94 Car with 95(?) Transmission

[Gojira94]

Back from the dead thread.

With the help of some folks who do lots of GM EFI tuning on another forum , it was determined that the tune was bad. The 94 PCM mask was still used and the tables that are normally empty for PWM control were filled with 95 PCM data. This would never work because when the PCM reads its mask info it treats the normally empty areas of the EPROM as empty, no matter what.

So I got hold of a factory 95 tune and did it myself, basically not much more than doing the O2 sensor relocation since it has headers and duals. The guys at the other forum verified for me that everything was good and it was 95 code and the PCM was reading the tables for PWM.

It still throws a silent code 84. My last idea is to pull the internal solenoid harness, thinking it may be a custom harness of some sort or is just faulty. First pull it and clean it and check the pinouts vs what it should be in the wiring diagrams.

I'm just out of ideas...

[CPT]

You most likely have a '96-up 4L60E. Simply swapping the solenoid will get rid of the code, but it doesn't address the real issue. the actual valve body casting and 3-2 valve line up are different. Just changing the solenoid without addressing the other mismatch will cause forced downshift (kickdown) issues.

Frank

[Gojira94]

Thanks, Frank

I'd almost give my left nut for a copy of the build sheet on this transmission, lol. Can you elaborate on the 3-2 valve lineup and what those forced downshift issues look like? Would replacing the 3-2 valve be part of addressing the real issue? I'm going to go back and read the year swap thread if I can find it to understand the differences and how to make different years work back and forth. I may try the solenoid swap and see if that takes away the code and gives me the issues with downshifts like you said. Or If I knew what to look for on the valve body casting I can drop the pan one more time and look for visual evidence that it's a 96+ transmission.

[CPT]

Thanks, Frank

I'd almost give my left nut for a copy of the build sheet on this transmission, lol. Can you elaborate on the 3-2 valve lineup and what those forced downshift issues look like? Would replacing the 3-2 valve be part of addressing the real issue? I'm going to go back and read the year swap thread if I can find it to understand the differences and how to make different years work back and forth. I may try the solenoid swap and see if that takes away the code and gives me the issues with downshifts like you said. Or If I knew what to look for on the valve body casting I can drop the pan one more time and look for visual evidence that it's a 96+ transmission.

You can't just swap the valve. The actual valve body casting is different. The up to '96 valve body used a 2 piece 3-2 valve with 2 holes in the separator plate over the valves. In '96, the valve changed to a 1 piece design with only 1 hole in the plate. The problem now is that you can't simply swap the valve body and plate now because the pump has to match the valve body. The ONLY way to make what you have work correctly in your car is to pull the trans back out and have the front pump, valve body, separator plate, and internal wiring swapped. You can Ohm the 3-2 solenoid to see if you have the wrong one. Yours should have a tan connector with steel stem that goes into the valve body or a gray connector with plastic stem. Tan connector with plastic stem is the wrong one for a '93-'95 vehicle.
Depending on the mismatch, it either won't have kickdown or will exhibit a 3-neutral-2 downshift.

Frank

[CPT]

1996: The 3-2 downshift strategy was changed to an on /off arrangement. The 3-2 downshift solenoid was changed to a 20-31 OHM solenoid, from the previous 10-15 OHM solenoid. The 3-2 control valve was changed to the second design valve. The easiest way to identify the valve is, the second design valve will fall out as soon as the solenoid is removed. The first design has a plug and retaining clip. TCC solenoid remains 10-15 OHMs, which is the same as the '95 arrangement. Has PWM stamped cast in pump. pump is the same as '95. Will not interchange with '95 unless changing 3-2 solenoid, valvebody casting, and seperator plate. Has holes in plate marked in diagram. '94 or '95 computer will not accept the 20-31 OHM 3-2 solenoid and will throw an SES light and throw the transmission into limp mode. Some less knowledgeable builders will swap the solenoid so the computer will see the correct resistance, but the valve itself then causes downshift issues. If only the solenoid is changed, it will result in a 3-2 downshift cut loose. In other words...3-neutral-2 downshift. Speedo moved to passenger side of tail housing, but easily changed.

[Gojira94]

I get 11.8 ohms, right in the middle of the spec for 94-95's 3-2 spec of 9-14 ohms. The VSS is on the driver's side but that could have been moved when it was built. If it's a 96+ transmission after all I think I'd rather find a 94 trans and call it a day. I'm tired of fighting this thing. I did change the 3-2 solenoid when the problem first appeared in 2011, not knowing any better. I don't recall whether or not the valve tried to come out behind it but I don't think so.

[Gojira94]

Finally have some pictures of the valve body/ solenoid arrangement. I do see on one of them the valve body has 95 cast into it, and a number sequence that looks like 3678593 or 3678595 but my eyes aren't great and neither is the picture, so 3s look like 8s look like 5s and 6s to me, lol.

I guess next I need to dig into the internal harness. Pull it and compare to a known good one for 95 maybe, if I can't at least account for the presence of the right number of wires coming from the case connector.

[Gojira94]

I fished the case connector and VSS pigtail up to the engine bay where I can work with it easily. I have a 1 1/4" socket to pop the case connector out of the case. I'm trying to get the pressure control solenoid out of the way for that but it's hitting the accumulator housing.

Before I pull the accumulator housing I wanted to ask before I run into any surprises trying to reassemble. I know there's a pair of pistons and a pin that moves on the housing side, the other pin is part of the housing. Spring in the middle. Bolts are torqued to 110 in. lb. on reassembly, careful with the acc. housing gasket of course. I think I'm going to go ahead and just be careful getting it down so I don't have the spring scattering stuff around as it comes off. Then keep going with the internal harness and removal of the solenoids.

Goal here is to be able to bench test the whole arrangement outside of the trans using 12V available at the battery.

[Gojira94]

well, damned if I can get the case connector out of the case. I'd read that a 1 1/4" 12 pt socket is the way to go but I can't force it down onto the tabs to compress them. Trans is in the car, limited room but I can get a prybar on the back side of the socket and apply pretty heavy force to it but it's not going over the tabs. Maybe should have picked up a 1 5/16" lol.

Interesting what I saw when I removed the accumulator housing. From the acc housing going upward toward the case, I have 3 large washers on the fixed pin in the housing, a spring perch on top of the washers, a spring, just one piston, and another spring on top of that. It appears the separator plate blocks the recess that would be in the case. Maybe I'm thinking 700R4 and this is normal and the 1-2 and 3-4 are on opposite sides, with one of them in the valve body.


Getting the case connector out- I guess my next step is to try to get at it better from the top. For what I've got that means unbolting the cross brace and letting it hang a little lower and maybe get on top of it better and figure something out. Kind of pissed I'm this close and stuck.

[Gojira94]

Lowering the trans a bit helped me get the socket wiggle I needed to drop the case connector through the case.I pulled all the solenoids and checked them again for resistance. Values in ohms are:

1-2 shift 21.2
2-3 shift 21.9
Press. Control 4.6
3-2 control 11.4
TCC 23.8
TCC control 11.2

Here's the bench- notice the PCM removed so I can apply voltage down the wire to pin E and ground through the PCM connector pins for each solenoid (except the pressure control solenoid). PCS can be tested with a 9V battery briefly. Testing from PCM down to solenoids gives me more confidence things are working. Honestly, I'm hoping to find something wrong with the harness and just replace it and be done. I'm done for tonight, testing tomorrow and hopefully the final answer.