Eagle

Why are you using any wires from the Sun tach installation? The wiring for the factory tach is already there, it's plug-n-play.

Check your hard lines, especially over the gas tank, and check your rear height sensing valve. It was a panic stop just such as you describe that exploded the height sensing valve in my '88 MJ. The result is that you get a low pedal because the rear circuit is blown and you are now stopping entirely with the fronts.

It sounds to me like you have a lazy thermostat. The operating temperature doesn't stay constant -- the thermostat constantly cycles open and closed. The purpose of the thermostat is to keep the temperature UP, so if the cooling system is working, the temperature will get up to the setting for the t-stat, the t-stat will open, and the temperature will then drop to the point at which the t-stat closes again. Then the temperature goes back up until the t-stat opens. Rinse and repeat. The normal range, IIRC, is only about 15 degrees or so and most people don't notice that amount of change on the temperature gauge. Your thermostat may be allowing the temperature to drop too far before it reopens.

Yes.

You have a vacuum leak. The vent flapper doors are operated by vacuum. By design, the default when there's no vacuum is for the doors to direct airflow to the dash-top defroster outlets.

I agree -- this is just an ABS system, not a traction management system. And, as much as I generally dislike ABS, I think it makes moire sense for a pick-up truck than the failure-prone height-sensing rear proportioning valve used in the MJs. And IMHO the XJ's proportioning valve is even worse -- what you want is something that prevents rear wheel lockup in a panic stop. What the XJ "proportioning valve" does is exactly the opposite -- it prevents the rear brakes from working UNTIL you're in a panic situation and really stomp on the brakes. My wife's 2000 XJ has 105,000 miles on it. We're well into the second set of front brake pads. I just changed the rear brakes a couple of weeks ago, but the problem was a rusted line and loss of pressure. I changed out the wheel cylinders and shoes while I was working on the brakes, but after 104,000 miles the rear shoes were less than 50 percent worn. There's only one way that can happen -- they aren't doing anything. Why? That stupid proportioning valve.

Why would you need to reprogram anything? You would need to use the XJ axles, in order to get the tone rings, but the system works by sensing when the wheels stop turning. Why would it matter if the wheels are under an XJ or MJ chassis?

I found this one before I could find the procedure I copied from the FSM. http://comancheclub.com/topic/40428-brake-bleeding/

What year Cherokee? I think Jeep changed the maker of the ABS system somewhere in there.

Dunno. Did the Comanche ever come with ABS as an option?

Then you did NOT follow the factory-required bleeding procedure, and there is probably air trapped in the bypass line for the rear brakes. I've posted the procedure, quoted verbatim from the FSM, on this forum previously. Try that and see if it helps.

Sounds great in theory, but the fact is -- the a/c DOES cycle when wnen it's cold. I don't know which of the two reasons being discussed is the reason the system was designed this way, or if both reasons apply. The point is -- the OP asked why his system was malfunctioning, and the answer is that his system is functioning as designed. If y'all want to argue about why the engineers made it that way, have at it. From the 1988 MJ FSM:

There is no need to do this "a few times." The system operates under positive pressure. Turn on the key, let the pump run until it shuts off, then start the engine. Same thing you should be doing every time you start it.

Does your MJ still have the rear height-sensing proportioning valve, with two steel lines running from the front distribution block (just under the master cylinder) to the rear of the vehicle? If so, after doing all the brake parts replacements, did you follow the factory procedure for bleeding the safety bypass hydraulic circuit to the rear axle?

I remember reading that, too -- several times. And then I remember someone posting that the S-10 handle doesn't work. I wish someone knew for sure. (And, of course, it may depend on which year S-10.)

^^^ :agree: The factory spec is 13 psi minimum at idle with the engine at normal operating temperature. What's the pressure at 50 MPH in high gear? So far the photo isn't showing a problem. Also, what weight oil?

Grounding? The only ground involved for the headlights is forward at the lights themselves -- the ground connection behind the driver's side headlight bucket. If the headlights work when you flash the high beams, then the lights have ground. Your problem is somewhere in the power supply circuit upstream of the headlights. You can verify whether or not there's power to the headlights by removing one headlamp, turning on the headlights, and using a tester between the headlight socket and a known good ground to confirm whether or not you're getting power to the socket. Assuming you're not, then you start working back upstream along the power circuit until you find the point where there is power.

Lift reduces caster angle, and keeping caster angle around 7 degrees is important for resisting death wobble. The problem is, with a large lift if you dial in 7 degrees of caster you may increase the operating angle of the front axle u-joint beyond where it's happy (since there's a double cardan joint at the transfer case end, the operating angle at the differential yoke wants to be approximately zero). So generally setting caster on a lifted truck becomes a balancing act between getting enough caster without eating u-joints.

The guy in the shop clearly does not know what he is talking about. Tire balance is the primary cause of death wobble. Other factors just combine to dampen and hide the symptoms to a greater or lesser degree. In theory, an automotive tire is a gyroscope, which is inherently resistant to wobble -- IF it's perfectly balanced. If it isn't perfectly balanced, it will wobble. Secondly, camber in a solid front axle setup like the XJs and MJs is not adjustable, except by installing special offset ball joints. That's not so much an "adjustment" as it is a one-time fix for an out-of-spec axle assembly. Lifting the vehicle will affect caster, but will not affect camber. Lift also affects toe-in.

Also too hot for a Renix. With the standard 195-degree thermostat the gauge should show 210 degrees (straight up, mid-dial).

You have it backwards -- see post #3 above. You made me look it up in the factory electrical troubleshooting manual. It clearly says, disconnect wire, "Needle goes to H." Touch wire to ground, "Needle goes to L."

If there's any sure path to getting yourself flamed, it's jumping in after multiple people who KNOW how the system works have answered a question correctly, and telling them that what they wrote is close to BS. Before being so quick on the trigger, you might in the future stop to consider that some of us on this board are automotive professionals, and others of us have been serious automotive hobbyists for over fifty years. I also grew up before a/c in cars was commonplace. I think I was 35 yes old (or more) before I owned my first car with a/c. I understand that heaters will defrost the windshield without help from the a/c. That doesn't mean that a/c won't make it happen faster, and it certainly doesn't mean that the Jeep engineers didn't design the system to cycle the a/c when running the defrost.

Normal operation. The a/c runs in defrost mode. It's supposed to cycle.

In choosing any alternate filter for the Jeep engines, be sure the substitute has an anti-drainback valve.

Oyaji, I speak (okay, I write) not as a professional engineer (which I am not, although my education leading up to a master's degree in architecture necessarily included structural and mechanical engineering) but as an automotive enthusiast who has built and raced his own SCCA-legal pony car (1968 Javelin) and driven old military Jeeps, Cherokees, and Comanches both on- and off-road. I agree with you 110 percent about safety, which is why the first question I ask here when someone wants to lift their MJ is "Why?" The goal, IMHO (an opinion shared with any number of off-road experts) is to lift the vehicle as LITTLE as possible to enable it to go where you want to go. Any lift beyond the minimum necessary is wasting money, and making the vehicle less safe. That said, the bean counters at Jeep have decreed that they want to appeal to a wider spectrum of buyers. That means buyers who would not previously buy a Jeep because ... well, because it rides like a Jeep. It's not just a question of switching to independent suspension on all four corners. It's also things like spring rates, shock absorber valving, suspension geometry, steering ... a plethora of interrelated factors that all affect ride comfort, stability, maneuverability, and safety. The first Liberty was Jeep's first (modern) independent suspension vehicle, and it tipped over in a slalom course that previous, solid axle Cherokees had passed. That tells me something. I also know that when Jeep introduced the then-new 1999 Grand Cherokee (the WJ), they had to recall the export suspension due to some problem. IIRC (which is open to question at this point), the fix involved changing both spring rates and suspension bushing durometer specs. Again, to me this is indicative that even 14 years ago Jeep was already trying to make Jeeps ride like ... unJeeps. Your reference to the Ford debacle was another example. The problem wasn't the Firestone tires -- the problem was that Ford wanted what was basically a truck to ride as soft as a car, so Ford specified an insanely low tire pressure (contrary to Firestone's advice), and then Ford blamed Firestone when the tires began to explode due to [entirely predictable] overheating. I have no doubts that my wife's or my 2000 Cherokee would have no problem negotiating the evasive maneuver in the video you showed. The fact that a new Grand Cherokee failed so spectacularly simply confirms (for me, at least) my belief that Jeep is no longer building Jeeps.