No TC lockup!!! Please help.

1990 Cherokee Laredo Automatic 4x4

I pretty much just realized after all this time my TC is not locking up. At 65 it runs 2.5k rpm's. Should be around 1800. I replaced the TPS, IAC, Valve cover gasket, Intake/Exhaust manifold gasket. I know some have nothing to do with the shifting or TC. I also adjusted the TV cable. I unplugged the TCU which isn't going to fix anything because it eliminates TC lock up. I checked the brake light switch, NSS is fine, even checked something most people forget about which is the white box above the brake light switch that has a plunger on it. Now
It's not all the way back in the plunger, but I think far enough in. I know this problem has to be electrical because when it was floored the rpm's would drop. I've posted a few times about this but now I've tried everything people have said to look for. Also it shifts at 2300 rpm's not matter if it's floored. It always does and only way to get past that was unplug the tcu. I really really need to figure this out. I'm pretty sure the TC is good because it shifts perfect into all 4 gears. No hesitation into gears or hard shifts. I'm just really stumped and the only thing I can think of next is the manual switch for lock up which I really don't want to do because my gf had to drive this sometimes for the extra room. Please any help would be appreciated.

I should add my o2 sensor is unplugged right now. Plus I have a broken white vacuum line that connects into some metal thing that comes out of the evap canister. Best I can describe this is you have the canister, the hoses come out and on this one hose there's a metal round thing with an elbow coming out of it, that's where the vacuum line is broke. Not sure at all what that thing is. The rest of the vacuum lines on this car I believe are fine just that one. I'm really trying to describe everything, and it does run rich.

While not all-inclusive, this article covers everything you will need to know to figure out your TC lockup issue: http://www.transonline.com/transdigest/magazines/1997-10/Shift Pointers/index.html

There should be two lines off the canister, one will run to the intake and the other--with the orifice--runs back to the fuel tank.

Replace your o2 sensor, that is why you are running rich. Use Bosch, they invented them and IMHO are the best. Make sure you get the correct one for your 90.

I believe there is 3-4 lines coming off that canister. Does that vacuum line run to the gas tank or something else? I guess the real question is does this have anything to do with my problem. Only thing I get from that website is how to check voltage on the tcu. I hope when I check the voltages there I pray something is wrong!

Well, if you have to unplug the TCU to get the thing to "shift" properly, then that sounds most likely where the problem lies. And how did you check the brake switch? Has it ever been replaced? It is one of the most common reasons for lack of TC lockup and no cruise. You can always do what I did and install a TC lockup switch. It really is not hard.

Johnnie you have a great point, my cruise control does not work and I forgot that important fact too. How do I check the break light switch exactly? I just check it by making sure it was plugged in and my brake lights weren't stuck on. Figured that was a good sign lol. It shifts fine with it plugged in, it just won't run to redline if you wanted to floor it or pull out in traffic quickly, it just shifts to early.

JoJoDaKilla said:

I believe there is 3-4 lines coming off that canister. Does that vacuum line run to the gas tank or something else? I guess the real question is does this have anything to do with my problem. Only thing I get from that website is how to check voltage on the tcu. I hope when I check the voltages there I pray something is wrong!

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There are four pages to the article, page 3 has a chart and lists the ohm values for the solenoids. The page numbers are in the left hand column.

Haha Joe I got that, I just mean to really test anything it seems like it's all through the tcu connection. It just sucks and it's frustrating.

JoJoDaKilla said:

Haha Joe I got that, I just mean to really test anything it seems like it's all through the tcu connection. It just sucks and it's frustrating.

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You can unplug the harness down by the transmission, or drop the pan--more work that way though.

Good luck.

How do you test the brake switch exactly, is there something I can do with a volt meter test or what?

Yeah, DVOM will work, but never use the ohm function on a live circuit. When the pedal is up there should be an "open" circuit, pedal depressed closes the circuit.

Now, you may have two switched on your brake pedal--one the brake light/tc lockup and another for dumping vacuum to the cruise motor when the pedal is depressed, or that may be incorporated in the electrical switch, both styles were used.

Good luck.

Joe for some reason I got really lost there on that one. There's a brown switch connector thing on the lower part of the brake pedal with 2 connectors, and a white box thing on top with a plunger and connector. Not sure how to test those. Just check for open and closed circuits?

There may or may not be other issues, but the converter clutch isn't going to drop your rpm by 700. More like 300.

I learned tha hard way on my 89 that just because the brake lights come on when i step on the brake, does NOT mean that switch is adjusted properly.
I used a scanner to see when the switch told the trans that the brake was NOT applied. im sure a DVOM can be used to adjust it as well.

JoJoDaKilla said:

Joe for some reason I got really lost there on that one. There's a brown switch connector thing on the lower part of the brake pedal with 2 connectors, and a white box thing on top with a plunger and connector. Not sure how to test those. Just check for open and closed circuits?

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Ok, I think you have the two separate switches. The upper switch should have a vacuum line attached. If adjusted properly, when you depress the clutch it "dumps" the vacuum to the cruise control servo--cutting out the cruise control so you can slow down/stop.

The lower switch should have electrical wires connected--brake lights, tc-lockup. With the pedal depressed the brake lights come on, the tc unlocks.

In the parts catalog there is also a "combo" switch that combines all of the functions. There are no productions dates so they were used at various times in 87-90 and maybe beyond, but it doesn't sound like you have that.

Depress the brake pedal and fix it in that condition--like with a stick. hook up your meter and check from one side of the switch to the other, make notes. Pull out the switch, check the circuit conditions then--anything that doesn't change ain't working right.

Post up what you find.

Good luck.

I will do this today. Well as long as it doesn't rain. Yes I do have the 2 switches. The top one is white, bottom is the black one. I read you could adjust the top one so the plunger would go all the way in if out of adjustment. It's just that it was 110 heat index with 97% humidity. Today as long as it doesn't rain I will check it.