• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Advice on where to look for trans issues

TRCM

TRCM

NAXJA Forum User
Location
Newport News,VA
I have an 88 XJ with 306k on the tranny. It is the auto 4spd, I think the AW4, but can't remember right now.


It use to run at ~1800 rpm at 60 mph, and when in OD, it would slowly accelerate if you gave it just a little gas.

Now, it runs 2000-2200 rpm at 55 mph, and when you give it a little gas, the rpm jumps 300 or so rpm.

It acts to me like it is not going into lockup or OD fully, and sometimes it does, and sometimes it doesn't. the engine sound is defintely higher now crusing doen the road.


What can I check before I get a new tranny ??

The fluid level is fine, and fluid looks/smells normal.
 
sounds like the torque converter is not locking. try disconnecting the battery for a minute to get the ecm to reset. I dont think you need a new trans, the torque converter lockup function is controlled by electronics
 
I hope not on the tranny too, but then again, at over 300K, it is getting kinda on the old & worn side. My tranny guy said the dang things seem to run forever, but 300 K is a lot. He also agreed that finding a used low mileage unit to swap in would probably be better then a rebuild. Seems the stock clutches are far better than the available replacements.

I can try the power kill....that's easy.

I'm wondering tho, since this happened after doing a MC/booster swap, if maybe my cleaning the area up from the mess may have hurt something sensor wise. I didn't see any evidence of having inadvertently disconnecting anything.
 
MY 98 HAD ABOUT 300,000 AND DID THE SAME THING IT ENDED UP NEEDING A REBUILD ALTHOUGH I HAVE NO WAY OF KNOWING IF THEY WERE LYING OR NOT BUT THIS PLACE I WENT ONLY DOES TRANNY WORK AND HAS A REALLY GOOD REP THEY ARE EXCLUSIVE REBUILDERS OF MOST OF THE POLICE CARS IN THE AREA COST ME 2800 FOR A SWAPW/ 30,000 WARRANTY
 
Check the switch on the brake pedal with a meter. It's white and up near the top of the pedal. It'll have a vacum line on it for if you have cruise control. If that's gunked up, it will be telling the Trans computer that you're pressing the brake pedal and it will keep the t/c unlocked. If you have a meter, check continuity across the switch with press pressed and not pressed. The bracket that hold that switch has a screw on the right side, point towards the left - remove that and the bracket shifts right to remove. Easier than trying to get the switch out of the bracket.

As a test, you should be able to cruise along at a steady throttle and tap the brake pedal with your left foot. It should unlock the t/c and you'll see the rpm jump a bit.
 
I was experiencing a similar issue on my 93 and my sons 92. Turned out there was a vacuum line that came loose. it connected to the vacuum canister under/near the heater core inlet/outlet on the passenger side of the engine compartment. not sure if the 88 has it.
 
lawsoncl said:
Check the switch on the brake pedal with a meter. It's white and up near the top of the pedal. It'll have a vacum line on it for if you have cruise control. If that's gunked up, it will be telling the Trans computer that you're pressing the brake pedal and it will keep the t/c unlocked. If you have a meter, check continuity across the switch with press pressed and not pressed. The bracket that hold that switch has a screw on the right side, point towards the left - remove that and the bracket shifts right to remove. Easier than trying to get the switch out of the bracket.

As a test, you should be able to cruise along at a steady throttle and tap the brake pedal with your left foot. It should unlock the t/c and you'll see the rpm jump a bit.
Click to expand...

Would this still be an issue even if I don't have cruise ? i thought that particular switch was only the brake shifter interlock trigger.
 
I checked the tps, and it reads .2 v at idle, and 3.8 at wot on one side of the connector, and 4.9 all the time on the other side



what are the values supposed to be ? My book doesn't cover this item on my truck. it only covers carb'd engines in 88, and FI engines from 91 on....mine is FI.
 
WOW, Absolutely Amasing.I am suprised it even starts, much less drives. THe TPS is shot, dead, useless, finshed, toast even.

Check out the "ReniX Files" thread for all you ever wanted to know about testing a Renix Era TPS sensor.

It should 0.80 to 0.83 volts at idle on the flat three pin connector Pin C to Pin B.

The 4.9 volt all the time side (square connector) is the side that tells the transmission where your foot is on the gas peddle. That side is dead, no longer working on yours.

www.teamcherokee.com has a great price on OEM mopars right now, half the price of the aftermarket guys. Like $34.95.

TRCM said:
I checked the tps, and it reads .2 v at idle, and 3.8 at wot on one side of the connector, and 4.9 all the time on the other side.

what are the values supposed to be ? My book doesn't cover this item on my truck. it only covers carb'd engines in 88, and FI engines from 91 on....mine is FI.
Click to expand...
 
Last edited:
I think that 4.9 volts is the feed voltage to the TPS. If it's shifting ok, the TPS wouldn't be my first guess.

The white switch is for the TCU. The vacumn line for the cruise also seems to be there regardless of whether you have the cruise option. If you have cruise it's suppose to release the vacumn on the cruise system to protect against a runway cruise system. I've cleaned a few that had dried up grease that was preventing the switch from making contact. Sounds like you have a meter, so it's something relatively easy to check.

I believe the shifter interlock on a Renix is mechanical and not a vacumn/electrical.
 
Ecomike said:
WOW, Absolutely Amasing.I am suprised it even starts, much less drives. THe TPS is shot, dead, useless, finshed, toast even.

Check out the "ReniX Files" thread for all you ever wanted to know about testing a Renix Era TPS sensor.

It should 0.80 to 0.83 volts at idle on the flat three pin connector Pin C to Pin B.

The 4.9 volt all the time side (square connector) is the side that tells the transmission where your foot is on the gas peddle. That side is dead, no longer working on yours.

www.teamcherokee.com has a great price on OEM mopars right now, half the price of the aftermarket guys. Like $34.95.
Click to expand...

I never checked the square connector.

My book said to check voltage between the middle pin and one side pin at idle and wot, and then check the other side pin to middle pin on the flat connector. That's where I got the readings from.
 
TRCM said:
I never checked the square connector.

My book said to check voltage between the middle pin and one side pin at idle and wot, and then check the other side pin to middle pin on the flat connector. That's where I got the readings from.
Click to expand...

OK, Then the TPS idle needs to be adjusted to 0.82 volts (it rotates if you loosen the mounting screws, calibrate it, then retighten them), then check the square connector, it is the one that talks to the TCU (transmission computer), the one you checked only talks to the ECU (engine computer).

The Renix Files thread is very long, but there is a huge amount of test data there that is posted no where else on this planet that I know of. It also has posts with links to some other real nice sites with pictures and the test procedures I started with (before I came up with my one tests). Scan it end to end breifly, and then dig out the test methods and data you need. Its all there.
 
What white switch are you refering too??? Mine (87 Renix) is electrical on the brake to TCU interface, it has two connectors on the same brake switch, one for tail brake lights, one for the TCU signal. I have cruise, but do not recall a third vacuum switch connection on the brakes, did I miss it?

Are you refering to the NSS on the shifter interlock? If so it is at least electrical on the 87 Renix. Don't recall any vacuum on it. Replaced mine last year.


lawsoncl said:
I think that 4.9 volts is the feed voltage to the TPS. If it's shifting ok, the TPS wouldn't be my first guess.

The white switch is for the TCU. The vacumn line for the cruise also seems to be there regardless of whether you have the cruise option. If you have cruise it's suppose to release the vacumn on the cruise system to protect against a runway cruise system. I've cleaned a few that had dried up grease that was preventing the switch from making contact. Sounds like you have a meter, so it's something relatively easy to check.

I believe the shifter interlock on a Renix is mechanical and not a vacumn/electrical.
Click to expand...
 
I wonder if it was different on the earlier Renix. I've seen it on an 88, 89, and 90 in the salvage yard.

cruise_switch.jpg
 
The 88 FSM shows what you describe, so maybe that changed in 88/89? I think adding a mechanical vacumn release to the cruise was in response to the Audi 5000 sudden acceleration media circus. (Quoting Ralph Nader - The dumb sh*ts had their foot on the accelerator)
 
Oops. Just noticed I was looking at the 88 YJ diagram. The XJ diagam shows two connections on the brake lite switch - one for the cruise and one for the stop lite. It shows a vacumn valve further up the pedal. I'm still digging to see where the TCU switch is as it's hard to tell if that valve has the TCU electric connection. I hate the 88 FSM.

(edit). I didn't find the picture of the switch, but I did find the description and part number, 56002281.
 
Last edited:
lawsoncl said:
The 88 FSM shows what you describe, so maybe that changed in 88/89? I think adding a mechanical vacumn release to the cruise was in response to the Audi 5000 sudden acceleration media circus. (Quoting Ralph Nader - The dumb sh*ts had their foot on the accelerator)
Click to expand...

I will have to look again when I get the chance, as I just may not have noticed it yet (the white vac switch). Hell I may have all three of them, but I do recall the second electrical switch wires go to the TCU because I was just testing those earlier this week on mine. I found a puzzling trace voltage of 0.5 to 2 volts on the wire for the brake to the TCU on mine, the wire that gets 12 volts (which mine does, this same wire) when I hit the brakes. I still need to go back and figure out what that is all about.

If I do have the vac switch it is not connected to the TCU on mine, but it might be connected to the cruise on mine.
 
Hmm, now you have me wondering if I got it backwards. If I have a vacuum/electric switch up higher, I guess it could be the one talking to the TCU, as I did not trace the wires all the way. But why would they use a vacuum/electric switch on the brakes to signal the TCU to disco the TC?

Isn't their vacuum stuff on the Cruise control? I have not tried to fix my crusie control yet, so it is somewhat of a black box to me so far.



lawsoncl said:
Oops. Just noticed I was looking at the 88 YJ diagram. The XJ diagam shows two connections on the brake lite switch - one for the cruise and one for the stop lite. It shows a vacumn valve further up the pedal. I'm still digging to see where the TCU switch is as it's hard to tell if that valve has the TCU electric connection. I hate the 88 FSM.

(edit). I didn't find the picture of the switch, but I did find the description and part number, 56002281.
Click to expand...
 
The vacum part of the switch is just to release the vacumn on the cruise solenoid. The switch also has a set of contacts that close to signal the TCU when the brake is pressed. I'd think that they'd put both the electrical and vacumn functions into the single switch. Could be that the TCU line gets grounded and the brake light switch is getting switched to +12v.

That switch is near the top of the pedal.
 
You must log in or register to reply here.

Similar threads

N
Severe stumble, misfire and no start issues
2
Replies
27
Views
4K
maxbraketorque
M
B
2000 4x4 sport with 4.0 auto trans issues looking for help.
Replies
4
Views
1K
lawsoncl
L
S
AW4 TC Not Locking Up
Replies
6
Views
2K
sandfreestyle
S
R
1992 XJ AW4 doesn't want to shift
2
Replies
20
Views
3K
Rob Mayercik
R
R
2000 XJ Sport - Trying to diagnose intermittent sputtering
Replies
0
Views
1K
ramonesrazor
R
Back
Top