Eagle

The purpose for removing the fuse for the TCU is to determine whether the problem is mechanical (the transmission) or electrical (the TCU, or one or more of the solenoids). If he doesn't run this test, we'll be guessing forever.

Is the cooling system filled properly, and the thermostat opening properly?

Remove the bracket from the truck. Remove the castle nut. Place the bracket over a large socket, with the cut-off stud centered on the socket. Smack top of stud sharply with a large (heavy) hammer.

You're new here, so a little background. The XJ (Cherokee) has a distribution block in front, below the master cylinder, that also functions as a proportioning valve. The MJ has a similar looking distribution block under the master cylinder, but it is NOT a proportioning valve. The proportioning in the MJ is handled by the load/height sensing valve mounted to the left side of the frame, above the rear axle. Where things get more complicated is that the MJ system has two hard lines from the front to the back. One of them, the one that comes out of the "nose" of the distribution block, is for normal operation. It feeds brake fluid into the rear height sensing valve, so the amount of rear braking is proportional to the amount of load in the bed. But, if the front brakes fail, that would leave you with reduced (proportioned) braking at the rear wheels. So they built in a bypass circuit that opens up only if the front brakes fail, and bypasses the height sensing valve to send full pressure to the rear brakes. No, the rear height sensing valve is not available. Yes, it can be bypassed, and you can find instructions on doing that on this forum. Here's why you may not want to do that: Why do they proportion the braking to the rear? Because a pickup truck, when empty, has very little weight over the rear axle and wheels. That means the rear brakes would lock up long before the front brakes, especially when the bed is empty. Premature lockup of the rear brakes causes spin-outs. So they proportion the rear braking as a safety feature, to reduce the likelihood of spin-outs. I had to delete the rear height sensing valve on one of mine, because it exploded in a panic stop situation. So I did the bypass/elimination. Guess what? My rear brakes lock up early. In my case, that's not too bad because I'm old enough that I grew up and started driving long before there were such things as proportioning valves. I got my driver's license in 1960. The first vehicle I bought with a proportioning valve was my '88 Cherokee. By that time I had 28 years and almost a million miles of driving behind me, so my right foot expects the rear brakes to lock up. I can deal with it. You younger guys, who have probably never had to deal with that, probably should think seriously about intentionally creating a situation that invites premature rear wheel lock-up. It's better to repair the brakes and keep them operating the way they were designed.

You're still running the Renix system? Stock injectors are 19 lb. I'd say 24 pound is too much, but you might be able to dial them in with an adjustable MAP sensor.

We do need more information, but you still don't understand how the AW-4 works. Either that, or you're not explaining it correctly. Here's the manual shift diagnosis procedure from the FSM for the AW-4:

Never heard that one before. I like it. Too true!

There can be many reasons for a low brake peddle. The height sensing valve may be one of them. Deciding to eliminate the height sensing valve (which serves an important purpose) before knowing what the problem is is not a logical approach.

You do realize that this thread is almost six years old, right?

No.

There are only two connectors for the instrument cluster, both over on the left side (left as the cluster is installed in the dash). Both are rectangular and snap directly into the cluster. You make reference to "the dimmer/headlight switch," but those are two different things. Let's try again -- the headlight switch pulls out to turn on the headlights. It also rotates to control the brightness of the instrument lights, and at one end of the rotation it's OFF. In addition, the control is an old-fashioned rheostat, with a fixed contact blade that slides along a length of coiled resistance wire. Over the years, this may develop dead spots, causing the lights to flicker or go out even if the knob isn't rotated to the OFF position. So ... have you tried rotating the dimmer control on the headlight switch?

With a 5-speed, you should have 4.10 gears. Asking for advice after you bought the tires is unfortunate, because my advice would have been to NOT buy tires that big. The 4-cylinder isn't going to be happy trying to roll those big tires. Unfortunately, DesertRat is incorrect. Even 4.88 gears won't get you back anywhere near stock. Your factory tire size was probably 195/75-15, and the RPM in fifth gear at 60 MPH would have been 2411. With 31" tires, 4.10s at 60 MPH will only have the engine turning 1842 RPM at 60 MPH, and 4.88s will only bump that to 2192 RPM. That's way below where the 2.5L likes to run.

Aftermarket power window conversion. "Stripped down to the chassis."

The fuse for the TCM (Transmission Control Module).

No, not when shifting manually. It should manually shift through the gears. I believe it starts in first and skips second, then you can manually shift to third, and then OD. Either that, or it starts in second and then you can manually shift to third. But the transmission should respond to manual shifting. If it does, then you have an electrical or TCM issue. If it doesn't, then you have a transmission issue.

It's impossible to know everything, and I am frequently amused by people who like to think that they do. To survive (if not succeed) in this world, what's more important is knowing where to look for information, so that you DON'T have to rely on fallible, human memory.

He didn't say he couldn't write ...

First step -- pull the fuse and see if you can shift manually.

Pete - you've got mail

I can't lock up the brakes on my '88 XJ now, either. But it's on 31" tires. I bought it new, so I know I could lock 'em up when it was new. It doesn't apply to the MJ, but much of the bad rap the XJ brakes get is due to the proportioning valve getting gummed up and not allowing the brakes to get full (or any) pressure to the rear circuit. The corollary in the MJ is when people work on the rear brakes and then don't bleed the rear circuit properly. When (if) I get the old XJ back on the road, a high priority will be to open up the proportioning valve and clean out the gunk.

I have the hulk of an '86 XJ in the yard. It has a 2.8L V6, auto, and 3.73 gears. I haven't seen many '86 MJs, so I can't say that I've ever seen an MJ with 3,73s. Looks like for '86 the choices in the MJ were 3.31, 3.55, or 4.11

Like JustEmptyEveryPocket, I also disagree with this statement. I don't regard the change to the later booster as being at all mandatory. It's an option if you want to run larger tires, but IMHO completely unnecessary with any stock size tires. The original brake system on the older XJs and the MJ was completely capable of locking up all four wheels, and that's all the braking you need.

THe clutch peddle is supposed to go to the floor -- the brake peddle isn't. So your brake peddle is NOT bottoming out, it's building pressure like it should. You said the previous owner replaced the brake lines. My first guess is that he screwed up the two lines to the rear (one primary, one emergency bypass) and you have no rear brakes.

What do you mean "almost no peddle movement before it bottoms out"? That's impossible, unless your peddle starts out sitting much too close to the floor. What you are describing is NOT normal. On stock tires, you should be able to lock up the tires easily on dirt, and probably on pavement. It sounds to me like you aren't getting braking on all four wheels.

Carburetors are basically pretty simple devices. The problems arise when you take a simple device that has been working just fine for decades, and try to overlay computer controls on it. There used to be a guy here in Connectucut who went by the name of Mr. Carburetor. He did carb work for many of the stock car teams who used to race at the old Riverside Park speedway in Agawam, Massachusetts. I once took him a carb from an XJ 2.6. He got it running, but he advised me that the best thing I could do would be to discard that thing and buy a "real" carburetor.