o2 sensor problems

okay i went up to my uncles last night and worked on my jeep(he is the best diagnostic person i know besides a machine) and i think we might have figured out a beter part of my problems. the #6 cylinder isnt firing, so we pulled the plug and switched it with one from another cylinder, that wasnt it, so we pulled the plug and checked for spark, yep we have spark, so then we pulled the injector and put a new one in it, that wasnt it, so we checked the power and ground to the injector, and it was good, so we check compression, and it had 120#. so not sure just what that problem is, but it has been running very rich because the plugs were all black and its puffing just a tiny tiny bit of black smoke. so we check the o2 sensor by unpluging it while it was running, and it made NO DIFFERNCE whatsoever. so could the #6 hole be missing because its giving it way to much fuel and retarding the timing(or advancing cant remeber which is which) to a point where just the #6 is missing? i didnt even know it would run without the o2 sensor working. has anyone had a problem like this before?

kolby

If the timing is off, it will be off for all the cylinders.

Let me recap...

You determined that #6 isn't firing. You pulled the plug and it sparked. That is fine but getting a spark at no pressure is a long way from getting spark under compression. Try to swap a complete plug wire before you go any further. If that doesn't do it, try swapping injectors plugs. I know they are supposed to be in order, but just for testing swap 5 & 6. Now see if #6 is firing at all.

If all the plugs are black, the problem isn't just witn #6. Does it idle OK? Does it stumble off of idle?

ill try switching the wire, ive got two sets so spares shouldnt be a problem. is there a way to test them with a multimeter? then ill try switching injector plugs. we did try testing the injector plug gound, it was good, and the hot wire was pulsing like it should, but who knows.

kolby

We pulled the head from my sons old 4.2 YJ that he sold to a friend a couple of weeks ago, the number 6 exhaust valve was almost welded shut and would not operate at all. Might want to check if your valve train is working right too.
He sent the head out and had a valve job done, replaced the lifters and rods, he's still working on it.

hmm wouldnt that make it want to backfire tho? cause when the intake valve opened then that would be the only place for the exhast to go. or am i missing something? how was it running?

kolby

you can have compression, even with a broken valve spring. i would pull the valve cover and see what you find.

lankchevy said:

hmm wouldnt that make it want to backfire tho? cause when the intake valve opened then that would be the only place for the exhast to go. or am i missing something? how was it running?

kolby

Click to expand...

Yup, the YJ backfired thru the webber.

hmm well mine isnt backfiring so i wanna say thats not it, i ordered a new o2 sensor today and it should be in tommarow morning, so ill put that on after work, i tried a differnt plug wire and that had no effect, so i tried switching injector plugs, and when doing this i realized that the little metal spring clip on the wire plug wasnt on right and wasnt letting it go down all the way, so i fixed that when i switched them, and that made it run worse, so i switched them back to the proper order with the #6 injector plug on right and that helped some, at least now when ur going down the road it doesnt feel like its missing anymore, u can still tell something isnt quite right, and its worse at idle, if u rev it in park or nuetral tho. so hopefully when i get the new o2 sensor on that should help it some. im leaving for colorado tommarow evening for a week so id like to get this figured out since i get back a week from this coming saterday, and my brother is getting married the next saterday(in three saterdays) so that week is gonna be hecktack.

kolby

if you had 120 psi in cyl 6 what did the other cyls have, what are you comparing that to. if it has lower compression it could have a burnt valve, if it has similiar compression it could be a broken valve spring.

all the other cylinders carry between 120 and 130

kolby

are you sure it is only misfiring on #6? have you pulled the valve cover and looked for anything unusual.?