Eagle

Can you use wheels from another vehicle if the backspacing matches? Wheels for the TJ Wrangler (at least some of them) are 15x8, so that would gain an inch for you compared to what you have now.

Check out springs for TJ Wranglers. They are the same diameter and will fit an MJ, but my understanding (subject to verification) is that they are shorter. Or don't your rules allow using springs out of a different vehicle?

Nope. Those are not super basic wheels. Those are the 15x7 factory wagon wheels. The base wheels are 15x6 and have nine rectangular slots around the periphery of the web where it meets the rim. As I mentioned above, there are NO aftermarket rims that provide 5-1/4" backspacing like the factory rims. That means you can buy the cheapest steel aftermarket wagon wheels and increase your track by at least two inches, maybe more -- without spacers. Do the rules require that you run factory wheels?

The only way the ECU knows what flywheel is there is from the signal sent by the CPS. If the CPS doesn't match the flywheel, you don't get a signal (or you don't gat a signal that the ECU can understand). Actually, all three have to match up. What often happens is that someone with a Renix vehicle throws in an "new" engine out of an HO. They use the Renix CPS, but they forget about the flywheel. No go.

8-inch cross-section width, or 8-inch tread width? 8-inch cross section works out to 203.2mm, so a 205 x anything is an 8-inch tire ... but the tread width is never the same as the cross section width. What are you running now for wheels? The factory 195/75-15s and 205/75-15s came on 6-inch rims, and everything else came on 7-inch rims. I can't imagine that you can't fit 195s on Jeep rims. Correct. Tires are centered on the wheels. To increase track, either go to a wider wheel with the same backspacing, or go to a wheel with less backspacing. Changing tire size in the same wheels does not change the track dimension.

AMC cars from the 60s and 70 used 14-inch wheels with the same bolt pattern that the Cherokee and Comanche use, but I'm not sure a 14-inch AMC rim will clear the disk brakes on the front. The factory rims on the XJ and MJ are 5-1/4" backspacing. It's not hard to find wheels that widen that track -- there are (AFAIK) NO aftermarket rims that provide the factory backspacing, most are in the 40" to 4-1/2" range. Be careful about going too small in combination with wide rims to increase the track. The first number in a metric tire size (the 195 or 225 part) is the cross-section width at the sidewall, in millimeters. Pete mentioned a 195/45-15. 195mm divided by 25.4 mm/inch works out to a tire width (not tread width) of 7.68 inches. Jeep mounted the 195/75-15 base model tires on 6-inch rims. The 45 series have much less sidewall to play with than 75 series. If you try to mount those little tires on very wide rims, you may have other problems. 7-inch rims will probably work, but I think 8-inch might be pushing the envelope. Most tires list the acceptable wheel width range, so be sure to check that.

I think there was. Unfortunately, the Renix CPS operates on a completely different principle than the HO CPS, which is why the flywheel and CPS have to match. And why there aren't any factory CPSs any more. The Renix models have been out of production for 28 years, so the factory doesn't have to service replacement parts any longer.

The cooling system doesn't matter, but the temperature does. The coolant temperature sensor in the block is what tells the Renix ECU when to switch from open loop (pre-mapped fuel curve, set rich for warm-up) to closed loop (computer/sensors control air/fuel mix). I don't remember what the temperature required for the switch-over to take place is, but I think it's around 175 or so. So you need to be sure that the system is functioning correctly and keeping the temperature up. Most people don't understand the role of the thermostat. The cooling system is to keep the temperature down, but the thermostat is to keep the temperature UP. If it's too cold, or if it sticks open, you're stuck in open loop mode and the fuel economy goes out the tailpipe.

Okay, good. When was the oxygen sensor last replaced? What temperature thermostat are you running?

I believe you are correct. But the dashboard voltmeter still "dips" when he turns on accessories, headlights, or even turn signals. That shouldn't happen. Your suggestion to retest at the battery while having a helper turn lights and accessories on and off is spot on. That's what I suggested in post #4 ... so of course I think it's spot on.

WHICH coolant temp sensor did you replace? The Renix Jeeps have two. The one on the back corner of the head (which I'm going to guess is what you replaced) only provides input to the gauge on the dashboard. The one that sends data to the ECU is down low, on the driver's side of the engine block.

And you're now getting 12 volts or less at the battery. Either the alternator is bad, or your battery cables are toast.

Which temp sensor did you replace?

You also installed a new alternator. They are sometimes bad out of the box.

If the engine was idling, then you weren't testing the battery you were testing the alternator at the battery. The battery is 12 volts, not 14. The alternator puts out 13.9 to 14.5 volts when charging the battery. It is not normal for the voltage to dip that much when you turn on headlights or accessories. Do your test with the voltmeter again, and this time have someone turn on the headlights and blower fan while you watch the voltmeter. My guess is that the new alternator isn't putting out the rated amperage. It's producing 14 volts, but not enough amps to keep up with high current draw. (Not that just the headlights would be considered "high" current draw.)

I'm not scared of Crown parts. My Jeep dealer is the local source for them. They use Crown for parts that are no longer available from the factory. Crown is also the only source for a lot of parts for Hudsons (if any of you are old enough the remember Hudson).

When was your oxygen sensor last replaced?

Factory spec on oil pressure is 13 psi at idle (~ 750 RPM), and 37 to 75 psi above 1600 RPM, at normal operating temperature. All the XJs and MJs I've owned and driven have had warm idle oil presure around 20 to 25 and at 55 to 60 MPH the oil pressure is 50 to 55. The pressures you have now are well within specification, and if you remember them as having been higher I'd say that's VERY unusual. Voltage on mine generally hover around 13.5 -- not that the gauge can be read that accurately, but they're generally "just a tad" below 14. If yours drops to 12 or below when you turn on the lights, I'd say your new alternator is defective. Normal operating temperature on the gauge is always 210 for me, across multiple vehicles.

Somebody -- might have been Pete himself -- had a thread about this awhile ago, describing using white powder to trace the path of the leak. IIRC the source turned out to be the main electrical connector where it comes through the firewall.

Actually, they are exactly what they appear to be. I had an '84 XJ with a trashed push-on connector for the temperature gauge. I found a but that fit the threads, cut off the terminal and soldered on a new ring terminal, and all was good. But we need to know what year vehicle and electrical system this is for. Are we to assume it's for the 90-97 project truck? I haven't read the build thread, so give me a hint -- does it have the '90, Renix-era wiring harness, or has the electrical system been updated to the '97 Chrysler system?

What year?

The link won't open for me, but I don't think JK springs or shocks fit an MJ.

Yes, but there might have been a few owners who actually went back to the dealer when the light came on and had both the O2 sensor and the timer replaced. The timers can be reset, too. The FSM only says to replace it, but search the Internet and there are how-tos that describe resetting it. (I just removed the bulb from my cluster.)

At 14 MPG, that's 36 gallons of fuel. You don't need a 23.5 gallon tank, you need a Jerry can rack. And find out why your gas mileage is so bad.

Absolutely correct, and I skipped over that because I interpreted the opening post as saying that he was going to use the engine from the HO, so it would have the correct flywheel or flexplate.