Ladynred

Hello - hope someone can help. Took my 2004 Jeep Grand Cherokee 4.0 Liter to 3 shops & no one seems to be able to fix it. It all started with a cylinder #1 miss fire. So far they replaced all the spark plugs, coil pack & all the fuel injectors. It's still misfiring, running so rich it'll burn your eyes out & the smell of gas is terrible strong. Naturally hard starting & stalling a traffic lights. Any suggestions greatly appreciated - thank you

4.3L XJ

Sounds like it is running too rich. It likely needs new O2 sensors even though you don't have codes for them. They wear out over time and are a tune up part that needs replaced every 50 - 100K

dave1123

Check for a short to ground on the #1 injector plug. That will have the injector at full flow constantly. Normally the injectors are all powered up with 12v and are grounded thru drivers in the PCM to pulse them for proper mixture control. If the ground lead is shorted to ground, the injector will be full on all the time the engine is running. The PCM will still be switching it, but it doesn't know it's not getting a signal from it.

Bearstream

Check the wiring harness around the firewall end of the valve cover, I had to put a rubber cap on the stud protruding at the back of the valve cover, and double wrap the wiring harness with extra loom and heavy tape to prevent the stud from wearing through the the wires, which develop the kind of electrical shorts described by Dave in the previous post.

dave1123

Nice catch Bearstream! I just had an 02 sensor shorted to voltage because of that very same wire bundle!