coryforsenate

iTrader: (1)

Dynamic396, that pressure is only when it's unplugged.

From OP's post

"Unplugged line pressure was at 275psi in Reverse and 200 in all other PRNDL positions.

Plugged in, line pressure was at 100-110psi in Reverse and 60 in all other PRNDL positions."

I'm not an expert at all. Is what you're saying that since it's capable of generating that pressure, even though only when unplugged and turned to limp mode, that should rule out the boost valve as a problem?

Would that suggest an electrical problem then?

Dynamic396

Yes...

When it's unplugged, there is no current at the EPC solenoid and it defaults wide open. If the EPC were plugged or stuck closed, or if the AFL regulator had a problem, or if the boost valve was faulty, you would not get the healthy line pressures that I see here.

But when the transmission gets plugged back in and current returns to the EPC, pulling it closed, pressures drop to roughly where they should be at closed throttle (no EPC boost). I'd like to see a little higher than 60 psi, but it's certainly adequate. A stiffer PR spring would bring that up a touch.

mrvedit

The OP reports only 75 psi in Reverse with everything connected.
That is almost impossible with a properly working/fitting boost valve.

I try to help amateur/home mechanics fix their transmissions and the Sonnax boost valve has helped many fix related problems related, including worn bores and even missing parts. It also increases line pressure across the board for slightly firmer shifts.

I know that pro mechanics often have their own modifications and building techniques, but even when shared, they are often too complex for a home mechanic.

It sounds like you are a pro mechanic and therefore hope you will continue to share your valuable insight and knowledge here.

Dynamic396

Is it...? Hmmmm... A 25% increase over base line pressure with just R/I pressure. How much do you figure it should have?

Remember that you have R/I oil acting on the boost valve lands. In reverse, the manual valve is going to feed line pressure to the R/I clutch and, in turn, the boost valve. On an OEM .471" boost valve, the large land is .505". That's only .029" difference. You're just not going to get much of a pressure boost with 60 psi acting on that small of a differential. As line pressure increases, so will the amount of boost, but from 60 psi to 75 psi at base, with no EPC sounds about right...

clinebarger

I mean not at idle with the EPC at "Full Current", The only boost is from the Reverse reaction area of the boost valve, From the testing I have done on other 4L60E's....A 10 PSI boost is way low.

I think it would be a good idea to ditch the TG Boost Valve.....

I am all for him doing some EPC operation testing! Not sure if he has a scan tool to command the EPC through the PCM?? Or at least able to monitor commanded EPC Current & then he compare to actual Current applied with a Amp Meter.

Here is a Amp VS Pressure chart.

Dynamic396

Yeah, he can ditch the Transgo valve in favor of a Sonnax, but that's not what's causing the problem. He's getting no EPC boost whatsoever from a hydraulic system that's capable of making 200+ psi when commanded to. He needs to find out why it's not being commanded to.

He's getting a 15 psi R/I boost at minimum line pressure, and a 75 psi R/I boost at max line pressure. Seems about right to me. There's not much of a difference in diameter between the two lands. You won't get much at low line pressure, but the amount of boost will increase the higher the line pressure goes. A 60 doesn't need much R/I boost to work properly.

Those two tables you posted are for factory boost valve sizes; the first would be for a .420", and the second for a .471". Use them as a guide, not as gospel truth...

NJNETSFAN

iTrader: (15)

Sorry for my lack of participation in the thread. I plan on replacing the boost valve on Saturday. I have Hptuners and it looks like I can change Force Motor current through VCM controls. This seems like the way I can test the EPC solenoid.

Dynamic396

Yes, you should be able to manipulate the EPC using HPTuners. But, we already know that your EPC is working just fine, as are the rest of the hydraulics in the transmission itself. I think I'd go after the electrical problem that is causing your EPC to be pulled closed and kept there before I wasted my time changing that boost valve...

NJNETSFAN

iTrader: (15)

Can we 100% say that the EPC is working? Since no current=closed=max pressure, what if when it has any current going through it, the seals are leaking causing pressure not to rise? Besides moving the PRNDL, pressure does not follow load or RPM.

Dynamic396

No current=OPEN=max pressure. When you unplug your transmission, removing all current to the EPC, you get 200 psi in "Drive", and 275 psi in "Reverse". That's all working...AFL regulator, EPC solenoid, boost valve, pump, etc. Good, perfectly serviceable maximum line pressure.

1.0 amp of current=CLOSED=minimum pressure. With the transmission plugged in, you get 60 psi in "Drive", and 75 psi in "Reverse". This is normal for closed throttle idle, but your problem is that it never increases when you apply throttle.

Either your PCM is never commanding a REDUCTION in EPC current to increase line pressure for some reason, or some sort of a short is keeping the EPC closed, even though the PCM is commanding it open to send a higher amount of EPC pressure to the boost valve which, in turn, increases line pressure in order to handle the increased load the transmission is seeing from the engine.

What seals are you referring to...?

NJNETSFAN

iTrader: (15)

I was thinking of the pressure manifold when I mentioned seals. If you were in my position, where would you start your electrical diagnosis? My first thought is dropping the pan and measuring current at the epc connector while varying epc command through vcm controls.

Dynamic396

The pressure switch manifold is not involved in the EPC system. No chance for leaks there to affect anything with the EPC system.

I would definitely measure current to the EPC, but I'd do it at the PCM so that you can still run the car and measure pressures. You'll have to locate the two wires at the PCM that go to the EPC solenoid. They should be terminals 6 (red/black) and 8 (light blue/white) of connector 2 at the PCM. Once you locate them, first check both of them for continuity to ground (with the PCM disconnected); there should not be any ground on either. If you do have a ground on either one, find out why... Once you have verified that, plug the PCM back in and cut either one of the two wires so that your ammeter can be installed into the circuit to measure current on the circuit.

joecar

Use the scantool to sweep EPC/PCS current thru the range (1.1A to 0.1A and vice-versa) while watching a pressure gauge...

if pressure matches current (in inverse relationship) then problem is within the calibration and/or the PCM;

if pressure stays static (stuck low) then the wiring has a short (as said above).

NJNETSFAN

iTrader: (15)

Ran the continuity test today....checked terminals 6 and 8, both did not ground so no short found.

NJNETSFAN

iTrader: (15)

Dropped the pan this morning, fluid was pretty dirty for a transmission that only has 500 miles on it. I plan on replacing the boost valve while the pan is off, are there any electrical tests I should do while I have access to all of the solenoids?

Dynamic396

Not really. Nothing that can't be done from outside. Besides, we know that stuff is functioning properly inside the transmission. It's just not being told to...

NJmooch

I'm still concerned about the servo pin that hasn't been replaced. This would explain the 1-2 slippage.

Also, if the trans fluid looked dirty, would the EPC screen be clogged? And possibly the 1-2 and 2-3 shift solenoids as well?

Last but not least, would a bad throttle position sensor cause some of these problems? That sensor does send signals to the PCM which in turn sends signals to the EPC, right?

Please correct me if I am wrong on any of this.

Dynamic396

What's wrong with the servo pin? I pretty much don't ever have to replace servo pins. How much servo clearance do you have? You're slipping in 2nd because you don't have enough line pressure...

If you had a clogged EPC screen, you would not be able to make 200 psi of line pressure when you unplugged the transmission.

Yes, a TPS could cause these problems, but they're pretty reliable. I don't see too much trouble with them. Not impossible, though...

mrvedit

I know that Dynamic396 disagrees with me (he is an expert and I am not), but since you now have the Sonnax boost valve, install that to rule out problems there. I still suspect something wrong there - perhaps the Transgo boost valve was install but someone forgot the aluminum spacer which it needs in pre-ISS transmissions. Or something is upside down, etc.

Then, since you have a pressure gauge and HP Tuners, it is trivial to perform a preliminary test. If you can fully adjust the pressure in HP Tuners, that will indicate the PCM, harness and trans/EPC are working properly.

Then, if you still have low pressure in Drive/Reverse we can start to suspect sensors or the tune.

Install the boost valve and first check the pressure in Reverse. If now 150+ you might be all set. Else, hook up Hp Tuners and report the results of your test.

Dynamic396

I seem to remember that it is capable of making 200 psi in "D", and 275 psi in "R" when no current gets to the EPC solenoid. Sounds OK to me...