majines

I have a 2000 Chevrolet 1500 express van. There is a problem with the TCC lock up. Once the trans gets warmed up, there is, what I can best describe like a fish bite, happening. I can feel an occasional light bump, like a fish nibbling at the bait. That can happen once or up 3-4 times, without any pattern. But once the nibble starts there is a big bite coming and it can happen within a few seconds to a min after the nibbling starts.
I orginally thought the nibbling was possibly an engine misfire, but now I don't think it is. Again there is no pattern to when the nibbling starts and the bite happens, except it is after the trans has warmed up.
When I feel the nibbling start I can feather the brake peddle to disengage the lockup and then let off the accelerator and there is no bite. Or I can apply more accelerator to disengage the lock up and then let off it and there is no bite. Basically as long as I disengage the lock up I never get the big bite, which I am worried will screw something up if it continues.
This problem originated after having the engine rebuilt. I have had the engine builder-installer go over it and have had a trans shop go over it. The trans shop was positive there converter was going bad and possibly the 4th or OD gear going out. So with 178,000 miles on the van I decided to have the trans rebuilt and it has a new converter in it also. But still the same problem. So the trans shop is mystified and even a second trans shop is stumped after driving it and reviewing the work done.
My question is could the PCM be causing this ?
I also read a post in here about the PWM settings controlling the lock up or not controlling it etc. I can say the speed at which lock up occurs is about 40. I would like to change that to 50-55 if I get the fish bite problem fixed.

Any advise ?? Thanks !!

mrvedit

There are several possibilities:

1. Leaking TCC valve in valve body (VB) is VERY common; it generally gives a 1870 code.
2. Leaking TCC Solenoid - the one bolted into the pump.
3. Bad Torque converter as your trans shop thinks
4. Intermittent electrical connection
5. I don't know if a bad TCC PWM solenoid could cause this.

One question: Do you have a "Check engine" light on? If yes, you need to get the code(s).

You said it started when the engine was rebuilt. Perhaps they accidentally nicked or crushed the harness going to the trans. Or dropped the converter.

You mentioned that the trans was rebuilt. You could ask if the TCC valve in the VB was checked or replaced. It is quite expensive and time consuming to replace it, so perhaps they skipped this step.

Here is what I would do:

1. Drop the pan and replace both the TCC apply solenoid and the TCC PWM solenoid. You have to cut the apply solenoid out of the harness and splice a new one in. The
TCC PWM solenoid snaps out/in. With luck, that will cure it.

2. If you don't mind a firmer lock-up engagement, Transgo makes a TCC valve kit that replaces the finicky PWM valve with a on/off valve. (It is included in the HD2 shift kit, but should be available separately too.)

3. Else, while you might have a rare problem in the electrical harness/PCM, you will likely have to replace the converter.

WARNING - I'm not a trans expert, so take this as just ideas and not absolute truth.
Good luck and keep us posted.

majines

Thanks "mrvedit".....There is not a check engine light on. I will look in to your recommendations and hopefully I can get a resolution to this problem.

skiattle

I have exactly the same issue after having a new GM engine put in my Suburban. Did you come up with a resolution .. Before I take it onto the trans shop?

Had it back to the dealer who replaced the engine and they aren't able to determine the problem. Showed me a tech bulletin about TCC lockup. But that's not it. Definitely started after engine R&R

Catalyst code only .

Thanks for your response

99 K1500 burb 5.7 169K

majines

Still no resolution for it. It is going back to the mechanic that did the engine rebuild to see if he can find the problem. Taking it to him in the morning, maybe he can resolve it soon. I'll update after that.

majines

I'm starting to think there is a problem in the PCM. Engine guy says it's possible

majines

Also if they can't find the problem I will get them to either set the speed the TCC locks up to above 90 so it won't jerk hard anymore or disconnect wire to seloniod. Until someone finds a solution.

majines

Something different. I took the van on a quick trip to the store. it is cooler this morning . probably 15 degrees cooler and the nibble & bites / jerking took longer to start. about 4-5 miles further down the road before it started. When the temp has been warmer it was consist to when it would start. i actually had a mental spot on the road that marked when it would start. so is this a sign of a electronic component taking longer to heat up since it's cooler out today, hense it took 4-5 miles further to start jerking .

miker2

iTrader: (1)

since the tcc is applied by the ecm grounding the solenoid,there may be a spot where the harness is worn thru and rubbing on the engine or transmission.

majines

Well after many days of the mechanics searching for a solution, they have not found any explanation. They don't think it's the PCM or the PWM, but I'm still not sure of that. I got the van back yesterday, I have been out of town for a few days.

Thanks for the input miker2

I thought that possible also. They supposedly searched all the wiring. My only other choice is to go over all of it myself and if nothing is found, then maybe replace the PCM and see what happens.

AllenRuppert

Sorry for bumping a thread from 2012, but majines description is identical to a problem I am having in a GMC Sierra. Did you ever find a solution?

mrvedit

Allen: First, welcome to the forum.
Very likely the OP is no longer active here. Therefore since you have now made one post, you can start a new thread and we will try to help you out.