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Hi!
I just ran a line pressure test on my 2003 Buick Rendezvous 4T65E transmission and would like help interpreting the results. I used a Tech2 scan tool to adjust the EPC valve currents as outlined in the GM Service Manual, then recorded the observed line pressures at each setting. Attached are the results...... as you can see, the pressures appear to be in the normal range except for two current settings: 0.5 and 0.6 amps. At those 2 settings the pressure is slightly lower than specified, tho not a lot lower. (my Tech2 would not select the 0.0 amp, .95 amp, 1.05 amp or 1.1 amp settings even tho the Manual listed readings for these settings in the table provided)
Is there any reason to replace the EPC valve as a result of these readings? The EPC Valve in the 2003 Rendezvous is the newer style (doesn't have the large black cylinder at the top end)

The other thing I noted was that as I manually rev'ed the engine to about 1400 RPM per the table's specification, the pressure fluctuated quite a bit at the 0.5 down to 0.1 amp settings, but not much at the higher settings (lower pressures). Since I have never run this test before I don't know if that is normal or not.

If you have info to help me, I'd appreciate it!
Nick

[attachment=0]2003 RDV Trans Line Pressure Test.jpg[/attachment]


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File comment: Line Pressure Test Results
2003 RDV Trans Line Pressure Test.jpg
2003 RDV Trans Line Pressure Test.jpg [ 122.73 KiB | Viewed 3693 times ]
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Are you actually having a problem with the transmission, or just want those results interpreted?

As far as I can see, the readings that showed lower than normal really aren't that much lower than the low end spec, so there should not be any issues or need to replace parts. If you are having a shifting issue, or slippage, there can still be other problems inside the transmission that won't show up on a pressure check.
_______________

GM Dealer Technician For 18+ Years
In the automotive industry for 20+


   
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Thanks for the response!
Yes, the upshifts have become long and lazy and the 4-3 downshift is incorrect. I watched the pressure gauge during a forced 4-3 downshift yesterday: At the start of the downshift the pressure dropped from about 90Psi to about 60 for a second or two, the engine RPM increased slightly during that time, the the actual downshift occurred rather abruptly and the pressure sharply jumped up to about 150-160 Psi. During the downshift the Tech2 showed PCS current dropping to near zero Amps during the pause when the pressure was about 60Psi, so the pressure should have gone up to near max. I'm thinking either the PCS was failing at that time, or there was something causing pressure leakage when the shift was commanded then stopped leaking causing the pressure to jump up and the shift to complete. I'm not sure how to differentiate and determine what actually happened. Any ideas???

I have ordered a Transgo shift kit and new PCS valve asm, bought a new filter and fluid. Unless I can learn anything more, I plan to install all of that in hopes of curing the problem shotgun method.

Do you know where I can find illustrations of fluid paths during various operating conditions of the 4T65E like GM used to put in their official service manuals in the old days? I thought that having that info might help determine exactly what SHOULD be going on during the downshift internally in the trans. I fixed an old Turbo-400 trans years ago that way, replacing a $5 broken spring after logically figuring out what might cause the problem it was having...... saved a complete rebuild, which is what all the shops I called wanted to do.

One other piece of info: When I checked the line pressures and PCS current in the various gear positions, this is what I got:
[attachment=0]Transmission Pressure in Gears.jpg[/attachment]

Notice that with the trans cold, the observed pressure in the "1" gear selector position was 160Psi even though the PCS current was .66Amps which should have given a pressure or about 90Psi. Once warm the readings were normal. The pressure also varied a lot at WOT in reverse...... not sure if that is normal or average.

Thanks much for your help! Nick


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I'm not really sure where you could find an actual fluid/pressure path diagram like the old days. I know GM doesn't make those anymore. You might want to go to your local dealership and have the parts department print you out an exploded view of the trans so that can give you a pretty good idea of the internals and workings/attachment of things.

It would be great to find something simple like you did before, but usually these transmissions aren't easily repaired like that. You might luck out with a pressure solenoid or other small part, but I've actually never seen that happen. It's always been either a valve body issue, pump problem, or other internal hard part that is failing and causing lazy or 'slipping' shift points and irregular pressure readings. Good Luck!
_______________

GM Dealer Technician For 18+ Years
In the automotive industry for 20+


   
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Hi again!
Just to give you some feedback for possible future reference: I installed the Transgo shift kit and it has helped the long-soft upshift problem a lot. It now shifts crisply but still smoothly. I actually only installed the 1-2 accumulator and 2-3 accumulator parts that I could reach by just dropping the pan. The other parts in the kit require further disassembly that I didn't want to tackle at this time. The 4-3 downshift seems better but not perfect still. Perhaps if I had installed the new 3-4 accumulator springs that came in the kit it would have helped that more.

Also, I had searched for a tool to remove the filter seal from the case but couldn't find one made specifically for that purpose. I didn't want to use the hammer and screwdriver technique that I have read about on the internet, so I made a slide-hammer type tool myself and it did a good job of removing the old seal. If you'd like a photo of it I can send it. I don't always replace that seal..... only if the filter seems to fit it loosely when I remove the filter (like when I changed the fluid and filter in my cousin Rhonda's Firebird.... never seen a filter fit that loosely before.. it almost fell out of the case!).

I managed to find what looks like a very good reference for learning the 4T65E internal operation, including fluid charts. I haven't downloaded it yet but you can find it at: http://www.scribd.com/doc/60667775/Tras ... bile-4T65E in case you're interested.

Hope some of this helps you help someone else in the future!

Have a nice Holiday season! Nick


   
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