Occasional total power loss
Discussion
Car is a 2000 Lupo Sport, with the 100bhp AUB engine.
Occasionally at speed (always on the motorway/dual carriageway) the car will lose all power, no warning lights or anything, it's as if the accelerator has suddenly been disconnected for a few seconds.
It will suddenly jump back to life after a few seconds and be fine for hundreds of miles.
It is always when there is less than a quarter of a tank of fuel left. I did think fuel pump, but that would definitely bring up a fault code. I've tested the fuel pressure and its fine.
It has an electronic throttle, and has no other problems.
Could it be a throttle position sensor problem? Or something wrong with the sensor that detects how far the pedal is depressed?
Thanks
Occasionally at speed (always on the motorway/dual carriageway) the car will lose all power, no warning lights or anything, it's as if the accelerator has suddenly been disconnected for a few seconds.
It will suddenly jump back to life after a few seconds and be fine for hundreds of miles.
It is always when there is less than a quarter of a tank of fuel left. I did think fuel pump, but that would definitely bring up a fault code. I've tested the fuel pressure and its fine.
It has an electronic throttle, and has no other problems.
Could it be a throttle position sensor problem? Or something wrong with the sensor that detects how far the pedal is depressed?
Thanks
Lose power as in reduced power only but still going or a total engine cut ?
What happens if you're driving along and you also touch the brake pedal slightly ? Does that create a power loss too ?
Some cars will kill power if the brakes are applied ( mostly diesels, but some petrols might too )
If there was an intermittent brake pedal switch fault it may do that.
What happens if you're driving along and you also touch the brake pedal slightly ? Does that create a power loss too ?
Some cars will kill power if the brakes are applied ( mostly diesels, but some petrols might too )
If there was an intermittent brake pedal switch fault it may do that.
The engine is still running, it's as if I have taken my foot off the pedal, except I haven't. I just pump the pedal a few times and it will jump back into action. There is often a bit of a judder as if the throttle body has snapped open.
Good call with the brake pedal switch, never thought of that. They are a common vw fault too. But why would that only happen when it's low on fuel?
Good call with the brake pedal switch, never thought of that. They are a common vw fault too. But why would that only happen when it's low on fuel?
Any crank or cam sensor fault codes?
The level of fuel is a coincidence, unless your float sender is off and it really is close to empty. But even that shouldn't be an issue as VW pumps built-in surge tanks, so it shouldn't fuel starve even flat out round a hair pin bend.
My Corrado used to do the same thing and it turned out to be a dying crank sensor.
The level of fuel is a coincidence, unless your float sender is off and it really is close to empty. But even that shouldn't be an issue as VW pumps built-in surge tanks, so it shouldn't fuel starve even flat out round a hair pin bend.
My Corrado used to do the same thing and it turned out to be a dying crank sensor.
By electronic throttle I presume you mean a drive by wire system with no actual throttle cable?
If it was an ignition or fuel cut the engine would stop running. If the ecu thought the throttle was shut but it was actually open the fueling would also probably be insufficient to keep the engine running.
I conclude that the throttle is actually closing to the idle position because the DBW system has an electrical fault either in a connector or the stepper motor to the butterfly.
If this is the case you would see the same amount of engine braking as when you lift off the throttle normally. If the butterfly was staying open but the fuel or ignition was cutting the engine braking would be much less.
If it was an ignition or fuel cut the engine would stop running. If the ecu thought the throttle was shut but it was actually open the fueling would also probably be insufficient to keep the engine running.
I conclude that the throttle is actually closing to the idle position because the DBW system has an electrical fault either in a connector or the stepper motor to the butterfly.
If this is the case you would see the same amount of engine braking as when you lift off the throttle normally. If the butterfly was staying open but the fuel or ignition was cutting the engine braking would be much less.
The throttle will default to ~ 7% open if the power is cut to the servo motor.
Next time it happens, dip the clutch and see what the idle speed is. Will probably be about ~ 1700rpm instead of the normal idle speed. Then as the others have said, it's the throttle. However, owning a DBW VAG myself, I know for a fact there would be pedal / throttle correlation errors in VCDS if there was an issue here.
Next time it happens, dip the clutch and see what the idle speed is. Will probably be about ~ 1700rpm instead of the normal idle speed. Then as the others have said, it's the throttle. However, owning a DBW VAG myself, I know for a fact there would be pedal / throttle correlation errors in VCDS if there was an issue here.
SuperchargedVR6 said:
The throttle will default to ~ 7% open if the power is cut to the servo motor.
Next time it happens, dip the clutch and see what the idle speed is. Will probably be about ~ 1700rpm instead of the normal idle speed. Then as the others have said, it's the throttle. However, owning a DBW VAG myself, I know for a fact there would be pedal / throttle correlation errors in VCDS if there was an issue here.
What about if the fault was at the pedal sensor not the butterfly servo motor? The ecu thinks the pedal is fully up so it closes the butterfly yes? No faults to log.Next time it happens, dip the clutch and see what the idle speed is. Will probably be about ~ 1700rpm instead of the normal idle speed. Then as the others have said, it's the throttle. However, owning a DBW VAG myself, I know for a fact there would be pedal / throttle correlation errors in VCDS if there was an issue here.
Pumaracing said:
What about if the fault was at the pedal sensor not the butterfly servo motor? The ecu thinks the pedal is fully up so it closes the butterfly yes? No faults to log.
The pedal has two independent tracks, as will the blade feedback. If there is only a small discrepancy between any of these it will register a fault.It would be hard to envisage a pedal fault that doesnt register a fault of some sort. It's made that way deliberately.
I doubt it. Throttle to pedal translation is very tightly tracked. There would never be a situation where the throttle is still open when the pedal is fully closed, except for cruise control, which the Lupo doesn't have AFAIK. Even the slightest difference between the 4 pots is logged and the failsafe comes down like an anvil. It WILL be fault coded.
EDIT: Beaten to it by Stevie
EDIT: Beaten to it by Stevie
All I can say is thank god my car has a good old fashioned throttle cable. There's enough crap on modern cars to break down expensively without the OEs finding ways to add even more of it.
I did once have a throttle cable break in 35 years of motoring (Fiesta XR2) but at least you know what the hell has gone wrong and how to fix it cheaply.
I did once have a throttle cable break in 35 years of motoring (Fiesta XR2) but at least you know what the hell has gone wrong and how to fix it cheaply.
Yep! DBW just conjures up images of American pensioners driving through Walmart windows and the whole Toyota floormat stuck under the pedal fiasco.
Thankfully, DBW is extremely reliable. It has to be because of the Americans' love of class action lawsuits.
And don't get me started on modern cars and the stupid ancillaries that promote extreme laziness. Again, it's too much of America filtering over to the UK. The one that irritates me most, is the "Lane change courtesy flash". Instead of pushing the indicator stalk up fully (because it's such a huge effort to do so, right?), you just tease it up half way and it will indicate 3 times and switch off. My god. Have humans really become THAT lazy and obsessed with gadgets?
Thankfully, DBW is extremely reliable. It has to be because of the Americans' love of class action lawsuits.
And don't get me started on modern cars and the stupid ancillaries that promote extreme laziness. Again, it's too much of America filtering over to the UK. The one that irritates me most, is the "Lane change courtesy flash". Instead of pushing the indicator stalk up fully (because it's such a huge effort to do so, right?), you just tease it up half way and it will indicate 3 times and switch off. My god. Have humans really become THAT lazy and obsessed with gadgets?
SuperchargedVR6 said:
Yep! DBW just conjures up images of American pensioners driving through Walmart windows and the whole Toyota floormat stuck under the pedal fiasco.
Thankfully, DBW is extremely reliable. It has to be because of the Americans' love of class action lawsuits.
And don't get me started on modern cars and the stupid ancillaries that promote extreme laziness. Again, it's too much of America filtering over to the UK. The one that irritates me most, is the "Lane change courtesy flash". Instead of pushing the indicator stalk up fully (because it's such a huge effort to do so, right?), you just tease it up half way and it will indicate 3 times and switch off. My god. Have humans really become THAT lazy and obsessed with gadgets?
The courtesy flash is a good thing really. It saves people from driving for 20 miles along the motorway with their indicator on.Thankfully, DBW is extremely reliable. It has to be because of the Americans' love of class action lawsuits.
And don't get me started on modern cars and the stupid ancillaries that promote extreme laziness. Again, it's too much of America filtering over to the UK. The one that irritates me most, is the "Lane change courtesy flash". Instead of pushing the indicator stalk up fully (because it's such a huge effort to do so, right?), you just tease it up half way and it will indicate 3 times and switch off. My god. Have humans really become THAT lazy and obsessed with gadgets?
But modern cars are a bit ridiculous. They are too advanced for most people to actually repair them when they go wrong, which is just mental. Made worse by the fact the last people who would be capable of fixing are the dealers that sell the cars !
Ah, but if you push the stalk up (or down) fully, the indicators still stay on until the steering lock cancels them 
Yep, agreed on the complication and dealers being ill-equipped and / or inadequately trained to fix the problems. I know of someone who got £1000s worth of new ECUs and wiring harness in his Audi A4 because the dealer lacked the skill to trace a broken wire in the door harness.
All they can do is replace things. Their analytical skills are virtually non existent. £1000s worth of perfectly usable kit thrown in the skip for no reason.
Yep, agreed on the complication and dealers being ill-equipped and / or inadequately trained to fix the problems. I know of someone who got £1000s worth of new ECUs and wiring harness in his Audi A4 because the dealer lacked the skill to trace a broken wire in the door harness.
All they can do is replace things. Their analytical skills are virtually non existent. £1000s worth of perfectly usable kit thrown in the skip for no reason.
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