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YES, IT'S THAT ***** AUTO SHIFTING THANG AGAIN!

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Hard1
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PostPosted: Mon Jan 15, 2007 14:46    Post subject: YES, IT'S THAT ***** AUTO SHIFTING THANG AGAIN! Reply with quote

Hi All, please bear with me for this rather long post.  On the trail of improving my auto box's shifting manners which has been a 2 year quest. I have a '93 3.1 td auto and, like everyone elses, shifts in an erratic and annoying manner (downshifts only- upshifts are fine). In truth, this is the ONLY thing "wrong" withthe whole vehicle and has been since the day I bought it. It can be a tad disconcerting for the whole shebang to shift down when you're doing nicely in top @ 60mph and all you have done is to press the throttle slightly to pass the old biddy in front of you. Screaming diesels at 3,500 mph does nothing for me at all!

I thought I'd finally understood what was going on with the "blocked" gearbox filter. I haven't had it off to clean yet but I am sceptical this is the fundamental cause as the "fault" seems to affect nearly all Bighorn autos. By my reckoning, it is the "programming" via sensors that is to blame. This is the only logical conclusion because so many owners report the same "fault". If it was a mechanical link then that would be easy to fix, but it's not, at least not in my experience.

Now, we have got mixed up a bit with other faults such as overdrive problems, erratic speedos and other stuff which to my mind are actual faults unlike the erratic shifting which I believe to be an inherent design fault.

I am looking at investigating the TPS (Throttle position sensor) which may or may not contribute to this box's tendency to erratic shifting on kickdown. Then there's the Speed Sensor that has been mentioned. Now, it seems there is an ATF sensor? (post by Mikewalker reply by MartQ in Gearbox Trans Forum)

OK, these are my questions to try and pin this issue down once and for all..

On a 92-94 Bighorn 3.1td Auto (most basic engine and gearbox management system)

1. Has ANYONE out there actually cured the auto box's tendency to downshift at the slightest touch of the throttle?
2. Does anyone own a vehicle of the same spec and same years as above which actually WORKS properly? (Not overly sensitive to kickdown) and has always done so since purchase?
3. Do these models have a speed sensor - if so, where is it?
4) a Throttle position sensor? Location/description?
5) an ATF sensor (first I've heard of this). If so where is it?

Photos of these items would be great...

It seems to  me that there is an issue with the device (whatever it is) which controls kickdown and is relative to the throttle position. On older mechanical kickdown boxes, the remedy was simple: alter the length/ratio of the arm which connected throttle to gearbox. Job done. On these models however, it must be controlled by a sensor but which one? Is it the TPS? If there is, is this the most likely cause? Now, even if we change this sensor it is likely that they were all programmed (if that is the right word) the same way becasue they ALL seem to do it! So, simply changing it is not really a solution. The problem is, I don't know by what means a sensor functions, can they be changed?  

It can't be all TPS though, as the box will not kick down above a certain speed (probably 60mph) so something in there is telling the box not to change down and ignore the throttle position and thus this is speed related rather than throttle position.

I am trying to find a definitive solution to a problem that seems to be endured by most owners - and that must be quite a few, but hey! I'm not ruling out the old "clean the filter" ploy - it just seems a bit of a long shot, that's all..

Finally....Is there SOMETHING controlling shifts actually inside the 'box we don't know about (apart from the filter issue)???

Please excuse the long post but even after reading everything for over 2 years I'm still none the wiser...

Cheers all Keith
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Hard1
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PostPosted: Mon Jan 15, 2007 14:47    Post subject: Reply with quote

Not 3,500 mph you idiot Keith, 3,500 rpm.... Embarassed
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MartQ
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PostPosted: Mon Jan 15, 2007 15:32    Post subject: Reply with quote

Hi Keith,
To try and help answer your questions, this is what I have discovered so far:
1.  The 'hair trigger' kickdown can be cured by replacing the TPS.  These are manufactured with a finite life expectancy of 5,000,000 cycles (or presses of the pesdal) which sounds a  lot but not if you consider how many times you adjust your foot position.  They tend to wear in a certain area - about half to three quarters pedal position - funny old thing, which causes the conductive track to wear out. This then causes the resistance of the sensor to go high before full throttle position, making the gearbox ECU (located above the brake pedal) think you are kicking down.  The correct adjustment of the TPS is 0.3 to 0.5V at idle, >4.5V at full throttle.  It is located on top of the throttle body/fuel pump assembly and is a small black plastic circle with two fixing eyes grafted on opposite sides of the circumference.  It may be marked 'A147' in white on the top.  It has a 3 pin connector going to it, as you look down on it, the pin nearest the engine block is the +ve feed, the centre is the voltage sent back to the ECU and the last is the -ve reference or earth.  Measure voltages by disconnecting, inserting a thin wire into the centr pin and reconnecting, trapping the wire in the process, then measure voltage on this wire with respect to earth.  Adjustment is by loosening the 2 screws and turning the black plastic casing.  Careful though, it's really sensitive!!  Bad news is Isuzu won't sell these without the complete throttle body for which they will want at least one arm and possibly several vital organs as well as lots of cash!

2.  I doubt it!

3.  Yes these models do have a speed sensor, from underneath it is clearly visible at the very rear of the gearbox with again, if memory serves, a 3 pin connector (but dont quote me on the number of wires).

4.  See 1.

5.  They do have an ATF temperature sensor which I think is on the left  hand side of the 'box.  It prevents it going into overdrive when the ATF is cold and operates the warning light on the dash when the temp is too high.

Hope this helps.

Mart.
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Hard1
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PostPosted: Mon Jan 15, 2007 15:44    Post subject: Reply with quote

Damn! That IS useful!!!!

a couple more questions please...

Could you please explain what you mean by "Adjustment is by loosening the 2 screws and turning the black plastic casing"? Are you saying that we can alter the the kickdown parameters?

You seem to have gone into this in some depth. Have you actually replaced/altered yours with positive results?

What is your take on the filter cleaning strategy as a way of improving the downshift sensitivity?

I am presuming that even if we got a boneyard replacement TB and TPS we might still end up with a worn out one.

Thanks again for the really useful info...
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PostPosted: Mon Jan 15, 2007 16:21    Post subject: Reply with quote

Hi Keith I've just been and taken a photo of the TPS, unfortunately the camera couldn't see very well due to the operator being a bit of a shortar5e Embarassed

The screw at the top of the picture is one of the two, the other is opposite and just out of view on the photo.  Just loosen them and twist the TPS until the correct voltage is obtained (you will need ign on).


I did replace mine with one from a scrapper and it is much better (dodgy overdrive aside).  I can now accelerate uphill in top gear (when it works).  But I don't expect it will last long.

This has been a useful link:

http://autorepair.about.com/library/ts/obd-i/bl-dtcs-84.htm

There may be something in the filter cleaning thing.  I believe it may improve things but not that it is the cure all some people seem to think.  I haven't tried it yet, but am considering it just to eliminate it from enquiries as it were.

Regards,

Mart.
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PostPosted: Mon Jan 15, 2007 16:22    Post subject: Reply with quote

Forgot to say, the silver thing at the top of the pic is the front end of the inlet manifold.
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PostPosted: Mon Jan 15, 2007 16:24    Post subject: Reply with quote

Me again,

Also in the bottom R/H/S of the pic you can see a loose spade connector, this is on the end of the wire I inserted into the central contact of the TPS connector.
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PostPosted: Mon Jan 15, 2007 16:31    Post subject: Reply with quote

Cool, thanks..... 8)

That's this summer's project methinks. I'll report back to the forum.....
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PostPosted: Mon Jan 15, 2007 22:36    Post subject: Reply with quote

it's a coolant temperature sensor that can control the overdrive as well it's 1 of the 4 or so in the thermostat housing
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PostPosted: Mon Jan 15, 2007 22:41    Post subject: Reply with quote

Since reading MartQ's posts on the TPS, I have had a go at adjusting mine, and I can get the box to kick down at every opportunity, or not to kick down at all (ride the torque  8)  8)  ). As he said it is very sensitive, and still needs a bit of fine tuning, but could this be the problem everyone has been having? I posted some time ago about cleaning my box suction filter, which in my case improved the shifting markedly, but might not be the solution for everyone. I would certainly recommend having a look at the TPS, try unplugging it and see what happens.
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PostPosted: Mon Jan 15, 2007 23:11    Post subject: Reply with quote

IanP wrote:
Since reading MartQ's posts on the TPS, I have had a go at adjusting mine, and I can get the box to kick down at every opportunity, or not to kick down at all (ride the torque  8)  8)  ). As he said it is very sensitive, and still needs a bit of fine tuning, but could this be the problem everyone has been having? I posted some time ago about cleaning my box suction filter, which in my case improved the shifting markedly, but might not be the solution for everyone. I would certainly recommend having a look at the TPS, try unplugging it and see what happens.


Did you physically twist the unit? If so, which way for what effect and by how much?

Disconnecting it sounds fine if you are OK with manually downshifting ( it certainly wouldn't bother me and I would be a happy bunny if I could stop this damn box from downshifting every time I squeezed the throttle), but what else does the TPS control?
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PostPosted: Tue Jan 16, 2007 10:41    Post subject: Reply with quote

Hard1 wrote:
IanP wrote:
Since reading MartQ's posts on the TPS, I have had a go at adjusting mine, and I can get the box to kick down at every opportunity, or not to kick down at all (ride the torque  8)  8)  ). As he said it is very sensitive, and still needs a bit of fine tuning, but could this be the problem everyone has been having? I posted some time ago about cleaning my box suction filter, which in my case improved the shifting markedly, but might not be the solution for everyone. I would certainly recommend having a look at the TPS, try unplugging it and see what happens.


Did you physically twist the unit? If so, which way for what effect and by how much?

Disconnecting it sounds fine if you are OK with manually downshifting ( it certainly wouldn't bother me and I would be a happy bunny if I could stop this damn box from downshifting every time I squeezed the throttle), but what else does the TPS control?


You need to have a read of MartQ's posts as he knows alot more on the subject than I do, but when I disconected my TPS, the box shifts up at 2750 rpm, and into overdrive at about 45mph. It will not kick down in any gear, but changes down automatically as you slow, so no manual chahnging needed. Turned my TPS anticlockwise looking down, which inproved the shifting, but judging by MartQ's past comments I reckon its past its sell by date. Disconnecting it for a while made driving on motorways a pleasure as no manic gearchanging while overtaking!. As far as I know the TPS is only for the gearbox control on this engine Question  Question
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PostPosted: Tue Jan 16, 2007 18:09    Post subject: Reply with quote

Thanks for that, now we're getting somewhere! So, who needs the ***** kick down anyway? First chance I get, I'm gonna rip out the wires! (Carefully of course, but it just kinda sounds good when you say it like that  Twisted Evil )

Actually, you will probably need to go manual at times especially when towing just to keep momentum and the revs in the torque band, but it's a small price to pay...... Very Happy

Thanks everyone for their input and if anyone else has any other ideas by all means post 'em! If this really works then I propose we should sticky this at the beginning of the gearbox forum because so many people ask this question, and thus far, we have not had a consensus. I will mod mine and report back.

It would be nice if someone actually got hold of a "new" TPS and tried it out so that we could get the whole picture......

This is the only thing (apart from a lack of grunt) that spoils this great vehicle for me although I am toying with the idea of sticking in a VICC (later) turbo to get that sorted....Oh yeah Twisted Evil
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PostPosted: Tue Jan 16, 2007 20:44    Post subject: Reply with quote

I'm following this thread with a lot of interest but Exclamation
I always thought that the throttle position sensor was on the accelerator pedal Question  or is mine different being a 96/97 Confused
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PostPosted: Tue Jan 16, 2007 22:41    Post subject: Reply with quote

Hard1 wrote:
Thanks for that, now we're getting somewhere! So, who needs the ***** kick down anyway? First chance I get, I'm gonna rip out the wires! (Carefully of course, but it just kinda sounds good when you say it like that  Twisted Evil )

Actually, you will probably need to go manual at times especially when towing just to keep momentum and the revs in the torque band, but it's a small price to pay...... Very Happy

Thanks everyone for their input and if anyone else has any other ideas by all means post 'em! If this really works then I propose we should sticky this at the beginning of the gearbox forum because so many people ask this question, and thus far, we have not had a consensus. I will mod mine and report back.

It would be nice if someone actually got hold of a "new" TPS and tried it out so that we could get the whole picture......

This is the only thing (apart from a lack of grunt) that spoils this great vehicle for me although I am toying with the idea of sticking in a VICC (later) turbo to get that sorted....Oh yeah Twisted Evil


I forgot to mention that if you disconnect the 3 pin multiplug from the TPS, then the Check Trans light will flash on the right side of the dash. I just ignored mine Laughing  Laughing . As for the VICC turbo, I fitted one recently, and I would only do it when (not if  Very Happy  Very Happy ) the old one packs up. The difference in performance isnt that great Crying or Very sad  Crying or Very sad
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