Eagle

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?

Okay, then. As I wrote above, "If your engine starts but then dies, it sounds like the start bypass circuit is working but the normal RUN circuit has been compromised." That would explain why the previous owner hot-wired the fuel pump, but to fix it you need to trace that circuit to find out where the break is.

You need a wiring diagram to trace it back. By "bipassed" the ballast resistor, I assume you mean you just hot-wired/jumpered it. That will work if the problem is the ballast resistor itself, but your problem is the circuit. The normal path for power to the fuel pump is a circuit that runs through the ballast resistor. There is a true bypass circuit during starting, that skips the entire ballast resistor circuit and sends a full 12 volts to the fuel pump. If your engine starts but then dies, it sounds like the start bypass circuit is working but the normal RUN circuit has been compromised. When the key is in the RUN position, do you have power at the ballast resistor?

Back in the days when all cars had idiot lights and I routinely installed mechanical oil pressure gauges, the gauges usually came with plastic tubing. I scrapped that and used copper.

The actual bolt diameter is also a consideration, above and beyond the throat opening. The factory u-bolts are metric -- 12mm for the XJ and 14mm for the MJ. Just about any replacement you can find will be an SAE size, so you want to get a decent match. A lot of the u-bolts I've seen in the parts chain stores are 7/16", which is even smaller than a 12mm. For the MJ, 14mm is .5512 inches in diameter. 9/16" is .5625 inches, so it's larger than stock. It's a good choice if you can find them, but 1/2" is much more widely available. Personally, I would not hesitate to use new, good quality 1/2" u-bolts under an MJ, even knowing they are slightly smaller than what the factory used. (But slightly over-sized for an XJ -- since I have both, I just standardized.)

No, they won't work. The Dana 35 has a tube diameter of 2-5/8". The Dana 44 has a tube diameter of 2-3/4". The Chrysler 8.25 used 3" tubes. You need u-bolts with a throat dimension of not more than 2-3/4".

Yes, for the '87 thru '90 Renix 4.0 that used 19 pound-per-hour injectors.

You probably know this, but be sure to check the end gap on the piston rings when you assemble the engine. Especially with a very tight fit, this could be important.

If your truck isn't overheating, the auxiliary fan would not turn on. That coolant pressure bottle is like an extension of your radiator. Just as you should not remove the radiator cap when the system is hot, you also do NOT remove that cap when the system is hot. When the system is cold, the coolant level in the plastic bottle should be halfway -- NOT completely full. It's a sealed system, and the coolant needs some space to expand. Aim your thermometer at the left rear corner of the head. Temperature should be between 200 and 215 degrees F.

4.88s

Correct Why not use an aftermarket PRNDL indicator, as Hornbrod suggested?

Last time I bought a replacement for that vacuum harness it cost me $17. Today, we don't replace it -- we lock the front axle in the engaged position and don't worry about it. That little "issue" isn't a $1000 deduct, it's a half hour fix before you sell. I wouldn't sell that truck. You'll never be able to replace it for near what you'll get for it.

If you have an '88 Comanche you have a front axle with a vacuum actuated disconnect. It is possible for the transfer case to be in 4WD and the indicator light to be lit (yes, the "Part Time" light is the 4WD indicator) but if the vacuum disconnect isn't working, you don't really have functional 3WD.

Then he has to find a seal that will fit the right side of his differential housing -- which may or may not be set up to even accept a seal at that location.

Link?

But the Cherokee with the CAD never (to my knowledge) came with CV joints, so I don't think you can find a replacement that's set up for CV joints on the passenger side.