3.9 v8 efi 1996 discovery 1

Chrisvr46 · Apr 3, 2023

Hello

I have a 3.9v8 discovery 1 efi. there is a intermittent fault of the vehicle cutting out mainly when coming off the power/ idle. I have replaced the stepper motor on the back of the plenum but the issue is still present. does the base idle need re setting up after replacing this? I have also replaced the rotor arm and coil issue is still present any ideas into the fault? one other thing I have found is intermittently when putting the power on it may cough but not all the time any thoughts appreciated.

Many Thanks

discool · Apr 3, 2023

Replacing the idle control valve doesn’t require need re-setting, its set at the factory and thats it, but its a simple procedure to check if ever its required and detailed in a workshop manual for the D1.
Stalled engine when off power also with hot engine can be a result of a blocked crankcase filter, so remove the flame trap and clean in petrol or better still replace it, also remove the connection hose to the plenum chamber and clean.
Any hesitation on acceleration maybe ignition, like iffy coil top connections, plug leads or plugs, then u can look at fuelling, starting with an iffy fuel filter, so when was it last changed?.

Chrisvr46 · Apr 3, 2023

Hello many thanks for your reply only issue i have is the car is in spain. Seems to be worse when its hot. It drives perfect on roads and only seems to stop at idle and backing off the throttle ie going down hills. Ill get a new beather and try that. I have subbed a coil and rotary arm issue is still present. Not sure when fuel filter was last changed but doesnt seem to play up when needing power or hard driving only on low rpm.ive heard the spider imobolisers can cause cutting out ? Or would you start with engine breather ?

Thanks chris

v8250 · Apr 3, 2023

And as with all 3.9EFi's what's the TPS condition like? Same with distributor amplifier, if fitted. Re' coil's they normally breakdown under acceleration/constant running.

Chrisvr46 · Apr 3, 2023

Without sounding silly whats the tps ?

Thanks chris

v8250 · Apr 3, 2023

Throttle Position Sensor, commonly known as a throttle pot. There are two types, fixed and adjustable...but both need to be positioned when fitted into the plenum. They have habit of clogging up with carbon. If owning any RV8 engine it's really worth tapping into the v8forum.co.uk as there's a wealth of knowledge there https://www.v8forum.co.uk/forum/index.php?sid=90b0c097af925e96dc464e2ebe1c4467

plus this to get a proper understanding of how the EFi works http://www.g33.co.uk/pages/technical-fuel-injection.html

discool · Apr 3, 2023

v8250 said:
Throttle Position Sensor, commonly known as a throttle pot. There are two types, fixed and adjustable...but both need to be positioned when fitted into the plenum. They have habit of clogging up with carbon. If owning any RV8 engine it's really worth tapping into the v8forum.co.uk as there's a wealth of knowledge there https://www.v8forum.co.uk/forum/index.php?sid=90b0c097af925e96dc464e2ebe1c4467

plus this to get a proper understanding of how the EFi works http://www.g33.co.uk/pages/technical-fuel-injection.html

Enlighten me please.
How will a D1s fix throttle position sensor be not positioned when installed on to the plenum. Also my 25 year old 3.9 disco owned from new has never had an issue with its TPS. Or my 3.5 RR before, which had the TPS which was adjustable, and then set by the factory.
Question: How long or did you owned your 3.9 disco ? Or RUn just quoting other forums

discool · Apr 3, 2023

Chrisvr46 said:
Hello many thanks for your reply only issue i have is the car is in spain. Seems to be worse when its hot. It drives perfect on roads and only seems to stop at idle and backing off the throttle ie going down hills. Ill get a new beather and try that. I have subbed a coil and rotary arm issue is still present. Not sure when fuel filter was last changed but doesnt seem to play up when needing power or hard driving only on low rpm.ive heard the spider imobolisers can cause cutting out ? Or would you start with engine breather ?

Thanks chris

The Immobiliser has two circuits, one is the signal to the efi ecu and yes if onis way out out it will stop the the engine from starting… temporarily and it will start, and even on the outside lane of motorway then ithe engine will cut completely … as i found out its not sad a a single piece of wire will get u going again.
Anyway what is the rotor arm and coil issue that is still present? Hopefully u didn’t pull the rotor arm straight out

Chrisvr46 · Apr 4, 2023

Hello there is no issue with the rotar arm or coil i swapped these over to see if it would resolve the issue but it didnt.

Thanks

3.9 v8 efi 1996 discovery 1

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