Mikewv78

I have a persistent problem with my Cherokee. It runs like a top until it gets warmed up. Once it gets up to operating temperature, it starts missing and sputtering terribly. On cooler days it takes longer so it must be something temperature related. i have changed the coolant temp sensor, the intake air temp sensor and just for the heck of it, i changed the plugs, cap, rotor, and plug wires. nothing seems to help. NEED some advice!!
Thanks

1994 Jeep Cherokee Country
4.0 liter straight six, 5 speed
202,000 miles

PS. Also changed the oxygen sensor....

pdowty68

Map sensor? Maf sensor?

Mikewv78

Someone said if the MAP sensor went bad it would be running real rich and throwing black smoke.

AdriansXJ

I'm having a similar problem with my 1995. Runs great until it gets to operating temp and then misses, sputters, lags out really bad, stalls when I stop and leave it in drive, seems to have lost a lot of power. I did buy it like this, but I only paid $500 for a jeep that wasn't supposed to run which I put the key in and drove a few blocks to my dads house, I even went prepared with a dovetail with a winch.

Mikewv78

Have you replaced anything? Any ideas on what the problem could be?

BillyBoy

Possibly the temp sensor after the muffler? Mine went bad. Same symptoms. Had a check engine light on tho.

Mikewv78

I am unaware of a temp sensor after the muffler.

CCKen

The downstream O2S wasn't introduced until 1996 (OBDII).

CCKen

This is a heated Oxygen Sensor, which may not be heating.

Power for the heating element taps off the fuel pump relay and the ground circuit for the heater element is at the right rear of the engine.

You may want to 'refresh' your ground points in the engine bay. See if you can get Cruiser54 to post up his ground refreshing instructions.

Refreshing the grounds may or may not help, but it certainly won't hurt.

cruiser54

Even though yours is not renix, these still apply to a great extent:

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, failed emission tests, and wasted money replacing components unnecessarily.
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.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
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 03-04-2013



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 making sure they haven’t retracted into the plastic holder, and then 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. Also 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 plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.
Revised 07/23/2012

Mikewv78

Is there a way to check for that heating voltage at the sensor?

CCKen

Most, if not all, replacement O2S's have two White wires, they are the heater circuit wires. One is used for power and the other is the ground. The heater is not polarity sensitive but the source of power and ground from the body is. One wire from the body that matches one of the White wires will be power and the other will be the ground. I think your XJ body harness power wire is Black and the ground wire is Black/Tan tracer. To be sure check which White wires from the O2S match up with the body harness wires.

With the ignition switch to RUN, engine off, you can back probe the two white wires at the connected connectors and check the voltage by touching the two back probes with your voltmeter probes and see what you get, if reversed polarity is indicated switch probes. If you get no voltage start the engine and try again, if still no voltage there's an open in the fuel pump relay source wire or an open in the ground wire. If you think it may be an open ground, use the (+) of the meter to the white wires and the (-) probe of the meter to chassis ground.

I use Safety Pins as back probes. Got them at Joann Fabrics.

The other method, besides back probing, is to note which body harness wires go to the two O2S White wires, disconnect the O2S from the body harness and probe the two noted wires in the body harness connector using the method described above.

Mikewv78

okay, I'll try it out when i get home from work today.......crossed fingers.

Mikewv78

Well I check for the voltage at the oxygen sensor. There is 14 volts coming from the battery through the fuel pump relay. I'm at a total loss here....don't know where to go next.

cruiser54

Did you do the grounds yet?