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Did a tune up. Found this.

ZJ: 
8K views 43 replies 21 participants last post by  Badmunky 
#1 · (Edited)
Ok so I had some free time so I did a tune up on my 98 ZJ.

It was having a problem with bogging shortly after being started and not running smooth. Also seemed to be down on power.

So I removed the spark plugs and found this.


What is wrong with people?

It runs great now! Has a lot more power and seams to be getting better MPG as well. (Was getting 13.4 now getting 19.2) Doing mostly city and rural driving.

But there is one thing that it still will not do.
It still will not spin the tires off the line. It seams to have low power under 1,300 RPM.
My cousin has a 91 Cherokee with a 4.0 and he can spin his tires for a good 50 feet from a dead stop.
I cant even get it to turn the tire over at all. Is there still something wrong or is it just that I have ZJ and he has an XJ?
 
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#5 ·
Yeah they all look a little hot to me.

I plan to replace the injectors with the 4 hole 704s from the Neon next month.

Just need to find a good rebuilt set at a good price.

I should also let you guys know that my exhaust manifold is cracked, and I think the PO gutted the cat.

I don't have a CEL. And I thought I would get one if the cat was gutted?:confused:
 
#10 ·
We are both stock. Gearing and tires.

Xj = shitload lighter then zj .
True. The rear suspension is vary different as well.

ZJ has the Chrysler 4 speed, XJ has the Aisin. I always felt the Chrysler 4-speed with the I6 seemed mushy and slow compared to the XJ.

And the weight probably isn't helping either.
That could be it. It seams to to have less power under 2k the his dose for sure.
Can I change to the Asisn AW4 trans with out any problems or is the computer system going to be a pain the you know what?

Fix your exaust leak and it will run better, If the exaust leak is in front of the 02 sensor.

Are the two longer plugs a hotter heat range also? Maybe the po had a problem with a few cylinders and put a hotter plug in before he sold it.
It is in front of the up stream O2 sensor. And I plan to fix it as soon as I can. But I'm low on cash right now.
There all the same heat range.
 
#11 ·
Okay I don't understand this at all.:confused:
Now its back to running like crap and no power.
I just went to go pick the wife up and about 300 yards from the house it hesitated and lost power. I gave it more gas and it back fired threw the intake and tried to die.

I let off the gas totally and then it recovered and started to run fine. But its back to being down on power again.

Seams to run good. Idles good. Starts right up. No bad sounds when its running good.
But it lost like 25% of its power for no reason.

From a dead stop it will only spin its tires on a dirt road for about 3 feet!!!!
That's crap!:(

I don't want to just throw money at it trying to fix the problem ether. It dos NOT have a CEL. And has yet throw any codes as long as we have had it.

We have now run a full tank of gas threw it plus some. And still no CEL.
How can it run like this with no codes? Fuel mileage is dropping again.

Thanks guys.
 
#14 ·
It has the NP242. Its in 2wd right now.

Have you hooked it up to a scan tool to check for codes? The CEL light might be knocked out. I can't image it running that poorly and not throwing a code.
CEL light comes on when you turn the key then gos off as it should. So I know its working.
Had it scanned and it has no stored codes, no active codes.

It runs smooth after its been running for a few and you get past the hesitation it has a few min after a cold start.

I have never had any thing as good as this thing and yet have no power and no other problems that I can find.
 
#15 ·
Dont think for one minute it's not a problem just because it wont throw a cel. I had 3 almost flat cam lobes in my stroker last summer. It ran perfectly under 4000 rpm and ran like shit over 4000 rpm. Never once threw a code in the 1000 miles it took to find my problem.

I still think the missmatched plugs were in there for a reason. I would do a compression test to start with.
 
#20 ·
I will be doing a compression test as soon as I get home again.

Didn't the 4.0 have an issue with the distributor bushings wearing out and causing the shaft to move around affecting the timing? At idle there would be less force against the drive gear than there would be when you are accelerating so it may run fine at idle but get out of whack under load.
The distributor looks to be newer. But I will pull it out and check it to be sure.

wow, weird same here, except mine has the 249 tcase. Funny thing is my 96 ZJ 4.0 is running like shit too with a lack of power(I drive v8's tho), and doing the same hesitation for a few seconds when you first drive off, same as you describe. Ive done everything from a new plugs, cap, rotor, coil to a new fuel pump/regulator/filter. Also changed my O2 sensors. Still I think im missing something, maybe just 2 more cylinders.
I'm not 100% that I have the 242. It may have a 249 in it. Not sure how to tell. I was told it has the 242 but I don't know if they guy new what he was talking about or not. I know it has one or the other.

That did help. Ill be ordering a new TPS as well.


Right now the ZJ is totally stock. Tires, wheels, every thing. For now any way.

My plan at this point is this:
Replace cracked header with new one. (Not sure what to buy yet, little help here?)
Replace injectors with 703 Neon injectors. (Knew about this and was planing it already.)
Replace up stream O2 sensor. (Current one looks to be stock. Jeep has 152k on it)
Replace failing fan clutch and fan with electric fan from 99 GC, and a fan controller.
Replace drive belt.
Replace TPS.
Do a compression test.
Test fuel pressure.
Check for vacuum leaks.
Change oil and filter.
Service transmission.
Change oil in both diffs and replace leaking cover seals.
Change oil in T-case.
Replace leaking rear wheel seals and install new wheel bearings while I'm in there.
Replace leaking real main seal.
Replace leaking valve cover gasket.
Replace leaking oil pan gasket.
Replace leaking oil filter adapter seal.
Attempt to force the ECU to throw a CEL by unhooking engine temp sensor to be sure that the CEL circuit in the ECU is working. (Have been told Jeeps have a problem with this, and not throwing a CEL or code even when there is a problem.)

And I will look at relocating the AIT sensor as well. Why do people do this?
Where is it now? And will this work okay in extreme cold such as ND in January? Extreme hot such as NV desert in August? I ask because I may move at the end of the year, but I don't yet know where I will be going.


I understand that this thing is not going to do 0-60 in under 6 seconds. LOL
But stock it was rated to do 0-60 in just about 11 seconds. I would be happy with that. Right now I'm closer to 17 seconds, give or take a second.
And passing is just out of the question.

I will admit I am used to driving a much faster car then this is. But I have owned slower cars before. And its not a problem. As long as they run right.

My current DD is a highly moded WRX pushing about 460hp at the crank.
I don't expect the Jeep will ever keep up with it. LOL
But I do expect I can at least keep up with my sister driving a fully loaded Dodge Mini van pulling a trailer!

Yeah she smoked me, her and 4 kids, 2 big dogs, and bunch stuff for my brothers baby shower, PULLING A 1,400lb TRAILER!!!!!!!!!!!!!!!!!!!!!!

She drives like that mini van is a sports car. I was trying to follow her and had to call her and tell her to slow down or she was going to lose me. I could not keep with her in the city, or on the high way. (She was doing like 90mph on the high way with the trailer!!!! Yeah shes nuts!


If what I have planed dos not fix my problem where should go from there?

I have herd that there is a TSB for the ECU not throwing codes. Is this true?

And is there any thing I left off my list that I should just do?


Thanks for the help guys!
 
#16 ·
Didn't the 4.0 have an issue with the distributor bushings wearing out and causing the shaft to move around affecting the timing? At idle there would be less force against the drive gear than there would be when you are accelerating so it may run fine at idle but get out of whack under load.
 
#17 ·
wow, weird same here, except mine has the 249 tcase. Funny thing is my 96 ZJ 4.0 is running like shit too with a lack of power(I drive v8's tho), and doing the same hesitation for a few seconds when you first drive off, same as you describe. Ive done everything from a new plugs, cap, rotor, coil to a new fuel pump/regulator/filter. Also changed my O2 sensors. Still I think im missing something, maybe just 2 more cylinders.
 
#22 ·
It sounds like you have a little work to do and a good plan.
I have a $500 banks header that cracked just like the cheaper ones. I cant say its the headers fault because I wheel my tj hard and the exaust gets in the way sometimes.
I hate buying chinese but I would buy a rugged ridge stainless next time and save a few hundred.

Relocating the iat sensor make the ecm think it is colder out then it really is. It adds fuel to the mixture which can help because the 4.0 runs really lean from the factory.
I am not sure how effective it is on obd2 in the long run because I think the ecm will learn around the change using the o2 sensor. It will just keep leaning out to get the long term fuel trim where chrysler wants it for emissions and milage.

Im not 100% positive about this. I moved mine and it made it run richer on my wideband but I havnt run it enough to tell if it will lean out after 30 starts.

I have heard that it doesnt work well in cold weather. I left my stocker in the intake and just extended the wires. I put a new one from napa in my cold air intake tube just after my filter. If it doesnt run well in the winter I can just plug in the stock one.
 
#24 ·
I ran an Edelbrock Ceramic Stainless header on my XJ. Then I had the local exhaust shop fab up an exhaust from the header back using a Dynomax muffler I bought on here used.
 
#29 ·
So I talked to a friend of mine that's good with cars and he thinks that cat is plugging up.
And seeing as its been cut open and then welded back together I think he may be on to something. So I'm going to replace the entire exhaust from the block to the bumper.

I also have a new Accel cap an rotor coming tomorrow. I don't like the ones I put on it and the parts store is willing to take them back. I am going to do a compression test and test fuel pressure and timing tomorrow as well.
And check to see what the new plugs look like after 100 miles.

Ill post back what I find.
 
#30 ·
Looking at the plugs is useless, they will look new with a touch of white on them because the jeep ecm runs so lean.
You dont need a cat, it wont throw a code.
A 2000 intake may give you a little but imo a bored throttle body is a waste of money unless you have a bigger cam, head work, or stroked it.
The stock throttle body flows better then the stock head,cam,exaust combo so it really is not a weak point untill you address the other things.
 
#31 ·
Still have to pull them for the compression test.
I have been told I can remove the car by a few people now. I may try this to see how it runs without one.

I'm going to do the whole exhaust system now. And will probably do the head later this year, or next spring. May do mild cam at the same time. And its not expensive, so why not.

--------------------------------------------------------------------------------------

Ok so last night we drove the Jeep 8 miles to the movies.
For no reason (I have not changed any thing yet.) its back to running great! Its got good power, and I was even able to pass a slower car with no problems.

It still tries to stall, stumbles, and backfires a minute or so after a cold start. And the problem seems to be getting worse. It now dose this even if the motor is still worm. And the stumble/ hesitation/ stall/ backfire is lasting longer before it sorts its self out.

Also last night after the movie on the way home I floored it from a stop to see how long it would take to get to 60. It did much better then the 17 or seconds from the last time. Took it about 12-13 seconds. (Still a little slower then it should be.) But the trans did something I was not expecting. At full throttle its shifting out of first gear at 4,000rpm. I thought it should hold to close to 5,000rpm?
Is this normal?
I checked the trans cable. It is adjusted correctly. The trans is due for a service. The fluid is a bit darker then it should be and smells a little burnt. I am going to have the service done on it the next time I get home around the 4th of July. Until then it will not be driven much.

I don't know much about autos. This is really the first one I have owned as an adult. (Had a few beaters when I was a kid that never lasted long.)
I have been driving manual trans cars for the last 15+ years. (Could not find a manual Cherokee that was not rusted out, so we settled for the ZJ.)

Thanks guys for the help!
 
#33 ·
I bought one of the cheap stainless headers from Ebay for a project of mine. It seems really close to the same build quality as the much more expensive Edelbrock I put on my sisters ZJ. As said above, even the high budget ones crack, so I figured that when I have to weld it eventually anyway, I'll feel less ripped off than if I payed for the baller one.

Skife, the only thing he's "throwing at it" is the TPS and 02 sensor, which are also known to be troublesome. Isn't the Jeep recommended 02 replacement (service) interval less than 100,000 miles anyway? TPS's cost less than an hour of shop labor.
 
#36 ·
I have a hook up on parts. (Brother in law is the manager of a parts store.) So I get most things at or just over cost.

TPS sensor is going to cost me all of $12.00! Why no just replace it? Even if its good it has 152+ thousand miles on it, and at this point its probably not long for this world.

As for the O2 sensors, they look to be OEM. And again even if there not they likely have close to 100k on them.
The upstream one is like $56.

Remember guys this rig will also be my wife's DD. (At least for now.)

I would much rather spend an few extra bucks then worry about her getting stranded.

I knew it had problems when I bout it. I don't mind fixing them. And it dos not need to pull DD duty until the end of the year. So I have almost 6 months to get everything sorted on it before she will need it to get to and from work.

Thank you for the help.

Ordered parts:

OBX header. (Rip off of the Flowmaster)
2.5" x 8" flex section. (Will go after first bend off header to reduce stress on header.)
Head light housings.
Front O2.
TPS.
Steering box. (99 Durango box)


Still need:

Muffler.
Tail pipe.
Some pipe bends.
O2 bung.
Cat.
Some pipe.
Lots of other things.
 
#40 ·
With where my crack is I would have to remove it to weld it.
I'm not going to go threw all the trouble to remove it, pay some one to weld it, then put it back on just to have it crack again in 6 months to a year.

I already ordered a new one with a life time warranty.
 
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