The Renix throttle bodies have a strange and failure prone connector on the side where the MAP supply originates and then runs up to the MAP sensor located on the firewall. This hose/pipe assembly is no longer available for purchase.
The real kicker here is how critical this line is in supplying the correct vacuum signal to the MAP, the most relied upon sensor for the ECU to read regarding air/fuel ratio. Any cracks, melted spots, or loose rubber connectors can cause major starting and driveability issues.
There’s a simple fix though. All that’s required is a 1/8” NPT tap, a new throttle body gasket ( Napa FPG 60742 ), a vacuum fitting (Napa 05703-B102), two vacuum elbows (Napa CRB2670), and a length of new plastic piping (Napa CRB2672).
Remove the throttle body and take it to the workbench.
Using an oiled tap along with a driver, carefully thread the lower of the 2 holes of the throttle body where the old fitting was plugged in. Don’t go too deep. These are pipe threads.
Flush the hole with carb cleaner and inspect for any left over cuttings.
This is an excellent time to do a complete throttle body and IAC cleaning. See Tip 11.
Take the vacuum fitting (05703-B102 ) and apply a LITTLE bit of thread sealer on the threads only. I prefer Permatex #2 but almost anything is fine.
Carefully screw the fitting in until snug.
Install one of the vacuum elbows on the MAP sensor so it points toward the throttle body, and the other vacuum elbow on your new throttle body fitting so it points up to the MAP sensor.
Cut a length of the new plastic tubing (approximately 13 inches) to fit between the vacuum elbows and install it making sure there is enough slack for some engine movement. Route it according to the photo. We don’t want any rubbing or chafing with engine movement. Not a bad idea to use some contact cement or Gasga-Cinch sparingly on the tubing to elbow connectors.
The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, and behind the driver’s taillamp on an MJ.
Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture.
Locate the black wire on the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire.
Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.Solder the connection. Tape it up and reinstall the split loom covering.
At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces.
On 1984 to 1990 MJs and XJs, the blower motor’s factory grounding point is on the driver side inner fender under the sheet metal screw. This ground is shared with windshield wipers, front windshield washers, rear windshield washers, AC clutch relay, fan control relay, fog lamps, fan motor, headlamps, front turn signals, front side markers, and park lamps.
So your blower motor has its ground point 10 feet away from where it is located!!
What we’re going to do is leave that ground intact and also ground the blower motor on the passenger side inner fender much closer to the blower motor itself. This will also benefit the other components on the factory ground circuit. Take this opportunity to refresh the factory ground as a matter of course. Remove the screw, scrape the surface to bare metal and reinstall the screw securely.
Here’s what I do to get the ground much closer to the blower motor and add another ground point to this overloaded ground circuit.
Find the blower motor connector on the passenger side. Red and Black two wire connector.
Find a location where the black wire can be made to reach the passenger side inner fender, and cut the wire. You may have to do some rerouting of the harness to achieve this.
Take both cut pieces of wire and put them together into a yellow eyelet and crimp. Fasten the eyelet to a place on the passenger side inner fender with a sheet metal screw after applying OxGard to the contact surfaces. Be sure to scrape the attaching point on the fender to bare metal first.
Your blower motor will now turn faster and last longer, and the other electrical components on the circuit will benefit from a better ground path.
As noted in Tip #2, Renix C101 Connector Refreshing, in 1989 the factory wiring harness no longer included the problematic connector. For a long-term fix that will avoid many problems in the future, it is a good idea to just get rid of the thing entirely.
A helpful video can be found in the link below:
Unbolt the 2 halves of the C101 using a ¼” socket. On each half there is a plastic cover where the wires enter. They are removable but you’ll probably end up busting them off. Lightly bolt the C101 back together, away from the firewall. Peel back the split-loom covering from the body side of the C101 connector down to where the harness splits and goes toward the firewall, pretty much below the MAP sensor. On the engine side, remove the split loom about the same distance.
Now you can see from one side of the C101 to the other. Beginning at the top row, closest to the motor, be absolutely sure you cut the matching wires on each side of the connector off to about 1/2 inch. This will allow you to verify the original position of each wire color in case of mistakes or confusion. CUT AND SOLDER ONE PAIR AT A TIME. The wires may be wound a bit in their looms. See the first photo. Get them unwound neatly and do the following, ONE AT A TIME.
Slide your shrink tube over one wire. In a well ventilated area, solder the wires together and then slide the shrink tubing over the solder joint. Heat the shrink tubing so it seals your completed solder joint. Keep going until you’ve done all 22 or so connections.
Both sides of the C101 connection have a wire that is brown with white tracer. Follow each of these wires back until you come to a point where three wires are crimped together.
What you want to do here is cut the crappy factory crimp out of each set of three and bring both sets of three wires together and solder them together, using shrink tubing as well. All 6 wires. These particular wires will not end up in your normal C101 elimination loom. The sensor ground upgrade is found in Tip 6.
After all the soldering and shrink tubing is done, bundle the wires together in a new piece of 3/4″ split loom. Tape it up and secure it to the C101 connector’s original bolt hole or somewhere else along the firewall so it will be protected.
Most early and even later Renix 4.0s could be bothered by excessive oil in the air cleaner box.
A fix from my old days as Service Manager at a Jeep dealership follows. Information was provided to me from a buddy at JeepTech during those days. I don’t believe it ever came out in a Technical Service Bulletin.
Remove the valve cover and turn it over. Next, remove the fluted tubes that are now facing you by removing three screws on each.
Chop 1 inch off each of them. Then, drill a half inch hole as shown in the photo. The flat side of the flute that’s closest to the edge of the valve cover.
Clean and de-burr/sand all rough edges nicely, clean with solvent, and reinstall. Don’t be concerned about the chintzy gaskets that will probably crumble into oblivion when you remove the fluted tubes. They can go back together without gaskets.
Here’s a handy video from my friend Brendan showing more detail.