I have a 1999 grand cherokee 4.0l 2WD... It started by idling bad and I the check engine light flashing. I checked the codes and it read misfire Cyl 6. I change the spark plugs and checked for spark on the cylinder and its good. I then changed the injector fom cyl. 4 to cyl.6 and still same code. I put a test light on the injector (cyl 6) and after a minute or so after start up the signal cuts off. All fuses are good what could it be? i really need help here i use for work and its the only car we have and it goes thru a full tank of gas like nothing within 2 to 3 days is almost on empty. HELP!!! HELP!!!

 

I've got the same thing going on with my 2001 4.0 GC...... code P0306 - misfire in 6.

I replaced the spark plugs but it's still studdering.... where do I go next?

RIZ

 

Not sure this will help, but, my brothers 2000 chevy van 6 cyl. throws the same code, misfire cylinder 6. We are thinking it's more of a system fault that shows up that way, not necessarily something on 6. However, it's completely driveable with no problems other than a hard start condition about every 3rd or 4th start.
Is it completely misfiring on 6? From the mileage you indicate sounds like a hard failure somewhere on 6 ...compression? Valve?

 

Temperature failure of the #6 injector. Just a guess.

 

My jeep doesnt hesitate on start up at all buy it does feel like a misfire that i shakes when its on gear but on P and N it idles good. I cleaned and fixed all the grounds and i tested the ASD relay (its good). I even changed the opened up all the wiring harnest that that goes to tge injectors and the code keeps coming back but now it takes longer to go on. @dave1123 what do you mean by temperature failure because that rear part does get very hot compare to other cars ive worked on. Also when i accelerate fast it begins to kick and i hear like a popping sound from the exhaust and gas doesnt last at all. Its using it up like crazy..

 

It's possible injector #6 is leaking fuel all the time. Check your fuel pressure 10 minutes after shutdown. It should be holding pressure for longer than that. Sometimes they will leak only after they get hot, that's what I meant by temperature failure. The exhaust manifolds on the 99&up 4.0s are cast iron and get hotter than the old steel tube headers on older ones.

There are several things you can do about it. You can replace that injector with one from another cylinder, which is pointless but will prove that's what the problem is. You can replace that injector with a new one, also pretty unless because you'll have one clean one in the bunch, but then again will prove the malfunction. If it was my jeep, I'd replace all of them, IF that's what the problem is.

There are many thoughts about replacement injectors. Some people like using 4-hole injectors because they atomize the fuel in finer droplets. I can see where that might make for better power and fuel economy. Some guys even get them from the junkyard! Your choice.

Check for factory recalls on your jeep. My 2000 was recalled for (one thing) a heat shield on the intake manifold to isolate the injectors from exhaust heat. It's just an aluminum wafer blanket that just sits there.

About the ASD relay. If it wasn't working, it wouldn't start. The ASD turns on the ignition and fuel injector circuits. ALSO, the PCM turns it on after getting a CPS signal. Keep that in mind when diagnosing a no-start issue.