Eagle

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.

You can (and IMHO should) keep the original steering column. Chrysler switched from a GM Saginaw column to their own in 1995. The Chrysler column and steering wheel have a driver's side air bag. If you want the air bag -- switch. If you don't feel the need for an air bag, there's no reason to change the steering column. Yes. It will fit. But the '96 Cherokee cluster is all electronic, including the speedo. The MJ cluster for '87 used a mechanical speedometer. Cherokees did not have air bags until 1995. Comanches never did. The "work around" is to not change the steering column. Unless you want the air bag, there's no reason to change.

??? Huh? The single keys are double sided, and both sides are identical.

As already stated, two keys were the standard for the early XJs and MJ. It is NOT possible to rekey the ignition or the doors to use one of the original keys. I tried. The first locksmith just said, "Nope, can't be done." Later I talked to a younger locksmith whom I know through other activities. He explained that the ignition used six tumblers ("bits," in locksmith lingo), and the doors used five tumblers. The spacing is different, so it's impossible to make one key that can operate both a six-bit lock cylinder and a five-bit cylinder. Your ignition key should be rectangular (with rounded corners) and the door key should be oval. If you look at the key part closely, you'll see that they are similar, but they are not the same. It is possible to change both the ignition cylinder and the door cylinders to later, Chrysler one-key locks. But I thought I had read that the Chrysler door cylinders don't fit the early doors correctly.

First, going back to a previous post, you have an '89. That's a Renix. The Renix system doesn't throw codes -- at least, not that anyone can read without the very expensive dedicated scan tool that even the old Jeep dealers have thrown away by now. On to your questions: 1. CPS -- Engine would still crank, just no spark. 2. Ignition switch -- strong possibility. 3. Starter solenoid -- that would cause a no crank, but could not cause a random die-out.

CT has liberal gun laws now? Hardly. But, regardless of how difficult it is to believe, California's are worse.

Want to trade weather? I've just gone through three consecutive nights of sub-zero "global warming." It didn't get out of the teens today. Biggest problem about California, though, is the (anti-)gun laws. I couldn't live there.

None of those numbers are considered to be "mismatched." It's common for 4WD vehicles to have one diff in the front and another in the rear. Just within XJs and MJs, you could have (from the factory) a dana 30 in the front and an AMC 20, Dana 35, Dana 44, or Chrysler 8.25 in the rear. Different diffs have different ring gear diameters, so they have different numbers of teeth on the ring gear and on the pinion gear to achieve the "same" ratio. But, due to the different tooth counts, the "same" ration could be 4.09, 4.10, or 4.11. In factory axles, that's why we see some refer to the factory axle used with the 4.0L automatic as 3.45 and some call it a 3.55. Both are correct -- it's just a question of front axle or rear axle. I would like to see what vendor offers 4.09, 4.10 AND 4.11 gears all for the Dana 44. That doesn't make any sense whatsoever.

I have a Truetrac in my '88 MJ. I love it. When I bought it the price was $350, compared to $250 for a Trac-Lok. I had already worn out the clutches on the '88 Cherokee's factory Trac-Lok (they only last 150,000 miles, can you imagine that?), so I liked the idea of no clutches. It works great. That said, at the current prices, I'd go for a Trac-Lok. For the difference in price, I can buy a lot of friction modifier.

A limited slip is what you originally asked about, and IMHO for street use a limited slip is much superior to a locker -- but there is no such thing (that I know of) as a lunchbox limited slip. To convert to limited slip you have to remove and discard your original differential carrier (not the outer case with the axle tubes, the inner differential that contains the spider gears) and replace the whole thing with a new differential unit. This means moving your existing ring gear over to a new carrier, and that means to do it right you have to have the tools and the knowledge to check the setup of the gears. You'll be installing new diff bearings, and new shims to set the backlash between the ring gear and the pinion gear. If you don't know how to do that, it'll cost you to have it done correctly. The advantage to the so-called "lunchbox" lockers is that they just replace the spider gears inside your existing carrier. Because you don't change the diff carrier, you don't need to set up the gears again. But ... it's a locker, with all the performance advantages and disadvantages that carries.

Capsule summary: There are a couple that work differently, but most limited slips use spring-loaded clutches inside the differential to lock the two sides (axle shafts) together. When the tires have no traction, the two axles stay locked together and both rear wheels turn at the same speed. If both wheels have traction, when you go around a corner the tires generate enough torque difference to make the clutches slip, at which point the differential acts like a differential and allows the tires to rotate at different speeds. That's a limited slip -- which is what you originally said you wanted. A locker uses springs and things inside the differential to lock and unlock the two rear axle shafts. Basically, when you're coasting they unlock, and when you apply power they lock. When you run a real locker you have to learn all over again how to turn corners, because you want to go in fast enough that you can let off the power and coast around the turn. Otherwise, you'll be chirping the tires all the way through the turn. It's the opposite of a limited slip -- more power around corners when both rear wheels have traction will NOT unlock a locker -- it'll lock it up tighter.

But most of the fuses in the footwell fuse panel on the MJ are replaced by the fuse panel in the passenger kick panel on the newer XJs, not by the PDC under the hood.

That's not what you wrote above:

I would suggest you get a 2000 XJ wiring diagram and check it out. See what goes through relays and what doesn't. If I understand your plan correctly, you intend to retain the Renix setup, and just reroute some wires to/through the updated PDC. I don't think the OEM Renix setup runs the ECU through a relay, and I doubt it draws much current, so why do you want to run it through a relay?

I think a relay operating a solenoid is redundant, but I would not advocate eliminating it. There must be a reason why both Jeep's engineers and Chrysler's engineers use a relay. But if the basic functions are going to be transferred from the original Renix 4-relay array to the 2000 PDC, that means you'll have a bank or four relays doing nothing. Those could easily be re-purposed for things like headlights, fog lights, auxiliary lights, etc.

The starter relay is, IMHO, redundant, because the starter is actuated by a solenoid. In "the old days," we only had solenoids. In effect, the current setup is like using a relay to operate a relay to operate a device. Bottom line: A relay is only a switch. ANY relay can send power to a solenoid. You are aware that a 2000 Cherokee doesn't have just the fuse panel under the hood, right? There's a second fuse panel in the passenger side footwell, behind the kick panel.