Intermittent misfire

[prerunner1982]

My 93 has been having an intermittent misfire over the last week. I have replaced plugs and wires and ran some seafoam through the intake.

I still have the misfire.

I can get hard on the gas and bang through the gears once and it will run fine for awhile, eventually (about 30+/- mins) the misfire will return.

I have some seafoam in the gas as well, that will get used over the next 4 days.

I hate having to beat on the Jeep so hard to get it to run right.

Ideas?? Injectors? :thumbdown:

[4.3LXJ]

Have you taken a look at the TPS yet?

[prerunner1982]

no sir I have not.

[4.3LXJ]

You might try this. Before you start, but with the key on, depress the skinny pedal a couple of times to the floor and then start and see how it does

[prerunner1982]

Will try to remember to try that before I leave work today.

Went out and tested the TPS, .77 volts closed, 3.86 fully open and seemed to scale fine with throttle position.

If it starts misfiring I will test it again, during the act.

[cantab27]

buddy has same sorter problem we are hunting down jon .....will be following this post ....have done most things including 02 .....was thinking injectors as well let me know what you find

[slvmart]

You said you went through the wires and plugs, but did not mention the ignition system. Not sure how the '93 is configure, single coil with distributor or with the ignition control module. But you might want to check if all is fine there before you go too far into more involved issues.

[prerunner1982]

I cleaned the contacts in the distributor.

Coil is "fairly" new... say about 4 yrs old.

The plugs did look bad. Some of them had quite a bit of deposits on them. So I was really hopeful/sure that that was the issue..

[Mudderoy]

I only know the 97+ so not sure if this fits, but...

Pull all the sensors off the throttle body and clean them all, including the throttle body.

[prerunner1982]

You might try this. Before you start, but with the key on, depress the skinny pedal a couple of times to the floor and then start and see how it does

Ran good for about 20 mins... then ran like crap off and on for the next hour.. the longer it ran the worse it got.

[4.3LXJ]

OK, next time it starts misfiring, press the accelerator quickly as possible after you do the startup procedure. I am trying to isolate a marginal TPS with this. Also how long has it been since the O2 sensor has been changed?

[prerunner1982]

Not in the 7+/- yrs I have owned it.

Some mornings it messes up within a block of leaving the house so it's not always good from the start. Will try process again tomorrow.

[4.3LXJ]

Better change it then. It is probably worn out and causing your mixture to be off

[prerunner1982]

Compression test next? Oh I guess it could be a CPS issue too.

Would a compression issue be intermittent?

Sometimes is runs fine.. for miles at a time. Couldn't hardly get a block from the house this morning. Even flooring it and banging through the gears wouldnt help it this morning... it's getting worse.

When it misses it bucks pretty hard and puts quite a bit a of shock load on the drivetrain.

[prerunner1982]

Guess I am leaning towards an oxygen sensor. XJ is completely undriveable now. :(

[prerunner1982]

Don't know why I didn't think about the fuel pump... it has whined for the last 7 yrs that I have owned it and per the P.O. 2yrs prior to me owning it.

A bad O2 sensor should allow the vehicle to still be driveable, just use more fuel and possibly not run as smooth? Correct?

[4.3LXJ]

It would start and run for awhile then possibly not run at all when the engine starts relying on it for information. I think it would be a mater of just a couple of minutes or until it reaches operating temp

[prerunner1982]

Anyone want to disconnect their O2 sensor and drive around and see what happens for me? :D

[4.3LXJ]

On a Renix it won't run at all. Not sure on a 93

[prerunner1982]

Changed fuel filter and removed cat (bunch of crap poured out of it)... still no change. Seems that it is backfiring out of the exhaust. Next Will check fuel pressure....

[prerunner1982]

Ran codes though I never got a check engine light and got the following...
12- battery disconnected within last 50 key strokes
75- ????
73-???
33- a/c relay? I don't even have a/c..
24- TPS
41- Alternator...
21- o2 sensor


I disconnected battery and tried again and got all the same codes except 41 and 21....

:/

[4.3LXJ]

O2sensor will probably show up again later. TPS is of interest though too

[prerunner1982]

I seem to remember someone mentioning the tps early on.... lol

[cantab27]

yep tps can play heaps of little mind games on our jeeps ....

[slvmart]

Just throwing this out. But how old is your battery? I had a 5 yo battery in my 2000 and it started really acting up. Put in a newer battery and she's been fine ever since.

"Acting up" - would cut in and out, which felt like it might be misfiring. Would not idle. Those are the 2 most obvious problems I remember.

[prerunner1982]

TPS and O2 sensor replaced.... No change. Still runs rough, sometimes idles rough, backfires through exhaust, smokes, and has heavy fuel smell.

[4.3LXJ]

Any CEL now or codes?

[prerunner1982]

12- battery disconnected within last 50 key strokes
75- ????
73-???
33- a/c relay? I don't even have a/c.
35- fan relay (New code, but I don't have an e fan...was taken off prior to my ownership due to accident)

[4.3LXJ]

I have to admit I a little stumped on this one

[WhiteDevil1311]

Check the plugs. Insure the wires are routed correctly. Smoke test for vacuum leaks. I had a colorado work truck do this same stuff ended up being the ecm. Seal dry rotted and moisture got inside and caused major head scratching. Im old school and seem to check to vacuum system constantly. Timing is correct im assuming?

[prerunner1982]

Timing is set by the computer I believe. Plugs are new, wires are new and routed correctly. I found a vacuum leak at the fuel pressure regulator and fixed that, no change.

[4.3LXJ]

Jon, you have to set the basic timing even though the computer adjusts it

[prerunner1982]

Anything that would cause the timing to just mess up? Just for fun since I am having so much of it right now.... I pulled each plug wire one at a time and started the Jeep each time, saw no change on how it ran with any of the plugs..... :/

[4.3LXJ]

Jon, trick is to pull the wires while it is running. Then if there is no change you know where to look

[prerunner1982]

Went ahead and changed cap and rotor since it hasn't been changed since I have had the XJ. Figured it couldn't hurt.... but no change.

[denverd1]

If the dizzy hasn't been pulled, there's really no way the timing can mechanically change. So you've got to look at ecm issues I would think.

Had a misfire in my 98 that was just heat soak on the fuel injector.

[prerunner1982]

Fuel pressure checked out at 31psi at idle and up to 39psi under throttle. Pulled vacuum line to fuel pressure regulator and it jumped to 40psi. Now the pressure did leak down to 0 within about 5 minutes. The pressure regulator does not appear to be leaking as there are no external leaks and there is no fuel in the vacuum line.

I am going to pull the fuel injectors and see if they are leaking. Would be quite coincidental if they all started leaking but weirder things have happened.

[WhiteDevil1311]

Distributor can move if hold down loosens

[prerunner1982]

Fuel injectors do not leak and all spray.

[prerunner1982]

Compression test...

Cylinder 1: 120 psi
Cylinder 2: 135 psi
Cylinder 3: 140 psi
Cylinder 4: 135 psi
Cylinder 5: 120 psi
Cylinder 6: 115 psi

So... CPS... MAP...and CPU is all that's left.... what do you guys think?

If is a CPU.. does the transmission type make a difference?

[prerunner1982]

Well it looks like it is the CPS.. I started it up tonight again... it ran rough, revved it up a few times and got out of the Jeep to let it run. After a minute it smoothed out and purred great, which it hadn't done in what, almost 3 weeks? I had the hood up and while talking about the issues with my Father-in-law and how I thought it was the CPS I reached down and grabbed the plug for the CPS and as I moved it the engine missed... I was able to make it miss a few more times by moving the connection/wires for the CPS.

Now.... about 5yrs ago I thought I was having a CPS problem and purchased a sensor, however it ended up being for a 91 rather than a 93 and was also about half the price. ($35 vs $70)The only difference it seems was the plug was different. I wired the old plug to the new sensor and it has run fine since, for half the price. I am going to pull the sensor and check/repair the splice job and see if that will fix the issue... I suspect it will.

Will post once complete...

[XJ Wheeler]

Well it looks like it is the CPS.. I started it up tonight again... it ran rough, revved it up a few times and got out of the Jeep to let it run. After a minute it smoothed out and purred great, which it hadn't done in what, almost 3 weeks? I had the hood up and while talking about the issues with my Father-in-law and how I thought it was the CPS I reached down and grabbed the plug for the CPS and as I moved it the engine missed... I was able to make it miss a few more times by moving the connection/wires for the CPS.

Now.... about 5yrs ago I thought I was having a CPS problem and purchased a sensor, however it ended up being for a 91 rather than a 93 and was also about half the price. ($35 vs $70)The only difference it seems was the plug was different. I wired the old plug to the new sensor and it has run fine since, for half the price. I am going to pull the sensor and check/repair the splice job and see if that will fix the issue... I suspect it will.

Will post once complete...

Good to hear it Jon! No doubt this was a frustrating issue. Hope it stays problem free.

Sent via messenger pigeon - i talk, he types.

[prerunner1982]

Or not...Pulled the CPS and found that one of the 3 wires was rubbed half way through. It was so close to the plug I couldn't cut and splice it out so I put some solder on it hoping it would hold in place. Reworked my splices and shrink wrapped everything.

Reinstalled and no change... either it wasn't the problem or the bad spot in the wire was too far gone.

About done with this thing.

[prerunner1982]

For Matt:... amount of fuel from fuel pump in 15 secs.

[drakan1908]

For Matt:... amount of fuel from fuel pump in 15 secs.
Are you sure that is fuel? Lol

[NW99XJ]

Are you sure that is fuel? Lol

Great, now jon's posting pics of the trucker bombs he finds or creates....
:rolleyes:

[prerunner1982]

Looking a little dehydrated....

[prerunner1982]

video posted to XJtalk members facebook page. It's not great and I am not sure you can hear when the engine misses.. but you can hear it when at idle that is struggles to stay running.

[prerunner1982]

Appears the CPS was the culprit, or the bad wire in the CPS pigtail anyway.

Replaced CPS and it ran great........then the Alternator died on the way home from work last night. :bang:

I believe it has a lifetime warranty, so no biggy just have to find the time to yank it out.

[prerunner1982]

And consequently I now feel completely incompetent of providing any repair advice to anyone....

[Brasscatz]

c'mon dude... It's kinda like how a doctor goes to another doc when they're sick. Don't worry about it ;)

[prerunner1982]

c'mon dude... It's kinda like how a doctor goes to another doc when they're sick. Don't worry about it ;)

it's the fact I couldn't figure out what was wrong with it.. and it took so damn long.

[NW99XJ]

it's the fact I couldn't figure out what was wrong with it.. and it took so damn long.
Now you know how I felt with that whole "no bus" bull shit.
Troubleshooting an electrical problem is tough enough as it is... add the "intermittent" aspect to it all, and you might as well buckle up, because your gonna be in for a ride....
By the end I was pulling my hair out and seriously considering an (v8) engine swap.
But perseverance, and the fact i'm too damn cheap to buy all the necessary goodies for a proper v* swap, I had no choice but to continue my research and quest for some degree of advice that would point me in a direction I hadn't previously thought of.
... it all pays off in the end man. :p

[Brasscatz]

happens to the best of us bro. I certainly understand. I just don't want you to beat yourself up. The important thing is that it's fixed, right? Now you can just smile and shake your head at it

Sent from my SGH-M919 using Tapatalk

[WhiteDevil1311]

Took me 7 hours to remove the stabilizer bolt on the long tie rod....I was ase certified at a point In time and everyone be it shadetree or professional we all get stumped on the hidden things.