The dreaded MK3 limp mode in 5th gear

[chewy8000]

So we ran a test day and had great success in the new car (95' ITB golf). I had one issue that was consistent with a few of the new mk3 vw golf builds. The car reaches 5200 rpm in 5th gear on the straights and cuts out for 2-3 seconds. I know the issue is with the VSS sensor on the tranny and it's connection to the ECU. Conover Motor sports was aware of this and ran a jumper wire from the sensor straight to the ECU as a preventative fix but it's still happening. Is there anything else to check besides having the ECU bench tested? It's super anoying and surely killing my track times.

[Beran]

It could be the ECU programming - happened to Tim... they forgot to remove or change the top speed limiter.
If that is not it then it could be fuel related... Do you have a new fuel pump? I had that problem for a little while... old tank with old gas and crap in it sitting for so long that it just screwed my pump up enough not perform well enough to keep up.
just some .02
Beran

[jlinfert]

ECU's are free now. Dump the POS factory ECU and install a Megasquirt2 system. I believe there is a tremendous untapped potential in the ABA that a factory ECU is unable to access. Just my .02.

[Dave Zaslow]

VAG (now VCDS) the car. Any limp mode will inflict this limiter on you.

Make sure the VSS itself is good. It's read by pins 1 and 65 on the ECU. Ignition on, neutral selected, raise the left front wheel and turn (lift both wheels if diff-locked together). It should fluctuate between 0 and 4 volts.

Check the continuity of the jumper as well, just in case...

Where did the chip come from?

DZ

[chewy8000]

We ran the stock chip in it for the test day. It had more gains at the dyno than the Techtonics chip we tried using.

[spnkzss]

What is the top speed limit in a stock ECU?

[chewy8000]

I need to either drop some money on megasquirt/tuning or buy a VAG-COM for this thing.

[Dave Zaslow]

This situation brings back so many bad memories chasing this stupid thing.....

Not likely, but one other item the ECU is sensitive to is a spanking clean signal from the O2 sensor. Hook up a voltmeter and watch the rise and fall of the voltage. Hook up an oscilloscope and see if the signal is clean.

Take a look at the behavior of the injectors when you rev the engine (you can do this in the shop). If you are getting injector open times of 10-15ms or larger, you are hitting the full rich, dump as much gas as possible to save the engine, ecu limp mode.

BTW is this OBD1 or 2?

If you will share the dyno results I can send you both GIAC and TT chips mounted and ready to go in an OBD1 ecu. Both ostensibly custom, but not Dick Shines later creation. Plug and Play guy?

DZ

[chewy8000]

Thanks Dave,

The motor is OBD-2. I tried to contact Garret but he's impossible to get in touch with and there is no phone number on his site.

[dave parker]

Shine Racing Service phone number is 508.695.8888

cheers
dave parker

[Beran]

Yes - it sounds like the stock chip is stopping your top speed.
Funny how the stock chip performs better on the dyno :-)
IMHO a Mega squirt system is not needed for an OBD2 MK3 with a programmable ECU if you have the ability to program the ecu at the dyno. If not, then a Mega squirt makes it easy for most people to program a setup that works well. Although it is another area to tweak/break/configure time sync.
The limiting factor is air flow not fuel for the MK3 OBD2.

[Dave Zaslow]

All the stuff I have is OBD1.

One of the craziest reasons I have heard for this problem was a cracked crank trigger wheel that deformed at higher revs only That caused the crank trigger to lose signal and you know what happens then.... They had to pull the crank and change the wheel. If Cameron built the engine I'm sure he used a new one to avoid this.

If you want you can call me at work. http://bodouva.com/index4.html

DZ

[jlinfert]

ECU's are free now. Dump the POS factory ECU and install a Megasquirt2 system. I believe there is a tremendous untapped potential in the ABA that a factory ECU is unable to access. Just my .02.

And by the way we(Atlantic Auto Works) are now installing and tuning Megasquirt systems starting at $1400 COMPLETE! (This includes dyno tuning) 321-254-1344

[chewy8000]

Thats tempting but too far away.

[jlinfert]

You might check the VWVortex Carbs,ITBs and SEM forum I believe there are a couple of Megasquirt installer/tuners in your area. Several of them are very very sharp.

[Flyinglizard]

You can monitor the OBD 2 setup with an Actron reader. It wil give the freeze frame that set off the limp mode. (Verify the VSS problem.)
This reader also shows the active data, as the car runs. I keep a list of known good values for thse cars. Why??..
Along those lines, there may be a % speed reducer to fit inline with the VSS. Modify the speed imput,etc..
Maybe swap drive gears.
PS I think that the VSS is a hall gen. Take off every other lobe and see if that changes the deal.
MM

[Beran]

Which Actron reader do you use? Do you keep it plugged in all the time?

[Flyinglizard]

Yes, you can plug it and run with it, observing (most of)the data. VW has a lot of VW only codes and they may not come up. But the code # often does and the book can decode the # for you.
The Actron model is the second from the bottom, price wise. They have come down to about 100$ at Autozone. AZ may use one to check and reset codes at the store. Check your local store first and ask to try one.
MM

[Flyinglizard]

What was the final result of this?? Did you get it go go over 112 mph?? TIA, MM

[chewy8000]

Yep we had the issue fixed with a chip from the guys at Techtonics. They just re-programmed a chip and deleted the top speed limiter. No issues now car runs great! 3rd place in the first debut of the new car.