Hello all,

I have this Grand Voyager which has 253k on the clock, 83k on the motor I swapped in, and 73k on the last transmission rebuild.

It's been working okay, with a few electrical issues here and there lingering form the engine swap and being 16+ years old in general. Yesterday when driving home, however, I had the cruise set at 70 MPH and the transmission kept allowing the engine RPM to jump up a few hundred RPM momentarily, before jumping back down. This happened within a second, maybe less. You could feel it when the RPMs were pulled back down. It kept doing this every now and then, and continued to do so even as I slowed to 60 MPH.

Earlier in the trip I had noticed the odometer and PRNDL selector seemed to be flickering a bit, though they weren't anymore when I got home. I am now thinking "electrical problem!" and start checking all the grounds I know of. I decided I would remake the negative battery terminal connection, and did so.

So I took the van for a drive and I had no torque converter lockup at all. I didn't drive it for long, but I figured "okay, lockup clutch must be done." When I got home I checked the fluid and it's at the appropriate level and still bright cherry red from my filter change a few thousand miles ago. Whatever, no lockup doesn't bother me as much as the lockup cutting in and out all the time.

Late last night I took a 25 mile highway trip, though, and about 3 miles in at 60 MPH, I feel a familiar bump and look down at the tachometer and hey, lockup is back. I could tap the brake pedal to unlock the converter and a few moments after I released it, it would jump right back down. I tried to ascend a long hill on the highway applying the maximum throttle input I could before the converter unlocked, and it would never slip. It worked normally for the rest of the trip.

I don't believe there can be an issue with the solenoid pack, because the Low/Reverse solenoid becomes the lockup solenoid after the van leaves first gear, and first gear and reverse both work fine. I also don't believe there is something mechanically wrong with the lockup clutch because the fluid is not degraded and when the lockup clutch can decide to work fine, when it wants to.

I've arrived at the conclusion that there must be something wrong with one of the inputs the vehicle uses to decide if the torque converter should be locked. I cannot find very much information about what has to be in place before the lockup call is made. I imagine there must be a minimum transmission fluid temperature, and perhaps the throttle position sensor value is used as well, but I am hoping someone can shed more light on this.

I have already checked for two-digit (CEL flash) and four digit (ODB-II scan tool) codes, and nothing is out of the ordinary (nothing stored for ODB-II, and 12-55 for the two-digit DTCs.)

Additionally, although it hasn't caused me any issues in the past few thousand miles (but maybe it's related to the current issue) the torque converter in this van is pretty whiney when it's slipping. When I take off I hear it whirr up and the noise gets lower and lower as the drivetrain gets closer to the engine speed, until it's inaudible. I've stall-tested the converter as much as I'm willing to (I'm afraid of shredding the transmission), and the stall speed is around 1,900 RPM. Interestingly the level of whine I get out of the converter with it slipping at about 1,500 RPM is the same level of whine I get in some situations when reaccelerating after taking a corner. I will reapply the throttle to speed up from about 20 MPH and the van doesn't really want to speed up, and the converter is whining away with the engine at around 2k RPM. If I apply more throttle, the van "bumps" as the transmission downshifts (from third to second, I believe,) the engine speed stays about the same, but the whining noise lowers in pitch (since the drivetrain speed is closer to the engine speed) and I can actually go somewhere. I'm not sure if the converter should be transferring more power to the drivetrain than it currently is, or if the transmission is just trying to stay in a taller gear than is reasonable for the current speed. I probably wouldn't notice it much if it weren't for the audible noise and the bump when it downshifts, and it doesn't cause any drivability issues, but I include it here in case someone has some insight.

I plan on attempting to get my local dealership to apply the latest firmware to the transmission controller. The transmission was rebuilt at a Dodge Dealership in 2002 (I have the service records but didn't own it then; the converter was also replaced during the rebuild according to this receipt) so I would assume they would have updated it then, but I see no "authorized software update" sticker on the transmission controller.

Thanks for reading and for any input, and happy Thanksgiving!

 

I have just a couple thoughts/ideas on this. How warm is your engine running? I think the coolant temperature is factored into lockup. I had a bad tstat in my Dakota and it would never lockup because it wouldn't get to temperature. Does the in and out lockup occur only under cruise control? I had a bad cruise unit in a Neon that would lock and unlock only while in cruise control.

 

Thanks for your reply. I think that the engine temperature is fine under normal operation but when it wasn't locking up at all it was probably very cold. I have never paid very close attention to how it locks up so I never noticed that it only works when the coolant reaches a certain temperature.

As for the cruise control, that is a very good possibility! I can't say for sure that it's happened when I was not using cruise. Also, the day it started happening I noticed that sometimes I would press Set an it wouldn't activate, but it would activate later on. I wrote that off as a fluke. So I suppose the cruise module must have other inputs to the TCM and its not just using the mechanical throttle linkage?

Last night I went on a 70 mile trip. On the way out it only did this once and on the way back in it did it three times. I'll refrain from using cruise control for a few days and see what happens.

Thanks very much!

 

Check the speed sensors in the transmission. They get gunked up with metal because there are magnets in them. They send signals to the computers (PCM & TCM). Remove them, wipe them off, and reinstall. If they get too bad you'll go into "Limp mode"

 

Mike, thanks for your response. When I replaced the fluid and filter a few thousand miles ago I pulled the speed sensors and cleaned them. They weren't very dirty on my van, but I have a magnet in the transmission oil pan which may be stock or may have been added when the transmission was rebuilt last. The magnet, which I cleaned, had some gunk on it that I assume was worn clutch material. It wasn't metallic at all. It was some very fine black goopy material that was really hard to get off my hands. Heh.

I haven't yet seen it slip out of lockup since I stopped using the cruise control. I'm leaning towards that being the problem but I'm not really sure how to fix it, since as far as I can figure out I don't have a standalone cruise control module. Would this mean the PCM/ECU is at fault?

Thanks for all your responses!

 

Not saying you should buy this exact one but that was the fix on my Neon.
http://www.ebay.com/itm/96-TOWN-COUN...498#vi-content

 

This vacuum tank that GRSWAT gave a link to is located under your brake fluid reservoir. They are notorious for having small cranks in the larger vacuum lines (which cause cruise control malfunction problems), loss of set speed, etc.
On my 1999 I used to have transmission "Shutter". I changed the fluid to ATF4+ (Not cheap), cleaned the "metal Goop" out of the pan (magnet is factory install), and the shutter problem went away (after the new fluid mixed with what was in the torque converter). The increased viscosity of the ATF4+ fluid changes the internal pressures inside the transmission and does marvelous things to improve transmission performance.

 

Ah okay. I was thinking there was some electrical module that did the cruise control.

Do you think this could be the issue even if the cruise control holds my speed fine? It doesn't ever feel like the cruise control is jerking the throttle or anything unusual that would make it come out of lockup. I'm still going to look over the vacuum lines in the morning to be sure they're not leaking.

Is there some electronic way the cruise or PCM in relation to the cruise control would unlock the converter due to a problem with the unit? I only see three solenoids as part of the electrical connector in the wiring diagram.

One thing I have considered is that possibly the TPS has a dirty spot, and since cruise is constantly adjusting the pedal, it may pass through that dirty spot more frequently than when I'm driving it manually, since I don't attempt to compensate for each and every slight hill and valley and mostly leave the pedal stationary.

For what it's worth I haven't seen the problem reoccur in the past few days. Whatever is causing the trouble is probably waiting for me to get 200-or-more miles away from my house so it can break completely.

The van does have fresh ATF+4 in the transmission, and a recently-replaced filter.

I very much appreciate everyone's input and suggestions.

 

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