• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

1992 Cherokee runs like junk, ready to burn it down

79ford302

NAXJA Forum User
Location
Paragould, AR
This is going to take a while. I got a 92 cherokee with the 4.0, auto, 4x4. When I bought it a couple months ago it was running bad, i got it on the trailer figureing it had water in the tank and the kids i got it from didn't know how to fix it. Dropped the tank, no water but i drained it anyways, fresh gas, new filter, plugs, cap, rotor, the works. Fired it up still rough idle, popping through the intake, backfiring on occasion. Hold it to the floor and it doesn't want to take gas, popping and snapping gets worse. It was flooding out pretty bad at this point. Changed coolant sensor, O2 sensor, and plugs again. Still running rough, not driveable. Fixed a couple of vacuum leaks I had overlooked one day and it started running like a top. Got it in the shop fixing some odds and ends to take it on a wheeling trip, started running like junk again after a few days. Unhooked the battery and still about the same. Figured out on friday night before my trip that if I got it good and hot, shut it off for a few minutes it then would run good for a while. Unloaded it off the trailer at the off road park the next day running like crap, I let it sit and idle for a while. Floored it a few times, then shut it off and let it sit a few minutes. Started it back it ran great for about 3-4 hours out on the trail, stopping and chilling a few times along the way. Got ready to head to the trailer almost couldn't get it to climb the ramps. I unloaded it at the house and haven't been able to get it to clear up and run right since. It won't even climb the hill to get in the shop. Plugs were black again, changed them, still the same. Don't really want to throw a bunch of parts at this thing, but i want it fixed or gone.


Cliff Notes: Really rough, low idle, backfires when revving the motor, pops in the intake, not driveable when running bad, won't take gas, sometimes it runs like brand new, most of the time not. Fuel Pressure is about 43psi with the vacuum line unhooked from the regulator.

New Parts: Plugs, Cap and Rotor, Coolant Sensor, O2 Sensor, Fuel Filter, Drained tank, Fresh Gas,
 
No codes at all? That could just be a bad sensor. Not that familiar with the older models but I had similar issue that turned out to be a bad TPS. Good luck with it bro.
 
Note from DJ
This is a no expense possible fix to your problems. I know it refers to Renix Jeeps but it also will apply to your’92.
As they say bad grounds make bad coffee. The same is true of the DC voltage system on Jeep’s. Some of the sensors only receive a 5V supply signal if they don’t have a good ground they will receive as far as they are concerned even less than 5V so data they return to the little silver box that controls the engine is false which causes a pore running engine. So my advice is take your time and do a good clean up the complete ground system.

If you have any doubts about the importance of Jeep grounds have a look at this post by muduck18.
99xj Electrical Issues - Identified, diagnosed, and resolved.
http://www.naxja.org/forum/showthread.php?t=1082137


Renix Main Ground Refreshing
By cruiser54

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of drivability issues, wasted time, and wasted money replacing unnecessary components.


The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. In other words all the extremely important stuff.


The factory was aware of the issues with this ground point and addressed it by suggesting the following.


Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. It must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.


While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.

---------------
NOTE from DJ I added thus information in on 3-1-2012

NOTE from cruiser54: I've seen where the dipstick tube stud isn't tight but the nut holding the wires on is.

Note from 5-90Battery to Engine Block next to oil dipstick support is a stud with a nut, but can be replaced with 3/8"-16 x 3/4 or 1" Hex Head Bolt. Since that's an electrical connection, I'd suggest using brass or bronze bolt to replace it with. Then use brass flat washers to take up the slack if needed”.
---------------
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for its intended use and subject to corrosion and poor connections at each end.


First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.


My suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.


A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa has them as part number 781115.


If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
Revised 11-28-2011
 
I've had the same happen on more than a few occasions, for various reasons. Your 92 has a different CPS type than my Renix, but the Renix CPS seemed to be temperature sensitive when in the process of completely failing. Worked when cool, not so much when hot.

The CPS wires have a tendency to burn onto the exhaust manifold, especially if the CPS has been replaced and they didn't get the wires back into the holder. I route the CPS wires up the speedo cable and tie them there with cable ties.

A bad MAP or MAP connector can do what you describe, the default for a faulty MAP sensor seems be full rich.

The rear O2 sensor after the CAT can get damaged, the wires pulled loose or even the wires can burn on the exhaust. The motor will run with the rear O2 disconnected, not so much if the wires are shorting out. Most any shorted 8 volt (5 volt on some models) sensor supply wire will affect numerous sensors. Many sensors share the same supply voltage.

I've also had a head gasket leak, water into a cylinder or two do just about the same thing. It would usually screw up when the engine was hot and the cooling system had built some pressure. Sometimes it would plug itself for awhile, then break loose randomly. I finally caught on when I pulled the plugs and saw two very clean spark plugs (steam cleaned) with a slight tint on the insulator part of the electrode that matched the color of my coolant. Shinning a light down the spark plug holes I could see the top of the piston was also way clean. I also seemed to have an excessive amount of condensation coming out of my exhaust. On a hunch I dabbed at the condensation coming out of the tailpipe with a white paper towel and could see the tint from my coolant. My coolant actually smelled like exhaust at the filler cap. Less likely to be a head gasket reading your description, my first instinct would be a CPS or shorted CPS wire.

I like to hook up a timing light to the cap to coil wire, point it at something dark and just watch the pulse. You can see a miss. You can even do it with each individual spark plug wire and watch the miss. A bad CPS can cause a serious miss (among other things, some simple, some not), when it partially fails, my guess is a weak pulse, the PCM can sometimes read the CPS pulse and sometimes not (randomly).

Some MIL codes are persistent, some are not. Some are false codes, some never happen, even after a sensor failure. MIL codes aren't real reliable.

Just a few possibilities you may want to look at.

And lastly a CAT that has disintegrated can plug up the exhaust. I've taken handfuls of powder out of a muffler before and had CATs I could barley blow through. Kind of like terminal constipation.:moon:
 
I like the grounding suggestions. I've seen poor grounds cause the very symptoms you've described. I've also had similar adventures stemming from failing/crappy Throttle Position Sensors. It will run fine one minute, lousy the next. And it also controls tranny functions, for an added round of fun. The HO era engines have no EGR valve, and yours has no second O2 sensor, at the cat (<'95), so there's two things you won't need to worry about.
 
Grounds and TPS would be my first things to check.
 
Thanks for the suggestions, forgot to mention I tried a MAP sensor off my buddies jeep with no changes to how it run. It also has had the cat removed already. I checked all the grounds to make sure they were hooked up but didn't physically remove and redo them, I'll try that later. I was thinking prolly a cps or tps, but i hated to just throw money at it. Also it had a throttlebody spacer on it when I got it, are those know to cause any problems?
 
Note from DJ

Don’t replace anything on the assumption that it might be bad.

If you want to test something and don’t have the information on how to do it, please save your money and ask! Because someone has already done it and posted a how to write up about what they did, as they say the only stupid question is the one that was never asked.

I don’t know anything about throttle body spacers, sorry.

Please keep us posted on Progress or Questions information is cheaper than the gallon of gas necessary to burn up your Jeep.
 
Intake leak will cause a lot of driving issues. Check to see if all your intake/exhaust nuts are tight.
 
Checked the TPS and it was bad, 4.45 volts at idle then 5.2 at WOT, put on a new one thats within the info I read. I think it tested .7 at idle. I gave the throttle body a good cleaning, especially around the IAC motor housing(very nasty). Fired it up, still runs like junk! I pulled a couple plugs, they were kinda black and smelled of gas a little. I'm going to change them again for the third time and see if that changes anything. The CPS tested good and I'm going to redo some grounds just for giggles. Anything else that mite be worth looking into. Is there anyway to test the coil?
 
I've got the grounds redone, added one between the block and body. It's been running better for the most part but not consistent. It did throw a code 13 for the first time today right after it started running bad. Has just been throwing the 12 and 55. Any new ideas?
 
Try this:
I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals, and adding dielectric grease before plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.
ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then dielectric grease should be added before plugging them back in. I do this on every Renix era Jeep I purchase or work on for someone else.
Revised 07/15/2012
 
I give that a try next. Think I figured out the code 13, realized when I was cleaning up to come inside that I didn't put the vacuum line back on the map sensor when I was messing with stuff earlier.
 
Have u checked fuel pressure when its running poorly. Had this same this in my 92 and my buddys 89 turned out to be bad fuel pump. Just a suggestion.
also be sure and check the fuel pressure when regulator vac hose hooked up. To see the difference.
 
Last edited:
I've checked while it's running rough it bounces a little but that was back when it was running really bad. I'm planning on replacing it soon as I get a chance since the sending unit is bad and I can get the whole assembly for a little over $100 at autozone. Either that or I looked at another jeep today that is stock that I can swap my lift and stuff on to.
 
It electrical not mechanical. So even when its running badly at idle it should stay steady. I had mine read the right pressure but would not hold the volume when I accelerated. Same exact symptoms black plugs popping in the intake. You may try and check the relay for the pump or the ballast resistor on the drivers fender two likely culprits
 
I wired around the resistor at one time with no change to how it ran so I hooked it back up and I've swapped relays around. The more I've read and thought about it lately I've been thinking the pump may be acting stupid. So I'm planning on changing it to get my gauge working and some piece of mind if nothing else.
 
Have u checked fuel pressure when its running poorly. Had this same this in my 92 and my buddys 89 turned out to be bad fuel pump. Just a suggestion.
also be sure and check the fuel pressure when regulator vac hose hooked up. To see the difference.

Expanding on that suggestion, the time to check everything, grounds, sensors, pressure, etc, is when it is running poorly.
 
I've checked while it's running rough it bounces a little but that was back when it was running really bad. I'm planning on replacing it soon as I get a chance since the sending unit is bad and I can get the whole assembly for a little over $100 at autozone. Either that or I looked at another jeep today that is stock that I can swap my lift and stuff on to.

Check for a bad fuel pump ground that may be causing the gas level sensor to act bad. Could be a sticking fuel injector. Also check cap and rotor for damage (Yes I know they are new), and check the fuel pressure regulator vacuum nipple for a gas leak!!!

Most of your problems so far sound like a bad vacuum connection the MAP sensor, and bad TPS. You may have most of the problems solved. Take a close look at both ends of the MAP sensor vacuum hose, look for a vac leak!!! Hose on the fuel pump, in the gas tank is known to go bad or come loose!!!!!
 
Back
Top