Eagle

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.

This is the first time I have ever encountered a recommendation to wear ear plugs when welding. What's the reason for that? What kind of plugs -- are the cheap foam rubber ones I use under my shooting earmuffs adequate>

Chrysler used to sell a kit for converting the carburetted 4.2L Wranglers to electronic fuel injection. The kit was basically the complete engine room harness from a '94 Wrangler 4.0L. All the engine sensors are different, the ECU is different and mounts in a different location. I have not done the conversion, but basically you are scrapping everything that's associated with your engine and computer, and you're keeping the wiring that runs things like horn, headlights, brake & tail lights, and hazard flashers. The CPS for the HO operates on a different principle than the Renix, so in addition to replacing the wiring you will have to replace the CPS.

https://www.autozone.com/fuel-delivery/fuel-tank/spectra-premium-fuel-tank/163611_127816_0_7348_40163 14 x 18 is 252 miles. That should get you to a gas station. Even if you only use 14 gallons, that's still 196 miles. But 14 MPG is pretty awful for an MJ. Maybe it needs a new oxygen sensor? It should get closer to 20.

That's correct. AMC did the same thing with the XJ -- the early ones had either a 20-gallon tank or a 12-gallon tank. They were the same tank externally, the smaller one was just set up to accept less gas. They did it because the most base of the base models had such small tires that a full 20 gallons of gas put them over their rated load!

Take the bolt you have to Lowe's to match the thread. They probably won't have a grade 8 replacement (or whatever the metric equivalent is of grade 8), so you may have to go to Fastenall or on-line to find the right one. Use a helicoil to repair the stripped-out thread to the correct size.

It doesn't fit.

Try this: http://www.lunghd.com/Downloads_and_Links/CPS-87-90-update.pdf Note that this TSB is intended for use with a replacement harness that was available from the Jeep factory, so it has a rubber grommet that fits the 1/2-inch hole to seal it against water intrusion. If you're rolling your own harness, before you start drilling take a couple of minutes to figure out how you're going to seal a hole through the firewall (letting the outside inside), and size the hole accordingly.

You have a shortbed? The tank is 18 gallons. There was only one size tank for the shortbeds. Long bed could be 16 or 23.5 gallons. As others have commented, the tank from the longbeds is too long to fit into the shortbed chassis. What kind of range are you looking for? My '88 was good for 19 MPG in general, mixed driving. Figuring 16 gallons usable, that gives a range of 304 miles. I can't drive 300 miles in an MJ without stopping.

The actual response may be flaky, but look at the numbers. 9 + 5 = 14, 14 + 5 = 19. Equal sweep for equal numeric values. Linear. Then look at the temperature gauge. There's no way you can interpolate accurately on the temp gauge, but the oil pressure gauge is also calibrated on a linear scale.

"Car"? Go to your room -- no supper for you tonight!