully warmed up? Dirty injectors? Bad plugs? Help please.

BVCRD · **Posted:** Fri Feb 26, 2010 11:38 am

Usually, a backfire is a sign of a lean condition or timing. Is yours doing that or is it just a miss?

jeremesh · **Posted:** Fri Feb 26, 2010 11:45 am

BVCRD wrote:

Usually, a backfire is a sign of a lean condition or timing. Is yours doing that or is it just a miss?

Just a miss.

JeepinJarhead03 · **Posted:** Fri Feb 26, 2010 5:03 pm

check the plug, if it looks ok, swap Coil #2 with Coil #3 and see if the misfire moves to 3

if it still misfires either get new plugs, or swap plug 2 and 3 and try again and see if its the plug

jeremesh · **Posted:** Fri Feb 26, 2010 7:56 pm

JeepinJarhead03 wrote:

check the plug, if it looks ok, swap Coil #2 with Coil #3 and see if the misfire moves to 3

if it still misfires either get new plugs, or swap plug 2 and 3 and try again and see if its the plug

I replaced all the plugs (except one because it was getting dark and I didnt feel like taking off the radiator reservior). I also found that after I removed the air box last week to replace the cam position sensor, I forgot to connect the small hose that comes off the side of the air box. What is that for? Either way, the miss seems to be fixed but I wont feel confident until it sits over night and I get a real cold start. The plug that was in #2 had some dried up oil on the outside. The inside was bone dry. There was no wet oil anywhere so I am assuming it is from a poorly placed oil fill I had done at some point. I also noticed on the ceramic of plug #2 that there was dark sooty looking scorch marks. Could that be from the plug or should I plan on replacing the coil for #2?

JeepinJarhead03 · **Posted:** Fri Feb 26, 2010 8:46 pm

ceramic - could just be 'tarnished and dirty' electro grease from inside the coil boot

that hose to the airbox goes to the crankcase filter inside the airbox

- the dried up on on the outside of the plug and what not near the threads is probably just from some valve cover seepage

if it continues to do it, and the plugs are relatively new, pull the plug outside the parts store take it in and ask for a new one, could just be a defective plug that isn't firing right until it's warmed up or the gap wrong

if the 'scorch marks' don't seem to be dirty electro grease, and more like an electric charge leaking out of the ceramic, it points back to a defective plug

Misfire while cold

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