Misfire Troubles....

[TallGuyJeep]

I have been having trouble with an intermittent misfire lately, that just recently turned into a constant misfire. It didn't seem to be a big issue at first, it seemed to go away after the engine warmed up, or if I fiddled with the spark plug wires. Now it won't go away, so the jeep has been grounded to the driveway, which makes me sad. :(

I just finished replacing the spark plug wires that were bad, but I am still having the same issue. I've been reading up on the forums and it seems there have been similar problems because of bad sensors like the CPS.

I guess I'll just continue with the easy stuff like spark plugs and injectors, and continue from there, but I just wanted to see if ya'll had any suggestions.

Josh

[TallGuyJeep]

I forgot to mention, I have been doing the key trick to pull the codes, but there haven't been any the whole time.

Also my jeep is a 92.

[4.3LXJ]

How long since the )2 sensor has been changed?

[TallGuyJeep]

I'm not sure. Not since I've had it, which has been about six months.


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[4.3LXJ]

You can probably assume it has not been changed before you got it if ever. Most people neglect them until the engine starts misfiring or milage goes in the toilet. I would suggest changing it so you can have a good base to work from. Most of the time that fixes it though

[TallGuyJeep]

Thank you for the suggestion. I'll go get one right now, I've got the day off from work. :) I will update once it's in.


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[TallGuyJeep]

That definitely helped a lot to smooth it out, thanks a ton. I went for a spin around the neighborhood and it was much, much better, though when I got back to my house I got out and listened to the exhaust and it seemed to still be sputtering once in a while. Any more genius suggestions? :)

[4.3LXJ]

Run the tank down to 1/4. Put in a bottle of Seafoam and go for a nice long drive. It will clean out carbon and shellac in the fuel system. Glad that made am iprovement

[TallGuyJeep]

Thankfully I picked up a can of seafoam the other day. Unfortunately I also filled up. I just drove to my night class and it started missing pretty bad again. Now I'm not sure if the new O2 sensor actually helped or if it was just a fluke. I'll siphon the tank and seafoam tonight and go from there.


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[Brasscatz]

Another thing to look into replacing is the distributor cap, rotor and coil.

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[4.3LXJ]

dies it miss only at full throttle or near full throttle?

[TallGuyJeep]

Another thing to look into replacing is the distributor cap, rotor and coil.

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I did take off the cap, it looks nearly brand new, same with the rotor. Hard to tell with the coil but it seems to be in good condition. Is there a way to test it?


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[TallGuyJeep]

dies it miss only at full throttle or near full throttle?


It actually seems to miss more at idle and initial acceleration, then smooths out a bit, then sometimes is rough again. If I jump on the gas it feels like it's smoother under hard acceleration. Sometimes it's rough all the time, and sometimes runs smooth like after I replaced the O2 sensor. I can't find a pattern to it, it just runs bad overall.


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[slvmart]

How about the leads from the Distributor to the plugs, are they in good shape ? This used to be a pretty regular issue with ignition systems in the old days. I didn't notice where you live but up here in the Great Lakes area, rain and snow (moisture) would definitely induce this type of thing if the ignition wires were in poor shape.

[TallGuyJeep]

How about the leads from the Distributor to the plugs, are they in good shape ? This used to be a pretty regular issue with ignition systems in the old days. I didn't notice where you live but up here in the Great Lakes area, rain and snow (moisture) would definitely induce this type of thing if the ignition wires were in poor shape.


Yeah, those are brand new, just replaced yesterday. I live near Salt Lake City, UT so I'm used to rain and snow, even so it's been dry for the past week or so. I will be sure to keep an eye on them though, thanks!


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[Brasscatz]

I did take off the cap, it looks nearly brand new, same with the rotor. Hard to tell with the coil but it seems to be in good condition. Is there a way to test it?


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None that I know of, but have you also checked all of your grounds? Hopefully it's not the distributor itself...

[TallGuyJeep]

None that I know of, but have you also checked all of your grounds? Hopefully it's not the distributor itself...


I haven't seen any bad grounds, but I'll check tonight after work/school. I would be so happy if it was just a bad ground. :)


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[4.3LXJ]

One other thing. Now that we are narrowing things down a little, if the problem persists after the Seafoam, then you have two options. One is dirty injectors, but not likely. The other is that your crank position sensor is beginning to fail. I bet that has never been changed either.

[TallGuyJeep]

One other thing. Now that we are narrowing things down a little, if the problem persists after the Seafoam, then you have two options. One is dirty injectors, but not likely. The other is that your crank position sensor is beginning to fail. I bet that has never been changed either.


That's what I was thinking. CPS is the one on top of the bell housing right? And maybe it's time to upgrade my injectors anyway...


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[4.3LXJ]

I would look at that CPS, on top of the bell housing first. It is another sensor that needs to be changed every 100K that only gets changed when it fails

[TallGuyJeep]

I would look at that CPS, on top of the bell housing first. It is another sensor that needs to be changed every 100K that only gets changed when it fails


I'll do that. Hopefully I can pick one up tonight and put it in tomorrow.


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[WhiteDevil1311]

Any update yet?

Im having the same issues. monday it ran fine, yesterday it started to act up but smoothed out figured the cold has something to do with it but went to move the XJ today to get into the garage and it ran like crap, started to pull wires and found all cylinders but #2 reacted to being disconnected. I just replaced the wires, had to get the cap and rotor shipped from another store should be in tomorrow morning. I dont think its the coil or CPS as it produces a strong blue spark. I am sure my CPS is factory as everything else is.

Im doing plugs, cap and rotor tomorrow, did wires today and IAC removal, clean and reinstall with new O ring.

I had the FSM but lost my HDD on my PC completely last week so I am at the mercy of Haynes' BS. Please update.

[WhiteDevil1311]

http://tapatalk.imageshack.com/v2/14/11/20/0da9ebf29ee126f9be1b9388fbc6f381.jpg

My misfire issue solved. Plugs had no cores
Left to right is #6-#1 aswould be in the engine

[TallGuyJeep]

http://tapatalk.imageshack.com/v2/14/11/20/0da9ebf29ee126f9be1b9388fbc6f381.jpg

My misfire issue solved. Plugs had no cores
Left to right is #6-#1 aswould be in the engine
Sorry for the late response,been crazy busy with work and finals coming up. I'm glad you solved your problem. :) as for an update the parts store still hasn't received the sensor i need. I've finally got some free time tonight so I'm going see if i can track one down somewhere else.

[WhiteDevil1311]

I try to go napa with everything but the zone has come in handy when in a bind

[TallGuyJeep]

Napa is usually great,they have been in the past, but not this time around i guess. They were supposed to have it Saturday morning but i think someone bought it before they could take it to my local store.

[WhiteDevil1311]

I use thm online to reserve first had that happen at alot of stores so ive upgraded myself to using a machine to secure the parts needed. Sucks but atleast we arent slaves to apes

[TallGuyJeep]

No, we're slaves to machines instead. ;) I'll have to do that in the future though,thanks

[WhiteDevil1311]

It helps on the limited quantity items. Had to reserve my tune up due to not having all the plugs in stock. Hopefully you get her up and running again soon. Now just to try and drain the 15/40 from the engine in sub freezing temp....world's longest oil drain anyone?

[TallGuyJeep]

That sound like a lot of fun! (Sarcasm) if she isn't running by the end of the weekend i think i may have a shop take a look. I don't want to keep just throwing money at the problem with my very limited college student funds. Besides i need i save some money for my Christmas present to myself!;)

[WhiteDevil1311]

Misfire can only be a few things. Id run it and pull the plugs to inspect for fuel (easiest way) if there is fuel then other then a tune up it can be crank,cam position sensors or a broke distributor. What have you already done to chase the gremlin?

[TallGuyJeep]

Well i originally thought it was just bad wires from the cap to the plugs, i could wiggle them and feel the contact points losing contact. When i replaced those i pulled the first two plugs which seemed nearly brand new as they should, less than 3k miles on them. I've scoured the engine bay and surrounding looking for bad wiring(finding some other things to fix) but couldn't find any bad wires. I replaced the O2 sensor and ran most of a can of seafoam through the gas tank but still runs like crap. Also i pulled the distributor cap, looks brand new along with the rotor. The whole time I've been checking the codes with the key trick, but there haven't been any codes.

[TallGuyJeep]

I think I'll pick up some new plugs while I'm running around and replace those anyway because they are cheap and easy and I'll be able to cross them off the list.

[WhiteDevil1311]

I thought i replied.... are you sure you have spark and fuel at each cylinder?

[WhiteDevil1311]

My rotor was toast it looked ok but upon removal and closer inspection i had a 7 layer dip of torched carbon on the button

[TallGuyJeep]

Oh i was going to ask how to check that, I've never done it before. Are you just pulling the wires off the plugs while it's running?

[WhiteDevil1311]

Yes one at a time gently. The motor will run like dookie if the cylinder is ok on spark and fuel. No change means you found the dead cylinder. If the dead cylinder has fuel it will be in the ignition components ie plugs wires cap rotor ect. The plug will smell like gas and be a little moist. Also youll see a puff of fuel vapor when you pull the pkug on the no spark cylinder

[TallGuyJeep]

Thanks for the instructions. I'm going to be busy tonight.

http://tapatalk.imageshack.com/v2/14/11/20/6a2ff1e2137ecb570079e630a28bcf34.jpg

[TallGuyJeep]

I can't believe it. I can't freaking believe it. I put the new CPS is, and she still ran like crap. Change the spark plugs, probably the very first thing i should have done and she purrs like a kitty. I guess the lesson learned is do the simple cheap stuff first. I did learn a lot however, replaced some stuff that would need it soon anyway and added some new tools to the bucket so it's not all bad. Thanks for the input from everyone, i really appreciate all the help.

[WhiteDevil1311]

Dont feel bad mines a 94 that is loaded with factory crap that should have been replaced a decade ago.

[TallGuyJeep]

Ah whatever, it's actually pretty funny. :) plus it's always good to learn more about the jeep, which i did a lot of.

[WhiteDevil1311]

Hows it running? Mines purring like the day she was assembled. All pings ticks and knocks are gone.

[TallGuyJeep]

She sounds so good! I drove around all day yesterday for work, not a single hiccup. 😀