[John V.]

Any Jeep techs?

My Jeep has suddenly decided to misfire.

For several years have been getting a code for TPS. CEL would light up, but come and go on its own. Seemed to stumble at idle on rare occasion, set the CEL, then go away. So I ignored it.

A few months ago, my son who drives it started experienced a momentary very high idle on start up. It was intermittent. Wouldn't happen every time. My recollection was no code. Just would rev to maybe 2000 for a second or two then return to normal idle.

I told him to spray the throttle body good with Throttle Body cleaner. He did and that problem went away. That was months ago.

Last Sunday, he was here. Hadn't changed the oil in awhile, so we did that. On the way to get the oil, he noticed it was vibrating abnormally, I sensed it was running a bit rough. I didn't think much of it, He filled the tank with gas as I got the oil. We changed the oil. He then headed home, got to the highway. He said it was running poorly so he pulled over. Check engine light on, would flash on occasion while trying to accelerate in higher gear. I went to meet up with him, drove it to parts store.

Seemed to rev fine in neutral.

Checked codes. They said misfires on cyl 2 & 6, plus TPS. He told me original plugs were std copper. 86,000 miles on them. He suggested misfire was probably tune up, told me to start by changing plugs.

Engine has a coil pack right on the plugs, no distributor or plug wires.

I installed Autolite Platinums. Seemed to run fine at low speed in 2nd gear. But took it out on the road, and it stumbles. Seems to accelerate fine in 1st 3 gears, but if I cruise at 50 in 4th or 5th, then drop back to about 40, then try to accelerate hard, it will misfire, hesitate, no power.

Seemed "better" than before the plug change, but definitely something still not right.

So next thing I did was change out the TPS using NAPA part. Had to remove the TB to get the screws out so cleaned the TB while it was off with Seafoam that I bought "just in case". It was pretty clean and the intake below the TB looked brand new (left it alone).

Took it back on the highway. Same symptoms.

So next I poured a can of B12 Chemtool in the full tank. I then sprayed the rest of the Seafoam thru the TB following can directions. Sprayed it in with idle about 1700. Let it soak with engine off about 5 mins after can was empty (they said 1/2 can but I already used some to clean the TB).

Back on the highway. Same symptoms.

Took it back to auto parts store. Read codes for random misfire, misfires on 2 & 6, and a TPS code (weak signal I think). I think these were same codes as before, not sure about the random misfires, couldn't remember if they said that the 1st time.

So I had them clear the codes to see what might come next. Guy suggested it could be Idle Air Control. Said to disconnect it and see what happened to idle. I drove off.

No codes set, but it was still stumbling a bit. I pulled over, disconnected the IAC. Didn't seem to change the idle to my ear. I rev'd it at idle, seems to rev fine. Drove back to parts store, no codes. Bought can of TB cleaner. 2nd guy came out to car, took a look, recommended to check for vac leaks.

Drove home, lots of stumbles, misfires. No CEL at least for awhile (8-10 mile trip home). But somewhere near home it set the CEL. I didn't notice it until I pulled in the driveway.

I had my wife watch the tach as I sprayed around. No change in idle speed. Didn't spot too many possible hoses to spray. I did fix a break in the vac line for the cruise control, but it had no affect on the idle even when disconnected.

So I pulled the TB again, removed the IAC. It was bit crusty with carbon. I cleaned it up real good, cleaned the passage in the TB. Put it back together. Same symptoms.

I plan to check to see what code has been set. I'm guessing misfires again. Maybe the TPS (could the NAPA part be the culprit?).

I wondered about bad gas but I think the vibration we felt before filling up was probably an indicator that there was already a problem.

What do I do next? Unless I get a different code, I'm at a loss. Hate to throw parts at it. Would a diagnostic test be able to pinpoint anything?

Help!

[77 Canamman]

A defective airbag clockspring in the steering column will cause those irregular misfires, and high idle, since a bad clockspring will cause a spike in voltage in the TPS because of the fact that they share the same reference voltage inside the PCM. This is more common on the Wranglers with the roof removed since rain water will wreak havoc on the clockspring. I had a bad one in a '01 Cherokee that caused the exact same symptoms as you are experiencing.

[John V.]

77, thanks a bunch for the input.

That is interesting, hadn't considered that. Top is rarely off, occasionally on a sunny day. For most of its life, it wore the hardtop, but the soft top has been on steadily the past 2 years.

You say you had same symptoms. But my intermittent high idle on start was resolved by cleaning the TB. I think was caused by a sticking IAC. Until this past weekend, it had been running/idling with no issues since the TB was sprayed.

I do sense a bit of a rough idle now. I started it cold this morning and just let it idle a few minutes. At start up it idles just about 1000 rpm, maybe a hair over the line. As it warms up, it settles down to the 2nd dot which I judge at about 700 rpm. I think this is normal idle speed for the man trans motor. But I do feel some "throbbing" roughness". Not a lot, just enough to say it doesn't feel silky smooth.

From what I read, the clock spring will also affect horn & cruise. Do you know if your horn and cruise stopped working? Any air bag light?

I ran it on cruise yesterday at 50 mph, worked fine. Hit the horn this morning to test, it worked. No air bag light (except the start test cycle).

Do you know how to access the connector for the clock spring? I read that I could disconnect it and determine if the clock spring was at fault or not. Symptoms go away, replace clock spring. Symptoms remain, look elsewhere.

I also read that I might be able to pull the horn relay to see if the clock spring is the problem.

I did pull the horn relay, still has the roughness at idle (I didn't drive it on the road).

I'd like to be able to test it for a bad clock spring before replacing, I understand it is a pricey part.

Can the clock spring affect engine performance without causing the other problems (inop horn, cruise, air bag light on)

Your thoughts?

[77 Canamman]

That Cherokee did have issues with the cruise and horn not working. Did not have an issue with the air bag light coming on. The clockspring should be considered whenever this problem pops up on a Jeep. BTW, the horn/airbag can still work, yet cause TPS voltage problems. I have also heard about defective horn relays causing the drivability issues on this era Jeep too.

[John V.]

Well, don't know what to think. Cruise & horn work fine. There is a break in a vac line that controls the vent doors. That line broke a few years ago, I duct taped it together, it's been fine since, but I did just repatch it with a pc. of rubber hose "just in case". But still nothing changed.

About 3 years ago, I pulled the fog lamp relay because the multi function stalk was turning the fog lamps on with the switch off. So I pulled the relay and it has been out since. Don't think that can be related at all.

I mention this because I just made an appt to bring it to the dealer. If it is the clock spring, I just don't want to fool with it (I've read the write ups for replacement, just not up to it especially being unsure that is my issue) and figured I will have them repair the multi function stalk at the same time.

I expect a big bill no matter what and will report the outcome.

Sad day for me, been a long time since I've thrown my hands up and handed a problem off to the dealer.

They can't take me in til Monday so I will have the codes read over the weekend just for yucks and because I won't go down without a fight. But my wife gave up her car so my son could get home and she wants to swap back ASAP. So I am about out of time.

[skipp65]

Id try an ignition coil,about $100 and easy to change,more than likely that's the cause of the misfires.

[geeteeohguy]

The first thing I would do is hook up a scanner and drive the car reading the data stream. Freeze-frame data at the time of misfire will let you see what the ignition voltage output is for the suspect cylinders at the time of the hiccup. I agree with Skipp65, very probably a coil/plug boot problem (the boots like to short to ground). A TPS and idle control motor would have absolutley zero impact on a misfire condition going down the road. ZIP. And the liklihood of an injector problem is extremely rare. Check your ignition events with a scanner or DSO, that's where I'd begin.

[BB70]

I believe #2, #6 are paired cylinders in the coil pack. Another vote for a coil assembly. If you ran the plugs 80 k without changing, you probably killed the coil.

I would also repl the tps sensor , as it has set codes multiple times and wiill cause hi idle issues.

This comes from a ex 15 yr mopar tech, try to use oe parts also, try to stay away from the aftermarket on driveability parts.

One other note, I like autolites in my hot rods, but perfer champions in the mopars.

John

[beemergary]

Me and everyone in the family loves jeeps and the only problems have been iac and egr sticking. Where talking 2-3 hundred thousand miles and still going. Still got my 73 cj5 with AMC 304. No misfires just sluggish and poor idle

[John V.]

Guys, thanks for the comments.

I made a new appt at another dealership for Fri morning. Wife wants it fixed before Mon, she has to have a car next week.

Recall, I erased all codes. New CEL shows single code P0302, #2 cyl misfire.

It seems the problem is best described like so. Bit of a rough idle, but steady and normal rpm.

Accelerates in low gears pretty strongly with what I would call light throttle.

Hesitates badly, misfires, will even sound like a backfire with heavy throttle when trying to accelerate in higher gear from about 40 mph. If I use light throttle, have taken it up to 55 mph with pretty smooth acceleration.

So it seems it is only when I try to open the throttle more heavily in higher gears that I get the misfire.

I'm beginning to "like" the coil pack idea.

I'm wondering if maybe I didn't get the boot seated real well on one (or more plugs)?

Or maybe you are right, the old plugs killed the coil pack?

So I have 2 choices, throw a new coil pack on it tomorrow. I plan to pull the coil pack to at least inspect the boots and reseat. If reseating the boots doesn't fix it, I'm not sure I'll try replacing the coil pack.

Might just hand it off to the dealer Fri at 8 am.

I'll sleep on it and make the decision.

Thanks again, and I'll report back.

[Lightfoot]

Originally Posted by John V.;

Seemed to run fine at low speed in 2nd gear. But took it out on the road, and it stumbles. Seems to accelerate fine in 1st 3 gears, but if I cruise at 50 in 4th or 5th, then drop back to about 40, then try to accelerate hard, it will misfire, hesitate, no power.

This symptom would make me suspect the coil pack(s). The problem showing up with engine under load, but not bothering when in neutral or light load.
Does this have six coil packs? One for each cyl.

You could swap the coils around to different cylinders, then see if the diagnostic readout for misfire "moves" to the appropriate cyl. Just make sure you clear the old codes out before you run the engine. I'd try this before I resigned it to the dealer.

[John V.]

Unfortunately, I think the coil packs are not individually moveable.

A single "rail" assembly with 6 rubber boots attached.

The boots are separately serviced. I think there are 3 coil packs built into the rail, don't think they can be moved around unless somebody knows different.

I will pull the rail and look.

When I changed plugs, I didn't disconnect the rail connector, just pushed the rail out of the way.

I'm thinking I might not have gotten the boots seated correctly by doing it this way, so I'll pull the rail, disconnect the connector, inspect, and reinstall. If the coil packs can be moved I'll do that. Otherwise, I'll look for some sign that the boots weren't seated.

Thanks.

One other thing. I see lots of Jeep guys claim the Autolite AP 985 single platinum doesn't work so well in the distributorless 4.0, tell you to use the APP 985.

That doesn't make sense to me because I think the only difference is more platinum.

But since I used the AP 985....

Opinions?

[John V.]

This is the best post I could find about the problem with the AP 985.

http://www.jeepforum.com/forum/f9/ap...29/index3.html

['ol Pinion head]

Originally Posted by John V.

This is the best post I could find about the problem with the AP 985.

http://www.jeepforum.com/forum/f9/ap...29/index3.html

Arguing & insults over sparkplugs. wow............................................... ................
Was thinking of joining that Jeep forum, as of late. my son's XJ has been a little diversion project, was bought as something for him to cut his teeth on mechanicall. In purchasing it, we purposely avoided the last of the XJ's, the 00's & 01's, due to DIS & redesigned cylinder head. Talked to a 15 year Jeep tech yesterday & he wasn't that down on DIS. Hope this turns out as inexpensively as possible for you John.

[77 Canamman]

My personal Jeep is a 1999 Cherokee, which was the final year for the good head and a distributor ignition. After all of these years and well over 100k miles, still runs like new and does not burn or leak any oil. I have used OEM Mopar parts for tune ups, and regular Champion plugs in it, changed at every 30k miles. Takes all of 10 minutes to change them, and that's if I am sipping on a cold adult beverage between each plug change.

[blue goats]

John V
Another good reason to change plugs at 30K on a coil pack system is the energy sent to a bad plug goes right back to the coil. I changed out 2 coil packs on my Grand National years ago because a spark plug wire was bad and cooked the packs before I figured it out.

HTH. George

Nevermind. Just reread post 8.