A question for the Transmission experts

NiftySVX · #1 05-13-2009, 09:21 PM

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 · #2 05-13-2009, 11:02 PM

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?

Trevor · #3 05-14-2009, 10:07 PM

Quote:

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.

oab_au · #4 05-14-2009, 01:35 AM

Quote:

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 · #5 05-14-2009, 11:40 AM

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 · #6 05-14-2009, 04:20 PM

Quote:

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 · #7 05-14-2009, 05:15 PM

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 · #8 05-14-2009, 07:33 PM

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 · #9 05-14-2009, 09:20 PM

Quote:

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.