Isuzu Trooper Owners Club UK™

crocket · **** Joined: 14 Sep 2005 Posts: 315 Location: Midlands

It'd probably be easy to fix some sort of unit in the 3-pin plug to fool it into thinking that it's still connected. I guess it'd need to give 0.4 volts so that the ECU thinks the throttle is shut. That should mean no kick-down malarkey but also the "check trans" light would go out.
I'll get my technical-wizard mate on the case to see what he thinks then get back with the results.
Mine doesn't do all the downshifting *beep*, mind - am I just lucky or will it do it one day? I have driven one that does, though, and it drives ya nuts don't it? Surely that ain't right and I wouldn't put up with it.
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1994 BIGHORN 3.1TD LOTUS
1995 MONTEREY LTD 3.2V6

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Hard1 · Posted: Wed Jan 17, 2007 18:12 Post subject:

Hi there Mart Q; checked the lump and sure enough everything is as your photo. Not doubting you mind, just making sure we have the same set up. Rather than just disconnect the 3 pin plug, there does appear to be a factory designed adjustment range in that the 2 retaining screws for the TPS are in curved slots following the radius of the TPS. The range of the slot appears to be quite large (approx 3/4" and these slots are obscured by your photo unfortunately) so presumably after connecting a meter you twist the unit until the desired voltage is achieved. Not having the means to do that, the other method I could try is trial and error.

I would like to try adjusting before disconnecting the unit (which I will do if I can't get satisfaction!)

Now, at the moment (and worryingly) the TPS appears to be at the extreme of the adjustment on my set-up so I'm kind of supposing that if I twist the device in increments it might in fact get much much worse (don't think I could handle that).

What says the panel? Of course, thinking positively it might get tons better, but knowing my luck...... Rolling Eyes

Crocket: You are an extremely lucky man to have a unit which functions as designed. You have also driven a wonky one so you now know how 3/4 of us with auto bighorns feel! It's a total bummer and spoils a good motor, so much so that sometimes I feel like taking a hammer to it. Good idea on the "fool the ECU"ploy. However, I'm wondering if you disconnected just one of the wires whether that would NOT trigger a "Check Trans" condition. i.e. the -ve earth perhaps? It's a long shot though as the ECU will probably still think it's disconnected.

Thanks again for all the info on this great thread.

I'll report back later!!! Very Happy

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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

Hard1 · Posted: Wed Jan 17, 2007 18:18 Post subject:

Crocket: Also meant to say that MartQ reckons this "fault" is down to the wear and tear on the copper track as it is only good for so many cycles, so those of us with motors that have either done a lot of miles (100K) or have perhaps driven a lot in non motorway conditions will evetually suffer this problem by the look of it. Many of our import vehicles came from Japanese city areas with over 40K miles on them so I guess the drivetrain and ancillary components will have more wear on them than those who have done a relatively high motorway mileage instead.

Will it happen to yours?

It might...... Wink

But at least you'll know how to fix it!!! Twisted Evil

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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

IanP · ** Joined: 13 Jun 2005 Posts: 100 Location: North East

Had my TPS off today (in a snow storm Sad

) just for a look. Like MartQ says it is a sealed plastic unit so no chance of getting it apart without damage. At the bottom on the shaft is a rubber bellow, which I suppose is a seal, anyway on mine it is hardened and split, so it looks like any c**p can get up the shaft and contaminate the track. I gave it a good spray with electrical cleaner which gave better results with a multimeter. I stuck it back on and just test drove it, stopping every so often to adjust it using the screws in the slots. Not quite the best way to do it Laughing

, but it seemed to work. It is really sensitive to being moved, and is obviously on its last legs but things have improved a huge amount. Just wish I had found this out 2 years ago when I bought the truck, 50000 miles cursing the box every inch Mad

. Just a thought, when replacing the TPS, make sure that the slot in its shaft lines up with the peg on the fuel pump. If its right you can look at the front of the pump andsee them move in unison when the acclerator cable is moved.

Hard1 · Posted: Wed Jan 17, 2007 19:50 Post subject:

Cool Ian... 8) Good info. My turn tomorrow!

You're right, 2 years of cussin' the damned box - if only. Still, that's what these forums are all about.

You got snow??? Shocked

It's like "warm" down here but very very wet and gonna get wetter apparently. Sad

Need snow! Send us some down Twisted Evil

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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

IanP · ** Joined: 13 Jun 2005 Posts: 100 Location: North East

Hard1 · Posted: Thu Jan 18, 2007 22:39 Post subject:

OK guys, where do I start?

Right, in a 70mph gale down here I decided to attack the TPS (Throttle Position Sensor for the benefit of anyone entering this thread at this particular point) following all the info in this thread.

Found it easily enough and slackened off the 2 locking screws (see earlier photo). Ensured that it was at one end of the adjustment range locked it off and went for a drive.

No discernible difference Confused

Bummer. Not to be downhearted decided that adjusting it in small increments was just not the way forward for me, and turned the unit to completely the opposite end of the adjustment scale (approx 1/2"). As I previously posted, my fear was that it was already at optimum and that adjusting in this direction was going to make it worse.

WRONG

In my case (other members experiences might be totally different) making this change completely altered the characteristics of the kick-down and thus driveability of the auto trans by a huge degree. I can now "ride the torque" and actually accelerate uphill in overdrive top without undue downshifting. This 5 second mod has made a world of difference to my enjoyment level of this fine machine. Why on earth did we not discover this earlier?

As I have already said, other members experiences might differ but it got me to thinking.

Why is there an adjustment to the TPS within easy reach of anyone with a screwdriver? Remembering that these are imports without manuals and that there is no equivalent UK model we may have missed something that is a "normal" adjustment in Japan.

So, why would you need to adjust the TPS and be able to alter the kickdown parameters?

I came up with several alternatives but none made much sense, but the factory went to a lot of trouble to put this facility there. I can't believe it's to compensate for wear. If it's worn - replace it. That's the economics of mass production. This seems to be a designed variable in performance characteristics that can be readily changed at service, such as the old "Summer/Winter" routine.

I invite all here to comment on the why's and wherefores because I am intrigued, but I am also a bloody happy bunny as well and a big thanks to all those on this thread that put me on this path after 3 long years of suffering.... Very Happy

Oh, and I forgot... Very Happy

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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

crocket · **** Joined: 14 Sep 2005 Posts: 315 Location: Midlands

Hard1 · Posted: Fri Jan 19, 2007 8:06 Post subject:

Yeah, should have mentioned this: All the way counter clockwise. Try it - it only takes a second or 2. One of the biggest problems with this "fault" is the subjective nature of the results after "fiddling" with a) the filter mesh and now b) the TPS. It is extremely difficult to judge whether there has been an improvement or not because we are doing this by the seat of our pants, so-to-speak. So, the only way to be sure that things have changed is to make BIG steps so that we KNOW if it's much better or much worse.

After I made the change, it was MUCH better, so much so that I couldn't stop driving it for an hour or so afterwards - it was like I'd jumped into a different vehicle... Very Happy

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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

crocket · **** Joined: 14 Sep 2005 Posts: 315 Location: Midlands

Cheers. I'll not be rushing to try it myself as I seem to be in an extremely small minority of people lucky enough to have one working right but, if that changes, I'll remember this. Nice one.
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1994 BIGHORN 3.1TD LOTUS
1995 MONTEREY LTD 3.2V6

MartQ · Posted: Fri Jan 19, 2007 11:52 Post subject:

Sorry I haven't been around for a few days, been working out in the sticks with no web access. As you can just tell from my photo, mine is nearly fully clockwise. Hard1, if you have it fully ccw it may be an indication that it is nadgered or disengaged from the end of the throttle butterly shaft. It should be in virtually permanent kickdown in this position, the voltage output being at maximum. if you put a shorting link in the diagnostics socket, you will probably get a 21 fault code flash on the check trans light. If not, I would say it is definately stuffed.

A way of fooling the ECU into thinking the VPS is still connected when in fact it is disconnected would be to connect two resistors in series (available from Maplins stores), rough resistor values of 2.2 kilohms should do. Lay the two resistors down parallel with each other, solder one leg of each resistor together effectively making a device with 3 legs. connect the "double" leg into the centre pin of the VPS sensor (the half that feeds back to the ECU - not the sensor). Connect one of the other leg of the resistor to the positive supply pin (closest to the engine block) and the remaining leg of the device into the remaining pin. This should give a feedback voltage of round about 2.5V to the ECU. This should fool the ecu into thinking you are at around half throttle all the time. You would still have no kickdown though.
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94 Big Horn 3.1 Lotus Auto
Torque Flung Dirt Technique!

Hard1 · Posted: Fri Jan 19, 2007 13:34 Post subject:

Hi Mart, welcome back. The TPS was originally fully clockwise and I turned it fully anti-clockwise (pauses to go and check....Yup! It's fully anti CW). Before I did this, I assumed (as you have just posted) that this being so, it was already in the right position and that any adjustment from there would be going the wrong way, but weirdly, the opposite has happened. I haven't tried it in the 1/2 way position or even put a meter on it, but the kickdown is fully functional, it shifts into O/D top at around 36 mph on a light throttle and the current setting allows me to "lean" on the throttle in top gear without it immediately kicking down into 3rd and 2nd in quick succession. This makes it so much more driveable I can't tell you. Very Happy

By the way, it can't be disengaged because I didn't remove it, just turned it, and because a distinct change in kickdown behaviour was immediately evident that obviously, it must have turned something!

It's quite possible that the device is knacked as you say, but at the moment, it drives right, there are no fault codes and we'll see how long this lasts. If it's only a temporary fix, at least we know pretty much what the culprit is.

Now, to my main question Mart. Why do you think that they put a "variable" TPS in such an easily accessible position?
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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

Hard1 · Posted: Fri Jan 19, 2007 13:40 Post subject:

Hey Mart! Just checked your photo again and agree that yours is fully CW. But, why is there an outline of the device (clean bit) which looks as if it was in the fully CCW position?

Mine now looks exactly the same except the opposite way! I know mine was in the full CW position so now I'm assuming yours was in the fully CCW position! (are you following this?) and had been running that way for some time, or is that a trick of the light? Confused

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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!

MartQ · Posted: Fri Jan 19, 2007 18:14 Post subject:

Hi Hard1, Sorry, me being a spanner again. Mine is nearly Anticlockwise, slightly off the full setting. It will go a lot more clockwise from the position shown. The clean bit in the photo is where the original sensor was. I originally used this as a guide for fitting the replacement and then adjusted it from there using a voltmeter.
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94 Big Horn 3.1 Lotus Auto
Torque Flung Dirt Technique!

Hard1 · Posted: Fri Jan 19, 2007 23:09 Post subject:

Ok I can live with that. I don't actually think we're miles apart here - I am not only keen to sort my own issues out (I am reasonably happy I've achieved that) but I'm also keen to leave a legacy for the guys (and girls) on this forum so that they can follow some good advice and sort out this very annoying and prevalent feature of Bighorn 3.1 auto box behaviour in the future.

I will report back after a couple of weeks and see if my fully CCW ploy works but in any event, I would like to thank all participants in this thread thus far for re-igniting my passion for this fantastic vehicle.... 8)
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1999 Cougar with a NICE motor..

Click HERE to see under my bonnet!