Category Archives: Cruiser’s Mostly Renix Tips

Technical DIY instructions covering common issues on the Renix XJs (1987-1990). Some Tips also transfer to later years, or the techniques can be adapted.

Renix Vacuum Harnesses


Vac harness 7151367

The vacuum harness that attaches to the front of the valve cover and includes the grommet/fitting, and is called the front harness, is Napa part number BK 715-1367 or is a Dorman 46003.

Vac harness 7151366

The vacuum harness that is closest to the air cleaner, EGR etc, and is called the rear harness, is Napa part number BK 715-1366 or is a Dorman 46004.

Vac harness 7151365

The tube from the rear of the valve cover to the intake manifold is part number BK 715-1365 or Dorman 46005 and comes with the valve cover grommet.

The Throttle Body to MAP hose is no longer available. Click HERE to access a fix for that.

Vac Diagram 4.0 Renix

Revised 2-6-2016

EGR Valve Test


Valve Opening Test

  • With engine at normal operating temperature and at idle, rapidly open and close throttle. Open throttle sufficiently to obtain at least 1500 RPM. Movement should be noticed in EGR diaphragm.
  • If diaphragm does not move, probable causes are: faulty vacuum signal to EGR, defective EGR diaphragm or defective backpressure sensor diaphragm (if equipped), or leaks in vacuum lines or connections.

Valve Closing Test

  • With engine at normal operating temperature and at idle, manually depress EGR valve diaphragm. RPM should immediately drop, indicating that EGR valve is not leaking and had been properly cutting off exhaust gas flow at idle.
  • If there is no change in RPM and engine is idling properly, exhaust gases are not reaching combustion chamber. Check for plugged passage between EGR valve and intake manifold.
  • If engine idles poorly and RPM is not greatly affected by manually moving diaphragm up, EGR valve is not closing off exhaust gas flow. Check for carbon between pintle, leaking EGR valve gasket or bad EGR valve.

Revised 1-31-2016


Shifting the Transfer Case


Here’s how the factory suggests you shift the transfer case and I’ve been doing this since these things were new and I worked at the dealership. Quoted from the owner’s manual. The suggestions in BOLD are mine.

“To engage, shift the transfer case lever from 2H to 4H while the vehicle is moving at any legal speed”. I let off the gas, throw the lever, tap the gas, and let off again.

4L position: ” To engage, slow the vehicle to 2-3 MPH , shift the transmission to Neutral, then shift the transfer lever to the right and pull firmly rearward to 4L”.

To shift out of 4L, stop the vehicle, shift the transmission to Neutral, shift the transfer case lever to 4H, then the transmission to Drive (if you have an automatic), or First gear (if you have a manual), and continue on.

Revised 1-31-2016

Headlight Harness Upgrade

Putco relaysHeadlamp harness

It’s easy to install a supplemental headlight harness.

From the factory, the voltage to the headlight bulbs travels from the battery, through connectors, inside the cabin, to the headlamp switch, and then back out to the lamps via undersized wire and more connectors. It’s not uncommon to find only 10.5 volts at the lamps.

The supplemental harness is installed so that it provides battery voltage to the lamps and is just triggered by the factory wiring. The result is about 35% brighter headlamps and headlight switches that don’t melt and burn out.


Ebay has the harnesses. 2 headlamp H4 with ceramic connectors is what you want. You’ll likely be warned that the harness won’t fit your Jeep. It will.

Absolutely plug and play:

  • Remove grille and headlamp bulbs. I fed my harnesses from the passenger side starting between the battery and the back of the headlamp housing, over to the driver side.
  • Plug the driver side bulb into the new harness.
  • Attach the new harness’s ground wire under one of the small bolts on the radiator support after scraping the paint off under it.
  • Attach the harness to the existing harness behind the grille working toward the passenger side.
  • Plug the new harness plug into passenger headlamp.
  • Plug original headlamp plug into receptacle on new harness.
  • Attach the ground for the passenger side just like you did the driver side under a radiator support bolt.
  • Attach relays with provided bracket on the passenger side inner fender.
  • Connect power wires to battery.
  • Revised 1-31-2016

Improving the Instrument Panel Ground


The ground point for the complete instrument cluster on your XJ or MJ is located up under the driver’s side dash. If you lay on your back and look up under there with a flashlight, without wearing a hat, you will see a black wire attached to a shiny piece of metal almost directly above the hood release knob. The screw will have either a ¼” or 5/16″ head on it.

This ground point is responsible for handling the ground circuit for the following items: Dome lamps, seat belt and key warnings, transmission power/comfort switch, wiper switch, headlamp switch and delay module, fog lamp switch, cargo lamp switch, all instrument panel grounds and illumination, power windows and door locks, cruise control dump valve, and a few more things.

The problem is that where the ground point is located does not share good contact with the chassis where the ground should be. The solution is simple:

  • Make up a jumper wire with #10 gauge wire about 10″ long. On one end, crimp on a ¼” round wire terminal. On the other end, crimp on a 3/8″ round wire terminal.
  • Remove the screw from the existing ground wire and attach the small terminal of your jumper so that the original wire and your new jumper share the same attaching point, one over the other.
  • Look above the driver’s side plastic kick panel just forward of the top of the hood release knob. You will see an 8mm stud there. Attach the large terminal end there with a washer and nut over it tightened securely. Use a coating of OxGard at all ground contact surfaces when attaching the screw and nut.

IP ground location

**Special note for Comanche owners: Make your jumper wire 12″ long and attach it on the driver’s side kick panel close to the fusebox on the 8mm stud.**

HO into Renix Swap


This swap is easier than some will lead you to believe. And generally Pooh-poohed by those who have never done it. Those of us who have done it, like myself, will share with you the things that need to be done for a successful swap. Just think of it as swapping in a long block.

  • XJ Cherokee and ZJ Grand Cherokee 4.0L engine blocks interchange.
  • 2000+ TJ Wrangler and WJ Grand Cherokee 4.0L engine blocks interchange.
  • YJ and 1997-1999 4.0L TJ blocks will interchange in XJ/ZJ
  • XJ/ZJ blocks, and the 2000+ TJ/WJ blocks do not interchange without significant modifications.

TJ/WJ 4.0L Engine blocks underwent clean sheet design changes effective in the 1999 WJ Grand and 2000 TJ Wrangler. These blocks are not interchangeable with XJ/ZJ engine blocks. The reason is motor mount bolt holes and belt driven accessory mounting bolt holes are in different locations, or not present at all, TJ/WJ vs. XJ/ZJ.

Now that we know which engines we can use, let’s get down to business.

The HO and Renix have some differences but none that can’t be overcome very easily.

One running change was that the rear of the head was no longer drilled and tapped for the temperature gauge sender beginning in the 96 model year. The sender can be relocated to the threaded hole in the thermostat housing taken from an HO engine. You’ll have to extend the wire to that location. Some brave souls even drill and tap the HO head at the rear for the sender.

You will be using the intake and exhaust manifolds from your Renix, along with all your sensors and wiring. Since the intake ports of the HO are slightly different, you use a new Renix gasket. Exhaust ports are identical.

An alternative on exhaust manifolds:

As far as exhaust, you can use the Renix exhaust manifold and be fine.
If you want to use the HO exhaust manifold, you must go with an HO headpipe and screw your O2 sensor into that headpipe. Standard Renix harness is plenty long to do so.
A bung can be welded into the HO manifold to accept the EGR tube.

You will need to use your Renix distributor as it is different than the HO design. See Tips #12 – Setting Your 4.0 to #1 TDC and #13 – Distributor Indexing to be sure you get the distributor installed correctly.

The flywheel or flexplate from the Renix must be used so your CPS gets the correct signals. The valve cover from the Renix allows you to keep your CCV system intact and requires no modifications.

The HO block will have a plug in the coolant galley on the driver’s side of the block, closest to the front, which needs to be removed so your Coolant Temp Sensor can be installed in it’s place just as it is on the Renix. It requires a 5/16” square drive or a modified 3/8” drive that has been ground down to fit. Do this before installing the engine.

As for the knock sensor, which is located just above the oil pan on the driver’s side of the engine about mid way, all the blocks I’ve seen are threaded for it. If not, I’ve heard they may be drilled but not tapped. Tap the hole if that’s the case.


XJ: “Regular” (not Grand) Cherokees ’84-’01
ZJ: Grand Cherokee ’93-’98 (Gen1)
WJ: Grand Cherokee ’99-’04 (Gen2)
YJ: Wrangler ’87-’95 (Gen1)
TJ: Wrangler ’97-’06 (Gen2)


Vacuum test for exhaust restriction


Your vacuum gauge should come with an instruction booklet outlining the procedure.

Hook the  gauge up to a vacuum source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum.

Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle.

Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

Revised 1-31-2016

Rear Main Seal Diagnosis


I’d be looking up ABOVE first, and VERIFYING the source of the oil leak YOURSELF.

Everybody, who doesn’t own or have to pay for or perform your vehicle repairs, loves to poke their noggin UNDER the Jeep and come out bearing the false bad news that your RMS is leaking. Many mechanics, friends, and good old Uncle Bob seem to enjoy telling you it’s the rear main seal. Has a catastrophic ring to it, doesn’t it?

A simple leak at the back of the valve cover or other source could produce the same symptoms. You don’t need to be a mechanic to figure this out. If you have good eyesight and a dim flashlight, you’re good to go on your own. Don’t jump on the RMS/oil pan gasket bandwagon right off the bat.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for two simple reasons:

First off, the engine sits nose-up and any oil will run back to the RMS area.

Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber’s adage apply here: “Crap flows downhill”.

Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket, in that order, have to be eliminated as possibilities first.  A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly. 



Revised 10-10-2018

Renix Throttle Body Butterfly Adjustment

1-Throttle body setting

Okay. Let’s start from scratch.

First off, that’s not an idle adjustment screw. It’s a throttle butterfly stop screw. It’s purpose is to allow the butterfly to be as close to completely closed as it can be without binding or wearing into the throttle body. It was never intended to be adjusted in the field. But, Uncle Bob didn’t know that, did he?

Engine off. Back off the butterfly stop screw with a 3/32″ allen wrench until the butterfly is completely closed. Now. turn the screw in until the FAINTEST movement of the butterfly opening is detected. If you have a .003″ feeler gauge, or something  that thick as measured with a caliper, use that to set the clearance. We’re talking sticky note paper here.

This can be done more easily with the throttle body removed. If you remove the throttle body, be sure to replace the gasket underneath it after thoroughly cleaning the old one off.

Readjust your Throttle Position Sensor.

Revised 10/9/2018

Distributor Indexing

Firing Order

Renix dizzy indexing

  1. Remove the distributor cap and cut a “window” into the side of the distributor cap at the #1 spark plug wire post . The “window” should be large enough to allow easy visual inspection of the position of the distributor rotor at the #1 spark plug wire post. Reinstall the distributor cap.
  2. Use Tip 12 first to guarantee you’re on #1 TDC.
  3. Install a ¾” wrench or socket onto the vibration damper retaining bolt. Rotate the engine in a clockwise direction until the #1 cylinder is at top dead center. Align the timing mark on the vibration damper with the “0” degree mark on the front cover timing scale. The tip of the distributor rotor should be near the #1 spark plug wire post.
  4. Disconnect the distributor electrical connection. Remove the distributor holddown clamp, holddown bolt and distributor. Remove the distributor cap and rotor.
  5. Place the distributor housing upside down in a soft jaw vise. Scribe a line 1/2 inch from the end of the distributor locating tab. Cut the distributor locating tab at the scribed line with a saw.
  6. Remove any burrs and metal filings from the distributor. Reinstall rotor.
  7. If necessary, using a flat blade screwdriver, turn the oil pump gear drive shaft until the slot is slightly past the 11 o’clock position. The oil pump gear drive shaft is accessible through the distributor mounting bore in the engine block. A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024.Dizzy o ring
  8. Visually align the modified locating tab area of the distributor housing with the holddown clamp bolt hole.
  9. Turn the rotor to the 4 o’clock position.Dizzy tab cuts
  10. Lower the distributor into the engine block until it seats. The rotor should now be very close to the 5 o’clock position.
  11. Reinstall the distributor cap with the cutout “window”. Rotate the distributor housing until the trailing edge of the distributor rotor tip is just departing from the #1 spark plug wire post terminal .
  12. Reinstall the distributor holddown clamp and bolt.. Reinspect the position of the rotor to the #1 spark plug wire post to insure that it has not moved.
  13. Install the new distributor cap, reconnect the distributor electrical connections.


Distributor indexing explained:

For clarification though, that’s not a cam sensor inside the Renix dizzy. It’s there to fire the injectors sequentially with the firing order. You’ll never notice if it went bad because the ECU will try to “guess” where it is and does a heck of a job at it.

As for the “timing”, it is controlled by the ECU. Ever notice how wide the tip of the rotor is? Try and wrap your head around this:

When the ECU yells “Fire” to the ignition control module, where is the rotor in relationship to the dizzy terminal? Not to the terminal yet? Past the terminal too far?

What happens to the spark/secondary ignition strength when it has to jump the Grand Canyon in comparison to shooting from a rotor tip? Poor ignition performance, bucking, jerking, longer crank times.

The factory was aware of this and issued a Technical Service Bulletin on it. This Tip, #13, is a condensed version of that factory TSB. You wouldn’t believe how many we found out of whack when I worked at the dealership. Yours is probably messed up also. RARELY did we find one set accurately.

Use Tip 12 first to guarantee you’re on #1 TDC.

Revised 08-19-19