Disco Help. It cuts out

Kustard · Apr 16, 2006

I have a 1994 Disco 3.9 V8i. It is marked up as FXi and is left hand drive I believe for the Saudi market. When I bought it a couple of months ago it had no thermostat in it. Despite freezing my plumbs off the motor was very strong and ran without fault.

I have put a thermostat in and the temperature is nice and warm however when at normal temperature the engine dies. When I dip the clutch the motor ticks over but when I set off again the engine dies and will only idle. I have traced the issue to the coolant temperature sensor situated just right of centre to the front of the engine above and to the right of the thermostat housing. When this is unplugged the motor runs fine. When plugged in and the engine is hot it cuts out as described. I have replaced the sensor but the fault is still there.

I now believe that the Electronic Fuel Control Unit (The black box in the passengers footwell) is duff.

Can these boxes be reset after a fault is rectified??

Or does anyone out there have any other ideas that may help.

Thanks
Kusty

discomania · Apr 16, 2006

Yes you can do some mods to these to sort these things out, I may be very mistaken but a nice big resistor could solve your problem.

eightinavee · Apr 16, 2006

The Ecu does not need to be reset after a fault occurs,it will just store it in its memory until it is erased by someone using testbook etc.I very much doubt there is anything wrong with the Ecu - they are very reliable,and the last thing you want to change.
Can you check the colour of the wires plugged onto the coolant temp sensor - they should be green/blue and red/black.Not slate/white and red/black.The slate/white one should be plugged onto the fuel rail temp sensor.(uses the same sensor,screwed into the tubular fuel rail around the inlet manifold)If these connectors are swapped over the engine will cut out when it gets hot as the rail temp rarely gets over 30 c making the Ecu think the engine is still cold - and will dump loads of fuel into what it thinks is a cold engine.
Does your truck run oxygen sensors and cats ? - please post back what set up it has. !4 cux efi is one of the most reliable systems around,and is also very easy to diagnose faults without the use of testbook - a good multimeter is just as good but a bit slower.Have you got the correct electrical troubleshooting manual for your truck ?You really need this to sort out any efi problems.Good luck !

Kustard · Apr 16, 2006

Thanks for the replys so far.

Eightinavee. Just checked the colours of the wires. The sensor does have the green/blue & red/black wires connected to it. I have to run with this disconected as when the engine is hot it cuts out to an idle. Any other ideas please.
Thanks

Andy

eightinavee · Apr 16, 2006

So what about the oxy sensors etc,where are you based,give us some more info,the ecu is using a default value of about 60 c coolant temp when its disconnected,which is why I asked about the oxy sensors - to see if the engine is running open or closed loop.Give me more info and I will try to help.

ghazz · Apr 17, 2006

I have had this same problem, looking forward to advice as well.

Kustard · Apr 17, 2006

Thanks for the reply again 8inavee.

I have not checked the oxy sensors as I do not know how to. But would this sensor breaking down cause the same symtons that my disco has? I take it the oxy sensor is the unit on the air intake?. What do i need to look for and check on this. The manual I have is not very specific.

Is the coolant temp sensor used as a cold start (choke) mechanism telling the ecu that the motor is cold and thus allowing more fuel in to start?

I live in East Yorkshire about 25 miles north of Hull.

I hope you can help as I am exporting the monster to Spain in July. It would help if it was 100% reliable

[email protected]

Regards
Andy

l3on · Apr 17, 2006

Kustard said:
I take it the oxy sensor is the unit on the air intake?.

No thats the air mass sensor, the oxygen sensor is in the exhaust

Kustard said:
Is the coolant temp sensor used as a cold start (choke) mechanism telling the ecu that the motor is cold and thus allowing more fuel in to start?

Basically yes, as the engine reaches correct operating temperature the fuelling is altered accordingly

Kustard said:
I hope you can help as I am exporting the monster to Spain in July. It would help if it was 100% reliable

At least it's hot out there, might just work plugging it back in

Kustard · Apr 17, 2006

Thats the problem. When the engine gets hot it cuts out. If I disconnect the sensor it works fine. Thanks

eightinavee · Apr 17, 2006

From your questions it sounds like you need more help with your truck than we are going to be able to pass on to you to use effectively,does anyone know a decent independant near to you.
To give you an idea of cost,I usually quote a max of two hours labour to diagnose a fault like this,so around £60 +vat.Plus whatever parts are needed,none of the bits likely to be faulty take much time to fit so I think your bill might be quite small.

Kustard · Apr 17, 2006

Thanks 8

Are you close to Hull?

l3on · Apr 17, 2006

Be worth just tracing the wire from the temp sensor all the way back to the ecu, just to make sure that the wire isn't melted/shorted somewhere on it's return and giving a 'false' or out of range signal to the ecu, seems strange that this alone resolves the problem as it doesn't interact with anything else pre-ecu and the sensor has been replaced.

Disco Help. It cuts out

Kustard

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discomania

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eightinavee

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Kustard

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eightinavee

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ghazz

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Kustard

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l3on

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