I have an 88'XJ. A few months ago it had a problem where, when I went up a slight hill (street) it sounded like it was missing. Its hard to describe the sound but it was kinda like vroom (pause) vroom (pause) and would cause the vehicle to move back and forth. It did it going down hill as well. My husband is at a standstill with what could be wrong with it.

It started its problem again today but even did it on a flat surface. Only at high RPM's does it do this

The plugs are good and as well as the injectors.

Now mind you, the previous owners decided to block the EGR Tube with sandpaper and the header was broke at the welds on two of them. I dont know what could be wrong with it so if anyone has any ideas let me know. Thanx

P.S. It also studders while at idle. and when you go to take off, it misses. I know spark plugs but ours are good.
Distributor cap? Wires? IDK

 

No guarantee, but check your plug wires. Look at the metal part where it attaches to the plug and cap. I was having a similar problem and that was the solution. Here's where we hashed it out...

https://www.cherokeeforum.com/f2/i-t...-found-131329/

 

yeah F1, I remember your pic, haha.
Anyway, I'm not familiar with the Renix Jeeps (others will be with you for this), but IF you have an automatic, this all could be very well related to the CPS (crankshaft position sensor). All the stalling/backfiring etc. matches that.

Before this:
when was its last tune-up? Like F1 stated, you can come across some basic electrical failures and when you r not sure about when this has been done, get a tune-up done, also for future 'reference'.
See how you go and let us know.

 

Basic tune-up first including plugs(Champion Coppers or NGKs), distributor cap and rotor (brass contacts) and quality plug wires like Belden from Napa.

Clean throttle body and IAC.

If nothing improves, do a fuel pressure test.

 

I just put a new cps on it. last tune up is unknown but everything looks brand new however yesterday i pulled the cap to check everything inside and the rotor looks a little rough, so i wire brushed it and the cap I also pulled the plugs yesterday cleaned them and gaped them at .035. This problem just started after i fixed the exuast manifold. I had to weld the back two outlets and. I pulled and cleaned the intake manifold, throttle body, egr valve, air sensor and, the tps.

 

You had the TPS off the throttle body?

If so, did you adjust it upon reinstallation?

 

No I did not take the tps off the throttle body. Today I replaced the O2 sensor and it got rid of the rough idle and the missing, while driving once it hits about 2000rpm it hesitates until I hit 3000rpm and smooths out but between 2000 and 2900rpm the hesitation is there not sure completely stumped.

 

Try this. The grounds for the O2 sensor and other sensors are critical.

Renix Ground Refreshing
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 driveabililty 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. All 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. 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.
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 it’s 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.
A 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 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

 

Ill try this once it stops snowing another thing I forgot to mention is I put fuel system cleaner in the tank on a full tank of gas just wondering if this could affect anything the stuff was techron for 12gal treatment

 

It's unlikely that's the cause of your problems, those treatments are usually pretty benign. You've got a fuel delivery or ignition/spark/ground issue for sure, just a matter of finding it. We will, just be patient.

 

Just to cover all the bases, have your alternator tested. For me, the hesitation came right before alternator failed all together.

 

1. Never clean a rotor. Replace it and when you do that, replace your distributor cap. These secondary ignition components can have cracks in them that you cannot see which affect their performance. Fresh spark plug wires every 60k, or at the very least test them for resistance with an ohmeter. Never underestimate the importance of tuneup hardware. Failure to do this can result in the chasing of your tail.

2. Any situation where you have an issue within a fairly narrow RPM band, I suspect the throttle position sensor. Test it. Here's how, courtesy of cruiser54.
-------------------------------------------------------
RENIX TPS ADJUSTMENT

Before attempting to adjust your TPS be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.

MANUAL TRANSMISSION: RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body. This manual transmission vehicle TPS provides data input to the ECU. The manual transmission TPS has three wires in the connector and they're clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Adjust the TPS until you
have achieved this percentage. If you can't achieve the correct output voltage replace the TPS and start over.

AUTOMATIC TRANSMISSION: RENIX automatic transmission equipped XJs has a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as the manual transmission equipped vehicles—

FOR ENGINE MANAGEMENT RELATED ISSUES. However, the automatic TPS also has a square four-wire connector clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.
If you have TRANSMISSION issues check the four-wire connector side of the TPS.
If you have ENGINE issues check the three-wire connector side of the TPS. For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.

 

Time to refresh the grounds and test the TPS.

 

So I cleaned all the ground wires by the dip stick also put a new one on the block to the fire wall. Still the same. Rechecked the fuel lines going to the rail on the back one i noticed the old oring wedged in the tube took it out replaced it but i think the little plastic clip is letting fuel leak out. going to get a new clip and see if that helps.

 

Still need to test your throttle position sensor.