Need help with a Range Rover 4.6ltr V8 running issue.

[porker928]

Hi

I’m working on a kit car with a Range Rover 4.6ltr V8 (fuel injected) engine, the car starts and runs perfectly, until the coolant temperature reaches 100°C at which point the engines tick-over suddenly jumps up by an extra 500 RPM, and stays there. You can still drive the vehicle around, but having a constant extra 500 RPM on the revs isn’t very good for fuel economy on a car that already drinks petrol.

The car has a 1990s Lucas ‘hot-wire’ fuel management ECU, so I connected a ‘Rover Gauge’ diagnostic system to it to read any fault codes, and see live monitoring but, unfortunately, I can’t get the dam thing to communicate, so I’m going to have to diagnose the fault the hard way.
My suspicion is that one of the ECUs thermal sensors has gone open circuit and without the correct data the ECU is just defaulting to a pre-set fuel delivery amount, does this sound plausible? To make matters worse, the fuel management ECU has a custom ‘Tornado Chip’ fitted.

Is anyone familiar with this setup? – Any advice gratefully received. (I have a complete electrical schematic for the car).

Ben

[Belle427]

Try and get Rovergauge up and running as it will help.
Its worth checking the coolant temp sensor, also the wiring to the maf sensor.
Im assuming its a 14cux system?
If so some info here.
http://g33.co.uk/pages/technical-fuel-injection.ht...

[porker928]

Thanks Belle427 - Some very useful information on that website, and the ECU is a 14CUX.

I disconnected the ECU and measured the resistance between pins 7 & 25 at the plug (coolant temperature sensor) and got 3700 ohms, I then ran the engine up to temperature and measured the resistance again and got 325 ohms, which tells me the temperature sensor is working fine, however the fault with the tick-over did not occur, so now I'm completely confused. Is the fault intermittent, or a poor connection, or something else? - I did leave the cap off the test port, would this have made a difference? - the cap does have a grounding pin, does taking the cap off the test port effect the ECU, I don't know, but if it fixes the problem then I'm just going to leave it off. lol.

I'm going to to get the vehicle MOT'ed and taxed and give it a good drive, hopefully the problem does not not come back.

[100SRV]

Air leak between plenum top and base opening up once it's hot?

[Belle427]

I believe its grounded when not in use to stop electrical interference but I cant say for sure what effect leaving it out has if any.

[wuckfitracing]

Here`s a thought, do want to borrow the ECU off my TVR.

[scoobydo123]

Possible contact fretting depending on pins try a drag test. But seems like working so guess dont disturb

[porker928]

Yes, the ECU is crammed into a tiny space where the glove compartment would be (if the car had one) with the loom under a lot of stress, so it could have a broken wire or bad pin connection. I will continue to investigate as the ECU will have to go back in position at some point as I can't just leave it hanging out on passenger floor well.

[Belle427]

Its worth checking all the basics such as TPS value and set the base idle as these can have an affect how it behaves as you suggest. All the info should be in the link I posted.
The stepper motor is worth cleaning too.
On a TVR the wiring to the MAF gets cooked and the connections get a bit dodgy so another thing to bear in mind.
Air leaks can occur especially when things warm up, Rovergauge can give you an indication of this by looking at the stepper position which is normally open around 30% at idle, if its quite a bit less it can indicate its getting its air from somewhere else.
It can also give you a good indication of fuelling with the fuel trims.
500 Rpm is very specific, it does have an input to the Ecu for when air con is selected to raise the Rpm, Im no expert on this side of it though and am not sure how it would be wired in a kit car.