Eagle

This is a VERY unfair comparison, because the first photo does not show an undisturbed C101. It shows a rat's nest of loose wires after someone has ripped them out of the C101.

I am suggesting that it might solve some problems if you are having problems, but it won't accomplish anything if you aren't having problems. My own experience clearly demonstrates the wisdom of the adage, "If it ain't broke, don't fix it." I don't see how my experience in any way makes me "fortunate." I wasted $500 on being conned into having the shop perform a "fix" that didn't fix anything. How is that fortunate?

Interestingly enough, although there was a TSB covering removal of the C101 connector that came out around 1989, whether or not it makes any difference is very much random. I bought my 1988 XJ new in January 1988. Soon after I bought it, the dealership was sold. I didn't like the new ownership or the new service manager, so I tried another long-time Jeep dealer that was actually closer to home. On one trip in for something unrelated, the service manager told me about the TSB for the C101 and he strongly suggested that I have it done. He claimed it would make the engine start faster, give me better gas mileage, improve emissions, and cure "early morning drive-off stall." So I had the work done. The shop charged me $500 for it ... and it made ZERO difference in how the vehicle ran. No difference whatsoever. When I later mentioned to the service manager that I was disappointed because I had not seen any of the improvements he predicted, he told me he never said that. The same shop also charged me for an oxygen sensor replacement that was covered by a recall notice. It took me almost a year to get reimbursed for that. Needless to say, I stopped going to that dealership. My '88 MJ still has the C101 and it runs just as well as the XJ.

Seems pretty simple to me. Did it shake at 60 MPH with the old tires? No? Shakes at 60 MPH with the new tires? Yes? That's what we call a "clue." FWIW, tire balance problems (as opposed to true death wobble) seem to almost always start to kick in somewhere between 55 MPH and 60 MPH, and then disappear above 65 MPH. If your shake is in the range, IMHO there's about a 99.87 percent probability that the issue is tire balance.

You need seals for a 1986 2WD Comanche. Why do you even have to ask? http://www.autozone.com/autozone/parts/1986-Jeep-Comanche-2WD/Wheel-Seal-Front/_/N-iixsvZ8oxmo

Just DON'T DO IT. I've towed a much lighter trailer and (stripped) XJ behind my '88 MJ. I on;y did it once, and I won't do it again. As noted, stopping is the problem. But it's a lot more than just brakes. The MJ simply isn't heavy enough. I found the trailer was pushing the tow vehicle all over the road.

The springs may not have been cracked then. I don't think those aftermarket bump stops did you any favors. Where are you in Canada? I have a couple of sets of MJ leaf springs in the garage. There are some cracked leaves, similar to yours. My plan has been to make two "good" springs from the four busted ones. I also have some Wrangler YJ leaves -- I'll see if I can figure out what might work for you. Do you want to get back to stock height and ride, or do want to lift it some while you're doing it? (Please tell me you want stock height!)

No, we can't. If those Timbren bump stops aren't making contact with the axle tube, measure straight up from the top of the axle tube to the underside of the frame rail at the point where the bump stop attaches. Measure both sides. The correct measurement should be 8.2 inches for 2WD or 9.2 inches for 4WD (both plus-or-minus 1/2-inch).

Yes. The ones in your link are for the front. If you are consistently hitting those Timbren bump stops in the rear, do NOT remove them. Your springs are shot and the Timbrens are doing a lot of the work in your rear suspension. What you really need is new springs ... then you could think about stock bump stops.

We just discussed how to measure for stock ride height within the past couple or three weeks. I have to leave for work but I'm sure you can find the discussion thread.

Drain out what's left of the two-year-old fuel, put in 5 or 10 gallons of fresh gasoline, and see what happens.

So the front axle doesn't have a ring gear or a pinion gear and you're wondering why the 4-wheel drive doesn't work?

Correction: He's asking about an XJ. The '90 XJ would have an axle disconnect IF it has a Command-Trac (NP231) transfer case. If it has a full-time (NP242) transfer case it does not have an axle disconnect.

The fuel pump needs to be immersed in gasoline for cooling. My guess is that you cooked the fuel pump. (I hope I'm wrong.)

Mechanically, both engines were developed from the same in-line 6-cylinder predecessor, but they are very different. The original 4.0L had a torque peak of 220 foot-pounds at 2000 RPM in 1987, and then 224 foot-pounds at 2400 RPM for 1988 through 1990. But for the 4.0L the term torque "peak" is misleading, because the torque curve beyond the peak remains almost flat all the way up to about 4000 RPM. On the other hand, for the 2.5L the curve has a very clearly defined peak. For 1986 the 2.5L produced 135 foot-pounds at 3500 RPM, and for 1987 through 1990 it produced 141 foot-pounds at 3250 RPM. "Acceleration" is produced more by torque than by horsepower, so to feel acceleration in the seat of your pants you need to keep the engine running near the torque peak. Here's one torque curve for the 4.0L (This one is for an HO version but it's all I could find). Notice how basically flat it is all the way from 1000 RPM to 5000 RPM. Here's a torque/horsepower chart for the 2.5L engine. Compared to the 4.0L torque curve, note how the torque rises toward the peak and then falls off after the peak, with a very obvious spike right at the peak of 3200 RPM:

Hornbrod gave you the link to the electrical shop manual. The diagram you need is on Page 16.

You can think that but, as most of us have commented, you would be wrong. You can't regain what you never had, and the 2.5L Jeep 4-banger is simply never going to push you back in your seat like a 5-liter Mustang. You can get a little bit of acceleration feel in first and second gear, beyond that acceleration is "gradual," at best. That's just the nature of the beast. The only way to get more feel of acceleration is with MORE gear or smaller tires. You certainly won't get it by changing from 4.56 gears to 3.55s.

So give us a hint -- what was the problem?

^^^ This. The tires you want to run (225/70-16) are exactly the same size as 225/75-15. 3.55 gears were what the factory used with that tire size behind a 4.0L with automatic. You need more RPMs to be able to run a 2.5L at 70 MPH. According to my calculations (which are more accurate than most on-line speed-to-RPM calculators I've seen, with 225/70-16 tires you would get the following at 70 MPH: 3.55 ... 3040 RPM in 4th gear, 2280 RPM in 5th gear 3.73 ... 3203 RPM in 4th gear, 2402 RPM in 5th gear 4.10 ... 3521 RPM in 4th gear, 2640 RPM in 5th gear 4.56 ... 3916 RPM in 4th gear, 2937 RPM in 5th gear In reality, you're fine with the 4.56 gears you have. What too many people forget is that the basic design of the AMC engines (both the 4.0L and the 2.5L, since both are derived from the older 232 cubic inch I-6) dates to long before overdrive transmissions were commonly used. In the 1960s and early 70s, AMC cars came from the factory geared to run approximately 24 MPH per 1000 RPM. That worked out to 2500 RPM at 60 MPH, and 3000 RPM at 72 MPH. And that wasn't "burning the engine up." My brother had a 1970 Gremlin with a 3-speed manual tranny and the 232 c.i.d. engine that went over 300,000 miles. And he used it to win a couple of state autocross championships as well as being a daily driver. So the 4.56 gearing puts you right where you should be for the 2.5L. You could also get by with 4.10s, but I think you would be horribly unhappy with any less gear than 4.10s.

I think a new, high quality 1/2" u-bolt is probably at least as good as a rusty, 25-year-old 14mm u-bolt. As I wrote, I've standardized on 1/2" u-bolts and I'm not even a little bit concerned. Remember, the XJ was available with a heavy-duty tow package and was rated for the same towing capacity as the MJ. I think towing a heavy trailer probably puts more stress on axle u-bolts than anything else we could possibly do.

Looks like there's a diagnostic port to test the relay function. Terminal #6 in diagnostic connector #1. And the fuel pump relay is controlled by ground. With the ignition switch in the RUN position, there should always be power to the input leg of the control side (terminal #86). If you're not getting 12 volts there, the problem is between the relay and the ignition switch. If you ARE getting power there, you should be able to override the relay function by jumpering terminal #85 to a known good ground. Then you can probe the diagnostic connector to see if connecting and disconnecting the ground switches the relay on and off.

There are four wires (or there should be four wires) coming off the fuel pump relay: 14 gauge Yellow -- This comes from the ignition switch and should be hot when the switch is in the RUN position. Terminal #86 14 gauge Red -- This is the one from the fusible link. It should be hot at all times. Terminal #30. 16 gauge Green w/ trace -- this one is the relay ground for the control or "trigger" side of the relay. It grounds into the ECU. It should show hot when the ignition is in the RUN position. Since it goes to ground, you should also be able to test the ground independently. Terminal #85 14 gauge Orange -- this leads to a junction, and then to the fuel pump. This should be hot when the control side is closed. Terminal #87. Keep in mind that the ECU cycles the fuel pump depending on the pressure in the fuel rail. I believe that opens or closes the ground in the ECU.

Look at the link Hornbrod provided. On page 16, it shows that power TO the fuel pump relay comes from a fusible link. Check that fusible link -- if it's blown, you won't have any power to the fuel pump relay.

There is only ONE wire off the relay that goes to the fuel pump. The other heavy wire is power TO the relay. Your first post says you have power to two terminals on the relay, and you say that again here. But you still aren't being clear which two wires have power, and under what conditions, and how you are testing.

You're going the wrong way. With the key in the RUN position, do you have power to the ballast resistor? It sounds from your description like the answer is "No," so there's no point in checking anything downstream from there. You need to follow the circuit back UPSTREAM (toward the battery and power source) until you find where the flow of power has been interrupted. What relay are you referring to? Where is it located? How did you test it?