RR Classic 3.9efi running/stalling

Hi & welcome.........You state that you have changed the engine temperature sensor, is this the one for the ECU or the one for the gauge? As you know, they are cheap enough, if it's the one for the gauge you have changed, it will not feedback to the ECU and maybe the other one needs replacing. Rebuilt a 3.9 some years ago and mistakenly put the first injector plug, R.H. side on to the temp. sender as the colours had deteriorated causing all wierd and wonderful things to happen...............just a thought.

Hi thanks for the thoughts, no its def the ECU temp sensor, not the Gauge or temp switch for fans. The resistence measured at the sensor is the same as measured on ecu plug - so not a wiring issue me thinks.

Hello Perry,

stroicker said:

so in my mind it points to the ecu leaning the mixture due to temp, that is too lean to maintain combustion.

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With all that expensive new stuff and the checks already performed, what else could be making the mixture LEAN?

Check for rogue air leaks into the plenum, The ECU cannot compensate for these.

Try the process defined for my Rover 3.5 SD1 Efi system, it is readily applicable to your later system.

You'll find it in the PDF available here:

Rover SD1 Efi Plenum Chamber

when put into drive or reverse engine dies (unless i keep the revs up on throttle).

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I believe you may have on your car an anti-stall valve operated by the gearbox inhibitor switch to raise idle speed as the car goes into drive/reverse. If so, the switch, the wiring or the valve is malfunctioning.

The one on the Rover SD1 Auto works like this, yours may be similar.

Rover SD1 Efi Engine Stalling

On the other hand the existance of an uncontrollable air leak will also cause this fault TOO.

Ramon

Vintage Model Airplane and Rover SD1 3500cc Twin Plenum Vitesse

Hi Ramon, thanks for the pointer, sometimes i can't see the wood for the trees, which may also be blurring judgement and testing results. Have read both your recommended PDF's and will test then remove and thoroughly clean plenum and air galleries over the weekend, i'm not aware of any anti-stall mechanism, but again i'll get underneath and trace and see whats about, thanks for directing my focus in a direction i perhaps haven't explored as thoroughly as i should.

I'll let you know any findings.

Many thanks

Perry

Make sure you have not swopped over the coolant temp sensor plug with the fuel temp one - they fit and it happens.

Sounds like a royal pain in the behind.

Is your rotor arm a genuine Lucas one or a pattern part. I know from bitter experience cheap rotor arms upset V8's.

The only other thought I have is have you tried substituting your ecu? My original ecu was "tested" and returned with no faults found but it was totally shot, so I would say try substituting it with a known good one.

Thanks guys, all elec connections ok and rotor arm is genuine, ramon may have something, have tested the 'elephants trunk' and although no gaping holes the material has become porous letting air through, so, will see what changes when fire it up on sat after new 'trunk' and spotlessly clean ram and plenum go back on.

stroicker said:

ramon may have something, have tested the 'elephants trunk' and although no gaping holes the material has become porous letting air through, so, will see what changes when fire it up on sat after new 'trunk' and spotlessly clean ram and plenum go back on.

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Bliss!

Just music to my ears, reading that! I have this unfulfilled mission thro' my website, to persuade every Rover Efi owner to check these things out.

It's difficult because the task seems daunting to most owners, yet, air leaks into the plenum and gummy goo therein are the cause of most Efi problems.

To paraphrase Trigger praising his broom in "Only Fools and Horses".

"Look after your Plenum and your Plenum will look after you!"


Ramon
www.vintagemodelairplane.com

Hi guys, post weekend report is thus, new 'trunk' installed and plenum is spotless and all seals(throttle butterfly shaft) are air tight. Re-set up afr to 14.7:1 and runs so much sweeter, even with temp sensor connected, however as with every step forward, it would not restart again with temp sensor connected, disconnected its fine, as i was running out of time left it disconnected (however it starts better with it connected from cold). When drive selected it still dies, but if enough throttle to keep running its fine, its had a 250 mile test drive over the weekend and its smooth, and when braking to stop in drive it does as it should ie: it maintains its revs. Seems peculiar that at initial selection of drive/reverse it dies, but it knows enough the maintain idle if brought to rest whilst driven, my gut feeling is the current sensing part of the temp sensor in the ECU, or the ECU not selecting the correct fueling map, anyone have a circuit diagram of a 14cux ecu?

many thanks for your interest, Ramon, you definatley hit one of the nails on the head!

regards

perry

stroicker said:

i'm not aware of any anti-stall mechanism,

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I'm pretty sure thats what the air bypass valve (stepper motor) is for. Have you tried substituting your ECU?

stroicker said:

When drive selected it still dies, but if enough throttle to keep running its fine, its had a 250 mile test drive over the weekend and its smooth, and when braking to stop in drive it does as it should ie: it maintains its revs. Seems peculiar that at initial selection of drive/reverse it dies, but it knows enough the maintain idle if brought to rest whilst driven

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One of the differences between engaging drive when stationary and running on the over-run (i.e. engine braking), is that when engaging drive while stationary, the drag of the auto-box/torque-convertor etc. is trying to slow the engine down, when on the over-run it's trying to speed the engine up until the car stops.

This means that in the engaging while stationary case, engine load is increased and it's pretty immediate, in the over-run case, when you stop the RR, you are entering idle with a reduction in engine load rather than an increase.

Could it be that your ISC valve isn't reacting quickly enough because it's faulty or gummed up in some way or maybe it moves in quicker than it moves out ?

Hi guys, thanks for the continued pointers, ISC is fairly new having been replaced will trying to determine whats going on a couple of months back, when plenum was cleaned last weekend it was still clean and gum free, tested movement electrically being driven by the ECU - all fine, and reset using stepper motor reset proceedure. The only thing i haven't done or been able to do due to lack of hardware is try another ecu.

Anybody know of any reputable ECU testers that 'lend' substitute ECU's while they test yours?

Thanks for the continued interest

Perry

Very unlikely that anything is wrong with the ecu,where in the world are you ?

stroicker said:

and reset using stepper motor reset proceedure

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Not sure what it is, presumably it sets up the end-limits, but I would feel inclined to try doing this one again if it's not loads of work ......

bwarb said:

Not sure what it is, presumably it sets up the end-limits, but I would feel inclined to try doing this one again if it's not loads of work ......

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Its just clamping off the stepper motor hose and setting the base idle speed to 450-500rpm on a hot engine.It just ensures the stepper can control the idle speed over a good range,it usually shows as around 150 steps on Testbook,0 is fully open,180 is shut.
If he is confident that all is in place it needs 10 mins on Testbook to look at the sensor inputs as the ECU sees it.If all thats good then a session with an oscilliscope will find it.

There is a sense wire to Ecu that tells ecu it is in idle or gear- from memory on a modified rover P5 it is attached to park switch.
Look at wiring diagram.
There is a tune resistor plug for different countries- make sure it is correct and in spec.
Throttle potentiometer used to play up with bad tracks
Ignition amplifier was made remote on later discovery as distributor cooked them- change it as matter of course and check wiring.

Doubt ecu unless water damage

That took almost 11 years
Good post

mikieman said:

That took almost 11 years
Good post

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Well, the OP never posted the fix so presumably is still riding around with the temperature ECU disconnected?

Grrrrrr said:

Well, the OP never posted the fix so presumably is still riding around with the temperature ECU disconnected?

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Or he got rid of it and someone with right skills got a nice classic