Eagle

Even if you don't machine the block, before reassembly you should lightly hone the cylinder walls. That will clean up any light surface rust that might form, as well as prepare the walls so the new rings will seat.

How are your motor mounts? A broken motor mount would possibly allow the engine to twist enough that the fan hits the shroud.

All years of the XJ had rear sway bars, except that Jeep didn't use it on the XJs with the optional Up Country (off-road) suspension. I don't think it can be adapted to the MJ -- and it's so skinny I think it would be worthless anyway. Monroe makes the Load Leveler shocks, but there isn't one listed for the MJ. This was discussed here awhile back. We pretty much decided that there's no listing because adding load carrying capacity would have the effect of defeating the rear height-sensing proportioning valve. But Monroe does make one that's the right length and end fittings to use on an MJ -- you'll have to go to the Monroe web site and surf through the dimensional listings section to find it.

Yes. Yes. The lowest temperature thermostat you can get away with is a 180-degree. With the 160, the sensor that tells the ECU when to switch from open loop (warm-up) mode to closed loop (normal run) mode never tells the ECU to switch modes. In open loop mode, the air-fuel mix is basically not adjusted by input from the various sensors, it's based on a pre-programmed fuel "map."

The hood is different but I don't think they changed the header panel until 1990. And the '86 hood could probably be modified to fit an '88. The basic hood is the same, it's the latches that changed. Gauge cluster could be made to work, but the '88 used the nylon push-on speedo cable attachment, and the '86 used a metal tab and retainer screw.

My '87 was bought used and came with a factory roll bar and factory off-road lights. The lights were KC somethings -- "DaLiter," "HiLiter," i don't know what the name was but awile back I could find them on the KC web site. Now I can't -- they were rectangular, I think about 6" x 9", not the round lights we see on the KC site today. I refer to them in the past tense because there were horribly rusted, so I chopped 'em off and tossed them. Every MJ I've seen with a factory roll bar has had the same lights, so I'm fairly certain they WERE a factory option.

K-C Da-Liters, IIRC.

CPS

I believe it should work as a standalone. My reason for thining that is that the Mopar Performance Catalog used to offer (and perhaps still does, but these days it's only on-line and I'm old enough that I love thumbing through paper catalogs) an MPFI conversion for the carbureted 4.2L YJs. That conversion was essentially the EFI and underhood wiring harness from a '95 YJ. If it works for the 4.0L, it should work for the 2.5L.

I disagree. The gain will be worthwhile. The throttle body injected version produced 117 horsepower at 5,000 RPM and 135 foot-pounds of torque at 3,500 RPM when it was introduced in the 1986 model year. This was raised to 121 horsepower at 5,250 RPM and 141 foot-pounds of torque at 3,250 RPM for model years 1987 through 1990. The final, multi-port injected version produced 130 horsepower at 5,250 RPM and 150 foot-pounds of torque at 3,250 RPM. If you get the system from a '97 - '00 Cherokee, you'll also get OBD-II, which will allow using a hand-held scanner to read trouble codes.

Firewall part of the project? To go from a '91 to an '01 there's nothing to change about the firewall. Use the cross member that belongs with the transmission and transfer case you'll be using.

Any 1991 or newer Jeep YJ, TJ, XJ or MJ. Chrysler changed from throttle body to multi-port on the 2.5L in 1991. But it's also a Chrysler ignition, so you will need a new ECU and under-hood wiring harness.

VERY bad idea.

The symptoms sound like CPS. That's kind of what my '88 XJ did the second time it wanted a new CPS. The first time it gave no warning at all (or I was just lucky). That time I drove it home, parked in front of the garage, and the next morning it wouldn't start.

You can run 31x10.50-15s on a stock MJ with no lift. I'm running 31s on my stock 1988 XJ with no lift, and the MJ has larger wheel wells in the rear.

Here's how to test it: Renix CPS Testing and Adjusting Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark. Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad. The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark. Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected. You should get a reading of .5 AC volts. If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer. Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off. A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8” from the stock 5/16”, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts. Revised 01-26-2013 The problem with the ohms test (which is what the FSM calls for) is that you're supposed to check the resistance "at normal operating temperature." How are we supposed to get the engine (or the CPS) up to normal operating temperature if it won't start? And heat affects resistance, so it's not like we can pretend it doesn't matter.

Year? Engine? Could be CPS. Could be coil. Could be ignition module. Could be ECU. Could be wiring (especially if you have the C101 connector on the firewall) What have you tested so far, and how?

As the owner of both an '88 XJ (bought new) and an '88 MJ (bought used) I have to take issue with the statement that 88 is a bad year for electrical bugs. It's no worse than '87 or '89 or '90 -- you just have to understand the Renix system. And you have to remember that a 1988 anything is now a 26-year old vehicle. You have to expect that there will be some corrosion-related problems and simply be prepared to deal with them. The other thing is that he may think it needs five or six tries to start, but he may not be cranking it long enough. It's a characteristic of the Renix system that it has to crank over several times for the various components to synch. Even new, they never started with a touch of the key, like some older and some newer vehicles do. It's even worse if the driver doesn't wait for the fuel pump to build pressure before trying to start it. Just jump in and turn they key? It's NOT going to fire right up. No, I would not say it's a deal breaker. If it starts and runs, anything causing long starts can be addressed. Looks like a nice truck -- if you want a shortbed, grab it. (If the price is right.) How did he get a tow mirror on the driver's door only? Those came in pairs.

Just the difference in distance traveled by the front wheels vs the back wheels amounts to more than a couple of tenths of one percent, which is why we're not supposed to run part-time 4WD on dry pavement. On snowy days, I have to use 4WD to get up my driveway and out onto the street. Once I make the turn onto the street and get straightened out, I pull over to the shoulder and shift out of 4WD. Just in the portion of the turn that's on the plowed road until I stop I can feel the 4WD lurching and jumping due to binding. Tire size is deceiving. Most of the tire size calculators only give the unloaded dimensions of the tires, but what really counts is how many revolutions a particular tire turns in a mile. That's a function of both size, and sidewall stiffness. Way back when I made up my gearing charts, many of the tire companies published revolutions per mile as part of their specifications. I found, as an example, that a Cooper Discoverer in a P235/75-15 turned more revolutions per mile than the "same" tire in an LT235/75-15. The reason is that the LTs had stiffer sidewalls, so the axle stayed a bit higher off the road at the same load, resulting in a higher static radius. To be accurate, we really need to be comparing based on revolutions per mile, or (if that's not available) static radius. Cooper's web site no longer gives us that information. B. F. Goodrich still does: http://www.bfgoodrichtires.com/tire-selector/category/off-road-tires/all-terrain-t-a-ko/tire-details#techspecs

Really? Isn't a question? What else does the :dunno: signify?

Correct. Also available (also as an option) on XJs. And XJ or MJ that has that should also have a front skid plate and a gas tank skid.

I understand that you wrote 2% ... which is why I pointed out that your difference is greater than the factory difference by a factor of ten. The way you thanked me for the math lesson, I interpreted that to mean your 2% was a math error and that you had dropped a decimal point. And I suggest you save the attitude for some other forum. I'm here to try to help people. If you don't want help, then don't ask questions.

Not a math lesson. The difference between the mismatched tire sizes and mismatched axle rations you proposed probably would be at least 2 percent (not 0.2 percent), and very possibly 3 percent or more. Since the ratio differences I posted are all basically factory setups, they are considered functionally equal and won't offer any problems. But you're talking about an overall difference in ratios that's ten times or more greater than "functionally equal." I just don't know how that would work out. I think it would be okay in loose stuff off-road, but here in the northeast some of the little wheeling we have left runs over granite bedrock outcrops, and mismatched ratios on exposed (grippy) granite would probably not bode well for the drive train.

Top photo I think is the connector to the aux fan sensor in the radiator tank. The relay in the third photo is the relay for the aux fan. I think one of the connectors in the last photo is for the windshield washer pump. Not sure on the other two.

I think 2% may be stretching it a bit. The difference between 3.54 and 3.55 is 0.3% The difference between 3.07 and 3.08 is 0.3% The difference between 4.10 and 4.11 is 0.2% As long as you only use the 4WD on soft ground, sand, mud, or snow and ice, you won't have any breakage problems. Dunno if it might result in some unpredictable handling.