Thread: 4.6 ltr

Discovery 1 or Series 1?

Minimum you should do is upgrade the injectors to squirt a bit mor fuel in to the bigger space at the correct ratio,
4.6 injectors/ 3.5 or 3.9.
The ecu should work out the rest

Ok cool, thanks fitzy

Originally Posted by cjc_td5

Discovery 1 or Series 1?

I must admit, those were my immediate thoughts, too.

The injectors are plenty big enough at 18.5 lbs per hour. They are the same volume as on a Ford 4.6 V8.

The problem lies in the 14CUX ECU which has a cut off at about 70% of injector duration.

Mark Adams in the UK can reprogram the ECU.

The throttle body is smaller on a 3.9 than a 4.6 so you will not get the same top end.

Regards Philip A

Originally Posted by PhilipA

The injectors are plenty big enough at 18.5 lbs per hour. They are the same volume as on a Ford 4.6 V8.

The problem lies in the 14CUX ECU which has a cut off at about 70% of injector duration.

Mark Adams in the UK can reprogram the ECU.

The throttle body is smaller on a 3.9 than a 4.6 so you will not get the same top end.

Regards Philip A

I was thinking that instead of opening the injectors longer through the ecu, you could Use a larger flow injector.
Or am I misinformed?

I fitted a high comp 4.6 to a 3.9 Rangie and changed nothing else. Performance was quite adequate, the owner did over 100K in it towing all over the country. I'm sure you could claim that some top end was lost but the massive increase in torque made it academic. You just tromped on the loud pedal with the stick in D and hung on grinning like an idiot.

Oh and the simplest way to fiddle with injection volume is to fit an adjustable fuel pressure regulator, cheaper than a whole bunch of other options. After all, it's only 15% extra cc's (3947 to 4552)

I was thinking that instead of opening the injectors longer through the ecu, you could Use a larger flow injector.
Or am I misinformed?

It's along time since I studied fuel injection, but AFAIR if you increase injector size you will have trouble getting a stable idle and low throttle opening behavior as they are more inaccurate at low durations.

In fact the stock Lucas green bands were pretty unstable at idle in a 3.9, and the Bosch Yellow Gen 11 and Gen 111 that I fitted were much better as they were 4 hole rather than 1hose..

You could I guess fit a Unichip or other piggyback to compensate , but I think you would end up spending more than an ECU upgrade. This would still not probably give a good result and need a LOT of dyno time. I also found that dyno operators are not used to trying to improve part throttle behavior . They are only experienced in Flat out.

This is like the story with Motec or Megasquirt or the many other after market ECUs. They sound great in theory but never go as well as a stock ECU, in ALL circumstances. You could get one of those self learning ECUs if they are still available but you still would need the correct size injectors. You also need wide band O2 sensors with these and they are expensive.

I can recall a bloke in the RR club who had a you beaut Motec in a 4.6 in a RRC . We left Stockton after a clean up and turned off in say 34C . He tried for an hour to restart , while my 3.9 with stock ECU and Unichip started first turn.
Manufacturers spend millions on dyno time , and I recall that a Commodore had 200plus maps for starting.
Regards Philip A