miss fire on #1 cylinder

I have had a really bad miss fire on my 96xj for some time now. it sounds like like crap, and i can hear the miss fires in the tail pipe at idle and throughout the rpm sweep

specs are:
4.2 block
95 HO head
96 injectors
new plugs rotor and wires about 3 months ago.
flowmaster 2.25" 40 series
no cat, but i do have an o2 sensor hooked up in the straight pipe.

I am also running 87 octane gasoline, I've tried steeping it up to 91 but it didn't seem to help.

i got the engine from a buddy who rolled his jeep. he only had about 3k on it when it rolled and it has been in two of my jeeps so now it has about 15-20k miles.

i have pulled the plugs and they look to be burning correctly, I've got good fuel pressure and all that.

the only thing i can think of is timing, a burnt valve, or uneven compression. i

I had the codes checked by Auto Zone and they told me i had a miss fire from #1 and no signal from the o2 sensor. i fixed the o2 sensor in the tail pipe and cleared everything and i am still getting the miss fire. i am very confused as to whats going on with this engine.

oh and i searched around, pretty much everyone says its plugs rotor, and cap.

anyone?

1) compression test
2) ignition control module test (slight but possible)
3).............i'll have to think a little more about this.

scorpio_vette said:

1) compression test
2) ignition control module test (slight but possible)
3).............i'll have to think a little more about this.

Click to expand...

thanks i will do that as soon as i get home.

I had the same problems a few months ago....found out while looking at the engine in the dark that the #2 plug wire was intermittenly grounding to the block(even though the insulation was good and the wires were less than two months old)

jiggled the wire and ran normal,jiggled again and ran like crap....then I heard a click noise and seen the arc jump from the wire to the block.I just routed that wire differently untill it didn't touch the block=problem solved.

btw:I don't think a burnt valve, or uneven compression would throw a # 1 cylinder missfire code...

outlander said:

I had the same problems a few months ago....found out while looking at the engine in the dark that the #2 plug wire was intermittenly grounding to the block(even though the insulation was good and the wires were less than two months old)

jiggled the wire and ran normal,jiggled again and ran like crap....then I heard a click noise and seen the arc jump from the wire to the block.I just routed that wire differently untill it didn't touch the block=problem solved.

btw:I don't think a burnt valve, or uneven compression would throw a # 1 cylinder missfire code...

Click to expand...

this could be a possibility, the wires i am using now aren't exactly top notch. i will straighten them out and see if that helps.

Is it a dead miss??? A dead miss is defined as the cylinder in question does not fire at all...if the problem is a dead miss and the plug is not dark, wet, or oily....it has to be either a severe compression problem (usually unless it is really bad a cylinder will pick up and smooth out at higher rpm) or the injector is not fueling the cylinder.....first step is to check the compression or better yet do a leakdown test to determine the health of the engine....and progress from there...

I have the exact same problem, I have had alot of hours and dollars thrown at this issue. What I found to help was listed in a TSB that there are issues with the valve springs, I had all valve springs replaced and the issue cleared up for 3-4 months now it is back again. I have good compression, the injector is good (switched the injector from Cylinder 1 to 2) I have good fuel pressure, the plugs, rotor, cap and wires were recently replaced last 5-6 months, but still the #1 misfires. I don't know what to do next???
Daniel

PS I have 169K+ miles if that helps

PPS if you think it might be a wire switch it with one the same length (for me it was the 1 and the 6) see if that moves your problem in the computer code, HTH

It could be carbon build up on the valves. Use a can of Mopar combustion chamber cleaner but leave it sit for aboiut 3 hours instead of how long the can says. Otherwise follow the instuctions, it works great. BTW I'm an ex mopar tech and have seen this problem before.

If that doesn't work check the compression. If thats good swap the plug wire to # 6 to see if the miss moves. If there is still no change throw on on new Mopar cap and rotor(I've seen many bad aftermarket ones) and if that doesn't work swap the injector with one of the other known good ones. If it's still a problem after this let me know.

I was having this problem. Tried lots of products like Techron, Lucas, seafoam none of which helped. Installed new Coil, cap/rotor, wires, plugs with no help. A compression test showed 125PSI in Cylinder 1, a little out of spec with the rest, but not terrible.
Finally got 6 new injectors installled last Sunday, and my CEL is gone. Only been a week, but so far so good. Running very well, so I dont expect it to come back(cross fingers).
The condition of my new #1 plug only after a couple months before the injector swap suggested it was pretty rich, while the rest looked normal.
What do your plugs look like? This is that #1 that was a few months old, middle is #2, and right is an old one.

I am also having this same problem on my 91... good compression, new head with only about 1hr of run time, swapped number one and two injectors, new plug, swapped wires, and yet no help. its always on number one. i can pull the wire or the injector wire and still missing. it only does it below 1000 rpm. old plug was dark, but i think from experiance it would still fire. idk.. to bad the motor has to be pretty much missing from the car for obd1 to throw a code

I had a similar problem on my Ram last week. But I was lucky enough it only happened right after a plug change. Turned out one of the brand new plugs was bad right out of the box.....:gonnablow Thank God for scan tools! I would have been in there all day trying to figure out which plug was bad by swapping them out one by one......:confused1

aha! fixed it. turns out american cylinder head sunk a valve seat to far in to the head and it was pushing coolant out on the exhaust stroke. wouldnt have found out except for the green tinted plug. at least since it was a remand head they gave me everything to put the new head on. runs like a champ now. just need to work on the cooling a little bit more.

On My '98 XJ it appears to be a sticky exhaust valve in the #1 cylinder, will need to do a valve job, ouch