Cutting out under load

So recently I have been experiencing cutting out under any load on my Land Rover Discovery 1 V8 EFI 3.5 Hotwire 14CUX, so I thought I'd share it for others that might have the same problem.

Seems there is a fault with my speed transducer, when ever the vehicle is moving (even slowly) it makes my ecu cut out (a safety feature they have apparently) when I give it even a gentle bit of power.
I doesn't do it all the time.

I unplugged the transducer which makes it run in "good idle mode"
This mode is not great for fuel deficiency and it seems a little gutless, not sure if it is due to this or something else.

I do have one question, is there a way to change the need for the transducer?
I don't think all the 14CUX's have them do they?


Cheers Mark

They do that when there is an air leak on the induction, did you check the simple things first����

Yea, but ill double check for air leaks, its only been rebuild a year and I sealed it all up then

Spray wd around the plenum and see if the most is sucked in

discomark10 said:

Seems there is a fault with my speed transducer, when ever the vehicle is moving (even slowly) it makes my ecu cut out (a safety feature they have apparently) when I give it even a gentle bit of power.
I doesn't do it all the time.

I unplugged the transducer which makes it run in "good idle mode"
This mode is not great for fuel deficiency and it seems a little gutless, not sure if it is due to this or something else.

I do have one question, is there a way to change the need for the transducer?
I don't think all the 14CUX's have them do they?


Cheers Mark

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Mark,

I'm not sure if the problem is your transducer (they do "just die") or a short somewhere.Check connections between ecu and speed transducer, maybe see if you can get a spare transducer off t'internet somewhere. As far as I am aware the speed transducer is there only to tell the ECU if the vehicle is moving so it switches idle stabilisation on or off.

If the transducer packs up it just throws a fault and the efi warning light comes on. There should be no real running issue other than it might be a bit rich if the ecu has detected a fault and has gone in to limp mode but I can't remember if the speed transducer forces a hard fault that puts the system in to limp mode. I had a transducer die after a trip to Salisbury, drove most of the way home with no speedo (and no cruise!) and that annoying orange warning lamp in my face but there were no particular running issues.

I vaguely remember reading somewhere that some TVR models didn't have a speed transducer.

I read that it it also controls the cutoff if you are to accelerate to fast, I can gently accelerate and also give it full beans while slipping the clutch against the breaks with no issue. Only has effect when moving.
Its also had issues with it not wanting to drop the revs when you come to a standstill.. which is also now fixed.

discomark10 said:

I read that it it also controls the cutoff if you are to accelerate to fast, I can gently accelerate and also give it full beans while slipping the clutch against the breaks with no issue. Only has effect when moving.
Its also had issues with it not wanting to drop the revs when you come to a standstill.. which is also now fixed.

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I'm not aware of a cut off on acceleration but the speed transducer is used as a speed limiter so whether or not there is a fault that is telling the ecu you're going too fast is a possibility.

The other thing that might be worth checking out is the battery voltage and alternator output. Weak electrics can cause funny running issues, I have certainly had that issue in the past and a quick refurb of the alternator sorted it.

Good luck with it.

classic kev said:

I'm not aware of a cut off on acceleration but the speed transducer is used as a speed limiter so whether or not there is a fault that is telling the ecu you're going too fast is a possibility.

The other thing that might be worth checking out is the battery voltage and alternator output. Weak electrics can cause funny running issues, I have certainly had that issue in the past and a quick refurb of the alternator sorted it.

Good luck with it.

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I read it on this post.. I miss read it slightly but still the same effectively

Land Rover Owner • View topic - Transducer for LT77s gearbox

Makes sense about the limiter. hope to get a new transducer to try anyway.

The electronics are all good, got twin batteries with voltages gauges, one runs about 13.6 (older type) and the other runs about 14.5 (my home made regulator on the aux battery)

Well looks like you got good electrical power. Perhaps check earth points on injection loom but a bit of a wild stab in the dark.

Have you got a code reader? Ironic really I used to live just down the road in Dunstable so I could have popped round and had a butchers. About the only other thought is see if you can borrow another 14CUX ecu and see if it might be an ecu problem.

I do have one other thought for you - check the throttle potentiometer. I can't remember the numbers off the top of my head but you need to check the base voltage setting, scaling and resistance. If there is any stiffness in the throttle pot or the readings jump around it may be the cause. HTH.

classic kev said:

Well looks like you got good electrical power. Perhaps check earth points on injection loom but a bit of a wild stab in the dark.

Have you got a code reader? Ironic really I used to live just down the road in Dunstable so I could have popped round and had a butchers. About the only other thought is see if you can borrow another 14CUX ecu and see if it might be an ecu problem.

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classic kev said:

I do have one other thought for you - check the throttle potentiometer. I can't remember the numbers off the top of my head but you need to check the base voltage setting, scaling and resistance. If there is any stiffness in the throttle pot or the readings jump around it may be the cause. HTH.

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Ok ill check the earths, Haha.. typical!
I do as it happens have another ecu from a 3.5 to hand!
You can probably answer this, I brought a 3.9 ecu out of desperation a while back, should it work ok on it? not sure about the map is all.

Ill check out the potentiometer also, I did have it out recently and checked the resistance of it and it seemed to work ok, but didn't check the voltages (which in theory should correlate with the resistance anywho)

Thanks for all the help

Mark, ECU from a 3.9 should work fine but you say you had the throttle pot off? Chances are the base voltage isn't right IIRC it needs to be something like 0.28v - 0.3v (check the value though) when the throttle is closed. If the voltage is too low the engine won't idle, if it is too high the ecu will think the throttle is open and will add fuel or throw a fault because there will be a mismatch in throttle position and air flow values.

Try setting throttle pot first then do an ecu swap.

classic kev said:

Mark, ECU from a 3.9 should work fine but you say you had the throttle pot off? Chances are the base voltage isn't right IIRC it needs to be something like 0.28v - 0.3v (check the value though) when the throttle is closed. If the voltage is too low the engine won't idle, if it is too high the ecu will think the throttle is open and will add fuel or throw a fault because there will be a mismatch in throttle position and air flow values.

Try setting throttle pot first then do an ecu swap.

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ok, ill take a look tomorrow and see what its saying, I had it off previously to try and sort a misfire which was down to a bad alternator in the end.