KS02WS6

I have a 94 Trans Am GT with low miles. After 21 years the car still had the original Tranny fluid and filter. Decided to service the car and swap out a few parts at the same time. The only issue with the car was a somewhat harsh shift from 1-2. I changed out the pressure control solenoid, the 1-2 and 2-3 shift solenoids, the 1-2 accumulator piston and spring and the manifold pressure switch. Test drive had no shift to 3rd or 4th. It seemed obvious that the new 2-3 shift solenoid could be bad. Reinstalled the original 2-3 shift solenoid today and still have no 3rd or 4th. Sure could use some help with this before I have to put all the old parts back in. Any thoughts?

coryforsenate

iTrader: (1)

Do the rpm's shoot up when it tries to shift to 3rd?

Have you checked line pressure?

KS02WS6

No change in RPM as the car does not try to shift to 3rd and remains in 2nd gear. When in 2nd gear if I let off the throttle the car freewheels....if I add throttle rpms increase as it is still in 2nd gear.
Line pressure not checked as tranny was working fine prior to parts change.

mrvedit

It does sound like solenoid B being stuck in the ON position.
Since the pro builders here (like Clineberger) say that solenoids rarely are stuck ON, I would also check the harness carefully to look for a shorted or pinched wire.
Either that or you mixed up Solenoids A and B when you tried to reinstall the old B.
When you are upside down, it is easy to mix them up. Solenoid A is modestly spring loaded which will pop it out when you unclip it. Solenoid B will not pop out by itself.

Scanning for codes might help you diagnose the problem.
An engine sensor code could cause the trans to stay in gear until a much higher RPM than you expect.

Thought of something else: if you broke a weak wire to the manifold pressure switch, the PCM might think the shifter is in D2 and therefore not shift to 3rd. After 20 years, I would consider replacing the harness, or at least checking it very carefully.

KS02WS6

I am positive I changed out B correctly as I used a picture you posted back in 2012 of the underside of the tranny identifying A and B. B did not pop out.
I will take another look at the wiring on the manifold pressure switch, also known as the fluid pressure switch assembly, when I drop the pan again. I'm thinking now that this switch could be the culprit.
I am not getting any check light but will go ahead this evening and check for a code on my tester. Thanks for your help on this!

KS02WS6

Scanner indicated "no code"....but this is an OBD1 system and I am unsure of the scanner accuracy. The factory manual did indicate that if the PCM sees a bad voltage combination on the switch it should result in a code 028.
However, I still think the pressure switch is prime for review and I will likely switch it out for the old one unless someone has a better thought.

KS02WS6

To mrvedit: I pulled the new pressure switch today and found 2 very small split o-rings and 2 small circular brownish color lens appearing pieces laying loose on the switch. The new switch appears much like the old except it has a plastic cover on the top side which the old switch did not have. The new one also has a couple of o-rings that the old one does not have. It is possible that they came off in disassembly. I do not know the importance of the O-rings or the lens appearing pieces. By the way, the new switch was an AC Delco, same p/n as the original. At this point I am not comfortable putting either one back on the car. I am going to reorder another switch and hope I get a good one.

coryforsenate

iTrader: (1)

The little "button" inside the O-rings is the sensor is for the different gears. I'd guess if the O-rings or the "buttons" are damaged, it could confuse the transmission as to what gear it is in.

Per chance could you say which O-rings are bad? It'd be interesting if they corresponded with the 3rd and 4th gear sensors.

bbond105

The o-rings seal off the oil coming from the hole in the valve body under the switch. The valve body sends oil up to the switches through those holes and pushes on the “circular brownish color lens” to activate the switch, which in turn tells the PCM which gear the trans is in. If the o-rings are leaking the trans will confuse the PCM and the trans won’t shift. You can check the switch by using a scanner.

These o-rings will sometimes come off in disassembly or cleaning. Most rebuild kits have new o-rings to replace the old ones.

KS02WS6

Good question coryforsenate! That made me go back and look again. What I discovered is that the seal on D3 on the new switch was missing. D4 is good. Problem is I have three loose o-rings, two of which are split. That's 2 too many o-rings for the new switch. I am thinking there could be the possibility that a couple of o-rings from the old switch were stuck to the bottom of the tranny and I might have installed the new switch over those o-rings. I have no idea where the two small circular plastic lens came from. Thanks for the question! Hopefully a new switch will take care of this issue.

coryforsenate

iTrader: (1)

I know AC Delco isn't the "be all end all" it used to be, and sometimes they just sell the name to slap on a part, but I'm surprised an OEM one was so shoddy. Usually their OEM stuff is pretty good and it's the "Advantage" line that's the cheapo stuff.

If you're ever curious about their "quality rankings" with regard to their different lines

Best OEM
Okay Professional
Junk Advantage

KS02WS6

Final Entry: 4l60e now functioning correctly after install of a second new manifold pressure switch (gm manual calls this a fluid pressure switch assembly). Loss of 3-4 was as a result of an installation error of the pressure switch by myself. I failed to see O-rings from the old switch stuck to the bottom of the tranny and installed a new switch over the old O-rings thereby affecting the O-ring seal and the functioning of the switch.

mrvedit

Excellent news.
There seem to be various names for this pressure switch, the tech manual calls it "Manual Valve Position Pressure Switch" but "Manifold Pressure Switch" seems to be more common and even works in Amazon.
I wonder how many people get their entire trans rebuilt because of a bad one.