Hi All,

First of all, a bit of history.....

I've got an ED 302 windsor with factory diff, auto , air con etc.

So, I had the standard diff ratio changed to a 3.45. The next day I had the gearbox serviced.

A day or two later while decelerating (to about 80 km/hr with the air conditioning on) and applying part throttle, the transmission suddenly flicked down a gear, causing the revs to rise to 3000 - 4000 RPM.

Its happened a few times now - pretty much similar, if not, exact same conditions.

Now, I know that engine load and air-conditioning load etc are analysed to 'select' gear and etc.

The question is: What is causing it, and how do I fix it?

Is it because of a sort of mis-match between my new diff ratio (3.45) and the gearbox control module (tuned for 3.23 diff ratio)?

Could it be (which I doubt) that some or one of the bands wasn't adjusted properly when the gearbox was serviced?

What can I do to stop this from happening?

It never did this before.

Thanks

Will

hi
did you change the speedo drive gear in the gear box aswell??

it could be because you have still got the speedo gear from the 3.27 so the ecu thinks the car is doing say 75 kms when its really doing 70kms?

although going from the factory3.27 to 3.45 wouldnt make that much difference .

but you should still cgange the speedo drive gear to keep your speedo correct..and it will help keep your shift points right.

Your better off leaving the existing speedo gear in there, but putting a speedo corrector inline with the speedo.

The cause of the main issue, it could be a fault with the trans TPS

Hi All,

Yeah, I forgot to mention: When I had the gearbox serviced, I got them to take the rear housing off so they could replace the speedo drive gear and driven gear.

The speedo gear is indeed coloured black - for 3.45:1 diff ratio.

So you think the TPS?

if thats the case i would say it more than likely would be the tps..

Hi All,

I had Ford check the TPS. They say that it is working as it should.

Any other ideas?

This one has got me stumped.

Will

swap tps's, basically unplug both, switch connectors and re-plug.. see how that goes.

What would happen - in the worst case scenario - if the trans TPS is indeed faulty, and I switch it with the engine TPS?

What should I expect to happen?

Thanks

Will

You need a Transmission control module from a car that originally had a 3.45 diff ratio.
They shift off indicated speed, not RPM.
By changing the speedo gear to correct the speedometer, you have also thrown out the shiftpoints.

Stock diff = 3.23, speedo gear that matches, TCM that matches.
Will shift 1st to 2nd at say 80km/h

Change diff to 3.45, leave 3.23 speedo gear and TCM
Speedometer says 80km/h, but actual speed may be only 65.
BUT the TCM doesnt know this, it still sees 80km/h at speedo, and so shifts at an indicated 80km/h.

Change diff to 3.45, change speedo gear to 3.45, leave TCM as 3.23.
NOW when speedo says 80km/h, car is doing actual 80km/h.
This obviously would take MORE revs because of the 3.45 ratio, TCM will still want to shift 1st to 2nd at 80, because thats what its programmed to do.
They will even hit the limiter at WOT sometimes if ratio change is that great.

So later shifts and harsher/earlier kickdowns, need 3.45 TCM.

Alternatively use speedo corrector to feed modified signal to TCM.
Swap TCM would probably be easier, worth s**t from a wrecker I'd say and simply plug and play.

If the TPS is faulty, when you swap them, generally the trans will come good, but the engine may flat spot etc as you accelerate. Its worth a shot to try isolate the problem anyway.

3.23 -> 3.45 as far as the TCM is concerned shouldnt be too much of an issue with shift points, its more of a problem with 3.7 or 3.9 diff ratios.
As stated above, a speedo corrector can fix it or a replacement TCM, but its not a major thing that needs to be done

Hi All,

Just ignoring the TPS issue at the moment.....

Is there a chip of some sort that I could get to alter the shift points to suit?

I read an article years ago written in the early 90's about fueltronics who put a chip into a 3.9 litre EA wagon.

If so, could someone point me in the right direction?

Thanks

Will

will, give me a call re the shift points on tues, 1300 663 128

Hi All,

The problem was found to be the TCM shift points.

Problem has be rectified by having the TCM chipped and having the new shift points programmed into the chip.

Will post details in a new post.

Will