Poes90XJ

I've got a 90 xj with 4.0 exhaust has a hole in exhaust just after O2 sensor. It was running fine then I put $20 in gas earlier and started it up and it sounded like a dragster loping. I started Drivin and it felt normal throttle response, then I went to leave the house and it started missin a little bit at partial throttle but at 50-100% throttle it when's out. Then at stop sign by my house it died while slowing down in 3rd gear before depressing the clutch.

ZINGGG

Do a tune up. Fresh champion copper plugs, quality 8 mm wires and brass contact distributor cap and rotor. Also could be an o2 sensor going bad

Poes90XJ

Also just started it again now has a bunch of blue smoke

ZINGGG

Oooooo sounds like a blown head gasket. That's never fun

Poes90XJ

Green sticker rig here I come...350 swap, full width and 37s

The Rooster

blue smoke is not a head gasket its oil or its to lean ... White smoke is a head gasket... Sounds to me like a Vacum leak... or I know this sounds funny but Clean and Check all of your Grounds.. it can cause this kind of problem on a Renix 4.0
another thing is it id common on high mileage Renix 4.0 for the fuel injectors to go bad... so check them as well..

cruiser54

Check the vacuum line from the throttle body to the MAP sensor located on the firewall. Make sure it's not cracked, melted shut, unplugged etc. If it leaks vacuum the MAP tells the ECU to go full rich.

Refreshing the grounds on a Renix is NEVER a bad idea as Rooster suggested.

DFlintstone

Is there oil in the air cleaner?

The Rooster

any update?

Poes90XJ

O2 good, vac lines good and all unclogged. Dust cap n rotor good. Pulling plugs tomorrow n also doin compression test tomorrow. Also started throwing black smoke today on way to cal 4wheel association dist meeting.

cruiser54

In this order are the sensors that most affect the mixture. MAP, CTS, IAT. Check the connections at each plug.

The hose from the throttle body to MAP is clear? Is it plugged into the TB securely?

Poes90XJ

Checked all of the above sensors, all good. Checked oil today just to see if contaminated and found fuel in the oil

cruiser54

Sounds like you may have an injector issue. Does it take a longer time to start from cold than it used to?

Another thing that Rooster mentioned is grounds. ALL those sensors rely on good grounds to give the ECU the correct signals. I recommend doing the following cuz it could only help and absolutely can't hurt.
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

Ace&Wrench

We just got a 90 Cherokee with a 4.0 for off roading in Arizona. It was running really rough. After seeing your post I went out and checked the Vacuum line to the Map Sensor. It was off. Plugged it in and the Cherokee is running good now.

Ace&Wrench

We just got a 90 Cherokee with a 4.0 for off roading in Arizona. It was running really rough. After seeing your post I went out and checked the Vacuum line to the Map Sensor. It was off. Plugged it in and the Cherokee is running good now.