I've posted this on Jeep Forum, as well as the Jeep section on Expedition Portal. Haven't really had any specific answers as to what my problem is caused by.
1999 4.0 322k miles very very meticulously taken care of.
there is a leak from the header. as well as from between the cat and muffler
new bosch injectors (rough idle before and after install of injectors)
the rough idle throws a check engine light. the codes consist of misfire in cylinder 1, misfire cylinder 2 cylinder 3 etc. as well as random misfire in multiple cylinders (think that ones P0300?)
it happens when i get on the gas a little to hard, high revs seem to cause it, and high revs seem to cure it.
example of this: get on the gas to pass someone on highway, it downshifts revs high, pass and were good. when i come to a stop it idles rough. if i put it in neutral and rev it for about 20-30 seconds it clears right up.
what we have noticed it when it is running rough removing the wires from injector one does nothing, if you rev it up and remove the wire it runs poorly so the misfire is ONLY AT IDLE when up to speed the motor is fine!
lastly, i have noticed with the new injectors it seems to be ever so slightly worse.
here is the theory of a 19 year old kid who grew up around cars (FWIW)
when i get on the gas the O2 sensor reads that the engine is running lean because of the exhaust leak at the header, because of this it causes the motor to run rich (which i know it runs rich, spark plugs smell like fuel pretty bad and the leak at the header is rich of fuel)
when i put the new injectors on they are brand new as compared to the old ones so they run alot better so im guessing its slightly worse with them because they are getting better flow from the beginning and when it makes it run rich its getting a better flow than the older injectors so dumping slightly more fuel causing it to run ever so slightly richer
yal think thats a likely scenario? i just cant figure why it would clear up with more revs... and why its only at idle.
any way i can help prevent this a bit till i can afford a new header? maybe adjust the gap to give a hotter spark?...
let me clarify on this statement
"what we have noticed is when it is running rough removing the wires from injector one does nothing, if you rev it up and remove the wire it runs poorly so the misfire is ONLY AT IDLE when up to speed the motor is fine!"
at idle removing wires from cylinder one's injector has no adverse affect on the idle. it still runs ****ty leading you to think that injector one is not working properly, test of wire shows it is sending a current. when you rev up motor and the rpms smooth out then you remove the wire the rpms become rough so its safe to assume that for some reason at idle cylinder one is misfiring but at rev (sorry stupid cluster has no tach so idk what rpm its at) it runs fine. thus we are led to believe problem is only at idle. though affects on MPG are very present still.
also at idle removal of any other wires results in an even rougher idle so they are good. it is just cylinder one that is messed at idle.. well. in the case of when we checked. if there is random misfire in multiple cylinders im guessing the outcome of that experiment would be different.
i have been told i should do a compression check, which i am waiting on the right fitting for (have the gauge but the part that screws into the head is the wrong thread) i was told if the compression is low in cyl 1. that i may have a worn or missing valve seat. i was also told i should get a leak down test, which unfortunately i have no idea what that consists of. at the moment I'm in college, no job, and after dec. i should be shipping off the the military so im limited with what i can do. i already have a ton wearing down on the jeep (needs: u-joints, tires, brake job, rear main seal, tranny filter/fluid, fluid change in t-case, oil change, the exhaust work, etc) so i can't just start replacing random stuff and hope it fixes the issue. my dad has said it has had the problem for quite some time before the jeep was given to me (we are the original owners) when i got it, it would misfire if you drove faster than 72mph. replaced cap and rotor and now its just at high revs...
thanks for your help guys. I'm kind of in desperation with the jeep at the moment...
