• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Help Needed: Passing Smog with My Renix-HO Hybrid XJ!

88pioneerxj

NAXJA Forum User
This may be the thread to end all SMOG threads..

Hi everyone,

I have an '88 RENIX 4.0L XJ Pioneer (230,000 miles) with a donor engine from a 1991 High Output 4.0L XJ, and I didn’t realize what a massive headache it would be to pass smog here in SoCal (I'm from out of state).

So far, I’ve failed smog 3 times, with Gross Polluter results across all measurements—even after replacing the catalytic converter. Until I researched a bit;


The Issue:

  • The ECM, electronics, wiring harness, and transmission are from the original 1988 RENIX system.
  • The engine is a 1991 High Output model, which was designed for computer-controlled injection and timing (i believe)
  • The 1988 RENIX ECM controls timing using the Crank Position Sensor, while the 1991 HO engine relies on its own computer controls for timing and injection.
My Question:
- Assuming that new Cat, ignition system and fuel injection is replaced - car driven 40 miles pre-test, kept running while waiting and all the forum tricks mentioned followed, would replacement parts need to be for the 91' engine?

- What can a 20-something mechanic (me) do to get this car to pass the California smog test? Have any of you seen this type of setup before or know of a solution? I love this car and really want to make it work - keep it alive as long as possible.

TECH SPECS:
1 . 1988 Jeep Cherokee Pioneer

2. 4.0L

3. Automatic Transmission (4 speed)

4. Factory Transfer Case

5. Engine is from 1991 XJ High Output 4.0L
 
Edit: forgot the context for whoever is interested: Bought the car at 21 y.o, changing head gasket from overheating issues, discovered two pistons are cracked. Buddy sold me his donor engine for cheap- paid mechanic to do the Remove&Replace.

Done plenty of repairs to it, followed fantastic advice from lurking on forum like https://naxja.org/threads/1987-renix-high-idle-issue.1168290/
but looking to know if this is a losing battle.
 
This may be the thread to end all SMOG threads..

Hi everyone,

I have an '88 RENIX 4.0L XJ Pioneer (230,000 miles) with a donor engine from a 1991 High Output 4.0L XJ, and I didn’t realize what a massive headache it would be to pass smog here in SoCal (I'm from out of state).

So far, I’ve failed smog 3 times, with Gross Polluter results across all measurements—even after replacing the catalytic converter. Until I researched a bit;


The Issue:

  • The ECM, electronics, wiring harness, and transmission are from the original 1988 RENIX system.
  • The engine is a 1991 High Output model, which was designed for computer-controlled injection and timing (i believe)
  • The 1988 RENIX ECM controls timing using the Crank Position Sensor, while the 1991 HO engine relies on its own computer controls for timing and injection.
My Question:
- Assuming that new Cat, ignition system and fuel injection is replaced - car driven 40 miles pre-test, kept running while waiting and all the forum tricks mentioned followed, would replacement parts need to be for the 91' engine?

- What can a 20-something mechanic (me) do to get this car to pass the California smog test? Have any of you seen this type of setup before or know of a solution? I love this car and really want to make it work - keep it alive as long as possible.

TECH SPECS:
1 . 1988 Jeep Cherokee Pioneer

2. 4.0L

3. Automatic Transmission (4 speed)

4. Factory Transfer Case

5. Engine is from 1991 XJ High Output 4.0L
A engine is a engine, it doesn't know whether your building a Renix, OBD I, or OBD II!
 
<snip>
  • The 1988 RENIX ECM controls timing using the Crank Position Sensor, while the 1991 HO engine relies on its own computer controls for timing and injection.
My Question:
- Assuming that new Cat, ignition system and fuel injection is replaced - car driven 40 miles pre-test, kept running while waiting and all the forum tricks mentioned followed, would replacement parts need to be for the 91' engine?
<snip>

Did you put on the Renix intake/exhaust manifolds, egr, throttle body, etc., or use the '91? I don't think the '91 block has provisions for a knock sensor. The intake/exhaust lack the EGR. The TPS is different.

Post the actual numbers. GP typically means very high HC, CO so you're running very rich. Did you fail any of the visuals?

This would be my guess. The Renix ECU needs the inputs from the other sensors. The '91 needs the CPS signal to manage the fuel pulse. The split across 2 fuel management systems likely means neither is getting all the needed inputs to properly run.

Past threads on HO engines into Renix say keep the Renix manifolds, sensors and harnesses.
 
Did you put on the Renix intake/exhaust manifolds, egr, throttle body, etc., or use the '91? I don't think the '91 block has provisions for a knock sensor. The intake/exhaust lack the EGR. The TPS is different.

Post the actual numbers. GP typically means very high HC, CO so you're running very rich. Did you fail any of the visuals?

This would be my guess. The Renix ECU needs the inputs from the other sensors. The '91 needs the CPS signal to manage the fuel pulse. The split across 2 fuel management systems likely means neither is getting all the needed inputs to properly run.

Past threads on HO engines into Renix say keep the Renix manifolds, sensors and harnesses.
Good advice here, thank you. Posting numbers below:

 
Is the correct O2 sensor for a Renix installed in the exhaust? Correct temp sensor as well? Either being wrong would cause it to stay in open loop. How is the gas mileage?
 
I'll ask again, did you put on the Renix intake/exhaust manifolds, egr, throttle body, etc., or use the '91's?
 
OP, you could use either set-up but you MUST use ALL the components of either system!
 
Back
Top