A question for the Transmission experts

[NiftySVX]

Okay so my transmission has the following line pressure readings,

With resistor:

75 psi at idle in D

Short jump then settles back to 75 psi at stall

Without resistor:

270 at idle

75 at stall??!!?

This is going to kill my transmission, it doesn't have enough pressure to hold the brake band in 4th. I have tried 2 seperate TCUs and the tps resistance is 75 or so ohms at close and 4.9k at wide open.

Please help!

[Trevor]

The TPS resistance is in line with the specs. However so that you have everything correct, you should set the TPS for a voltage output of 0.45 - 0.55 with the throttle closed. Easy to do and full instructions are here in the selectable "How-Too" documents.

Can you measure line pressure while the car is on the road?

[oab_au]

Originally Posted by NiftySVX

Okay so my transmission has the following line pressure readings,

With resistor:

75 psi at idle in D

Short jump then settles back to 75 psi at stall

Without resistor:

270 at idle

75 at stall??!!?

This is going to kill my transmission, it doesn't have enough pressure to hold the brake band in 4th. I have tried 2 seperate TCUs and the tps resistance is 75 or so ohms at close and 4.9k at wide open.

Please help!

The throttle voltage increases as the pedal goes down. This progressively, turns off the A solenoid to allow normal line pressure.
There is another TCU control over the A sol to reduce the line pressure, responds to shifting, temperature, etc.
Disconnecting the resistor will give full pressure from throttle position, but the pressure can be reduced by the other signal.

Harvey.
PS traveling so small write.

[NiftySVX]

Yeah, but what could possibly be telling the tcu to back down line pressure to the base value it is at idle, unless the TPS is indicataing the throttle is closed, or the engine is at idle?

[oab_au]

Originally Posted by NiftySVX

Yeah, but what could possibly be telling the tcu to back down line pressure to the base value it is at idle, unless the TPS is indicataing the throttle is closed, or the engine is at idle?

Well you have the stall and idle pressures back to front,270 at stall, 75 at idle is about right. I don't have the book with me, but that is about it.

If you want to eliminate the TCUs action, you have to disconnect the A solenoid wire at the transmission plug.

Early model pumps could have a leaking gasket, that gave low line pressure at idle, normal at stall. The high gearing, resulted in low rpms, at low speed in D, hence low line pressure, with wear more leakage, lower pressure.

Harvey.

[NiftySVX]

Unplugging the connector at the trans makes a constant 270 line. With the resistor in place, throttle opening makes no difference on line pressure. It won't leave 75 psi, even with the tps Removed and manually rotated. However, with the dropping resistor unplugged, line is at 270 with throttle closed. As soon as you move the tps it backs down to 75. I'm going to start with replacing the TPS since it has a dead spot anyway, and if that doesn't fix it I'll have to pin out the tcu and read values. It seems like my tps is somehow operating backwards. Line should increase with throttle opening, not decrease. This is quite a trip, I've never seen one do this before.

Also it should be noted I have a level ten complete trans. It has about 80 miles on it. I also have lan's tcu.

[NiftySVX]

Oh and what i meant by short jump to 270 then settles at stall is that at stall speed it will not maintain 270, only for a short while, meaning the pressure drops back to 75 with the converter still at stall

[Trevor]

Originally Posted by NiftySVX

Unplugging the connector at the trans makes a constant 270 line. With the resistor in place, throttle opening makes no difference on line pressure. It won't leave 75 psi, even with the tps Removed and manually rotated. However, with the dropping resistor unplugged, line is at 270 with throttle closed. As soon as you move the tps it backs down to 75. I'm going to start with replacing the TPS since it has a dead spot anyway, and if that doesn't fix it I'll have to pin out the tcu and read values. It seems like my tps is somehow operating backwards. Line should increase with throttle opening, not decrease. This is quite a trip, I've never seen one do this before.

Also it should be noted I have a level ten complete trans. It has about 80 miles on it. I also have lan's tcu.

“Unplugging the connector at the trans makes a constant 270 line. With the resistor in place, throttle opening makes no difference on line pressure. It won't leave 75 psi, even with the tps Removed and manually rotated.”

Special thanks you for publicising this information as being a fact.

The resistor circuit most certainly does not constitute a direct control of line pressure relative to throttle position, as has been several time claimed of late and in difference to what I stated over a number of years.

The TPS signal is but one of a number of combined inputs, analysed by the TCU in order to arrive at the required setting of line pressure, via solenoid ‘A’. Why would it be otherwise?

As a result of the recent consistent incorrect reporting of relevant facts, I again set up an oscilloscope and checked the line pressure control circuit and resistor circuit, as I did years back. This in order to again confirm the then posted results. However the tests were as before, carried out while the car was stationary, so that I now anticipate vigourous error based argument.

In order to establish what is fact in the mind of the sceptic, I have recently purchased a 12 volt DC to 230 volt AC inverter, so that I can operate a small scope within the car, while it is being driven. Hopefully I will have an assistant and will be able to record results on camera.

Unfortunately I have been unwell due to the effects of an accident some thirty years ago, but which will come right given time. I will in due course continue with my measurements, destined to doubly prove that which is correct.

If history is repetitive, I anticipate sarcastic comment regarding alleged contrived delay, in which case I will provide full details regarding my ailment, which in itself is very interesting. However there will be many who will not have read even this far, and thus will remain misinformed regarding the main subject matter. Meantime it is therefore best that I abstain from further explanation.

[NiftySVX]

If you know what the answer is or where i am going wrong, i would ask that you please tell me before I waste any more time and or money on this endevor. I already have almost $6000 in this transmission.

Something is keeping my transmission from increasing line pressure. This is not allowing me to drive the car without risk of serious damage. WHY will my line pressure not rise above 75?

[Trevor]

Originally Posted by Trevor

The TPS resistance is in line with the specs. However so that you have everything correct, you should set the TPS for a voltage output of 0.45 - 0.55 with the throttle closed. Easy to do and full instructions are here in the selectable "How-Too" documents.

Can you measure line pressure while the car is on the road?

Have you verified and or set the voltage at closed throttle?

You and all those interested must start from a verified correct base and go from there.

P.S. It would appear from your advice that pressure is leaking down. There are many points in the system where this could occur. A faulty "A" solenoid or dirt fouling the seat could well be the problem. Please provide more data on the history of the transmission. On the basis of your qualifications, one must assume that you have taken all the basic steps in fault detection, including checking for codes. At this point you must expect only random suggestions.

[svxistentialist]

Originally Posted by Trevor

Unfortunately I have been unwell due to the effects of an accident some thirty years ago, but which will come right given time. I will in due course continue with my measurements, destined to doubly prove that which is correct.

If history is repetitive, I anticipate sarcastic comment regarding alleged contrived delay, in which case I will provide full details regarding my ailment, which in itself is very interesting. However there will be many who will not have read even this far, and thus will remain misinformed regarding the main subject matter. Meantime it is therefore best that I abstain from further explanation.

Trevor, sorry to hear you are suffering this ailment.

You sure are a tough old coot to say this accident had to wait 30 years to sneak back up on you! . I hope you get sorted soon.

Nifty I don't want to appear petty or unhelpful here but it appears to me you are experiencing a dropping pressure in what is a rebuilt gearbox with only 80 miles on it. Why are you not challenging Level Ten about this problem? They may have left out or squashed a seal or something.

Also you are running Lan's tcu with it. No reflection on Lan's quality work, I have great respect for his knowledge and his quality of output, but if I had your problem I would bolt in a standard TCU for a while, just to eliminate one variable, any possible problem with the electronics.

Joe

[longassname]

I'm just psyched someone in the SVX community other than myself has a line pressure gauge. Go nifty.


Good news is I don't think it's a leaking seal since it holds 270 lbs at idle. So if there is something wrong it should be addressable through the valve body and not require pulling the transmission again. I think my first suggestion would be make sure you are hooked up to the right port. Their is pretty much a port for each fluid circuit so if you just plugged into any port you could be watching the pressure on a fluid circuit that is doing exactly what it is supposed to be doing. The correct port is the bottom test port on the drivers side side of the pump. It's illustrated along with the pressures you should see when on page 3 of the pdf below. I'd expect your pressures to be on the high side assuming level 10 worked on your valve body.

http://www.ecutune.com/posts/4eatChecks.pdf

[NiftySVX]

I have not contacted level ten because I want to be sure it is not a control issue before I do, because I already sent the trans back once because it had a defective brake band.

Lan, I am sure I have the right port, I can see how it would be easy to make that mistake since the line pressure port is actually recessed into the oil pump body. And actually, I have ordered a permanent line pressure gauge that I will install in the ash tray area once it arrives.

I of course checked the tps voltage and at base it seemed normal. My TPS does have a slight dead spot in it. I pored over the repair manual last night and I think my problem may lie in the idle contacts in the TPS sensor, although I was not able to find a description of the specifications that would suit me. As I usually do during diagnosis like this I removed the TPS and manually moved it to try and and get it to raise line pressure, as I assume it would from my understanding of the way this system works. However, with the dropping resistor in place, rotating the tps sensor makes absolutely no difference in line. Interestingly, with the dropping resistor unplugged, (which raises base line to about 270) rotating the TPS sensor causes the line pressure to back down to 75 . This is what really confuses me, but It may be because I do not fully understand how line pressure is controlled by the combination of inputs, the manual doesn't really explain it.

At the time of initial diagnosis, I had only minutes to miss the cutoff for ordering subaru parts, so I quickly decided to replace the TPS sensor, which is known to have the dead spot, as a guess. However, I am not 100 % on this diagnosis.

I am going to outline assumptions and values which lead me to this diagnosis, based on the assumption that the following factors influence line control: Range Position, vehicle speed, engine load, and TPS (athough exactly how the TPS influences it is not clear, and what the idle contacts do for it)

Range position works because line raises to the higher spec in R.

Vehicle speed works because the speedo works, and that wouldn't effect line pressure at a stall test anyway

engine load has yet to be tested, it looks like this will require a pinout of the TCU

TPS is known faulty.

[longassname]

Nifty,

It sounds to me like you are taking measurements in either P or N. In either case 75 psi is within spec. You have to put it in gear and power brake it to stall to get full line pressure readings (with the tps correctly installed on the throttle body so that it's indicating a real throttle position along with the resulting power being transmitted to the pump and box.)

[NiftySVX]

I know it sounds like it's in P or N, but it's not. I am afraid to test it anymore because I don't think 75 is enough to hold the clutch together, but when the resistor is connected, and the tps is on the body, and the car is in D, 3, 2, 1, Line pressure is at 75 psi, while RPM is about 3000 and wheel speed is 0.