My $.02:
The 87-90 ECU is called "Renix" (a combination of Renault/Bendix). They do not store codes, but are very, very easy to work on and diagnose as long as you know how to read a $5 multimeter. In other words, not too much computer shit to worry about with those years.
Here is some info pasted from another website:
1984-1996
Much in the same way that American automakers had downsized many of their cars in the previous decade, Jeep downsized one of its nameplates, the Cherokee, for 1984.
Prior to this year, the Cherokee moniker was attached to what amounted to a sportier version of Jeep's Wagoneer. Mostly unchanged since its debut in the early 1960s, the Wagoneer was a large, truck-based, four-door wagon with four-wheel drive.
The former Cherokee, introduced as a 1974, shared most everything with the Wagoneer, including dimensions and engine selections. The major differences between the two were that the Cherokee was initially available only as a two-door (with the same wheelbase and length as the Wagoneer) and the Cherokee cost less than the more luxurious Wagoneer. A four-door Cherokee joined the lineup in 1977.
The 1984 Cherokee shared nothing with its predecessor, save its name. A shorter wheel- base (over 7 inches less than the "old" model, at 101.4 inches) and overall length (at 165.3 inches, a decrease of 21 inches) combined with a much lighter weight of around 3,100 pounds (over 1,000 pounds less than before) went a long way toward better fuel mileage and easier maneuverability, on-road or off. Two-door and four-door body styles were offered.
Styling for the trim Cherokee was chiseled and taut, with muscular wheel well flares and a tall greenhouse that afforded good visibility for driver and passengers alike. The interior continued this theme with a likewise simple dash and control layout. Seating capacity was listed as five, though it was tight for three adults to ride in the backseat.
Trim levels were comprised of the base Cherokee, more luxurious Pioneer and the sporty Chief. The Pioneer featured carpeting, additional instrument panel gauges, full center console and a rear window wiper/washer. The Chief was the most stylin' of the trio with blackout exterior trim, hood striping and white-lettered tires.
Motive force came in the form of either four- or six-cylinder power. The 2.5-liter four banger inhaled its fuel and air through a one-barrel carburetor and made 105 horsepower. The optional, 2.8-liter, two-barrel V6 (which was actually supplied by Chevrolet) produced but 115 horses. Although these powerplants were adequate, serious thrust for the Cherokee was a still a few years away. There were three transmission choices for the V6: a standard four-speed manual, optional five-speed manual and optional three-speed automatic. The four-cylinder was limited to the four-speed manual as its gearbox.
Considered by many as the leader in the four-wheel-drive (4WD) vehicle segment, Jeep offered not one but two 4WD systems for the Cherokee. "Command-Trac" was a part-time, shift-on-the-fly unit and the "Selec-Trac" system allowed the option of full-time 4WD operation. A "Quadra-Link" front suspension design (which featured a solid axle suspended by coil springs and four links) contributed to the Cherokee's quickly acquired reputation for off-road prowess.
The new Cherokee was well received by the motoring press and the buying public alike, with nearly 78,000 Cherokees sold in its first year.
1985 brought the Laredo trim level to the Cherokee family. Standard on the Laredo were most of the features of the Pioneer with upgrades such as plusher interior materials, pinstripes, alloy wheels and chrome grille treatment.
Changes to the Cherokee in general included the addition of front headrests and passenger assist handles (for easier ingress and egress as well as something to hold on to when the driver went hog wild off-road). Two-wheel-drive versions were now offered for those who didn't need the capabilities of four-wheel drive. A few new options debuted as well, such as keyless entry and a Renault-sourced, four-cylinder, turbodiesel engine.
Two major hardware upgrades were hot topics for the Cherokee in 1986. A redesigned and more powerful four-cylinder engine was now standard. The replacement of the stone-age carburetor with fuel injection helped the 2.5-liter mill pump out a respectable 117 horsepower, an increase of 12 horses over the previous motor. Smoother operation and easier starting were other benefits of the more modern induction setup.
Geared toward serious off-road enthusiasts was a new "Off-Highway Vehicle" package that included heavy-duty suspension components, bigger (225/75/15) tires, skid plates, tow hooks, a 4:10 rear axle ratio (to help in climbing up steep grades and slogging through mud) and higher ground clearance.
Serious power became an option in 1987 when Jeep dumped the 2.8 V6 and put a stout, 4.0-liter, inline six-cylinder engine of Jeep's design on the option list. Kicking out 177 horsepower, the new "Power-Tech Six" could catapult the Cherokee from rest to 60 mph in around 9 seconds -- pretty quick, especially for an SUV. Another benefit of the increased muscle was more towing capacity -- rated at 5,000 pounds. The 2.5-liter, four-cylinder was tweaked for an additional four horsepower, for a total of 121 ponies.
A new, electronically controlled, four-speed automatic transmission replaced the former three-cog unit. The new automatic also offered selectable shift modes: Power (which provided better performance through higher-rpm upshifts and quicker downshifts) and Comfort (which was more relaxed and economical in operation). And the primitive, four-speed manual was history, leaving the five-speed for shift-it-yourselfers.
Cosmetically, the Cherokee received the option of two-tone paint. Inside the cabin were found new door trim panels with stowage bins.
A new, loaded-up Limited four-door model debuted halfway through the model year. Just about every luxury, performance and convenience feature was standard on the new top dog Cherokee. The Limited came with the powerful, 4.0-liter inline six teamed with Selec-Trac and could be identified by its color-keyed bumpers, gold wheels and gold pinstripes. Leather seats, power everything, keyless entry and an eight-speaker sound system were additional highlights of the Limited's lengthy standard equipment list.
Other models received minor changes, such as new plaid seats in the Laredo and revised blackout trim on the Chief.
1988 saw the addition of a Limited two-door and the subtraction of the unpopular turbodiesel engine option. Sharp-eyed enthusiasts could discern an '88 by a new eight-slot grille that replaced the former 10-slot unit.
Laredo models received new chrome trim as well as lower bodyside cladding. In an effort to offer a Cherokee for everyone (and leave no part of the potential market uncovered), a Sport two-door model was offered. The Sport added alloy wheels and special graphics to the plain-Jane Cherokee, allowing those on a budget to drive a sharp rig without breaking the bank.
The availability (on models equipped with the 4.0-liter engine, automatic transmission and Selec-Trac) of a four-wheel, antilock braking system (ABS) was the big news for the 1989 Cherokee. Jeep's ABS operated regardless of whether the Cherokee was in 2WD or 4WD (unlike some competitors who offered either only rear-wheel ABS or four-wheel ABS that wouldn't function when the vehicle was in 4WD).
Other functional upgrades for 1989 included two former options that were made standard. Base models received power steering and all Cherokees swapped their former 13.5-gallon fuel tank for a 20-gallon unit.
Changes were few for Jeep's most popular model for 1990. Safety was improved through the fitment of three-point seatbelts for all outboard occupants. And a new overhead console on the Limited featured a compass, outside thermometer and storage compartments for a garage door control and sunglasses.
Power for both the four- and the six-cylinder engines was boosted for 1991. A new, multi-point fuel-injection system helped the four-banger squeeze out 130 horsepower — an increase of nine horses over the 1990 model. And the big six now cranked out 190 horsepower, bringing the zero to 60 mph time of the Cherokee down to under nine seconds.
Trim levels were shuffled about; the Pioneer was dropped, a new Briarwood debuted, (identified by its fake woodgrain trim on the bodysides) and a four-door Sport model joined the two-door Sport.
Making life easier for the owner of a '91 Cherokee were new double-sided keys, highlighted underhood service points and an optional illuminated entry system.
1992 saw carpeting added to the standard features of the base Cherokee. And Laredo four-doors could now be fitted with (optional) leather seating, just like the fancier Limited. Other than this, not much else changed for the Cherokee this year.
The Cherokee line was simplified for 1993, as the previous five trim levels gave way to just three; base, Sport and the new Country. The Country featured champagne-colored lower body, fender flares and bumpers as well as most of the luxury features of the defunct Limited. And Sport models were updated with a two-tone treatment that featured black on the lower body sides.
A long-life, stainless steel exhaust system was fitted to all models, helping to lower ownership costs.
Safety refinements were added for 1994. Side-impact beams were now found in the doors, the roof was beefed up for more crush resistance and a center, high-mounted stoplight sat atop the liftgate. Air conditioning now used CFC-free refrigerant.
For those who didn't like the champagne (the color, not the libation) of the year before, the Country was now available with silver as the secondary color. And in an effort to make the base model sound more appealing, the entry-level Cherokee now had the "SE" moniker added to its name.
In spite of looking very much like the 1984 version, the Cherokee continued to be popular among those looking for a manageable (both in size and cost) and capable SUV. 1995 brought a few notable changes, a driver's side airbag and the availability of an automatic (albeit just a three-speed) transmission for the four-cylinder SE. Sport and Country models continued with the 4.0-liter, six-cylinder engine hooked up to either a five-speed manual or four-speed automatic gearbox. A few new colors, such as Moss Green and Aqua Pearl, completed the changes for this year.
Minor refinements continued for the Cherokee in 1996. Both the four- and six-cylinder engines were tweaked to run smoother and quieter. The inline six now produced its power at lower rpm, making it more responsive whether accelerating from a light or towing a trailer up a steep grade.
Safety and reliability were both enhanced this year. An automatic transmission/brake pedal interlock reduced the chance of an accident by requiring the driver to apply the brake when moving the gear selector out of Park. The electrical system was upgraded via a heavy-duty alternator and battery. And the engine received a stiffer block, new aluminum pistons and a new powertrain control module.
In addition to the aforementioned improvements, some new colors, such as Bright Jade and Stone White, helped extend the appeal of the Cherokee, now in its 13th model year.
1997-2001
Fourteen years after it debuted, the Cherokee finally received a facelift, well, actually quite a bit more than a facelift. The $215 million update occurred in 1997 when the front and rear ends were smoothed out, the interior was updated and noise, vibration and harshness (NVH) levels were reduced.
Although one had to look close to pick off a '97 versus an older Cherokee, a more cohesive appearance was achieved via softened corners at the nose and tail and with wheelwell flares that blended into the bumper ends. The front vent windows were dropped for a cleaner look and lessened wind noise, and larger side-view mirrors, new bodyside moldings, new wheels, optional deep-tint glass and a center high-mounted stop lamp completed the changes outside.
Inside, change was much more apparent, as the more modern cabin featured several key improvements in ergonomics, safety and style. A new dash (now with a passenger airbag), revised gauges and a new center stack with easier to use controls for the stereo (now available with both cassette and CD players) and climate control system sported a cleaner design with fewer pieces, which decreased the likelihood of squeaks and rattles. Other interior refinements included new door panels, lighted power mirror and window switches, a trip computer for the overhead console and a new center console that boasted integrated cupholders.
In an effort to improve build quality, Jeep made changes to the plant that made the body panels, using new or reconditioned stamping dies and tighter tolerances. More testing, including all electrical functions and increased use of robotic paint sprayers were employed, as well.
Having made extensive engine refinements in 1996, Jeep left well enough alone, but did improve the electrical system via upgraded connectors and a decreased amount of wiring.
For 1998 trim levels were juggled. The Limited returned to replace the Country as the top-of-the-line Cherokee, and the Classic debuted, slotted between the Sport and the Limited. The Classic added color-keyed bumpers and moldings, a roof rack, air conditioning, power mirrors and alloy wheels to the Sport. Three new colors, Chili Pepper Red, Deep Amethyst and Emerald Green, joined the palette.
Soldiering on into 1999, the Cherokee line continued with minor changes. The Sport model now had color-keyed bumpers and grille, a Sentry Key anti-theft system debuted, heated front seats became optional on the Limited, and engine efficiency was improved via revised electronics and a new exhaust catalyst.
The 2000 Cherokee got a more refined version of the 4.0-liter inline six. Introduced the previous year in the Grand Cherokee, the revamped engine ran quieter and cleaner (it now met Low Emission Vehicle standards) than the previous iteration. A new five-speed manual gearbox with improved shift quality was mated to the new six in SE (if the six was ordered) and Sport models, and a four-speed automatic was standard on Cherokee Classic and Limited.
The Limited traded its monochromatic appearance for a flashier appearance this year. Chrome highlights on the grille, headlight bezels and rear license plate brow along with silver alloy wheels served to further distinguish the Limited from the other Cherokees.
Lastly, some new colors debuted, including Patriot Blue and Silverstone Pearls.
The last year for the Cherokee, 2001, would pass without much fanfare. The 2.5-liter four-cylinder engine was finally buried, child seat tether anchors debuted, and Steel Blue replaced Desert Sand on the color chart.
For what its worth, the D35 axle is just fine. I dont wheel hardcore, but I tow my 3500 lb. boat, and do a lot of offroad hunting and fishing type shit with it. I don't have lockers, but I did put in a posi. And I'm running 31's. I love the new bodystyles myself, but I've done a few mods to my 89 to make it more comfortable. I swapped in a console off a 97+ cherokee, got some seats out of a grand cherokee, etc. That way I have the creature comforts of a newer rig, but the advantage of the Renix ECU. Plus, you can pick the Renix year rigs up for cheap and have money to do some nice mods.
I'm also a full time student @ UF, so I need something reliable, easy on the budget, fun to play around with, and most importantly, cheap to mod...
