Engine/Transmission (1994 - 1998) torque converter lock up?

[Flying_gage]

Hey guys,



How do I tell if my T/Q is locking up. I do not think mine is locking up.

 

[Joe G.]

Welcome to the TDR.



Please fill out your signature showing what year and what model your truck is. These trucks are NOT the same from year to year.



If you mean the lockup after the truck is in OD, watch the tach after is shifts to OD. If RPM drops again after the shift to OD then the TCC is locking up.

 

[Flying_gage]

That's what I thought.



Sorry bout not filling out the thread. Will get to that hopefully today.



The truck is a 98 2500 2wd short bed. It has 4:10 gears in back. The truck has only 83k on it.



The reason I posted this thread was because I have been getting only 15 mpg at 72mph with the engine turning 2300rpm. I never noticed after I got to cruising the rpm's drop a couple hundred like my wife's van does.



Will this damage my trans. if left like this till I get home?



So, can anyone recommend and good shop in the Denver area? I live in Illinois and am in Denver on business and I would love to get this checked out prior to heading back as the fuel mileage is killing me!



If this helps, the truck sat on a dealership parking lot for the better part of a couple months without being started. I have only had the truck a couple months. I don't know if that helps at all?

 

[CBeeman]

the TC should drop the tach about 500 rpm when it locks up. when you are cruising at freeway speed and blip the throttle you shouldnt see the tach jump. I would try a TPS first. i would think driving w/o lock up would cause high transmission temp if driven for any length of time.

 

[Joe G.]

I drive with mine unlocked quite a bit when I'm towing. No problem with high temps. Lockup will help, but with 4. 10 gears you will still have low fuel mileage.

 

[Vaughn MacKenzie]

FLying_gage I also have a '98 2wd shortbed automatic, a bit of a rare truck. Just curious is yours a club cab or quad cab? My TC locks up in 3rd and OD. I get about 22 MPG cruising at 70 but I have 3. 54 gears. With 4. 10s and the TC locking you should get 19-20 easy, you're definitely getting lousy mileage for a 2wd shorty.

Vaughn

 

[Flying_gage]

Yeah, that is what I was figuring when I bought her. I figured I would be able to manage at least 18mpg. I have the 4 door model. Thats the club right? I have had a couple people mention there aren't too many of these out there.



I found a bad ground tonight and got that taken care of. No change. I will pull the TPS and check it tomorrow. Any other thoughts out there, let me know. I appreciate the help so far.



After REALLY paying attention tonight while driving her, I noticed the T/Q locking up except in Overdrive. We'll see.

 

[Vaughn MacKenzie]

Interesting that it locks in 3rd but not OD. Not sure what to think about that.

You have the Quad Cab, mine doesn't have the quad doors. I'd say about 70% of the 98s are Quad Cab, but I'm happy with mine. There were a few Club Cabs in 99 but they are VERY rare, only one I saw was in Massachusetts.

 

[Flying_gage]

Alright. I broke down and took the truck into a local shop yesterday. When he used his snap on computer to check for codes, nothing came up. When he probed a little deeper, he found the computer was reading that the o/d was constantly turned off? O/D works fine, so go figure.



I then took it to the local Dodge dealer and they now have it. They think that the computer needs to be re-flashed. I am a tad leery but if that is all it takes then I will be happy.



I looked at installing a mystery switch but it does not appear as though I could do this on my truck. Will update when I find out what is happening.



By the way, they had a newer dually in with an obvious no start condition. Obvious because they kept cranking the snot out of the poor thing till they wore the battery down. I kind of wanted to say something. Then one of the tech's walked out with a can of starting fluid. When he noticed that I was looking at the can he immediately hid it in his back pocket.



Needless to say, if it is anything more than a re-flash they will not be doing it... .....

 

[Flying_gage]

F#%$*k!!!!

Alright, got the call from the service writer. He says that it is an "engine performance issue". He warned me that I might need a lift pump and and new injection pump, but he will know more in the morning.



Any thoughts out there. I already told him he will not be replacing a lift pump and or injector pump. I will head back to Illinois with it "as-is".



Damn this sucks. My wife is going to shoot me in the head with a bazooka as I swore up and down this truck wouldn't be a money pit. I already went through this once with my 93 CTD. But that thing was wrung out when I bought her. This truck was immaculate and only had 75k on her.

 

[Howard Durand]

How can a new lift pump and injection pump improve operation of the transmission?



Did anyone check the TPS?

While messing with the potentiometer that I am using, I find that if the signal voltage to the PCM is constant and below a certain level, the OD shifts OK but the TC will not lock up. If your TPS signal is not advancing, you would have the same situation.

 

[AWray]

"He says that it is an "engine performance issue". He warned me that I might need a lift pump and and new injection pump. "



Do you have a 24v or does the tech just think you do? Or that you don't know the difference and he can easily lift $2k+ from your pocket?

 

[Joe G.]

Engine power has NOTHING to do with your problem.

 

[DMcPherson]

nope and I think you may not realize the lockup in OD because it doesnt unlock from 3rd to 4th once its locked up, your rpms seem about right for that MPH, depending on tire size. and to cruise at that rpm you car going to be down in fuel mileage. my next question is, when was the truck built, Im thinking you have a 24v and dodge is trying to throw parts at it. and it has nothing to do wiht that, especially if you have to codes.

If yo uhave trans problems try to go to a reputable trans shop, engine problems go to cummins, if its not warranty try your best to stay away from chrysler.

 

[Joe G.]

You really need to fill in your signature. There were two engine possibilities in '98. Trucks made before Jan 1, '98 were 12 valves. Those after were 24 valves.



I'm a little bit confused by your symptoms. Does the TC lock up in 3rd with OD locked out? If OD is not locked out, how many times does it shift after it shifts to 3rd?

 

[Flying_gage]

Fixed!!!!!

First off let me say thanks to everyone that posted. I was in one of those situations where your are up to your proverbially ***** in alligators and then something else happens. I wasn't quite panicking but I was starting to get nervous when he went down that road. I am pretty familiar with these trucks as I had a 93 12 valver. I was 99% sure the guy was feeding me a load of crap, but the way my luck has been running lately... ...



I purchased the truck specifically because it was a 12v. I personally would not purchase a 24v truck due to the lift pump/injection pump issues.



Thankfully the diesel tech who looked at my truck was decent and didn't try and soak me. They could not get it to throw any codes what so ever statically or dynamically while driving. He finally worked his way to the externally mounted speed sensor for the transmission, a $12. 00 part. He was then able to set the computer up where he could make it throw a code.



Now instead of my truck driving like my 93 CTD with an auto, it feels like it should. Surprisingly even at lower speeds I can notice a difference. The truck just feels better.



For posterity's sake, I would recommend anyone who has limited time with auto transmission's, like myself, drive a vehicle that is working correctly for a baseline and this will offer tremendous info.



I am on my first tank of fuel since the fix and therefore haven't calculated my mileage, but I can tell you there is a huge difference! I will post in a couple hours where she is at.

 

[Howard Durand]

Thanks for the report. It is good to be reminded that there are honest, competent mechanics and technicians around.

 

[AUrban]

I'm pretty new with my 12V 98 but I'm typically getting around 19-20 in mixed driving and as good as 23 on rural highways with speeds around 60. The 4. 10's keep the rpms high but the 12V pulls great from any rpm. I'm thinking of replacing the 4. 10's with 3. 54's as I don't tow much. But I like the extra 'pep' off the line that the 4. 10's give.

 

[Flying_gage]

One week ago: 72mph + 2400 rpm = 14. 7 mpg



Today: 70mph + 2200 = 18. 3 mpg.



Obviously the mph is different but it does not account for the difference in mileage. I hand calculate my mileage on every tank and always fill it to the same level.