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Loss of overdrive 1989 2.8

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Loss of overdrive 1989 2.8

Postby teach » Fri May 06, 2011 7:26 pm

After doing a little more research, I think the reason why my automatic transmission is not changing into high gear is something to do with sensors.
A couple of posts on this and other forums talk about TPS sensors.

Losing overdrive seems to be a fairly common problem.

My question is this. Are there any good diagrams or pictures that will show me what I need to be playing with?

Are there a few things I should be looking at.

I want to become more mechanically minded and do small jobs myself. I am a little embaressed to admit on this forum that I have only just learnt how to change the brake pads myself. Luckily a workmate has a good workshop and has been showing me how to do lots of stuff, but he does not know Isuzus and can't help.

Any ideas or hints?

I can't contribute much in the way of mechanical advice to the forum myself, however I can give trout fishing advice for Otago/southland!
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Re: Loss of overdrive 1989 2.8

Postby 4x4SWANNY » Fri May 06, 2011 7:59 pm

Wish i could help ya mate...We spent 5 grand fixing wifes ubs69 V6 auto...To complicated for this kid.
Saw the Auto in Parts at the shop...Man they are a maze of bits...Then 6mths later the torque converter bolts came loose and stuffed the seal..I took out auto and fixed that though..If Auto is stuffed just buy a whole second hand one they to dear to fix.
We only fixed wifes because we had the money and she loves here baby lol..If it Packed up now i would Wreck the truck..lol
Oh well, can some one hook up the winch i cant open my door !!!!!!!!!
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Re: Loss of overdrive 1989 2.8

Postby electrifying » Sun May 08, 2011 10:19 pm

Hi Mark,
What i suggest u do is just unplug this sensor wire:
trans temp sensor IMG_6976.jpg

(it's the one just below the A/C or powersteering belt (u should have 2 belts side by side), just to the left of where that red line points)
It has a terminal like a male spade-lug.

All this sensor does is allow the trans to go into overdrive when the coolant reaches the correct temperature.
This is because the engine coolant will heat the auto-trans radiator (which is built into the engine radiator) so it is the correct operating temperature (which leads to the correct viscosity of the trans fluid), therefore allowing the transmission to operate normally.

If you un-plug this wire, all it will do, is it will allow the transmission to change into 4th gear (overdrive) when the engine temperature is cold.
If the sensor is broken, then your transmission will most likely not go into overdrive.

To compensate for not having this sensor plugged in, just drive gently until the engine warms up a bit, or let it warm up for 5 mins or so (which is good practice, as it also allows other engine fluids to change to the correct operating viscosities)



Im not sure about the O/D light tho. Can't remember what happened to it (as i have stuff on the dash covering those lights).
If this isn't the problem, i think Geeves said on another post somewhere that a filter in the trans may need to be cleaned.
Hopefully all goes well.


By the way, it took me 2 weeks to change the break pads on the rear of my truck, finally discovered that i needed to wind in that allen-key shaped thing to re-set the park break so the calliper would go in all the way, haha. :lol:
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Re: Loss of overdrive 1989 2.8

Postby electrifying » Sun May 08, 2011 10:29 pm

oh yea, let us know if it works or not
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Re: Loss of overdrive 1989 2.8

Postby teach » Mon May 09, 2011 6:53 am

Cheers for that. I had a fiddle last night in the dark. I couldn't get the plastic lead attachment off the lug part. But I did not want to force it. My mechanically minded mate is going to rip it off for me tonight.
Hopefully it works. I have already sent some enquiries off to online parts stores to get some prices for a replacement sensor.
Thanks for your help.
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Re: Loss of overdrive 1989 2.8

Postby teach » Mon May 09, 2011 4:30 pm

Well I got the lead off the sensor. But that made no difference. The o/d off light stayed on and I didn't get to top gear.
I rang isuzu parts specialists in auckland. They have a sensor but the joker there told me that the overdrive sensor is the one on top with 2 wires coming out of it. Not the one to the side as in the photo above. I think I might just have to admit defeat and go to the garage.
I think the next step is getting the Automatic transmission filter cleaned.
Any other suggestions, rather than have my mechanic shag around guessing as to cause.
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Re: Loss of overdrive 1989 2.8

Postby geeves » Mon May 09, 2011 6:09 pm

Its a common auto Go to an auto trans specialist if there is one down there.
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: Loss of overdrive 1989 2.8

Postby electrifying » Mon May 09, 2011 7:08 pm

Sorry to hear that it didn't work, hopefully it's not too serious then.

Although, i don't remember the O/D light coming on in my truck (as it shouldn't when the temperature is low for the sensor).

I do remember a long time ago looking at a wiring test schematic for the auto transmission for a transmission specialist or mechanic to test each gear individually, just by applying a voltage to each wire that goes to the transmission, but i didn't save that PDF at the time (& wish i did cos i wanted to change mine to a tiptronic system), & there are like 8 wires, so would need the wiring info before tampering with anything.

It could be something simple like a loose wire somewhere, but as Geeves said, the auto trans specialist would be the better place (rather than a mechanic), as they would know what the O/D light flashing means, & could probably source the problem fairly quickly.


The other option is that you could put really big tyres on the truck (this would effectively change the gear ratio) & make use of the 3 gears that it does have, so it isn't revving as high when going at 100km/hr :D
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Re: Loss of overdrive 1989 2.8

Postby chrisprice » Wed Jul 13, 2011 7:17 am

Just fixed my '94 3.1 thanks to fix photo! hurray!!
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Re: Loss of overdrive 1989 2.8

Postby TomCooney » Sun May 12, 2019 12:29 pm

Disconnecting the temp sensor worked for me!
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