gamefreakgc
Elite Member
You guys have obviously never commuted in CA lol. Yes, in a perfect world in wide open highways you are supposed to have 5 seconds of separate. CA roads are not a perfect world!
throttle stuck at/near wide open on hwy
- Thread starter d_benet
- Start date
You guys have obviously never commuted in CA lol. Yes, in a perfect world in wide open highways you are supposed to have 5 seconds of separate. CA roads are not a perfect world!
According to Google, I live 4263kms from LA. Just about as close as I'd like to get!
I had to drive through a city of just 1 million on the weekend to get a part for my tractor. Didn't care for it!
thennen
New member
Plus, if the brakes are good, at highway speed in 5th gear, the brakes should overcome the engine. You can test that with both feet on an empty road if you want, but be careful. In 5th gear while braking hard, you'll move down the weak side of the torque curve fairly quickly (torque peaks around 3600RPM, I think). An automatic would downshift for more revs and keep fighting you, but it can still be done.
Just a thought.
Worth noting, again, that this only works for maybe two presses of the brake pedal. You have to commit to a stop pretty much first time. If you dab the brakes a couple of times, before deciding to pull over to the shoulder, you're probably not going to be able to overpower the engine.
Give it a try, traffic conditions, be safe, don't speed, etc, etc. But keep it in 5th, floor it, keep it floored, and press the brakes once, twice, probably by the third time you'll feel the pedal go stiff and you'll have a hard time getting much braking out of it at all.
thennen
New member
You may be correct - sounds like you've been there before. I haven't tried that (multiple pedal presses in a panic situation), and my 3rd Gen is automatic, so a bit different. Just threw it out as another option.
I just tried it back when Toyotas and Lexus cars were speeding 'out of control!' and the drivers were unable to stop them. Some of them dying in fiery high speed crashes.
But people kept saying that there's no way that could happen, the brakes are more than strong enough to haul a car to a stop, even with the engine floored.
But I knew how the vacuum assisted brakes worked, and that there's no vauum when the throttle is wide open, so I jsut tried it, to see how many power assisted pedal pumps you get. It was really only 2 full power dabs on my '99, then a half power one, then nothing at all. And the brakes on a 4Runner really don't do much with absolutely no power assistance at all.
But people kept saying that there's no way that could happen, the brakes are more than strong enough to haul a car to a stop, even with the engine floored.
But I knew how the vacuum assisted brakes worked, and that there's no vauum when the throttle is wide open, so I jsut tried it, to see how many power assisted pedal pumps you get. It was really only 2 full power dabs on my '99, then a half power one, then nothing at all. And the brakes on a 4Runner really don't do much with absolutely no power assistance at all.
gamefreakgc
Elite Member
Yes. The thoughts of killing the engine and coasting to a stop with no power brakes are coming from people who obviously have never tried to stop a modern SUV with the engine off. I have. It's near impossible unless you have an endless stretch of road ahead of you with 0 risk of ever hitting anyone.
thennen
New member
Help me learn here...
Toyota's brake design, including past years/decades, is pretty much industry standard, if I'm not mistaken. If so, what you've said will apply universally (proportionally) across all makes and models - they'll all have this problem. So why would only Toyota (and Audi years ago) be the only automaker who has recently had to deal with this issue? And it wasn't SUVs, I think it was mostly Camrys and other vehicles. And if I remember correctly, many of those were low speed crashes, like someone driving through their garage wall or in a parking lot or something. Additionally, I think Toyota legally addressed the issue at least partially with floor mat placement (maybe a pedal friction issue too?). Audi addressed pedal positioning and their problem vaporized. I don't recall that an analysis was made that Toyota (1) had vehicles that randomly launched at full throttle, and (2) that the drivers attempted 3+ full brake applications and then were at the mercy of the vehicle.
Of course, with all things being normal, maybe none of us has attempted to achieve brake failure via repeated full-throttle stops. I'm not disputing that that could happen, but I have a Scion xA 5-speed I might try it on ;-). As I said earlier, I want to learn. If what you say is true, I find it hard to believe that it's not an industry-wide problem.
Fyi, if I sound contentious, I don't mean to be. I'm not interested in arguments, and I bailed out of Facebook 5 years ago for that reason. All I'm thinking is, if what you say about multiple brake applications is true, then they must be true everywhere.
Thanks.
JayRolla
New member
Denver highway is the same way. Bumper to bumper at 70mph and lane switching with no blinkers is the norm. 60 miles away in the springs and you get shot for doing that shit. Lol
JayRolla
New member
Don't turn off motor till your stopped. The rev limiter is there for a reason.
It is absolutely *NOT* specific to the 4Runner, Toyotas, or even SUV's in general. I would say that it's generalized to 'most gasoline engined passenger vehicles'. The vast majority of cars use vacuum powered brake boosters because it's simple, and a gasoline engine provides a practically free source of vacuum, since the intake manifold is in a partial vacuum MOST OF THE TIME. The notable exception being when the throttle is wide open, at which point it's pretty close to normal atmo pressure (less some flow resistance from the air filter and throttle body and rest of the intake plumbing.
Some cars do not have brake boosters powered by the engine's intake manifold vacuum. Diesel cars, for example, have no throttle plate, the intake manifold operates at (close to) ambient air pressures. But many diesel cars still have vacuum operated brakes, because they share most components with their far more common gas-powered siblings. So cars like our neat little beater TDi wagon have a separate vacuum pump. And for a variety of reasons, some other cars have non-vacuum powered brake boosters. Sometimes for packaging reasons. Some had hydraulic boosters, powered by the power steering pump. Turbocharged and supercharged cars usually still run regular vacuum powered brakes attached tot he intake manifolds, since the engines are USUALLY perating in a vacuum, other than brief periods of time where they have comrpessed air in there (vroom vroom boom).
But the vast majority of gasoline-powered passenger vehicles have brake boosters powered by vacuum sourced from the intake manifold. The engine has *far* lower pressures there during idle and low throttle, as the throttle opens the pressure rises, until at WOT it's pretty much ambient pressure. To prevent the amount of brake boost varying considerably based on the throttle position, the brake booster features both a large chamber (that big metal pancake/cylinder mounted between the master cylinder and the body on most cars) - larger than needed for just the specific direct use, and a one-way valve in the line leading from it to the intake manifold. That way the large chamber gets a good vac pulled on it at idle, then the one-way valve holds that vac in there as the pressure in the intake manifold goes up and down as you drive.
It helps that practically always - when you want to stop, you take your foot off the pedal, the throttle closes, and the engine pulls a vacuum in the intake manifold, and that booster chamber gets pulled down, providing full assist.
But in an unusual situation, say... when the throttle is stuck open, the engine is not producign vacuum. The one-way valve will hold the vacuum in the booster chamber, but that is 'used up' every time you press the brake pedal. You press it once, and the vacuum in the booster chamber drops Since the engine is WOT, no replenishment. You press it twice, same thing. At that point, there's really not enough vacuum in the system to help boost the brake pedal. You press it again, and you have unassisted brakes.
Now you might be into an area where the type of car makes a difference. Old cars, even large trucks, didn't have power brakes. Smaller cars didn't have them for even longer. But their hydraulic systems were designed to provide more of a mechanical leverage effect. But most modern cars, end especially, larger and heavier cars like SUV's, have brakes that are 100% designed to have that booster adding pressure. There's not a lot of direct mechanical 'leverage' designed into it. Once you lose power assist, the pedal goes very stiff. And you have to *REALLY* mash it to get even a small amount of braking.
Again, this isn't a Toyota issue, or an SUV issue, it's a design that's common to the vast majority of gas-powered passenger vehicles. If the engine is off, or if it is stuck at WOT, you only have a couple of presses on the brake pedal before you lose assistance, and the braking power of the vehicle goes down very dramatically.
And again, I'd second the advice already given in this thread about what to do if the throttle sticks on: put it in neutral (auto or manual), and then steer to the shoulder and stop it, then turn the motor off.
With it in neutral, the brakes are not fighting against the engine, even if the power assist situation isn't improved with the engine on vs. off. With the engine running, you still have power steering, so you're not fighting a heavy steering wheel as well.
My two points were simply:
1) Don't assume that the brakes can overpower the engine, unless you commit to bringing a car to a halt within the first two presses of the brake pedal. If you press that pedal down a couple of times without stopping, you're not going to have power assist anymore. And even tentative presses on the brake pedal 'use up' the vacuum.
2) Even though I wouldn't advise on turning the engine off while the car is still moving, I was just pointing out that the steering wheel only locks when the key is actually pulled all the way out of the ignition, it will not lock when the ignition is turned to 'OFF'. You could turn it off and continue to steer, you'd just lose the power steering.
With it in neutral, the brakes are not fighting against the engine, even if the power assist situation isn't improved with the engine on vs. off. With the engine running, you still have power steering, so you're not fighting a heavy steering wheel as well.
My two points were simply:
1) Don't assume that the brakes can overpower the engine, unless you commit to bringing a car to a halt within the first two presses of the brake pedal. If you press that pedal down a couple of times without stopping, you're not going to have power assist anymore. And even tentative presses on the brake pedal 'use up' the vacuum.
2) Even though I wouldn't advise on turning the engine off while the car is still moving, I was just pointing out that the steering wheel only locks when the key is actually pulled all the way out of the ignition, it will not lock when the ignition is turned to 'OFF'. You could turn it off and continue to steer, you'd just lose the power steering.
thennen
New member
Thanks a bunch JohnMc for your excellent and patient explanation - I really appreciate it. I've definitely learned a few things that'll stick in my challenged brain, specifically the concept/theory of the vacuum-assist system. My apologies for jumping the gun by making an under-informed statement. Thank you again for clarifying.
JayRolla
New member
I completely agree with this. In my situation the floor mat got stuck on my accelerator. Like anyone I hit the brakes few times and I was not going to be able to overpower the engine. I slightly panicked for one second. The reflexes kicked in and I put in neutral then immediately used my foot to pull up pedal and then reached down too pull the mat off.
This all happened in a few seconds and I was coming up to a red light in full traffic at about 45mph. IMO not anyone could have handled the situation as I did and I'm pretty sure 90% of others would have wrecked. Or maybe I just don't put faith in my fellow man. Haha.
