So the problem is, I've replaced all the plugs, wires, ignition coil, distributor cap and rotor. And still out of thee blew I have multiple misfires and its killing the rig. It doesn't happen consistently either. It seems secondary ignition related because it doesn't always do it at every start up, 75% of the time it starts and runs fine.
Any ideas or need more info please let me know.

 

Test AND adjust your throttle position sensor. (and while you're working in that area, clean your throttle body and idle air control)

More on the TPS below...
-----------------------------------

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 one 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 other 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 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 four-wire connector clearly embossed with the letters
A,B,C, and D.. For the automatic transmission equipped vehicles the four-wire connector
provides data to the TCU.

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.

 

The Tps has been replaced and tuned, the TB is clean and all the sensors are new.

 

Doesn't seem like something that could be caused by the TPS. But ill check it out.

 

so ive now heard so many different possibilities in regards to this. im almost certain it is secondary ignition related but i have heard alot of options(listed below)

• fuel pressure regulator
• fuel pump
• timing
• plugs
• SP wires
• Dist cap/rotor
• ignition coil
• tps
• alternator

all but the alternator, FPR and timing have been replaced.

any other ideas would be greatly appreciated.
planning on tearing it apart and inspecting all the whole secondary ignition system.

 

throttle position sensor is a very common failure on the 87-90. Don't rule it out.

But in an earlier post you said it was replaced and adjusted? Confusing.

 

how is your upstream o2 sensor acting ?
it could very well be bad

 

Renix Jeeps only have one O2 sensor. When it fails, the ECU goes kinda rich in open loop. Poor idle quality is a symptom of that. That being said, the O2 sensors were only good for about 70,000 miles before they got lazy.

A simple thing to try is removing the coil from the ICU. 2 Torx bolts hold them together. Clean up the pins and metal springy things that make the connection between the two and tweak the springy things to grab the pins tighter. Add dielectric grease while you're at it.

Unplug the connectors from the ICU. Spray out the ICU connections and teh harness connections with a good quality electronics cleaner.

You could also test your sensor ground circuit as described in the beginning of the TPS adjustment procedure that TJwalker posted up.

You might also review the TPS adjusting procedure he posted up because it gives you the ability to test each side of the TPS independently . Most procedures have you check only one side of the TPS and it makes no sense to test the trans side when you have a driveability problem as the engine side of your TPS could be bad and you wouldn't know it.

 

when i replaced the coil i cleaned those up and pushed them down a little bit and it kinda helped, it made the problem stop happening so often but it still seems to happen when its ran a little long.

just tried readjusting the TPS and couldnt find any spot where the rpm's wouldnt fluctuate.

im not sure on how to tell if an 02 sensor is bad. it doesnt have a rich smell to it but it does run slightly rough.

any pointers or should i just replace it to be safe, im sitting just under 255000 miles so it might be time.

would the o2 sensor cause failure/bad missfire when warmed up to normal temperature?

 

CPS did the same thing to my 96. It was just random misfire until I replaced it

 

would it start fine, and run fine.. then once its off and you go to start it does the missfires? and restarting it would solve it?

so many questions but im clueless about this issue.

 

CPS works differently on an HO than Renix. If you PM me your email address I will send you the correct and simple way to check/adjust the TPS on a Renix..

 

Sent,

Also,
Does anybody have real photos showing where the cps is at? Im having a hardtime finding it.

 

If you are facing the engine, the CPS is at about 1 o'clock, bolted to the bell housing, kinda behind the intake manifold.

 

Is it back firing through the TB?