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Re: 1992 V6sei auto gearbox repair

Posted: Sat Mar 09, 2019 10:03 am
by Dean
Idle speed regulation is achieved by the IC valve which is controled by the engine ECU, the ECU is (on early cars) supplied with gear selector information to determind if the gearbox is in a Neutral or Drive state, later auto ECU's and all manuals seem to just assume gear selector state is always Drive,i am not sure why later ECU's would be setup to do this or what purpose this information was supplied to the ECU for but i would imagine it was something to do with the fuel cutoff on a trailing throttle and possibly part of the A/C clutch control strategy.

The gear selector switch provides a signal to the start inhibitor relay, gear selector display, reverse light switch and Engine ECU.

The ECU fitted to my car assumes Drive all the time, the previous one showed Nuetral or Drive selection but provided a jerky transition on the fuel cut threshold, a third ECU i tried would read the info backwards so the Lexia would show it was in Drive when the gear selector was in N or P and Neutral when D or R was selected, this ECU made the engine stall after snapping the t5hrottle open in Neutral, it struggled to catch the idle speed after being revved.

Either way, the gear selector switch will not be your problem, a total loss of Drive will be a mechanical issue with the gearbox, i have read before that many valves, if stuck, will result in a no drive situation, but equally, it could be a Torque converter or hydraulic pressure issue, for the sake of a £10 pressure gauge and a few more £ worth of fittings to connect the gauge to the test ports i would seriously be looking to do a pressure test, rising idle speed when selecting a gear, to me, sounds like a mechanical failure, why is the box offering less of a load on the engine when you try to put it in gear?

D

Re: 1992 V6sei auto gearbox repair

Posted: Sat Mar 09, 2019 6:09 pm
by xantia_v6
The most plausible explanation is that the hydraulic back-pressure is being released when a gear is selected, so there is less pumping work being done.

Re: 1992 V6sei auto gearbox repair

Posted: Sat Mar 09, 2019 9:46 pm
by MTXM
Thanks for your further contributions chaps and after trying a second valve block with no change I think I now have to accept there is some other internal pressure loss issue and it is engine and box removal time (No.5)! I will not be rushing into the task and as it happens the tax runs out this month. With regards, Matthew T.

Re: 1992 V6sei auto gearbox repair

Posted: Wed Mar 13, 2019 8:11 pm
by Julianw
I know next to nothing about auto transmissions, so this thread is a goldmine of information. Full marks to Matthew for his incredible persistence - he deserves much better luck with this car, and really soon!

Re: 1992 V6sei auto gearbox repair

Posted: Wed Mar 13, 2019 9:48 pm
by MTXM
Thank you so much Julian that is really kind and perhaps I am also a bit mad!! With regards, Matthew T.

Re: 1992 V6sei auto gearbox repair

Posted: Sat Mar 16, 2019 10:07 pm
by MTXM
My mechanic suggested that I could check operation of the pump by partially detaching a gearbox-air cooler hose and turn over the engine, which I have now done with rather interesting results. After detaching one and then both hoses and placing suitable receptacles there was no flow of oil through either hose! I have also tried blowing through the hoses with the result of only minimal discharge of oil and very little flow of air. My guess is there must be a blockage somewhere in the system, that would explain the on/off and then off for good operation of the box and perhaps the addition of the cleaner and recent oil change made matters worse? I wonder where the blockage might be and the possible cause, perhaps another piece of oil seal from the governor! Regards, Matthew T.

Re: 1992 V6sei auto gearbox repair

Posted: Sat Mar 16, 2019 10:45 pm
by xantia_v6
Could the rubber have come from a seal on the suction side of the pump? If such a seal is now gone, it would effectively stop the pump from picking up any fluid.

Can you tell us where the cooler is plumbed into the circuit? On some transmissions it is in the return line from the regulator.

Re: 1992 V6sei auto gearbox repair

Posted: Sat Mar 16, 2019 11:00 pm
by MTXM
Thanks Mike and here is a marked up illustration to show the location of the oil radiator flow and return locations. With regards, Matthew T.

Re: 1992 V6sei auto gearbox repair

Posted: Sun Mar 17, 2019 8:57 am
by Dieselman
Have you checked the filter?

It is definitely possible for a blockage to stop an auto box from working, i've heard of a collapsed filter doing just that.

Re: 1992 V6sei auto gearbox repair

Posted: Sun Mar 17, 2019 9:12 am
by MTXM
Yes I have checked the filter Will, but I thought I would at least detach the radiator hoses and check for blockages and especially against the water cooler and both have right angle bends where attached to the box. I also wondered whether an obstruction in the oil cooling circuit would prevent circulation as a whole and the operation of the box - probably not? With regards, Matthew T.