View Full Version : Changing from 3sp auto to 4sp

10-04-2010, 10:55 AM

I have a 1989 EA Fairmont which has the 3.9lt motor and 3sp auto.

I am considering finding a 4sp auto from a later EA/EB and doing the swap. The main motivation for this is fuel economy, general driving and towing ability (although I rarely tow).

The questions I have are ...

1. is it as simple as swapping the trans and trans computer over? or is it a bit of a headache?

2. will I gain better fuel economy by changing from 3sp to 4sp?

3. What is the latest model gearbox I can use?

I look forward to your advice and opinions :)



10-04-2010, 11:57 AM
As Far As I'm aware this is a difficult swap.
The Early EA's didn't have the wiring for the 4 speed auto.
The 3 speed is a mechanical device that receives relatively simple instruction from the driver and engine.
The 4 speed box has computer control, requiring rewiring of the electrical system.
It's possible that your car can be converted by getting the wiring harness and computer from the later model car. But it sounds like a big job for little gain.
The car your talking about is 21 years old and I don't think it will ever be a collectors item.

10-04-2010, 04:12 PM
Hey oliveoil_popeye,

Thanks for your advice - I understand the car isn't ever going to be a collectable, my goal is to make it a little more economic and pleasant to drive.


10-04-2010, 11:28 PM
Go to Pick-a-part and find a car (Series 2 with 4 speed auto) similar to yours.
You will have to take the dash out and keep it (The area where the warning lights on the intrument cluster has a green light labelled "power" this is the power mode for the 4 speed auto.)
Also the series 2 dash wiring is different as it is not physically directly connected to the speed controller.
Another reason why you need a series 2 dash, is on the fuse box, there is an auto tx fuse.
Also the dash wiring directly connects to the switch (Pwr/econ) that goes on the console.
You need the console plate (PRND321), and I think you need the mechanical levers.
Once the dash is out, you will need:
You will need the pedal box and the auto ECU. (the auto ECU is mounted on the pedal box.)
You will need the mounting bracket where the speed controller is mounted.
You will need the wiring loom that connects the auto ecu under dash all the way to the front of the car (horn and headlights i beleive).

But wait, that not all:

You will need the two throttle positioning sensors that are in tandem on the throttle body (next to manifold). It is easier to take the whole throttle body, so you may as well get the injector loom wiring. If you notice on series 2 EAs, in the middle of the fuel rail there is a small round connector.

Because pick a part charge $35 for wiring harness, and $50 for an Engine ECU,
I would also get the Engine ECU and Engine ECU harness, but thats personal opnion.

And you will need the wiring loom that connects the engine wiring to the Auto.

Personally I think its worth changing to 4 speed (or T5 manual), and you can keep the original 3 speed items in the garage.

I hpoe this helps


11-04-2010, 08:32 AM
Wow, that is more complicated than I thought.

How much different do you think the fuel economy will be? Would it be worth it financially? (I do over 500kms highway driving a week to/from work).

12-04-2010, 12:47 AM
My first three points are against converting:

1) The amount of work, money, and time, you are going to spend, perhaps you may be better getting another car with an existing 4 speed?

2) A car should never be modified. Some modifications look tacky and as time progresses, a stock car will hold its value. (This is my opinion)

3) It is more expensive to recondition a 4 speed compared to a 3 speed. (I hope I am wrong about this as this info I got from the mid 1990s. I remember in 1995, it was about $2500 to reco a four speed and a lot of taxis were going back to 3 speeds)

My next points are for the conversion.

1) I have been driving an EA series 2 Fairmont Ghia for two years. 100 km/h corresponds to approx under 2000 rpm. I recently purchased a series 1 LTD DA (3 speed), and before driving it I thought that it would not be much of a difference. I was shocked. 100 km/h corresponds to approx 2500 to 2700 rpm.
Therefore more fuel is used to get up to 2700 rpm

2) Abundance of spare parts. Currently now is the time to convert. There are a lot of EA at wreckers and pick a part places. If you go to a pick a part place, you should be able to find a EA fairmont and take the dash and wiring harness out. A dash is not difficult to remove (4 bolts on the bottom and some screws on the top). All the bits that you need for the conversion, should not be too expensive. Also the stuff that you need you should be able to get, At the pick apart places most people take the easy to take stuff like trip computers, power steering pumps and gas tanks. Otherwise people are not touching these as mainstream have upgraded to late model e-series.

3) Keeping it original. This conversion, if done properly, would not look tacky, and you would have little problems with registration authorities and insurance. However it is your duty to disclose any changes to rego people and insurance companies. If anything should happen it would be highly unlikely that the insurance would say hey you have modified it to a four speed. But all it takes is an insurance assessor to have the relevant info of the car's options, but I would leave it up to you. Before attempting any work see what the insurance would say. I sort of gone off track with this point, but keep the 3 speed stuff in the garage. that way you have the option of preserving originality in the future.

12-04-2010, 12:56 AM
Also, another point worth converting is that in this day and age, you need some sort of overdrive function.

Another thing you may want to look at is a T5 manual conversion.

Hope this helps


12-04-2010, 05:19 AM
Because of the cost and hassle in converting it over, I'd only look at doing it if the car was in 110% condition. The EA will most likely never get to the same level of collection as the previous models due to it's inherent flaws. Same goes for the XF.

If it's immaculate, as in zero rust, perfect interior, and the suspension and mechanical side has been well looked after. Then it may be worth looking for a whole cheap EA to wreck for the conversion. Otherwise you'd be much better off looking for a latter model with the 4L motor and 4-speed already in there. Plus, you can pick up top of the range EBII/ED's for next to nothing now. I got my own just before the prices plumeted, but mine was perfect when I got it.

12-04-2010, 07:36 AM
Thanks guys! That was the info I was after.

The car is not in 110% condition - although I'd rate it around he 80% mark - I think I'll pass on the conversion.

In the end, it was a cheap car to get me to work and back - which it does fine :)

Thanks again - your advice and opinions have been more than helpful!

Dr. Miracle
12-04-2010, 05:12 PM
what about an LPG conversion? if its a car you want to keep for a few years.

12-04-2010, 06:03 PM
Thanks Dr. Miracle. The car is already on LPG - I get about 380kms per 60Lt tank (sitting on 100kms/hr).