Can't get rid of an engine light

[slamgranderson]

Hi, I've had an engine light that's been bugging me for about a year now. The code is P0302 or cylinder 2 misfire. Here's what I've done: replaced all the spark plugs, replaced the fuel injector for cyl 2, and swapped the ignition coils with another cylinder to find out if it was the coil - it wasn't, when I put the coil from cyl 1 on cyl 2, there was still a misfire on 2. The engine doesn't run rough, and the misfire is not consistent. If I clear the light, it will run for about 100 miles before the light comes back on. It doesn't affect performance enough that I want to waste money of having a mechanic diagnose it - it seems to run fine as is (although it doesn't get the best gas mileage). Nevertheless, engine lights are annoying and I'd love to get rid of it. Any thoughts or ideas on what this could be? [2004 Jeep Liberty v6 w/ 118k miles]

 

[LibertyTC]

How many miles on this engine? Wonder if it is stem seals ...Have you done a leak down test and full compression test on all 6 cylinders?

 

[Billwill]

Could be a bad connection at the PCM that needs cleaning or a bad connection anywhere that other connectors are in series with the injector or coil pack wiring.

Or could be an intermittent wiring short to chassis/engine that happens as you go over a bump or the engine rocks around a bit...not fun to find!

The problem with the wiring is that generally the leads from say the BCM to the injectors/coil packs do not take the shortest path but rather join together with other leads in a large harness going all over the place!

So you could have one of these relevant wire chaffing through to chassis/engine or to another random wire within the harness...been there done that after a front end collision damaged the harness up front.

 

[Berserker]

Cylinder 2 is the last cylinder in the firing order. I had the same code for a year with no issues, same as you. Its your fuel pressure regulator. Have your fuel pressure tested, see if it holds pressure. On my 4.7 the FPR is inside the fuel pump. Hope this helps.