Can't Decide if TCC/TCC Solenoid Is Bad

[1987 GMC Jimmy]

Okay. I'm having an issue with my Torque Converter Clutch circuit on a 1986 700R4 with over 252,000 miles unrebuilt. I initially thought it was an ignition problem, but I learned otherwise after unplugging the transmission connector and thoroughly testing it for repeatability. I came up with a vehicle that runs great with the connector disconnected but has no lockup. The thing is that I don't know if it's a bad torque converter clutch inside the converter, which would warrant replacing the converter, or if just the solenoid is bad. I already jumped Pin A and Pin F on the ALDL and got the specified voltage, I know my ECM ground is good, and I have cruise control and brake lights so I know my brake switches are good.

Here are the symptoms when the TCC solenoid connector is connected:

*On a cold vehicle, nothing. It's my understanding that the TCC solenoid will not engage until the CTS says it's getting close to switching out of open loop operation (around 150*F), which makes sense because in the moment that it's cold, it does great with the connector connected.

*On a warm vehicle, plenty.
It'll do well until it hits fourth gear. If I keep accelerating through to interstate speeds, it'll be okay, but if I hang around at say 40 mph and try to accelerate from there, the car will buck, shudder, and chug like crazy. If I let it kickdown to third, it'll do much better. It sounds like really nasty detonation to me, which is why I assumed it was an ignition problem at first. Also, putting it into gear, reverse or forward, when the lockup is connected, especially starting from an inclined surface, will sometimes make it stall out at worst or bog down really bad when doesn't completely die. I also notice a lot of vehicle shudder when coming to a stop (fresh brake job completed) but none when accelerating. It runs all around better without the lockup connected. The idle is nice and stable in gear, and the throttle response is more like what it's supposed to be with a tip top fuel and ignition system. I have heard that the innards of the original torque converters can wear out and cause these exact issues, as I've heard the same about the solenoid and/or pressure switch on the transmission. I'd like to escape with just doing the solenoid, but I don't want to have to service the transmission twice because I gambled on the lesser of two jobs.

 

[yevgenievich]

Sounds like it is the lock up clutch it self. Or something else in the transmission that gets bind when lock up is engaged. But coming to a stop and low speed shudder does not make sense with the lockup, but could if it is the torque converter it self. Maybe try to put a test switch for manual lockup engagement for testing

 

[1987 GMC Jimmy]

If I do a test switch, and I hear the solenoid click, is that a for sure test that it's working properly? I'm leaning towards the torque converter, but I've read about people having similar issues, replacing the solenoid, and being good to go.

 

[yevgenievich]

It can still be sticking, but having a switch can help with troubleshooting. You can enable it in any gear, can disable it, can cycle a couple of times to check if it is sticking, etc... The issue at low speeds and slow downs/ start ups is what concerns a bit.

 

[1987 GMC Jimmy]

The issue at low speeds and slow downs/ start ups is what concerns a bit.

With the TCC and/or torque converter itself?

 

[yevgenievich]

Studder at low speed can be torque converter related or bind somewhere in the transmission due to load that also shows up later when tcc engages. Or could be other reason. My thoughts were along the lines of using a test switch for tcc to determine exactly when and how the issue happens. So then could point a finger at something more speciffic.

 

[1987 GMC Jimmy]

Studder at low speed can be torque converter related or bind somewhere in the transmission due to load that also shows up later when tcc engages. Or could be other reason. My thoughts were along the lines of using a test switch for tcc to determine exactly when and how the issue happens. So then could point a finger at something more speciffic.

I'm gonna try to do this over the weekend with one of the little parts store transmission pigtails. How do I approach making the switch. I need to ground the ground wire on the pigtail and apply or subtract power to which of the two other wires?

 

[Honky Kong jr]

Ground source to switch, switch to pig tail.

 

[1987 GMC Jimmy]

Gotcha

 

[yevgenievich]

Need to also have 12v at one of the pins. Just probe the existing plug to see which pin gets 12v

 

[87scotty]

We sure its not fuel related

 

[gpmorgan]

*On a warm vehicle, plenty.
It'll do well until it hits fourth gear. If I keep accelerating through to interstate speeds, it'll be okay, but if I hang around at say 40 mph and try to accelerate from there, the car will buck, shudder, and chug like crazy. If I let it kickdown to third, it'll do much better. It sounds like really nasty detonation to me, which is why I assumed it was an ignition problem at first. ........................................................... I had this same issue with a 700 r4 in a 92 c1500. Turned out to be the dist cap.

 

[yevgenievich]

For me, good testing with manual lock up can hekp bring out what the issue is. Having the load on demand to see when the problem really comes in

 

[4WDKC]

hold on back up you said 86 and ECM is it TBI or Carb? Reason I ask is my was stumbling like you're describing in OD lock up when the ecm opened the EGR/AIR. It could also be the same thing you are seeing when cold ECM ignores all the sensors and uses preset values, when warm it tries to enable air and/or EGR with an exhaust leak causes the truck to snort,buck and even die. Any chance you have access to a scanner to see live data?

If its carbed pretend I said something witty and helpful.

 

[1987 GMC Jimmy]

We sure its not fuel related

Almost certain. Everything from start to finish in the fuel system has been checked, and it's all about fifteen months old. It runs great when that lockup connector is disconnected.

*On a warm vehicle, plenty.
It'll do well until it hits fourth gear. If I keep accelerating through to interstate speeds, it'll be okay, but if I hang around at say 40 mph and try to accelerate from there, the car will buck, shudder, and chug like crazy. If I let it kickdown to third, it'll do much better. It sounds like really nasty detonation to me, which is why I assumed it was an ignition problem at first. ........................................................... I had this same issue with a 700 r4 in a 92 c1500. Turned out to be the dist cap.

I checked this one, too. Cap is about fifteen months old, and it has no corrosion, burning, melting, etc.

hold on back up you said 86 and ECM is it TBI or Carb? Reason I ask is my was stumbling like you're describing in OD lock up when the ecm opened the EGR/AIR. It could also be the same thing you are seeing when cold ECM ignores all the sensors and uses preset values, when warm it tries to enable air and/or EGR with an exhaust leak causes the truck to snort,buck and even die. Any chance you have access to a scanner to see live data?

If its carbed pretend I said something witty and helpful.

It is carbed, but it has the CCC system with an E4ME Quadrajet. I tried to test this by plugging the line going into the EGR valve, and I also tried unplugging the diverter to see if I could notice a difference. It ran just as the bad. The only thing that will eradicate the symptoms I'm having is unplugging the lockup. It'll still do a little of that shudder right before you come to a complete stop, but the shaking and all those grandiose symptoms go away. Plug it back in, and it comes back immediately.