4L60E low line pressure, 1-2 upshift slip

[cope1980]

2004 Envoy XUV 4.2 L

History:

1 year ago, was stopped at a light at the bottom of a hill. Took off and as going uphill, lost 3 and 4 gears.

I followed a video by Transmission Bench on YouTube to the letter and rebuilt the transmission myself. Replaced all clutches and steels, replaced the band, replaced bushings and seals, replaced A and B shift solenoids. Cleaned and reused EPC solenoid and TCC solenoid. Replaced separator plate gaskets only. Separator plate was dimpled from a check ball, not punched thru. Gently reformed plate with hammer on a vise. Replaced 1-2 accumulator piston and seal.

After reinstalling transmission, I noticed that transmission was not shifting from 1 to 2 on hard acceleration. 1st gear would hold until approx 15 mph and approx 2200 rpm, rpm would flare up to approx 3000 rpm. If I let off the throttle, it would upshift and be fine. I learned to baby the acceleration and it shifts normally. Drove with light acceleration until now.

This last weekend, I was able to check line pressure and it is definitely low. 65 psi in park, 75 psi in drive and 115 psi in reverse at 1500 rpm. Pressure rose about 25 psi over each of the readings at 2500 rpm. I was unable to test EPC solenoid (incremental amp test).

 

[cope1980]

Update:

I reinstalled the pressure gauge and checked the line pressure at idle in park, about 65 psi. I then disconnected the ground wire to the EPC and line pressure went to about 205 psi. I drove the car about 2 miles with EPC ground disconnected. Transmission shifted thru all gears without slipping, however the shifts were pretty harsh.

I am at a loss as to what to check now. I am assuming that my issue is electrical?

 

[cope1980]

I have an amp meter installed in series with the EPC ground. At idle, I am reading 1.01 amps in Park, Reverse, Neutral, Drive, 3rd, and 1st. And I am reading .86 amps in 2nd.

 

[TJBaker57]

I have an amp meter installed in series with the EPC ground. At idle, I am reading 1.01 amps in Park, Reverse, Neutral, Drive, 3rd, and 1st. And I am reading .86 amps in 2nd.

Do you monitor these amperages in Torque Pro or equivalent?

I am assuming the PIDs Torque Pro uses are the same parameters here.

 

[cope1980]

Do you monitor these amperages in Torque Pro or equivalent?

I am assuming the PIDs Torque Pro uses are the same parameters here.

I do not. I only have a DC amp meter in series with the EPC solenoid wire.

 

[Mooseman]

And I am reading .86 amps in 2nd.

Maybe that solenoid is bad or has a bad connection?

 

[cope1980]

Maybe that solenoid is bad or has a bad connection?

I think you are referring to the shift solenoid.

I'm measuring the pressure control solenoid. I think it's also called the force motor.

 

[cope1980]

 

[AmpOverload]

If you haven't already done so, I'd suggest downloading the incredibly detailed, useful, 185-page PDF file for the 4L60E transmission (and others) that's attached to this post by @mrrsm.

Did you decide on a scantool yet? Honestly, with the right software, a very inexpensive scantool can be incredibly useful.

 

[cope1980]

If you haven't already done so, I'd suggest downloading the incredibly detailed, useful, 185-page PDF file for the 4L60E transmission (and others) that's attached to this post by @mrrsm.

Did you decide on a scantool yet? Honestly, with the right software, a very inexpensive scantool can be incredibly useful.

I actually have downloaded it. I also have downloaded the service guide from Mooseman.

There were no codes for the transmission, so I'm hip shooting in the dark. I know the line pressure is not correct.

I have not been able to buy the scan tool yet. I had the funds, but hours got cut at work and the money got diverted.

 

[cope1980]

Today, I dropped the pan and checked the EPC solenoid, AFL valve, Boost Valve and Pressure Regulator. I am very suspect of the Boost Valve Sleeve. It seems slightly loose in the pump bore and the lands on the Boost Sleeve are scored. I did not replace the Boost Valve or Boost Sleeve when I rebuilt this transmission. I think I am going to order and replace the Boost Valve and Sleeve before I chase this any further.

The EPC solenoid screens are clean, and the AFL and Pressure Regulator are very tight in their bores.

For now, I am replacing the filter and pan gasket and driving as I have been until I can replace the Boost Valve.