Yet Another Cruise Control Thread... '89XJ

Still trying to chase down the cruise control problem on my '89, (4.0, AW-4, NP231) no luck so far and I'm considering an aftermarket replacement... The story so far... fuse OK, vacuum OK (at least I assume 16 in. of vacuum at the servo is OK), switch on stalk is OK per all the continuity tests in the manual. I got a spare module and servo from the boneyard on the cheap, swapped out in various combos, no soap. Been systematically testing with a volt/ohmmeter as per the factory service manual. All the tests are OK so far down to the one for the vehicle speed sensor, which should show 30-50 ohm resistance (IIRC), but shows none - so I'm hoping it is the culprit, though I swear it tested good the first time through. Anyway, I went to the parts store to see what one would set me back and they only have them listed back to '91, why do you suppose that would be??? It's about a $60 part at the dealer, so I'll probably be crawling back under the ones at the boneyard some more...


I've been looking at aftermarket systems, and I wonder if anyone here can tell me if they're any good? There are some pictures in the J.C. Whitney catalog, and some look remarkably similar to the factory one. I wonder if one of those could use the existing switch (which tests perfect) instead of having to tear the steering column apart to put a new one in??? Any guesses??? Some of them say they use the existing speed sensor, so I'm probably going to have to deal with that anyway, but I was wondering if anyone here had any experiences to relate along this line???

Thanks!

Marty

You don't mention checking the cable(s) to make sure they are sliding in their tube(s). Just a thought!

Thanks, Michael! Yes, I've checked the throttle cable from the servo, it is not binding. And I've had one of the servos apart to test mechanical operation (which was interesting). There are two solenoid valves in the bottom of the servo which connect to the vacuum system - one normally closed (charge side) and one normally open (vent side). I applied battery voltage to both to open/close them, and then applied vacuum, and the servo cable moved as it should. So, for some reason, the proper signals are not being sent to the vacuum valves in the servo. I'm hoping (again!) that the speed sensor is the problem, it's one of the few components I haven't swapped out yet...

There's a test in the manual that I've tried (and failed) that I find hard to believe would work... with the tranny in park, e-brake on, supposedly holding the R/A switch in will open the throttle, release to throttle back... Should this work, if the vehicle is not moving???

Check the switch on the brake pedal..

it's the one with the vacum line going into it.

Unless you allready mentioned that you did this... then... NEVER MIND...

RINGKONG,

No, I never mentioned checking it, but I did check it! Had it out fooling around with it, and checked continuity & function on the electrical portion. IIRC, open w/brake in normal position, closed when pedal pressed, but I might have it backwards...

I also did a vacuum check on the line going to it from the servo in the engine compartment. Looks like it holds vacuum fine, no leak. I believe this is the "vent valve", which immediately vents the vacuum to the servo when you hit the brake pedal, thus releasing the throttle.

Just got back from the local boneyard, bless 'em, they let me crawl around a bit and didn't charge me for the speed sensor I found. Checks out OK for the ohmage, now I gotta get it installed and see if it makes a difference...

Marty

By the way, I think the "vehicle speed sensor" listed for 91 and up vehicles is probably the one for the electronic speedo/ECU which started that year, not the one you would need for your cruise.

Oh well... the "new" speed sensor didn't make any difference, except now I have a little speedo needle shake And of course now the old sensor is testing OK on the bench...

Guess I'll keep running the test procedures until I find the next thing, or not...