Renix misfire help

Hi im new here ive been looking over all the misfire threads and cant find what im looking for,

so heres my issue My 1990 4.0 jeep cherokee, will start up rough, smooth out and idle fine as soon as you go to give it gas in park or in gear it will backfire out the exhaust and run like crap no matter how much gas is given

the things ive replaced
Cps sensor,
Cap, rotor, plugs, and wires.
ive also checked all the vacuum lines and they r fine

im stumped

Do this as you may be losing a ground when torque is applied to the drivetrain:

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

if ground clean-up doesn't net you any better results (still a good idea on any Renix vehicle) get a pressure gauge and check fuel pressure. You may have a pump that's not able to supply sufficient volume or pressure to meet demands greater than idle.

fuel pressure is great 31psi, im working on the ground thing and testing the tps

i will post if anything helps

werejackal said:

fuel pressure is great 31psi, im working on the ground thing and testing the tps

i will post if anything helps

Click to expand...

Then use this to test the TPS as most instructions have you testing on the "trans" side of the TPS. Not good when looking for a driveability problem.

Pay particular attention to the beginning where the sensor ground test is done. Do that first.

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 11-28-2011

my readings for the tps is 4.89 referance and the output is .67

Should be .83 output on the engine side. What happens if you move the throttle slowly? Any "drop-outs" of no voltage? Not all digital meters will catch this.

i moved the throttle super slow and slowly climbed in voltage on the reference side, no dropouts

Then adjust it.

Did you test the sensor ground circuit as described?

If the MAP and TPS are good, TPS calibrated, and grounds are good, and throttle body vacuum line to the MAP sensor is leak free, then:

Check the FPR vacuum line for leaking fuel. Verify good solid vacuum (not blocked) at the FPR and MAP sensors!

The Exhaust might be blocked, Bad cat?

Did changing the CPS solve anything? We have had a lot of BAD CPS sensors right off the shelf lately!!!!

GOT IT FIXED it ended up being that the distributor had moved about 1/8 of and inch just enough to let it idle fine but it was over advancing and causing the backfire in the exhaust, so ive learned to "Keep it simple, Stupid" in the wise words of a friend of mine. So the distributor can adjust timing to effect the way the engine runs, Thanks for all the posts and helpful info. And i did adjust the tps so it reads right now.

OEM Renix 4.0, and dizzy is not adjustable unless some one broke a locking tab that normally keeps its position non adjustable!!!!!

someone must have broken it cuz it moves on mine ive only owned this jeep for almost a year now so who knows its history im just glad it was a simple fix

As stated, the computer adjusts running timing, but it can only compensate so far, and it cannot adjust the timing of rotor to cap, so if it gets too far off, it will mess up.

Rotating the distributor affects injector timing, not ignition timing. Chances are yours is off a tooth and you compensated for it by twisting the dizzy.

cruiser54 said:

Rotating the distributor affects injector timing, not ignition timing. Chances are yours is off a tooth and you compensated for it by twisting the dizzy.

Click to expand...

That might be, but if it was indexed right, but then someone broke off the tab and it got rotated wrong, then he's put it right. Either way, it would seem the problem is addressed. It should be easy enough to determine if there's enough left of the fork on the distributor. If the stub or whatever, is centered over the bolt hole, it was indexed right and is now restored. If not, it was indexed wrong, and is now compensated.

Correct. A properly indexed distributor on a Renix will have the trailing edge of the rotor .020" past the inside distributor terminal at #1 TDC. This must be done with an old dizzy cap which has had a window cut into it around the #1 terminal.

cruiser54 said:

Correct. A properly indexed distributor on a Renix will have the trailing edge of the rotor .020" past the inside distributor terminal at #1 TDC. This must be done with an old dizzy cap which has had a window cut into it around the #1 terminal.

Click to expand...

That assumes the engine is actually at TDC compression on #1, as well.

cruiser54 said:

Rotating the distributor affects injector timing, not ignition timing. Chances are yours is off a tooth and you compensated for it by twisting the dizzy.

Click to expand...

Interesting, but if it is off enough, it will also fire the spark on the wrong cylinder, thus it miss fires.