Eagle

i learned the speedin issue from my dad when he had a cop gun him before, could my MJ bein stock hight with 235/75/R15s cause it to do 5 over or is that the speedo off from 27 years of never bein touched? Vehicle height has nothing to do with it. Your speedometer is driven by a gear that's turned by the output shaft of the transfer case (or transmission, if you have 2WD). The number of teeth on the speedometer drive gear has to be matched to the tire size and rear axle gear ratio to calibrate the speedometer. It doesn't really have any idea how fast you're going -- it's only reading driveshaft revolutions. So ... put on larger tires, and the vehicle travels farther for each revolution. That means you're going faster than the speedometer thinks you're going. The difference between 225/75-15s and 235/75-15s isn't much. It's about 1 percent. Call it 2 percent to be safe, and that translates to traveling 2 MPH faster than you think at 100 MPH, and 1 MPH faster at 50 MPH.

Shifting at 2200 RPM is lugging it? Not hardly. With the automatic and stock tires, 2200 RPM is about 68 MPH in overdrive. I don't think comes anywhere near ANY definition of "lugging it."

Correct. The change to the AX-15 was a mid-year change in the 1989 model run. Around the same time was when the C101 firewall wiring harness connector went away.

I beg to differ with you. There is NO American production in-line six cylinder that's more bulletproof than the AMC six that eventually morphed into the 4.0L Jeep engine. Never has been one more bulletproof, and in all probability never will be simply because today everything is "optimized," to the point that there's virtually no reserve strength to provide that "bulletproof-ness" we used to take for granted when I was young and thought I was immortal. Back "in the day" (and I lived in the day when the slant six had its reputation), when everyone else was running Offenhauser engines at Indy, there was one racer who came year after year with a modified I-6 street engine. His name was Barney Navarro, and the engine was NOT a Dodge slant six. It was the AMC (the 232 version, I believe). When I was in the Army I spent a year stationed at Edgewood Arsenal in Maryland. At the time I was driving a Rambler American with the smallest available version of the engine -- 199 cubic inches. One of my good buddies had a Dodge Dart with the famous slant six, and he made the mistake of challenging me to a drag race. So, late one night, we snuck off to a back road in a remote corner of the post where we hoped the MPs didn't patrol regularly, put out a couple of friends as starter and finish line judge, and we duked it out. Turns out we didn't need the finish line judge, because the race wasn't even close. I stomped him. And this wasn't even with the "hot" version of the AMC engine. My little 199 only had a single-barrel carburetor. The more famous 232 had a 2-barrel, and was a LOT faster. I can't imagine putting a slant six in an XJ or MJ. Sacrilege. (Not to mention a horrible waste of time, energy and money.)

No he's not. It's a Renix, not an HO. I have always shifted at 2200 RPM. My '88 XJ (287,000 miles) still gets 20 MPG, and the '88 MJ (125,000 miles) gets 18 to 19 MPG.

A bad or failing oxygen sensor results in poor fuel mileage because the engine is always running rich. Same thing can happen if you run a cold (or no) thermostat, or if the coolant sensor (the one on the side of the block, that sends data to the ECU) is bad.

I was in an Advanced Auto a couple of hours ago and I saw a set of body-side tailgate hinges in the "HELP!" aisle that looked like they could be adapted to work. They were for a Chevy. There are probably others listed in the catalog.

"Turning over" and "cranking" are the same thing -- they refer to the starter motor making the engine rotate. If you mean it started, then you would say it "started." If you mean it coughed and tried to start, but wouldn't, you would say something like it "fired but wouldn't catch and run." It's really difficult to diagnose by remote control when standard terminology isn't used. If you now have a running MJ, good.

Stock 15x7 rims have 5-1/4" backspacing, and are the optimum setup (on stock axles). An 8" rim is 1 inch wider (duh!), so to sit in the same place the wheels would need to have 6-1/4" backspacing. Now take an axle that's 3 inches wider, and that adds 1-1/2" on each side. So to pull the tires back to the stock location, the wheels would now need 6-1/4 + 1/1-2 = 7-3/4" backspacing. If such a critter existed (which I'm sure it doesn't), it would have so much offset that it would eat up wheel bearings due to eccentric loading, and I suspect steering would be rather ... unusual.

We need to see the back face of the circuit board, the part that's against your hand. That's where the potentiometer is located.

"Fits many models" is not much of a description. If it's for full-size trucks, there's no way it could fit in a Comanche (or Ranger or S-10). Aside from that, it's ugly, and it's not a roll bar. It's a show bar. No structural integrity whatsoever.

I would opt for a '94. No air bag. Two problems eliminated. The difference between a '94, '95 and '96 is going to be more a question of what you can find -- they are ALL pretty old by most people's standards.

We have to see the back of the tach circuit board to tell if it has the potentiometer. Based on the design of the speedo dial, I suspect you have the early style cluster, which does not have the potentiometer.

3" or 4" lift on the front with the rear at stock height will look ridiculous. That's my opion. I agree completely. It will also make it handle atrociously.

There should be no adjustment needed when using a 4-cylinder tach in a 4-cylinder vehicle. Even if the tach came from a 6-cylinder, it wouldn't be that far off. The tach counts ignition pulses. The 4-banger has 2 pulses per revolution, the 6-cylinder has three. So let's say your engine idles at 1000 RPM (it doesn't, but it's simpler to visualize.) A 4-cylinder will then generate 2,000 pulses for 1,000 revolutions. A 6-cylinder will generate 3,000 pulses for those same 1,000 revolutions. So if a 6-cylinder tach is calibrated to read "1,000" when it sees 3,000 pulses, stick it in a 4-cylinder where it sees only 2,000 pulses and it'll read "666" RPM. Check the rear of your tach to see if it has the calibration potentiometer. Even if it does, it may not have that much adjustment in it. I suspect your "new" tachmoeter may be defective.

The Renix system controls both ignition (which a diesel doesn't have) and injection. The injection is calibrated to maintain an optimum air/fuel mixture for gasoline, in a 4.0 liter gasoline engine. Basically, regardless of whether it's a Renix system or a newer Chrysler system, none of the engine controls will be usable for a diesel conversion. You will have to get the injection and controls with the engine, and figure out for yourself how to integrate it into the chassis wiring harness. Not even the tachometer will work, since the Jeep tach operates off the ignition signal, and with a diesel there is no ignition.

Remember that the Renix system uses a different flywheel and CPS than the Chrysler system. The flywheel and CPS MUST match up with the vehicle's electronics.

A ZJ 4.0L engine will bolt into an MJ just fine. BUT ... The question is about using it in an '88 MJ. The '88 used the AMC/Renault Renix injection/ignition system. That went from 1987 through 1990. Chrysler introduced their own injection/ignition system in 1991, and that's the same system that was used when they introduced the ZJ in 1993. So, to use a ZJ engine as it sits, with the ZJ ignition and injection, will require significant rewiring. If you use the ZJ engine as a short block, or even a long block, and swap over the electronics and injection controls from the old engine, then you can drop the engine into a Renix MJ.

XJs and MJs are what we do here. DO NOT drop your cross member in an MJ.

Not just the air conditioning. All the flapper doors that control air flow for both heat and a/c are operated by vacuum. Yes, you NEED to connect those vacuum lines.

Modern automobiles NEED a thermostat to run properly. Many people simply don't understand that the purpose of the thermostat is to keep the temperature UP, not down. A properly-functioning radiator and cooling system are capable of keeping the temperature well below the temperature needed for optimum combustion -- in fact, often below the minimum temperature for the electronics to switch over to to closed loop operation, meaning the system is reading and reacting to all sensor inputs. For the Renix-vintage Jeeps, that switch-over takes place at somewhere between 170 and 180 degrees F (I used to know more exactly, but I haven't thought about it for a long time). Removing the thermostat could have you running in open loop mode all the time. The vehicle will run ... but it will be always running on a pre-mapped air/fuel curve that's far richer than optimum for an engine at normal operating temperature, and the fuel mileage will suck. Removing the thermostat is NOT a fix -- it's a temporary bandaid that just masks the symptoms of an underlying problem.

Oxygen sensor?

I burp mine, and I learned how to do it from a racing buddy who was a Jeep shop foreman and service manager when my '88 was bought new. I do it so I won't have to remember to check the coolant level later, but it's not a big deal and I'm sure most shops don't (didn't) do it. Back to your original post and overheating. You may still overheat after replacing the coolant bottle and cap. If your truck doesn't have a fairly recent radiator, it's probably clogged and not doing a lot of cooling. You reported that there was no thermostat -- people typically remove the thermostat because they think that's a "cure" for overheating. It's not.

That's interesting, considering that they didn't use the AX-15 in either 2000 or 2001.

Fill it (to the halfway mark, as indicated), then drive it. Check it after it cools down, and add coolant as necessary.