Accelerator stuck wide open while car is going fast: what should you do?

[NY]

Hmm. They were lucky the valves didn't punch a hole through the pistons.

I remember my garage warning me with my first diesel car that it was an "interference engine" - ie the valves occupied the same space as the top of the piston, though at different points in the cycle. Consequently it was even more important than normal for the timing belt to be changed at the manufacturer's stated intervals, in case it snapped and the pistons and valves collided. The garage also advised with my present car that they should change the water pump (driven off the timing belt) while they were replacing the belt, even if it seemed fine, so as to not incur a second engine removal cost if the pump should subsequently fail. The extra cost of a pump that may or may not need replacement was peanuts compared with the labour of making the timing belt accessible - so kill two birds with one stone.

[Harry Bloomfield]

NY submitted this idea :

A modern engine under ecu control will not exceed the redline, unless there is some outside influence.

The outside influence being either going down a very steep hill and heavily laden, or a diesel engine which has begun running out of control on its sump oil. Ignition switched to accessory (I) should work to kill the power from the engine, apart from a run away diesel. Hard on the footbrake should slow the car plus engine down.

If in the case of a run away diesel engine you cannot slow down enough, clutch down, into neutral brake and let the engine self destruct.

[NY]

How would the sump oil find its way into the cylinder? Via leaky piston rings? I presume top gear and hard on footbrake *should* stall the engine.

[Dave Plowman (News)]

Turning off the ignition doesn't stop the brake vacuum servo working. That will continue to work while the engine turns. Which will be as long as the car is moving, if left in gear.

[Dave Plowman (News)]

I've driven quite a few cars of the same make and model fitted with both manual and power steering. And the effort needed on a broken power steering one is way higher than the manual one. Making me think the hydraulics or whatever must introduce a lot of friction.

[Harry Bloomfield]

NY explained on 23/07/2018 :

There are various ways for the engine oil to get into the combustion chamber, there are numerous examples on Youtube of runaway diesel engines. Some have even tried to use it as an excuse for speeding for tens of miles. The footbrake certainly 'should' be able to stall the engine, the engine will have much less power available than normal.

[Dave Plowman (News)]

I'd not get driving a car you don't know how to at those sort of speeds, no. ;-)

[Dave Plowman (News)]

Yes - and quite likely break the transmission in the process.

Of course - a FWD with the handbrake on the rear wheels so with as little grip as possible due to the weight being over the fronts. Forgot about those.

Going to take a lot longer to stop it if you don't kill the engine first. But dunno these push button systems - are you saying it won't kill the engine on the move?

My car, which is an auto, will kill engine power if you stand on the brakes and throttle at the same time. Don't ask how I know this. ;-)

[NY]

I've vague memories of something my dad told me long time ago. He was first on the scene at a lorry accident (fortunately no-one was hurt) and he tried to turn off the lorry's engine at the ignition key. It carried on going. The driver told him to pull a lever somewhere and there was a lot of hissing and spluttering and the engine gradually stopped. Now the obvious thing that a lever would operate would be a fuel shutoff that was independent of the solenoid that was kept open by the ignition switch, but that doesn't match the hissing and spluttering. It make me wonder whether some lorries had a means of venting the cylinders to the atmosphere as a crude way of breaking the cycle and stalling the engine - maybe by holding the exhaust valve open during the compression and power stroke to avoid the compression ignition.

Was that ever done as a way of stalling an engine to turn it off. It would have been in the late 60s, so whatever technology (mechanical fuel pump and injectors) was around at the time. Not sure whether it was 2-stroke (eg Commer "Knocker") or 4-stroke.

[NY]

Yes I test-drove two VW Golfs that were supposedly identical part from one having PAS. I found that the one with PAS was a lot easier to keep the wheel at a non-straight ahead position on a bend (there was less self-centring) which surprised me as I was expecting the PAS to give greater assistance to return the wheel to straight ahead. But when I happened to turn off the ignition just before the car had come to rest, there was immediately a very strong force trying to centre the wheels.

[Andy Burns]

The electric parking brake on mine is a toggle switch, push on-/push-off, if you push it while moving nothing happens, but if you pull it while moving it will plant your nose into the windscreen ...

Not that I'm likely to stop to think "now, which switch do I pull?" rather than just stomping on the footbrake.

[Harry Bloomfield]

NY used his keyboard to write :

Certainly the had cranked static diesels of the era, had a lever to release the compression, so the could be cranked over. You moved the lever, cranked up to speed then released the lever to hopefully have it fire up. Possibly lorries had a similar device too, to allow the starter to crank the engine over. Called a 'valve lifter' I think (?)..

Such a lever would stop a runaway diesel engine, if used on all cylinders.

[Chris Bartram]

Often past failed turbo seals.

[Mr Pounder Esquire]

New Vauxhall Vivaro van in 2001. Arrived new with no wheel trims, they had all fallen off during delivery. No "special" tool to take the wheels off in case of a puncture. Wiper arm fell off after three weeks. Windscreen seal fell off after three weeks. Sat in van drinking coffee after four weeks, rested foot on the brake pedal and it fell off. Brake pedal, not my foot. The AA bloke said "owwwwwwwwwww". I never trusted that van again.

[Jack James]

Makes more sense to turn the engine off and use the foot brake to stop it unless you are tearing down a very steep hill fully loaded and likely even if you are too.

[TMS320]

Sometimes it does no harm to assume there is some intelligence amongst the readership and they don't need to be told the consequence of not having assistance.

An engine is nowhere near powerful enough to overcome the brakes; it would be just a matter of pressing the pedal harder than the foot is normally calibrated to do. People don't routinely dial in more than about a quarter g.

[Nick Finnigan]

The Freeloader button will kill and restart the engine on the move, but the action is linked to the clutch pedal position.

Well it's an auto, so you'll be left foot braking, and not think about the accelerator in an emergency.

[NY]

I've always wondered how the left-foot braking thing ever came into being. If you drive a manual car you are used to a fairly big movement with your left foot, and finer, more precise movements with your right foot to operate the brake or accelerator. Part of learning to drive is acquiring the different muscle memory in your two feet.

Which bozo thought that it was sensible to operate the brake in an automatic with your left foot, just because you won't need that foot for the clutch? It means learning a whole new muscle memory, so as not to press the brake as hard and as far as you would with the clutch, only to have to unlearn this if you ever have to drive a manual.

I have always used my right foot to brake in an automatic, exactly as I would for a manual.

[Steve Walker]

There may be some hydraulic effects, but there is also a simple mechanical reason - mechanical advantage. From my experience, non-PAS is typically 3.5 turns lock to lock, while PAS is typically 2.5

Regards, SteveW

[Dave Plowman (News)]

But why would you bother when it's simple to just turn off the ignition? Surely the important thing is to get the car to a standstill as safely as possible?