3rd to 2nd downshift trouble

[kjohns18]

I need help with my 4l60e! When taking off from dead stop it shifts fine from 1 to 2 but then the 3rd to 2nd downshift soleniod goes dead and the car falls on its face and some times even sounds like it is misfiring then it takes off and puts you back in the seat. I was told that the 3rd to 2nd downshift soleniod should always be on except when making a 3rd to 2nd downshift. please help!!!!

[joecar]

It goes 1->2 and then what happens...?

Are you saying the engine bogs down after shifting into 2nd...?

Does it shift 2->3...?

How do you know the 3-2 solenoid malfunctions...?

Are you able to test the 3-2 solenoid using scantool bidirectional controls...?

Are you getting a DTC (...IIRC maybe P0785 or P1886...?)

Engine shouldn't misfire... this is a problem all of itself.

[joecar]

The 3-2 solenoid controls the rate of 3rd accumulator exhaust.

(when going up into 3rd, the 2nd servo piston acts as the "accumulator for 3rd" gear; when going downto 2nd, the "3rd accumulator" must exhaust quickly... i.e. the backside of the 2nd piston must lose all fluid pressure to avoid impeding the the apply of this piston by pressure from the front side).

[joecar]

Follow these diagrams (look at what the 3-2 control solenoid valve does):

2nd Gear (http://img215.imageshack.us/img215/8404/2ndgearre2.png)
3rd Gear (http://img444.imageshack.us/img444/7513/3rdgearof8.png)
3-2 Downshift (http://img213.imageshack.us/img213/5373/overdrive32ct3.png)

See how 2->3 upshift pushes the 2nd servo piston to the released position (3rd accum)...
To apply the 2nd servo piston for 3->2 downshift, the 3rd accum pressure must be released in a hurry.

[joecar]

If the 3-2 solenoid was always off, then going 2->3 would cause 3rd accum fluid (which releases the 2nd servo piston) to bang into 3-4 CL fluid (pressent in 3rd and 4th)... the net effect being to still release the 2nd servo piston and to still apply the 3-4 clutch... (normal 3rd gear apply).

If the 3-2 solenoid is always off (exhausting 3rd accum fluid), then going 1->2 should have no problem since the 2nd servo piston would have no impedance behind it and it would just apply normally.

[joecar]

3-2 solenoid being off always doesn't explain what you described, but may be an additional problem.

[kjohns18]

I am using a scantool to see what soleniods are on and off. The 3rd to 2nd downshift soleniod when takeing off is not being turned on so it shifts from 1st to 2nd ok but when it goes to shift from 2nd to 3rd the car falls on its face like you pulled the ebrake. Then after this bogging affect the 3rd to 2nd downshift soleniod gets turned on and the car takes off fine and shifts good until you stop and take off again. I was told that the 3rd to 2nd downshift soleniod should always be on until a 3rd to 2nd downshift takes place. I hope this helps you more and Thank You for your help!

[joecar]

Hmmm...

Either:
- the PCM is not commanding the 3-2 solenoid on, in which case something may be wrong in your tune/calibration;
- you may have a partly broken/loose wire or ground somewhere;

Are you getting any DTC's...?

This is a tough problem to diagnose.

The question is: is the PCM not commanding it on, or is there some other problem.

When this solenoid is off, it should have no effect on 1st, 2nd, 3rd gears.

[joecar]

When the 3-2 solenoid is off in 3rd gear, fluid pressure gets past the 3-2 control valve (yellow circle "5c") and just equalizes on both sides of checkball #2 and orifce #12 (blue circle "12"), which is what checkball #2 does anyway...

I think you may have other "electrical" problems.


See the red squares in the attached pic...

[joecar]

Added pic to my post.

[kjohns18]

I did a little test of my own using a meter and reading voltage from my pcm white wire 3rd to 2nd downshift soleniod to ground and found that the voltage went to 0 when this bogging happened but after it cleared up the voltage never did come back to 12+ volts so is my info on the soleniod always being on correct or is this not true. I would also like to know what sensors could be bad like maf and what others could cause transmission trouble and I have check engine light on but have not got the scantool on it to see what code it is. Thank You!!!

[joecar]

I don't know that it is a particular sensor... retrieve all DTC's using the scantool (there may be more than one present).

Do you have a log of when this happens...?

0V on the white wire turns on the 3-2 solenoid, 12V turns it off.

Where/how did you probe the white wire, which connector/pin number (are you certain that it's the right one)...?

What year/model vehicle is this...?

[kjohns18]

I have a 2001 trans am trick flow heads,cam,push rods and hartland sharp roller rockers with a 3000 tci stall dyno tuned and making 430rwhp with 400rwft/lbs. I am splicing onto the white wire number 79 on the blue plug.

[joecar]

Yep, C1:79 circuit# 687 is the right one.

[joecar]

Were you able to view the DTC's...?

[kjohns18]

The code was a random missfires which I get alot of from the cam install. I want to get with my programming guy and get rid of the random misfire code. I would like to know if anyone can help me with what different sensors I need to look at for this 3rd to 2nd downshift soleniod being turned on and off on upshifts. I tried a new maf sensor today and I looked the tps but did not replace it. I still believe my problem is the soleniod because that is when the car bogs it drives perfect other than when this soleniod screws up.

[kjohns18]

I also wanted to ask if anyone had some wire diagrams of the pcm,sensors,and transmission or does somebody know of a website that I can get some diagrams from.