Eagle

As Hornbrod has posted, ALL Comanches (and Cherokees) had catalytic converters when they shipped from the factory.

Yes, I'm sure. I posted the link to the spreadsheet that shows road speeds for various tire sizes and gear ratios. Look it up. Your factory speedometer is only accurate for the tire size that came on the truck. If you increase the tire size significantly without changing the speedometer drive gear, your road speed will be significantly faster than what the speedoemeter says, because the speedometer doesn't know you changed the tires. Assuming your factory tire size was 215/75-15, the jump to a 31x10.50-15 is an increase of approximately 10 percent. That alone would suggest your true speed was 66 MPH. The spreadsheet I compiled is based on actual tire manufacturers' revolutions-per-mile data, which is the most accurate way to correlate road speed to engine RPM. With 215/75-15 tires, 60 MPH in 5th gear with 4.10 gears is 2319 RPM. If I then go to the data block for 31x10.50s, that same RPM falls between 65 and 70 MPH. Interpolating, it looks to me like it would be about 67 MPH. If the speedo is showing 70, your road speed is about 77 to 78 MPH.

Fog lights are supposed to be on with the low beams and off with the high beams. Some states are strict about that, others aren't. Since you are in California, I would expect that they are. The simple way to keep your fog lights legal would be to tap a feed to the input side of your dash switch from the headlight low beam circuit.

I have a 2000 XJ with the 3550, and I have an AX-15 in one of the '88 MJs. There is no comparison. First, the 3550 has a deeper first gear, so if you go off-road that helps your crawl ratio. The 3550 is MUCH smoother shifting, and it's quieter when driving. If you can get it for $500 -- go for it.

Valve seals (which aren't really seals, but deflectors) are very easy to install and don't require removing the head.

Agreed.

If your speedometer read 60, you were going closer to 70.

Instrument cluster ground.

On 35s, a true 65 MPH will only be turning 1995 RPM in 5th gear. That's far, FAR below both the torque and horsepower peaks of the engine. Even in 4th gear it's only 2661 RPM -- still way below where the engine makes usable power. 4.88s will bring that up to 2375 RPM in 5th and 3167 in 4th. Better, but not great. In fact, it'll be just about the same as what you have now with the 32s.

Link to the tire/gear/speed spreadsheet. This is based on actual tire manufacturers' revolutions-per-mile data, so it's more accurate than most of the other calculators you can find on-line. https://spreadsheets.google.com/pub?hl=en&hl=en&key=0AvuGamS7bzt-dHJxYy1QajhuVUFUbUVDUWdiZnVFbmc&output=html

Yes, you will.

Correction: This is THE problem. The 2.5L was never a rocket engine to begin with. Let's face it, it's a conventionally-aspirated 4-cylinder engine trying to push a 3,000+ pound vehicle shaped like a brick. And the '86 version had less power than the Chryco MPFI version. Then you lift it 6 inches and throw 32" tires under it without changing the gear ratio -- what did you expect? Since you have a 5-speed, it's probably safe to assume you have 4.10 gears. With stock tires (for an '86 we'll assume that means 215/75-15), 65 MPH would have had the engine turning at 2512 RPM in 5th gear, or 3349 in 4th. Now we switch to 32s. 2512 RPM is now actually about 74 MPH, so the frictional and aerodynamic drag factors are increased exponentially. And running at 2500 RPM (or even 3350 RPM when you drop to 4th) you are WAAAAY below the torque and horsepower peak of the engine. Your engine was rated (when new) for just 117 HP at 5,000 RPM, and 135 ft-lbs of torque at 3,500 RPM. And for the 2.5L, the torque peak really is a peak -- the 2.5L doesn't have a nice, long, flat torque curve like the 4.0L, it really peaks at 3,500 RPM and falls off sharply above and below that. You unfortunately have unreasonable expectations of what your engine can do.

Since Jim has started a new thread about this engine, I'll close this one to alleviate confusion.

I don't have my FSM handy to look it up, but I don't think that's where #1 should be located. IIRC, the #1 spark plug wire should be at approximately 1:00 or 1:30 when looking at the distributor from the passenger side of the engine.

91 flex plate thought of that too, also thought about orientation but read somewhere if it's on its rite because it will only bolt up 1 way? The flex plate only bolts on one way, but that only addresses orientation/indexing. There's still the fact that a Renix flex plate won't work with an HO CPS and ignition, and an HO flex plate won't work with a Renix CPS and ignition.

Huh? The block casting number will never match the cylinder head casting number. Head casting numbers are 4-digits, blocks are eight digits. Or do you mean make sure they translate to the same year range? Sorry. I meant match for year of manufacture, not that they would be the same number.

I think you indexed the distributor wrong. Spark timing should be set to fire before top dead center. Since the distributor on the 4.0L is not adjustable I don't even know if the timing spec is published, but with the engine at TDC (on the compression stroke) the blade on the rotor should be at or past the turret on the cap.

Swapped in. Find the casting number for the head -- see if it matches the block.

Actually, it went more by time than miles, but 82,500 was when you were supposed to replace the O2 sensor. Reason this sticks with me is the light didn't come on at the same time as a major, or any for that matter, service. Customers would be pissed. And, since the timer was nothing but a timer -- it wasn't a sensor nor was it able to read actual elapsed mileage -- the 82,500 miles was only a vague approximation. The timer sat there, ticking away at a constant rate, whether the engine was idling in traffic, bumbling along at 30 MPH on city streets, or zipping down the highway at 75 MPH. In reality, the O2 sensor might have gone bad long before the light came on, or the light might have come on when the O2 sensor still had a lot of miles left in it. It was one of the dumbest ideas the Jeep engineers ever came up with. Even dumber, the light module wasn't designed to be serviceable -- in addition to replacing the O2 sensor, you were also supposed to replace the timer module. Since then people have figured out how to reset it, and you can find instructions on the Internet, but resetting it was never supported by the factory.

Here's the engine ID info from the 1990 (Renix) Factory Service Manual. This is really the only way to determine when a particular engine was built. The number you posted appears to be the engine build code, NOT the block casting number. Based on that, it appears that you have "decoded" the date correctly, and what you have is indeed an older, Renix engine (or at least block) in an HO vehicle.

Don't misunderstand my point: The Dana Trac-Lok is a clutch-type limited slip differential. While it's the least expensive such unit on the market, it's also what the factory used. I have Trac-Loks in three XJs and one MJ and I have no problems with it for my use. For a street-driven truck, it's a good choice. That said, in generic terms it IS a "posi." Once you go beyond generic descriptions, "posi" is short for "positraction," which is a GM trade name. There has never been a positraction differential for the Jeep Dana 35 axle. I'm all in favor of supporting local businesses -- right up to the point where they show me they don't know what they're talking about. Once they start blowing smoke I'm gone. Non-Jeep related, a couple of years ago I needed some regrading and drainage work done in my yard. I brought in a local site and grading contractor. Small company, owner lives in town, good reputation. He came to the house, we stood in the driveway and I showed him exactly what the problem was and explained what I wanted done. I specified that the new material was to be 3/8" trap rock (broken stone). A few days later I came home to find the work finished. It was ALL wrong. Rather than remove material to grade away from the house (which was what I had asked for), he built the grade up near the house -- thereby creating a building code violation. He didn't use 3/8" broken stone, he used "processed gravel" -- which is a mix of ungraded broken stone and stone dust. And his processed gravel had organics ("weeds") in it, because within two weeks after he was done I had grass and weeds growing in my driveway. And -- what he did failed to alleviate the flooding. I had to have another contractor come in the following year to make other corrections in order to offset what the first guy did. Being a neighbor in no way equals knowing what you're doing.

I apologize up front, but I am already concerned about this shop. They quoted $1,300 with a limited slip. I assume that's a Dana Trac-Lok, which is what the factory used. It's about the least expensive limited slip you can get. But what's this about another $200 for "posi"? "Positraction" was a trade name used by General Motors for their limited slip differentials back in the 1960s. It has come to be used as a generic name for a limited slip, much like "kleenex" has become synonymous with facial tissue, but when you try to distinguish between a Dana Trac-Lok and something else -- there ain't no "Positraction" that I'm aware of for the Dana 35 axle, and never has been. Did they ever give you a satisfactory explanation of what's wrong with your diff? Did they tell you exactly what limited slip differential they're putting in?

Here's an image of the Custom 4x4 tow hook bracket set. It's pretty much a carbon copy of the factory kit. What's not shown here is the factory bumper brackets, which are used with this kit. Which part are you asking about? The following link will show you how it all goes together: http://jeephorizons.com/tech/xj_hook.html

I suspect the oxygen sensor. The clue that jumps out at me is that the backfire occurs after you've had your foot down, and then let off the accelerator. The ECU is supposed to "see" that and reduce the fuel flow to the injectors accordingly, based on the change in oxygen ratio in the exhaust, as reported by the oxygen sensor. When O2 sensors start to get weak, the response time tends to lag. So if you have your foot down (running rich for power) and suddenly let off, the O2 sensor doesn't report the change instantly, so the injectors keep dumping gas into the cylinders. The engine can't burn it all, so some of it goes right out the exhaust. ==> Backfire.

There's a lot to be said for making up your own parts for armor. In addition to the grinder and drill, toss in a Harbor Freight flux-core wire welder. Costs just over $100 and frees you up to do a lot. http://www.harborfreight.com/90-amp-ac-120-volt-flux-cored-welder-61849.html Flux core isn't going to give you the best welds in the world. With practice, it's good enough for a lot of general purpose welding. For critical parts, you use the cheap wire welder to tack your creation together, then take it to a professional and have him lay down the final welds.