ZJ: stuttering engine and electrical problem

[TOOLman]

I don't know if these two problems are related.

In the last two days, the VIC clock has been reset three times on start up. I can see nothing wrong with the battery. Voltage seems OK. I haven't tested the electrolyte, though.

The second problem is more worrying. Today, I drove some 250 miles on the highway. On the first leg of the journey, the ZJ was "jolted" several times. Sharp "tugs", which I at first thought was the beginning of the VC's swan song. On the return leg, it was happening more and more often. Mostly when reaching a slight incline at 55-80 mph, there was one or two jolts. Sometimes it happened, even more noticeably, when I let off the throttle to compression brake. I became more and more certain that it was in fact the engine acting up.

As I turned off the highway, into a small back road, there was no doubt anymore. The engine stuttered and run very roughly. RPM's fluctuated wildly although I kept the pedal still. I stopped at my colleague's house, to let him off. The idle was rough for a while. I revved the engine, and it sounded very strained above 3500 RPM, and the whole truck shook when I reached 4000-4500 RPM. I switched the engine off for a few minutes, while attending some other business. It started OK, and felt a bit better. I could still feel an occasional shudder, though. I filled up gas along the way, and observed that the mileage was apparently not affected. 19.5 mpg is as good as can be expected with the 31's.

I've checked all electrical connectors in the engine bay, as well as the fuel injectors. I'm thinking about replacing the spark plugs and cleaning the distributor cap. Last week I had it serviced (just oil change, no plugs), and it's not been long since I installed the Leach headers, at which point I also cleaned out the TB thoroughly.

The weather was humid and cool today. Thick fog and some light rain, 40°F. I removed the stock airbox when I installed the Turbo City air tube, and I saw that some mud has splashed into the engine bay. I don't think it should've reached the filter, though, since it's all the way back, against the firewall.

Any ideas what could have caused this are greatly appreciated.

[Howler]

Have you done the code check? Try that and let see if you have any codes that might help us out.
Howler

[TOOLman]

No, I didn't. I thought that only worked if the Check Engine light came on? I'll do it in the morning and come back to you (it's almost bed-time here).

[Howler]

I've had things come up without the check engine light come on. You go to bed. I'm going home from work and I'll bring in the book tomorrow.
Howler

[J's Jeep]

Always check spark first.

Could be fuel filter or pump.

[TOOLman]

I checked the codes this morning. Nothing. Just the 55. (BTW, it shows this only by blinking the Check Engine light. I thought it was supposed to show the numbers on the VIC or the OHC. Is that newer models only?)

I was thinking about fuel problems too, but it somehow "feels" more like an electrical problem. I'll change the plugs tomorrow and look at the distributor.

Any ideas about why the clock gets reset every now and then?

Thanks /Tommy

[Howler]

Hey Tommy. The models with the digital milage are the ones that display numbers. I found this site on how to check fuel problems.
http://members.nbci.com/minimopar/index.html
There is also a troubleshooter on this site. It might help you out. Not sure but I think I recall someone on JU was having trouble with the clock reseting every now and then. I believe it was the Battery though. Not 100% sure either.
Howler

[TOOLman]

Howler - thanks for the link. Unfortunately, when I tried the troubleshooter, the end result was:

Sorry, but this page is not yet available. Please check back soon!

:)

I know I posted this problem on JU this winter, when it happened the first time. I never got a satisfactory reply to that post. Now, I wouldn't even bother posting a tech question of JU...

I didn't know if there was a digital (meaning electronic?) odometer on newer GCs. I kind of assumed that was the answer, but thanks for the confirmation!

[Howler]

Hey I am here to help. Just seams you ask me the questions I am never 100% on. Now ask me about advertising and stand back. I'll keep my eyes open for you.
Howler

[MaineZJ]

Sorry to hear about your problems, Tommy. I'm assuming that you do take good care of your rig, so just as a guess, I would be thinking bad gas or fuel system prob's. Do you fill up at the same place all the time? Also, I learned never to fill up at a staion that is getting or has just got their undergound tanks filled. Reason being is that all the crap on the bottom is swirling around after they fill it. Good luck and let us know what you find.

[TOOLman]

The thought of bad fuel crossed my mind, too, but I think it's unlikely. It's very rare here in Sweden. I had filled up at another station than I regularly use before this, but it belongs to the same oil company, and I've filled up there many times before. It's been barely noticeable today. It seems as if it gets worse after driving for a long time at highway speeds. I'll see if the plug change makes any difference.

[MaineZJ]

Well good luck, Tommy, hope ya figure it out. You've got how many miles/km's on your ZJ?

[J's Jeep]

Sounds like you have serious electrical problems. If the clock resets that is like diconnecting the battery. Could it be a fuse or the fuse box, check your ground. It should not reset your clock. That does sound like more of a electrical problem. I had a 76' ford that would do that and it was electrical. The ignition modulator. That is not your prob but check the connections from you battery.

[Lou Corrado]

The part about it runing worse the longer you drive it sounds like a igniton coil that is breaking down under heat, you might want to check the resistance of the coil when it's hot to see it this is true. The clock thing sounds like the batt is at times disconnecting, check for high resistance at the terminals, dirty treminals, dirty/high resistance at batt ground strap, corrosion in the batt cables. What readings to you get on the volt meter while driving?? Engines with electronic fuel injection can do werid things when the running voltage drops too low. Also check the spark plug wires and the coil wire for high resistance/burning, or even shorting to ground.
Good Luck the electrical system is not ChryCo's strong point, we had a '67 Plymouth Fury III that used to short out the headlights every now and then, very exciting on dark country roads!!

Lou C

[TOOLman]

Lou - I'll check all of the electrical system tomorrow.
The Volt meter - and all other gauges - show normal readings. It shows about 14 V while driving, and there has been no problems cranking the engine or anything.

I checked the battery terminals, and they are securely tightened. I'll take a better look at the ground cables and the ignition tomorrow. I was also suspicious of the spark plug wires, since it seemed to act up more in moist conditions.

Thanks for your input.

/Tommy

[Lou Corrado]

Just had another thought--if only the VIC clock resets, but not the one on your radio, than probably the bat is not getting low or disconecting--whenever I've disconnected my batt to do electrical work, the clock in my radio always resets to 12:00, but I don't lose my radio presets. My ZJ doesn't have the VIC, it just tells you what 4 wd mode you're in . So that would seem to be specific to the VIC circuit, may need a FSM wiring diagram to figure that out--mine's a '98 so it's probably different.

Lou C

[TOOLman]

I didn't think of that. I haven't checked, but I think it's only the VIC clock that gets reset. I checked the battery acid today, and I think I need a new one. The clock hasn't reset since I posted this. Maybe it has something to do with air humidity or something. It was very moist the days it reset.

I replaced the spark plugs, and I haven't felt any jolts since then. The old plugs looked OK to me, but it might have been the problem. This morning, I felt one major jolt and a couple of smaller ones. With the new plugs - nothing. Also, I felt a clear performance gain. The engine is stronger now, no doubt about it. I'll keep my fingers crossed and hope that it was just the plugs.

Thanks to all for your help.
/ Tommy

[Lou Corrado]

When my ZJ got to about 32 K miles, I started getting little jolts while driving at highway speed, esp at low revs/high load with the trans in OD. I changed the rotor cap plugs and wires in January, and it's been fine since. Funny thing is that the plugs had normal wear, wires were fine, cap n rotor had normal wear too.Maybe the I-6 is really sensitive to ignition faults. I suggest you also check the resistance of your spark plug wires and coil lead,and take a look at the cap n rotor too. Bad coils seem to be common in ZJ's, so I'd check the resistance of that too (hot). Gotta have a digital multimeter these days!!!! We used to have an '88 Toyota Camry, one day (60K miles) it started running on 2 cylinders, I thought it burned a valve, I checked the resistance of the spark plug leads, 2 were way out of spec for resistance, replaced wires, all good!!

Lou C

PS oh and the moisture thing, that might suggest a bad ground in that circuit, does anything else act funny when it resets--check what eles is on that circuit

[TOOLman]

Spark plug wires will be my next move, if the plug change doesn't help. The symptoms are exactly like you described - low RPM, slight load, O/D.

What should the resistance of the coil be, approximately?

[Lou Corrado]

If yours is like mine, and the jolts went away after doing the plugs, you may be done. For your information here are the specs for the coil and ignition wires:

Coil
Primary resistance (between small terminals A&B)
Diamond Coil 0.97 to 1.18 ohms
Toyodenso Coil 0.95 to 1.20 ohms

Secondary resistance (between terminal A and secondary terminal--the large one that the wire for the dist cap connects to )
Diamond coil 11.3 to 15.3K ohms
Toyodenso coil 11.3 to 13.3K ohms

Spark plug wires--
Min Max
250 Ohms per inch 1000 ohms per inch
3000 ohms per foot 12,000 ohms per foot

HTH,

Lou C

[TOOLman]

Lou - thanks a lot for your information. This is great!

[TOOLman]

Last week the problems began again, only worse this time. This weekend I removed the distributor cap. There was quite a lot of oxide on the contact points inside, so I cleaned them. I also cleaned the rotor, which had some oxide on it. Result: it ran even worse! I thought I wouldn't make it home on Saturday night. I had to keep 40 mph. As soon as the O/D kicked in, my ZJ was skipping like a schoolgirl. At 30 mph though some small villages, the RPMs varied rapidly +/- 500 RPM even though I didn't touch the accelerator.

This morning it was much better, although I could feel one or two jolts at 70 mph on the highway. Although it could be fuel related, I think it's electrical. I guess I'll have to try to measure the resistance of the coil, somehow, and get new wires.

One thing I've noticed: these problems usually occur when the voltage gauge shows just below 14 V. This morning, when it ran better, the voltage was clearly over 14 V. I know I need a new battery, but could this have anything to do with the engine problems?

[DrGP]

Sorry to hear about your problems Tommy
I cant tell you what is wrong, but I can tell you what I should have done if I was in your place.
I do think it sounds like a faulty ground strap - not necessarily the one at the battery, there should be one connecting the engine to the body. Check them all, disconnect them and put them back again/replace them.
Meanwhile, if you have cleaned the throttle body and the IAC you can continue with checking the Throttle Position Sensor and the Crankshaft Position Sensor. I think it is possible to check the resistance of the injectors by disconnecting the electrical connector and measure the resistance (12.4 Ohm?). Working with all this I think you will find what is wrong just by spending time with your jeep;)

But first put in a new battery, wires, plugs, rotor and distributor cap. (My battery broke down last spring, I had no "electrical problems" more than that it did not got charged and I finally could not run the start engine)

Good luck!

[TOOLman]

Thanks Gert.
(Good to see ya again, BTW!)

I cleaned the TB recently, when I installed the Leach headers. I haven't messed with the IAC, but there are no problems when idle. It's low RPM and slight load, especially in O/D, that causes the problems.

The plugs are new. Changing them made a world of difference - for two weeks. The strange thing is that it became worse when I cleaned the distributor cap and rotor.

I thought about the ground strap, also. I haven't managed to find one yet, though. First step will be to clean the engine compartment, it's really dirty. I think I'll stop by the dealer's on my way home today and ask the price for a new cap, rotor, and new wires.

The engine usually runs fine between these "fits". No performance loss or decreased mileage. That's why I think there is an electrical problem somehow. Sometimes it runs just fine, while it sometimes barely runs at all :(

[J's Jeep]

Did you ever get this worked out?

[J's Jeep]

o2 sensor? I think if your clock is reseting it has to be electrical unless you have two problems.

[TOOLman]

The problem disappeared when I changed spark plugs, but now it has come back. On Saturday it was really bad. Yesterday and today I could feel it, but no biggie.

The O2 sensor was replaced a few weeks ago when I did the Leach header install. I should check if it needs re-tightening, but I don't think that's the problem.

I checked for prices at the local Jeep dealer's yesterday: cap $15, rotor $23, spark plug wires $76.50! It would probably be cheaper to order Kolak's ignition system from the US! I'm going to check with another shop to compare prices. The dealer is notoriously pricey.

I have a feeling that the bad battery has something to do with this, too. I'm going to get a new one. The VIC clock hasn't reset for ahwile now, but experience tells me that doesn't mean the problem has gone away :rolleyes:.

[TOOLman]

I just talked to the guys at the shop where I usually service my ZJ. He says there's some kind of TSB or something about this exact problem.

It seems as if the valve springs are too weak. When soot builds up on the valves, the springs cannot keep them closed correctly, and this shows in particular at 50-70 mph in O/D with a light load (slight uphill etc.).

The bad news is that it's not covered under any warranty, so I'll be looking at $400-500 for the job if that's what it is :(

He also said that they (probably) replaced the spark plug wires last August, at a big service.

[DrGP]

First I would try a fuel additive like STP Complete Fuel System Cleaner or Mopar Combustion Chamber Cleaner and Mopar EOS (Engine Oil Supplement?).

Edit:
I used the CCC (Moparmans method) and the EOS last summer since I had very noisy valves, it became much better. Reading posts from our fellow jeepers it seems like it is common to use fuel additives (previous to engine oil changes), I guess there is a reason for this.

[TOOLman]

I did a service in early April, where the invoice showed that they had used a fuel additive. I know they use this stuff, but I can't remember what its name is.

He said that these additives don't work against the problem that the TSB addresses, at least not well enough.

[DrGP]

Found this on…the other forum…(some of us think it is not such a bad forum ;)…)

"A few of the early 1996 4.0 engines did have a bit of an oddity about them; the valve
springs would lose their tension after about 30-40,000 miles. This happened on only a few
of them, and the problem would usually happen early. Mine presented with the problem at
about 60,000 miles and was not that expensive to fix."


Yours a -95, isn't it? Perhaps you should give Moparman a call?

[TOOLman]

Yes, mine's a '95. About 75,000 miles.
It was quite bad this morning :(