[nvusuvu]

My father was gifted a 1972 Buick Regal. I was asked to drive it on I-85 (interstate) During acceleration on the onramp, the cable controlling the throttle got stuck and the gas was flowing into the carb and UA continued to occur. I was reaching speeds in excess of 100 MPH (160 Kmph). The brakes did nothing to slow me me down. My wife, driving adjacent to me in another vehicle, thought I was showboating or just being wreckless. I had to kill the engine with the key, slow down, and then crank the car, begin accelerating, then kill the engine to 'manage' the vehicle until I could get off the interstate. Terrifying ordeal.

[vikingerik]

In such cases, if you can't brake or release the throttle, one other out is to gear-shift into neutral. The result of slamming that power into neutral won't be great for the engine or transmission, but at least you'll be able to stop accelerating and coast to a stop.

[macintux]

I recall riding with a friend who had an automatic, and his engine was racing at every stoplight (I don't recall the name of the hardware that's supposed to disengage the engine when the brake is fully applied, but clearly it was broken).

So, he sat at every light with the brake pushed hard to the floor, trying to keep it from plunging into the intersection. As a long-time stick shift driver, I asked him why he didn't just shift it into neutral.

[2143]

> I asked him why he didn't just shift it into neutral.

What if the engine free-revs and redlines on neutral?

Maybe turning it off might be a safer alternative.

[op00to]

I would take a blown engine over flying into an intersection any day of the week.

[dotancohen]

  > I would take a blown engine over flying into an intersection any day of the week.

And this is why we need to build experience. Young drivers very often are confronted with decisions like this but their mind phrases it as "Blown engine that I do not have to funds to pay for in Dad's car, or just hold this pedal firmly and everything will be all right".

Unfortunately, the problem with experience is that the lesson comes only after the test.

[Kon-Peki]

A "modern" car is unaffected by free-revving to the redline. The computer shuts off fuel intermittently to prevent damage.

[Syonyk]

And most older engine will float the valves and, assuming nothing collides or comes apart (floating valves isn't good for the rest of the valvetrain), self limit that way.

But almost any engine with electronic ignition (so early 80s or later for a standard car or motorcycle, with plenty earlier having that feature) will cut spark to control RPM as needed. Unless you just start getting ignition breakup at RPM (not enough dwell time for the coil).

[dotancohen]

I actually saw a small block Chevrolet or Mopar (don't remember which) dent the hood this way. I suppose the rocker rotated when the valves floated, when the valve broke the stem went right through the valve cover. Funniest thing I'd ever seen at a drag strip.

[gonzo]

with nothing resisting the crankshaft, the rods will ensure a ton of stress at the bottom of the “power” stroke, and will shortly depart the earth.

[sidewndr46]

Even very old cars have a rev limiter based off the RPM that momentarily disables the ignition.

[gonzo]

Define “very old” because this is not true without an ECU

[sidewndr46]

You don't need an ECU to act as a rev limiter. Gasoline engines have had rev limiters in all different kinds and types for over 100 years. Some cut fuel, some cut spark, some cut both.

For example pre 1900:

https://en.wikipedia.org/wiki/Hit-and-miss_engine

Later:

https://www.jalopyjournal.com/forum/threads/mechanical-rev-l...

1970s electronic type:

https://www.428cobrajet.org/id-governor

Even my push mower has a rev limiter, it just gets called a governor on that engine.

The majority of large American engines used the valves as the rev limiter. The valve springs were so weak that past a certain RPM the performance of the engine falls off so fast it isn't going to rev anymore, even in neutral. The valves never fully close, so performance is very poor. This is well below the mechanical limitations of the crankshaft, so nothing is really going to happen. Once interference engines showed up as common place in the market, it became mandatory to have a rev limiter. This happened as electronic ignition and fuel injection became more common, so it was logically incorporated into the ECU as time went on.

[Enginerrrd]

Not sure, but you might still have power steering if you leave it on but in neutral. If you turn it off, you'll definitely lose hydraulic steering assistance.

[abawany]

Yep, plus brakes - one typically gets two or so powered hits before the brake pedal also becomes unmanageable after the engine is off.

[CPLX]

That’s ridiculous. The brakes work fine without power you just have to push a little harder.

Not to drop old man wisdom here but back in the day power brakes were an option that you could pay for.

[amluto]

At any respectable speed in a well constructed car with a mechanical steering linkage, power steering is basically unnecessary. My old car used to have glitchy power steering— at 35mph, I could generally tell when it wasn’t working, but it wasn’t very obvious. At 5 mph it was quite obvious when it wasn’t working.

[l1tany11]

It’s really dependent on the car. I was driving a C7 Z06 and the power steering cut (it overheated—car warned me well ahead of time). Let me assure you it was not trivial at all to steer the thing. It was shocking how heavy the steering became. I could turn the wheel—barely. Would not really call it control.

The next day my friends e90 BMW m3 power steering boiled over. And another friends F80 M4 had multiple power steering failures. They weren’t exactly happy about it either.

[toast0]

If it's only an issue at stop lights, it might just be a very high idle for whatever reason, and putting it in neutral wouldn't necessarily redline.

For throttle stuck fully open, going very fast on the highway, yeah you're gonna redline, but it's probably better to redline in neutral while you pull over than to turn the key off while you're still driving.

[dotancohen]

  > Maybe turning it off might be a safer alternative.

Young drivers might not understand the difference between the powered-down and the pull-the-key-out positions. There is a real danger of locking the steering wheel in this case.

[ranger_danger]

Most cars today do not have traditional keys in an ignition cylinder.

[slingnow]

Safer for the engine? Absolutely. Safer for you? Definitely not.

Which one are you optimizing for?

[throwaway0a5e]

If replacing an engine would not be economically sensible in whatever you're driving you should probably chance it running the intersection or whatever. If you fail you're buying a new car, but if you blow up an engine you're buying a new car too. But you might not fail so the relative expected value is greater. I hope your horn works...

[winrid]

There is no hardware to disengage the engine when your brake is pressed. The torque converter just allows some slip so you can stop.

Likely he just had a high idle due go some vacuum leak or whatever, as you said.

[hatsunearu]

uh what the fuck? why didn't he fix the damn car?

[sokoloff]

I suspect a lot of people find themself in a situation where driving a car with a mechanical problem is a sensible local optimum for some period of time.

The statute of limitations has passed on all of my “she’ll be a’ight” endeavors, but they included having to manually apply throttle to keep the engine lit, driving on partial service brakes, driving without a working charging system, having to push start the car, reckoning speed by gear and RPM, and fueling based on ded reckoning with an INOP fuel gauge and odometer.

[dotancohen]

I notice that a lot of people who have never driven 1980's era and earlier cars have no idea that cars were _always_ broken in some form or another. Every single car had developed some problem or another every year, one simply got used to this car having a bad window motor, that car having a bad started solenoid, this one torque steering to the left, that one thumping on brakes, this other one running rough when driving to the east, that one leaks transmission fluid, that other one won't restart after five minutes but will restart after half an hour, this one has no A/C, this one has terrible wind noise, this one blinks left when the radio is on FM, this one drips radiator fluid into the cabin when the heat is on, that one will spontaneously activate ABS in the last second before coming to a complete stop 50% of the time, this one squirts washer fluid onto the roof of the car to your right, this one dims the dash lights when the radio DJ talks instead of playing music, that one overheats, etc etc.

[throwaway0a5e]

The partial brakes is the only thing on that list I'd consider to be more than just an inconvenience.

Obviously if you want to drive like a jerk you need the car to be in tip top shape so that you have the most freedom to make control inputs but if you just want to putt along and drive in a mild mannered way having a bunch of mechanical oddities that constrain what you can do isn't a big deal.

[twofornone]

Shifting to neutral under load is probably not harmful. It's the opposite that is harsh on the drivetrain.

However if the throttle is stuck and you are in neutral you'll end up revving at redline until you turn off the engine. Not the end of the world momentarily but you don't want to leave the engine revving that high for a prolonged period of time.

[kemiller2002]

"Funny" enough, my family had a similar experience. My parents owned a 1984 Ford conversion van. On a family road trip, a squirrel got up into the engine and built a nest or something around the component which was used to control the amount of gas going into the engine (I don't remember the exact specifics), my dad had to shift it between drive and neutral until we could make it off the highway as well.

[tempnow987]

I was boating and same issue - broke to full throttle on a gas engine. So I just came flying in and killed engine. I could have restarted probably if needed. These things are almost always stoppable.

Another boat had a diesel. This boat had serious flooding and I went over to help ($1M+ boat, owner had backed it hard into concrete pier and not noticed a transom crack that opened). Engine would not shut off (electrical all shorted out). That diesel engine was running full tilt almost totally submerged - was pretty impressive. Eventually someone got a mask and snorkel and dove to fuel cutoff before it ingested a bunch of water through air intake (which I'm sure would have stopped it). With diesels I always liked knowing where manual fuel cutoff was after that.

[hatsunearu]

Hijacking (kinda): diesels are vulnerable to a phenomenon called "diesel runaway", where unintended fuel (for instance, engine oil leaks) seems into the intake/cylinder. The engine is controlled by how much fuel is injected, so if you just add an extra amount of fuel it will start increasing torque all on its own, and in the worst case, will cause unintended acceleration.

Nowadays diesels actually come with throttle bodies for emissions reasons which I think also will serve a safety function against runaways.

[sokoloff]

A major part of diesel efficiency comes from a lack of a throttle plate. I’d be surprised if adding one was beneficial for emissions. Do you have any reference here? I couldn’t find one with a quick googling.

[GeorgeWBasic]

I don't know if it's for emissions reasons, and I doubt it does anything for emissions, but Volkswagen diesels have a throttle that's there to make engine shutoff much less shaky. It's called the anti-shudder valve, and it activates every time the engine is stopped, and it would stop a runaway diesel.

[namibj]

I'd guess too-lean combustion in idle is bad, and throttling the intake so that it starts out with reduced pressure and at the fixed compression ratio, won't reach as-high pressures (which waste power by some of the adiabatic heating coupling to the cylinder walls). Might only work on individual cylinders, as it seems like it'd easily prevent ignition, but still...

[hatsunearu]

https://www.team-bhp.com/forum/technical-stuff/188332-explai...

from what i understand it's mostly to have a control over the air fuel ratio.

[gonzo]

That’s what the injectors are for.

It’s for emissions

[hatsunearu]

what the heck are you talking about, if you're at partial throttle, by design a normal diesel has no control over how much air is entering the engine, so your only way of modulating torque is changing the injection. This means your air fuel ratio will be uncontrolled, which is bad for emissions.

[moron4hire]

A place I worked years ago was a manufacturer of industrial lifting cranes. They had a problem one particularly hot summer of the diesels in the cranes starting up in their own.

These were massive engines. The block was bigger than my whole car. Terrifying watching one of them run away. They tended towards "violent, unscheduled disassembly" if they couldn't be shut down.

[Markoff]

Doesn't steering wheel get locked on some cars when you kill the engine? Seems switching to Neutral is safer option.

EDIT: I read that on some cars you can have problem to change to Neutral without brake, so even if brake fails I guess your only option is slowly pull the emergency brake.

[WalterBright]

Happened to me once. I stuck my foot under the gas pedal and forced it back up.

The throttle return spring is rather weak, and it doesn't take much to gum it up. A little force the other way will usually unstick it.

[kevin_thibedeau]

That only fixes a stuck pedal. If its stuck at the other end you'll just slacken the cable.

[WalterBright]

pulling the pedal back pulls the cable, not slackening it.

[hef19898]

Vaccum leaks can do the same, in idle that is. My '82 Rover V8 has that attitude sometimes when it's hot and not a lot air gets to the engine (traffic jams and so). Needs some load to get revs down, ideally the engine get cooled down. Have to hunt the issue down.

Apparently it can happen with carbs in general. I knoe people tgat had issues switching this engine off in the desert because the fuel in the carbs evaporated and continued to be pulled in the engine. Which was hot enough to to ignite it for a while...

[WalterBright]

Yeah, it's called run-on. Just let out the clutch and force a stall.

[tomcam]

OK that’s a straight up nightmare. Really cool thinking under pressure.