canada_man

I have a 1990 Jeep Cherokee 4.0L aw4. The tc does not seem to lock up. At 60mph is sits about 2350rpm. At 65mph its around 2500rpm. When I let off the gas there is no coast and the rpm's drop a lot. I have to then give it quite a bit of gas to get back up to speed.
Since I purchased the jeep I've cleaned and put some die-electric in every connection I've come across. Haven't yet taken out any sensors to clean but recently made an adjustment to the tv cable which seemed to make no difference. Engine and driveline have all new fluids.
What should I be lookin at next?

cmartin2112

Possibly tps sensor? You mentioned you changed fluids I'm assuming you did the trans fluid as well?

Radi

Try lifting the brake pedal with the back of your foot, see if the TCC locks up. The brake pedal switch disengages it.

DFlintstone

Cool tip Chuck! Canada Man...I see you posted it's a 90, then 99 is in your "info" I doubt there is a difference there but don't know. I thought I saw that someone here had less than perfect eye-sight, but not sure I saw that right.

So Radi..you know I'm learning here. You're pretty sure a 90 will disengage the converter with the brake?

Radi

They all sense the brake pedal, some years had a separate switch for the TCC and cruise just above the switch for the brake lights, I don't know if '90 is combined or a separate switch.
I do see in some notes I had saved on the AW4 that '90 and older need a positive 12 volt signal from that switch to lock up, while later years use positive signal to unlock. So....theoretically the earlier units should not lock the TCC if the brake switch comes unplugged or fails since the positive signal won't be there- it'll think your foot is on the brake.

Radi

Found a pic. (Credit here: http://www.jeepforum.com/forum/f11/i...light-1219435/) This is an '87, but '90 should be similar. The white switch towards the top is said to be for the TCC, the lower switch is for the brake lights.
Looks like one of those goofy switches that can be moved back and forth to adjust. Might be as simple as re-adjusting it so the plunger is fully depressed when foot is off the brake.

canada_man

Thanks guys this is the help I was looking for.
Trans fluid was changed. Cmartin2112 I've been reading some threads on tps problems and think this may be the culprit. The jeep also has a rough idle once warm and when I accelerate from this it will sometimes hesitate a bit. What is the best way to test the tps, best to replace? Read lots of comments saying they don't take well to cleaning. I have a haynes manual just not with me, is there instructions for testing in the manual? and are they correct?

DFlintstone I also have a 98 2.5L which is the jeep in my "info".

Thanks Radi I'll test the brakelight switch like you mentioned tomorrow.

DFlintstone

Once again Radi, you are amazing! Who woulda thunk that. Yes, my 90 has one as well. Mine is harder to photo though!

Radi

You really can't clean them. A shot of electrical cleaner might work, but if it comes to that I'd just replace it. They're pretty cheap.
Usual way to test them is to measure the voltage on the center connector with the key on, engine off.
Yours is still Renix, I believe? That's a little different than the HO and I don't recall the exact reading you should get. I believe yours can be adjusted to achieve a specific voltage where the HO's are not adjustable.
Still- you can check that the output voltage (center connector) increases smoothly as you open the throttle by hand. Any dropouts or dead spots will cause trouble.

DFlintstone

The 90 adjusts, Cruiser has stuff in my signature. On mine the stupid screw twisted right off! I found the letters on the trans side connector> https://www.cherokeeforum.com/f2/90-...4/#post2371660

cmartin2112

DFlinstone has the link. I printed out that thread and threw it in my haynes manual for future reference. Lots of good info in there!

canada_man

Don't think it's the brake switch. Pulled back on the brake while letting off on the throttle and tc still didn't engage. Also with jeep parked I could hear the switch working when applying the brake. I also have the white TCC switch, haven't gotten down there to see if the switch is fully depressed with foot off the brake.

Some things I have planned for the jeep this weekend:
-new plugs, cap, rotor, and wires
-clean the engine to firewall ground and the ground by the dipstick
-Figure out how to use my dmm so I can test my tps...
-Also I've been reading and am convinced that the jeep could benefit from a throttle body and iac cleaning.

DFlintstone

Feel free to pm me if you don't get an answer to your post. I'm in and out allot, don't always catch everything. The DVM is pretty user friendly once you get the hang of it. I'm working Tuesday though.

DFlintstone

I'll be adding resistance sweeps from both the engine, and trans side, as well as what happens if you drill it and spray it through with CRC contact cleaner.

I did have a 2.7, to 7 on the 20K scale(ohms), on the trans side. (and still have that, roughly opposite, on the engine side.) Now after "cleaning" blasting with crc, I've achieved no continuity on the trans side. Drilling right, with it open misses more metal.

My "probe" (paper clip) went all the way back. I think they share the same cavity. (the two pots)

cruiser54

TPS is suspect here. Remember this: They are sensitive and you're not gonna "clean" any problems away. The wear out a ribbon inside.

Also, the two sides of the TPS have their own ribbons and wipers. Therefore a TPS that is bad on the "trans" side but good on the engine side will not be the cause of an idle issue.

It's like 2 TPSs in one, each side working opposite of the other. The HO TPS has one ribbon and wiper for both functions and doesn't need adjustment.

If it were me, and I didn't want to screw around, I would get a new tPS and adjust it. You COULD check each side of the existing TPS for fun if you're so inclined.