Stuck Throttle

Hi Doug (@dbg), I am sorry to hear about your "off track excursion".  Are you alright?  A few pieces of information would be helpful in diagnosing what went wrong.  What chassis number is your car?  Judging for what little I can see about your car it appears to be an SR3 RS but is it Fuel injected or carbureted?  I assume it is paddle shifted... is that correct? Roughly how many hours are on the chassis? There are several things that could be going on here, and your answers to some of those questions could help.

If your car is a paddle shift car you should look at the throttle cable where it goes through the throttle blipper.  As the cars accumulate higher chassis hours the throttle cable can fray in this area which can cause "bird caging", which means that as some of the wires in the cable break they tend to balloon out which can cause the cable to get hung up.  This could be a contributing factor in what happened.

The other issue that appears to be going on is it appears like you are pressing the gas at the same time you are pressing the brake.  This is VERY COMMON with these cars because the gas and brake pedal are so close together.  What happens is the driver brakes for a corner and when they move their foot to the brake, they catch the edge of the throttle with their foot which causes the throttle to be pressed with the brake.  The result surprises the unexpecting driver because the car is not slowing down as they are expecting, so they step harder on the brake hoping to slow down, but what happens is that the engine overpowers the brakes and seconds later the car is off track.  It happens VERY quickly and the drivers natural instinct to push harder on the brake is actually making the situation worse.  After the "off track excursion" the driver is often confused what happened because they believed they did everything correctly but the car wasn't behaving as expected.  The reason I know about this is I have done it myself.  I nearly drove into the back of a car while braking...at least I thought I was braking.  I swerved around the car and got to visit parts of the race track that I never planned to visit.  When I got towed back to the pits I checked out the car and the damage was minimal.  I very cautiously went back out on track the next session while driving the car much slower I discovered that sometimes I was catching my foot on the throttle and the car was not slowing as expected.  Once I realized what was going on I trained myself to make sure my foot was always fully over on the brake before applying pressure.

Having said that, it is interesting that when the engine accelerates while you are in the wall the throttle position on the video isn't changing, which seems odd.  That is why I asked it the car was carbureted.  The throttle signal on fuel injected cars comes from a throttle position sensor which should have recorded the throttle being pressed.  I don't know how the throttle position is measured with carbureted cars.

I hope this is helpful...

Thanks for the feedback. 

SR3 00846, and yes it has paddle shift. 

It may look like I'm pressing both pedals, but the ECU data doesn't support that hypothesis.  Throttle input drops part-way when I lift, and then very slowly trails off over 5-6 seconds.  And yes indeed I was pressing harder on the brake, not less!  If I clipped the gas pedal we should have seen the throttle input drop all the way and then come back up, and then increase more.  It did the opposite.

The reason the engine accelerates after a couple of seconds is I realized the throttle was sticking, and put in the clutch.  Unfortunately by that point I was already going onto the grass. Two seconds wasn't enough time to figure it out and recover. 

Two seconds on the grass and I'm in the tire wall.  And then as I'm sitting there still holding both feet in, the engine stops revving. 

The Radical Canada tech did inspect all the linkages, but didn't see anything wrong there.  The suspicion is that one of the throttle bodies was sticking. 

@dbg, This is a strange one.  The thing that is very odd to me is that the Throttle position on the Aim dash should be getting it's information from the throttle position sensor on the throttle bodies and the indicated position doesn't seem high enough to cause the high Revs that the engine is experiencing.  I don't know how helpful it would be buy I would be happy to review the data from your ECU if you would like.  My email address is CharleyH@RadicalSportscarRegistry.com 

Oof, bad luck. Those "I only had 2 seconds to diagnose and react to the problem" scenarios are always disorienting.

I had the throttle stick on my SR3 RSX a couple of months ago. Luckily it happened in the pit lane before going out on track.

I'd lift off the pedal, it would come all the way back up, but the engine would stay at 7k or so rpm with the clutch in. My crew sorted it out in the pit lane in a few minutes. The diagnosis was that it wasn't the cable sticking, it was something to do with the attachment point at the engine end. Sorry I don't have more details ... arrive and drive has plusses and minuses 😉

@charleyhradicalsportscarregistry-com 

Thanks - I was having trouble downloading the data myself, although the Radical tech had no trouble.  I think my cable might be intermittent.  Next time I'm at the track I'll try again to download it; I'll send it over if successful.  

My main concern at this point is that it never happen again.  Not worth the risk!  We don't yet have a "smoking gun" for the failure.  If they don't come up with something conclusive I'll probably have the entire throttle body assembly replaced.  

We now think the blipper is, in fact, responsible.  Will confirm next week.  Thanks for the tip!

Radical Canada has been absolutely awesome.  We'll have the whole thing repaired and ready for testing by next Saturday! 

On the bright side, my car will have a new nose assembly.  On the sad side, I have to pay for a new nose assembly.  And most of the FR suspension.  And a few other things. 

Well that sucks! Really!

but if you would press in the clutch when you felt car was pushing you would have saved the car at that point. 

same happened to me at nurbugrinh/nordschleife last year.  Was intense to push 5th gear flat out and when letting of just feel the power pushing on, luckily i pressed in the clutch and when he uprevved to the limiter i understood what actually happened.. so i had to turn off the man switch as well straight away. 

Reason was the one of the springs on the throttlebody /butterfly that avtually jumped off and rolled back one round, making it stuck.. 

Check this ones! As you can see it has rolled over and the tension is not same = gets wider and then gets stuck between

But doesnt the new life ecu have a stuck throttle function to kill engine? I have that now on my ecu master. I put it to cut  engine if my tps is over 50% and my brake in at the same

time for over 1 sec

Posted by: @lunatic

but if you would press in the clutch when you felt car was pushing you would have saved the car at that point. 

 

Easy to say.  I was on the grass inside two seconds.  Could you do better? 

Let's assume the typical 250 milliseconds human reaction time. 

You hit the brakes and it doesn't feel right.  250 milliseconds later your muscle memory automatically increases brake pressure.  It doesn't work.  Your conscious decision-making process is not as fast as your reactions.  Let's say you're really fast and figure out that the throttle might be stuck in just 500 milliseconds.  You decide to hit the clutch, and that actually happens 250 milliseconds later (being generous here - you have to move your foot over). 

That's a full second.  You are now one second from going into the grass, and now you have to figure out another problem - you have no steering authority.  A second ago you instinctively increased brake pressure, and your front wheels are locked.  

Do you have enough time to work out what to do?  And even if you did, do you have enough time to release the brake pressure and keep the car off the grass?  I think if you tried to do that you would just hit the wall harder. 

It was just an unfortunate place for the failure to occur.  Thinking about the other corners at Calabogie, in most cases I would have had enough time to recover.  I think corner 12 would have been difficult, too, but maybe there'd be a chance of saving it. 

@dbg, I agree.  When you are coming into a corner at high speeds and then for some reason you are getting significantly different responses to the inputs you have made thousands of times before you can only react on instincts.  It is a totally different situation when issues like this happen on a straight section of track where you have more time to react.  If something like this happens again, your instincts will be calibrated for it and you might try different things, but the first time it happens you just don't have enough time to react.

judging by the vid, you went out on the grass becous you blocked your front wheels.. car kept on pushing you off

for me my left foot is allwas ready on the clutch so it takes me no time to press it down, except reaction time..

 Same goes for exit turns as well, i have saved my self and engine many times from spinning out and around by holding in clutch in situatons like this.

i wish i could left foot brake like i did on rally and drifting, but my feet are just too big for this set of pedals

in this case i was comming full speed 6th gear into the first corner after the long stretch at nordschleife when this happens.. giving me a speed way over 200kmh .. lucky i was braking at the same time to make a downshift from 6th gear when i felt the car pushing me. And after clamping in the clutch i understood it hang up since i was pounding that rev limiter..

but check your springs. Unless there is something with your blipper. Donw know what system you have on this car?

The Radical tech checked the springs immediately afterward; he said they were fine.  I will personally check as well.  

CharleyH pointed to the cable binding in the blipper as a likely cause.  We'll be inspecting it carefully later this week when completing the repairs.  In any case we are replacing the throttle cable.  

Weather permitting we'll be testing the car on Saturday.  And yes my foot will be hovering over the clutch.