John Speake

In various threads there have been comments about non-op WOT throttle switches.

Also comments that they are not operating until 90% throttle open.

I have been given a faulty switch by a local owner, and so I was interested to what the problem was. This was from a GTS.

I found the switch was very well sealed against liquids gettig into it.

I found the WOT switch is indeed activated at 2/3 throttle plate rotation - 60 degrees, certainly not much later as has been reported. I took the point at which the closed throttle microswitch clicked as my reference for the angular measurement.

The WOT switch was in found to be functional, although the design of the activating cam does not encourage the WOT contacts to wipe slightly when operated, which I think would be desirable as they are just open, springy contacts.

In fact I couldn't find a problem with this switch, although I know that when a new switch was fitted to this particular car the problem was solved.

So it would appear that the S4/GT/GTS throttle linkage appears to be responsible for some loss of travel ? Is this due to wear in some of the pulley and linkage joints ?

IcemanG17

John
Hmmm......interesting...maybe this is a minor design flaw that can be improved with a new sensor mount or different throttle cable routing or something.....sounds like a great project for someone handy like yourself or porken!!

RyanPerrella

John,

what exactly does the switch do? When its on full throttel does the switch trigger a different fuel injection and ignition map for the engine? With the switch non operational are we loosing out on potential HP under full throttle?

PorKen

The difference in perception of the full throttle switch engagement point may be due to the gated action of the throttle linkage. The throttle plate opens very slowly for most of the travel of the pedal.

Louie928

John,
Are you sure that switch is from a GTS? It appears like an S4/GT switch that has the two internal switches and 3 pin connector. The GTS switch has one SPDT switch and a variable resistor inside and it has 6 output pins although only 5 are used. The variable resistor feeds voltage to the auto trans kickdown relay.

John Speake

Hello Ryan
Basically the answer is yes to all your questions. With a non-op WOT switch you loose out on WOT mixture enrichemnt necessary for maximum power, and also the optimum ignition timing as well.

A couple of people with Superchanged cars have been surprised to discover a non-op WOT switch on their cars when they used the SharkTuner to optimise the fuelling.

John Speake

Hello Louie,
Yes, that switch came from a GTS engined race car (std engine). I understand that the 6 pin version of the throttle switch only was fitted to the very last of the GTS cars, and not the early ones.

Schocki upgraded his GTS with this modification, for which I supplied him the conenctor parts.

John Speake

That's a good point, but IIRC Bill Ball was measuring the rotation of the throttle plate when he said it switched at 90% throttle open. But I may have misunderstood.

It does appear that these switches are quite unreliable due to their basic crap design. Not Mr. Bosch's finest hour.

I can't see why they couldn't have fitted a nice microswitch for WOT, like they did for the closed throttle part of the switch.

I might try to see if it is possible.....

John Speake

Hi Louie
I just checked the WS manual circuits and found that MY93 GTS had the old 3 pin throttle switch, and MY94 has the 6 pin version with the potentiometer.

derporsche928

I've had three of them fail with the same failure mode, in that they will check okay cold but when hot, they intermittently lose contact or have a higher resistance......
Drove me crazy the first time trying to figure out the problem, but finally did......
If you look at the switch picture where the contact arms go into the black plastic,..... there under the two shiny black dots, the contact arms go in there and are just a butt-connection to the metal strips going to the switch plug-in connector.... I took a small pencil grinder with a little burr and ground away the plastic till it revealed the metal contact arm and metal connector strip, and then soldered them.....Problem solved..... Just a poor design begging for failure or poor contact.
Also, if you look closely, there is a little yellow resistor(?) and it has very fine wires that go to the contacts too, so be careful to be sure they are also soldered properly. I could never quite understand whether this was for sure a resistor or what exactly its function would be though....
Best,

Louie928

I had thought all GTS were the same and I happened to grab the MY94 GTS section in the WSM to check. Interesting that the change was done on the last year for so few cars. At least the switch with the pot is available if someone wanted an actual throttle position sensor.

John Speake

Hello Greg
Thanks for that interesting insight. As the owner of this switch was quite sure it was faulty on the car, and a new switch from me fixed the problem, I looked at it again. Sure enough one of those but joins for the WOT switch is not soldered

The little yellow beasty is a small capacitor across the contacts. Maybe just there to bypass any noise that is picked up on the harness. There is no real current taken by those contacts to need a suppressor capacitor.

So, next time I get a faulty WOT switch I will make the keyhole surgery repair you describe ! This one may be past a useful future as I hacksawed the top cover off.

John Speake

Hi Louie
I haven't measured one of those type of MY94 GTS throttle pots, but it would be interesting to know if they would be useful with a system like your stroker...

Bill Ball

If there is a difference between movement of the levers at the throttle quadrant and the throttle plate opening, it is substantial. I'm still trying to figure out why I lost the WOT function. The switch actually will trip if I manually push the levers at the quandrant, but just barely and at 99% open. The throttle cables cannot pull the throttle plate that far even though all of the slack is out of the cable set.

You found nothing wrong with the non-working switch, but a new one works in the car. That's puzzling too. It's hard to blame installation as that is keyed to the idle portion of the switch, set to trip just barely off-idle, unless that was set way-off.

Not having the WOT function while crusing with the throttle floored for 20 minutes at a time as I was doing in the last open road race nearly fried the motor. But I lucked out as usual.

John Speake

Hello Bill,
Well, I have found the problem with that faulty switch, thanks to Greg's information.

It is strange about the one you have on your car, as you rightly say the WOT opening point is directly related to the idle switch operating point.

I assume there isn't any wear on the pivots on the throttle plate/quadrant ?