lefrog

I went off at the Burke hillclimb last weekend and I still have not figured out why. I did put a video together trying to gather all the data I have:


I still did win the event with the fastest run earlier in the day. Video of that run here:

If you have any idea of what I might have done wrong or what could have possibly failed on the car, I am interested in all the feedback I can get.

froggy47

Based on just one quick look at the video/data my guess is you got into ice mode somehow (no tire marks from braking). Ice mode is always there even with all nannies turned off unless you pull the abs off the car (that's my understanding). I have been in ice mode about 3x at autox immediately after a spin braking is reduced to about 10% - 20%. The only "immediate" fix is to come 100% off the brake & then jump back on the brake as much as she'll take, there is often no time for this, however.

It happens when the wheel sensors tell the BCM that 2 (or maybe it's 3) wheels have zero traction.

Glad you & car did not get too banged up.

Racingswh

How could the car still be on the limiter in 2nd at those low speeds? Why did it go straight? Was there something different about the surface this run? What kept it on the limiter? So strange the whole thing. Glad you were ok.

63Corvette

I hafta agree with this! The stangest thing (to me) was the on-the-limiter thing
HOWEVER, that is one rough road, and the least safe track I have ever seen!!!

lefrog

I am still puzzled by the limiter. It is normal that the car jumped their when I engaged 2nd gear as I was still too fast for it, but why it got stuck there until the impact is still a mystery.
I am wondering if the TC has something that keeps the throttle steady when the car goes in ice mode or whatever mode the car was in (originally set to Competitive Driving). I originally thought my foot was misplaced and I hit the gas but the throttle sensor and the video seem to show that I was indeed on the brakes (and the car was slowing down).
3 other cars went off or wide on that corner that afternoon, so there must have been something slippery there too.

lefrog

Would pulling the ABS fuse, disable the ice mode?

mgarfias

Yes. Watch your brake bias though.

froggy47

I think so, it has to.

froggy47

All the times I was in ice mode the throttle was closed & I had the brake pedal thru the floor.

Any loose stuff that could lodge between the brake pedal & on top of throttle? That would do it.

Do you heel/toe? I have on occasion (shhh, don't tell anyone) got some gas while I was mashing on the brake if I was braking with the ball of my foot.

:0

lefrog

The car is gutted, there is nothing left in the footwell.
I do heel/toe (side step technique as I have a broken Achilles tendon that limits my movements). I have the CCA pedals that help a lot with that. Look a video the same day, some footwork at the 2:20 mark:

The OBD2 throttle data shows a little bit of throttle about 25-30%, nothing that would pin the car to the rev limiter.

bags142

were you actually IN 2nd gear? It looks as if the gear **** is further forward than ~25 sec earlier in the vid.

I am not sure if that changes anything, but just trying to help

redtopz

Sorry about your car! Sure didn't look like it was your fault. That was one of the weirdest things I've seen with the engine banging off the rev limiter as your car was slowing down. You might have a faulty ebctm that went haywire. Pull the codes off the dash. If you had traction control on that may have been part of the problem.

lefrog

That is a good observation. It is hard to tell with the angle of the helmet cam but it looks like the shifter is moving around like it usually does when you are at the rev limiter (see video below).
It is hard to compare both videos because I screwed up with the cam on the crash run, the lens was tilted 90 degrees on the Contour so you don't get the same angle/view after the image rotation.

lefrog

This is not a track, this is a hillclimb. The risks are definitely much higher than a track if you go off and that is also why full rollcages are required. We have ambulance, wrecker and emergency personnel on site all the time plus of course all the corner workers.

It is still pretty safe compared to things like Pikes Peak but definitely not track like condition. To me, this is really challenging and I like it better than the track.

Regarding the road conditions, this one is one of the smoothest! If you want to see a bad hill, look at Ascutney. I am going there in 2 weeks but with the Subaru, can't take the Vette there!

ooldguy93

agreed on " Ice Mode "

same thing happened to me with an '02 Z28 ( ABS with traction control ), flat out in 3rd gear ( 100 mph ), into the brake zone, stood ( as normal ) on the brake pedal and no brake action ( pedal did not go to the floor - it may have felt like it as you've never applied that kind of pressure before - seeing the forest / Armco fast approaching ). Over the Armco I went.

I " interviewed " several Corvette / Camaro pro teams at the June Sprints at Road America and ALL stated that " ice mode " had happened to them once , resulting in a crash, and didn't occur again.

Contacted TRW ( no response ) and Bosch support ( Who stated that
" they never heard of ABS going into ice mode ", but, suggested contacting NHTSA ) .

It would surprise me greatly to know that John Heinrecy's rides had / have this concern.

froggy47

It's a puzzle why obd2 data not equal to reality of revs. But I see discrepancy in my data not equal to what I know the car did sometimes. Lag happens, miscalibration happens, sh*t happens. Rebuilt & go again.

Bluefire

Anyone know what the default brake bias is when the ABS fuse is pulled?

lefrog

I am not sure the OBD2 data is off. The RPMs match what we hear, and I did not have my foot on the gas pedal (though I may have grabbed some gas with the edge of my foot which would explain the slight throttle reported by the OBD2).
What doesn't make sense is that this much throttle shouldn't pin the engine at the rev limiter, something else did. I wonder if the ice mode is just ABS or ABS&TC combined that would maintain the RPMs at what they are to prevent the car from sliding on ice by lifting abruptly the gas pedal...

tytek

I had ice mode come on a few times when autox (after a spin) and when track driving (during aggressive, hard braking with more rear biased pad setup). Typically, the revs do not hang and the throttle body closes shut to idle RPMs. The incident in your video does look like ice mode, but the overrev is indeed strange. I have considered bypassing the stock braking system and doing front and rear brake master cylinders with manual brake bias. However, I hate to lose ABS, as flat spotting expensive rubber is a major concern for me.

What is your long term plan?

lefrog

I would like to keep ABS too. Now that I know about ice mode, I might be able to adapt to it and recycle the brakes to get braking power back instead of staying on the brakes like I did there. Ideally I would need a set of softer springs on my coilovers for bumpy hillclimbs.
I might try a slightly less aggressive brake pad in the back (I typically run same pads front/back). If the issue persists I will just stop using the Vette for hillclimbs and keep it for track usage only.
I am currently finishing lightening the car (headlight delete, HVAC delete, AIR delete) as I am repairing the front. I will try a couple of bumpy AutoX to try to reproduce the ice mode conditions to see if I can handle it in a safer environment (there is very little margin for error in hillclimbs!).