land rover discovery 3.9 rv8 ecu

rob b · Post by **rob b** » Sun Jul 29, 2007 4:06 pm

I have a land rover 3.9litre v8 hotwire injection system without cats installed in my Hilux and it has developed a juddering/jerking about type of fault, it is intermitant and i suspect the ecu may be at fault however i have found out that the ecu that the car came with is out of a range rover 3.5 litre so i have the wrong ecu anyway, it has worked without fault up to this point but i am now looking for another ecu for testing purposes. The problem is i don't know what i need. At the moment i have a PRC8702 but this is the wrong one for the engine. Does anybody know for certain what i should be looking for and does anybody have a good and known to be working one for sale?

mrcheese · Post by **mrcheese** » Mon Jul 30, 2007 10:53 am

Do you have a flapper or hotwire AFM?

I would have thought that a 3.5 ECU would not provide enough fuel for a 3.9 unless it has been altered. Not sure if that is really the case though.

Regards,

Paul.

Geoff King · Post by **Geoff King** » Mon Jul 30, 2007 12:14 pm

A 3.9 is hotwire. According to CAR ELECTRONIC SERVICES (http://www.carelect.demon.co.uk/index.html) the 3.9 ECU part numbers are PRC 6999, 7081, 8702, 9010, 9061, 9611, 9515 and others. PRC7081 allegedly develops a misfire at 2,800rpm. The 3.5 used ECU part numbers PRC 8138, 9059 and others.

I doubt if there is much difference between any of them but if there were a major difference I’d like to know what it is.

rob b · Post by **rob b** » Mon Jul 30, 2007 5:22 pm

it is a hotwire efi setup and it has been fine up unitl the last few months, i don't know if the current one has been altered in any way as it was in there when i bought it.

mrcheese · Post by **mrcheese** » Mon Jul 30, 2007 6:29 pm

If it was mine I would be looking to rule out ignition, fueling or air leaks before blaming the ECU.

Can you describe the problem in more detail?

Paul.

rob b · Post by **rob b** » Mon Jul 30, 2007 7:08 pm

yes i am going to replace the fuel pump and also fit a pre pump filter and replace the one after it as well, i am also going to replace the coolant thermistor for the ecu, the cap and rotor arm are both reasonably new as are the plugs and leads, the hotwire airflow meter was replaced with a used one about 2 years ago too. The problem is intermittant but is very annoying, it seems to happen every single trip, it seems to happen mostly when the engine is warming up but before it reaches the normal operating temp. It starts as a rather severe juddering from the engine, when you put your foot down it seems to stop but as soon as you have it on light throttle it seems to start again. This can carry on for 20-30 secs and then disapears normally for the rest of the journey, next time it is started from cold it normally but not always happens again. I have a friend with a rover v8 in his Hilux truck too who had the same type of fault and he spent big bucks trying to resolve it and his turned out to be the ecu so that is what he suggested i try it.

mrcheese · Post by **mrcheese** » Mon Jul 30, 2007 7:38 pm

Sounds like you are on the right road. As a check, unplug the 9th injector and see if the problem goes away. It is on the side of the plenum.

Paul.

rob b · Post by **rob b** » Mon Jul 30, 2007 9:18 pm

isn't the 9th injector only used on flapper efi systems? I dont remember seeing anything like that on the side of the plenum, at the rear there is the idle control valve/stepper motor.

mrcheese · Post by **mrcheese** » Tue Jul 31, 2007 9:58 am

I think you are correct Rob. My mistake.

Paul.

Beastmaster · Post by **Beastmaster** » Tue Jul 31, 2007 5:19 pm

Rob i have a 3.9 hotwire(95 disco) the eec is a 14 cux,give me a shout if you need to know pin numbers etc
cheers paul