bajaxj

My XJ is a 90. The problem Im having is that after I run it for awhile it will run fine but after turning it off and restarting it will bog and backfire. I was told it might be my cat and since I needed one to pass smog, I went ahead and installed one with no luck cause its still doing it. Any help will be greatly appreciated. Thanx guys! Merry Christmas and Happy New Year to all.

desertdog

fuel pressure
spark
throttle position sensor
fuel injectors and signal

These are the first things you should look at. A little searching should turn up a link with test procedures for ALL your RENIX sensors. The two that cause the most trouble are TPS and CPS. Also, the stock injectors suck. I have the same year and I fought with it for months before putting Neon injectors in. New fuel filter never hurts either. Check all your vacuum lines, unplug the O2 sensor and see what it does in open loop....methodical troubleshooting will eventually give you a solution. Couple things: you can rent Noid lights and a fuel pressure checker at AutoZone. If you need more help, let me know. I am local and cheap

DFlintstone

Sounds good^..When my 90 was doing just that the heat shield would expand while i was grabbing a 6'r, and short some wires to the O2, Temp& Knock sensor. Also usually wouldn't completely die, and go like hell it I went past 80% throttle. (Guess Renix goes into open loop there)

cruiser54

Do this first as all the sensors need a good ground to send a proper signal to the ECU. Every Renix era Jeep needs this done at least once while in your hands. It's free and/or costs $20 if you go all out and add a coupla cables.

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

crbnfibr

cruiser54

Albany, huh? I lived in Stephentown from birth til 9 years old!!!

crbnfibr

and now your warm... : )

bajaxj

Thanks guys for the reply's. I forgot to mention that a few minutes after restarting it, Ill rev it up a few time (it backfires a bit) them runs fine again till next time I shut it off for awhile and try to drive it again(running errands is a pita).

cruiser54

Do the ground refreshing first!!!!!

DFlintstone

NO! Look at the wires under your nose first! (tip head down)

cruiser54

OK, look at what Flintstone wants you to look at first. THEN, do the ground refreshing just cuz it's the right thing to do.

desertdog

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

After you check your grounds, take a look at the TPS.

cruiser54

Thank you for your support!! Need I post the ground refreshing instructions again?

UJSLOST

backfiring thru exhaust is caused from a rich condition
backfiring thru the throttle body/intake is due to a lean condition.

cruiser54

And, if you want simple instructions for adjusting the TPS, use these. They allow you to test either side of the TPS depending on what you're looking for. Most TPS instructions have you test it on the trans side of the TPS even though you have an engine driveability issue. That can send you on a wild goose chase.


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.
If you see more than 1 ohm of resistance 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 have 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.
Revised 11-28-2001