Manual VT with accelerator issues?!?!

26602 Views 89 Replies 20 Participants Last post by 3Sxturbo, Jul 7, 2013

cruisn76

Discussion Starter · May 2, 2013

Ok, I've been driving manual for years and years and one thing that is really bothering me is the accelerator pedal.

At a stand still, my style of driving on first gear is gas and clutch but on the VT I need to pump the gas one time and then release the clutch and then gas some more for transition. I hate that! I need to be able to do first gear in one shot without double pumping the accelerator. I usually do first gear at 1000-1200 RPM.

I tried many many times to hold the accelerator at at specific RPM but every time I hold that gas pedal it shoots to 2000RPM. The accelerator is not sensitive enough, it is almost preset set to shoot to 2000RPM, does anyone have this issue? Is this because I only put 1100km on the vehicle?

I already pulled the magnet out of the air box with no change.

Please help!

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Stone Axe

· #7 · May 3, 2013

Yeah, the accelerator has kind of a mind of its own sometimes. That's probably because it is "fly by wire" and not mechanical.

I get what you are saying but it has not been a problem for me. My style is to open up the accelerator to rev the engine and then ease the clutch as the revs come up and then hold the accelerator where I need for the amount of power I want. Often that leads to flooring it after the clutch engages!

It definitely took me awhile to learn the VT MT's cadence. Now it is second nature and I'm spinning the hard stock tires without any drama and fuss.

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Stone Axe

· #9 · May 3, 2013

Living in Atlanta traffic is a real pain and it made the decision to get a MT a difficult one.

Luckily on the highway during my typical evening commute it is more slow and go then stop and go so I can leave it in 2nd. The VT will launch in 2nd - especially in slow traffic and it can come nearly to a stop in 2nd without stalling. Launching in 2nd can be weird if you don't rev the engine enough though and I can get stuck with the revs too low for it to accelerate past idle. I've learned that just putting in the clutch and letting the engine rev and then letting it out fixes that problem - but it ain't pretty.

I hear you about making the clutch last too. I've never replaced a clutch in any of my previous MT cars even though they were used and I put a lot of miles on them. Everyone has an opinion on how to drive a clutch and I've often been criticized for slipping or feathering my clutch too much. I agree that minimizing jerking and abrupt transitions is best for making the clutch last.

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Stone Axe

· #28 · May 11, 2013

I don't spend a lot of time with the accelerator at the bottom so it doesn't bother me too much.

Once the VT's ECU is broken and made public this would be a very easy problem to fix.

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Stone Axe

· #63 · Jun 11, 2013

I'm a slot car nerd and I want to thank you for taking that assembly apart so I can see it.

Those aren't wipers per se. Those are bar magnets on the board and the "trigger" has Hall Effect sensors with contacts to provide wide-open-throttle (WOT) detection. I think those little three lines are the actual sensors and the gold is for WOT. It makes sense that the trigger touches the magnet when WOT occurs to close the circuit and have the circuit close through the gold contacts.

Any wiper system won't last 10 years so it has to be a Hall Effect system.

What is puzzling is why they have 4 different sensors. 2 of them have gold stops at both zero throttle and WOT so they could be redundant. The other 2 could be to measure the speed of the throttle transition and also redundant.

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Stone Axe

· #66 · Jun 11, 2013

Yes. It looks like both the fully closed and open throttle positions have a positive connection.

With this system there should be no dead spots and the extra little magnets past the gold contacts probably serve as another redundant system to determine closed throttle by the sensors if the contacts fail.

This assembly can't be tested with a multimeter other than maybe the stops. You will need an oscilloscope to read the TTL waveform - just like servos. The output is probably a square wave and I bet there are 6 wires coming off this assembly - positive, negative and 4 signal wires.

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Stone Axe

· #67 · Jun 11, 2013

Sure enough there are 6 wires coming off this assembly - but only 2 signal wires.

So that is a dual redundant system.

I'm surprised that the output isn't a TTL waveform. It doesn't appear to be a potentiometer and the sensors don't work at those voltage ranges. Those little things at the top could be FETs that bump it up to 5v.

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Stone Axe

· #78 · Jun 16, 2013

I don't have any dead spot on my accelerator pedal.

The nature of these kind of systems is that they can sense the neutral throttle voltage or resistance and call that zero. In another thread the accelerator schematics were posted and neutral was specced as a range - which makes sense because it will wear over time. Changing the neutral voltage will only reset zero in the ECU.

My accelerator pedal is too soft in the first 20% of its travel for my taste. The accelerator appears to have too much exponential in its mapping. This can be fun when you floor it but it lacks a linear feel when accelerating from a stop during daily driving. The VT has no torque at idle so I often over compensate by applying more accelerator and revs which can end up with briefly spinning the front wheels - which is also fun - and the clutch seems more than willing.

Now that my VT MT is broken in it definitely has no accelerator issues other than being a tad soft off the line. There is no surging or hesitation anymore. It pulls a lot harder all the way to redline and now makes a minor roar past 6,000 rpm so I don't have to look at the tach all the time. Full power is available every time in every gear and the response is crisp.

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Stone Axe

· #86 · Jun 25, 2013

My VT has no accelerator issues anymore. At first I was disappointed by the surging and the unpredictable power delivery as everyone else.

It slowly got better and the only modification I did was modifying the secondary intake flap thing. I didn't remove the magnet but I put some electrical tape over it to reduce its effect. At the time it kinda helped, maybe.

At 6,000 miles she started to make a little more power and the revs and the turbo became much more linear. Now at 9,000 miles she stomps through every gear every time. There is no hesitation at all when you keep the revs up and the throttle open. The main problem now is keeping it from the redline because she pulls all the way up to and past the redline now.

I removed the electrical tape from the airbox flap because it is not needed.

Maybe all she needs is a longer break-in before she comes in to her own.

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