89 3.2 Throttle adjustment / Full throttle switch

[teardrop]

1989 3.2 Carrera

Yesterday I was checking my Air Volume Sensor as per Bentley and had removed the boot between the throttle body and the sensor.

After it checked out ok and I cleaned some muck off it I started to check the Full Throttle switch and observed the following.

With me in the car and with the accelerator pushed fully down (a bit more force needed than I would like required) the full throttle switch closed and I could hear my meter sounding continuity. Fine thats ok then I thought.

I then pushed on the drag arm on the throttle body and observed where the throttle butterfly was when the full throttle switch activated and was suprised to see that it was at only about 70 degrees open. 0 would be closed/horizontal, 90 vertical.

This raises the following questions...

1. Should the buterfly be vertical when the accl pedal is fully depressed?
2. When should the full throttle switch activate?

Any ideas on this?

Thanks

Andy

[Nathan M]

Sorry, new to all this. At the risk of sounding stupid, what does the full throttle switch do?

[teardrop]

Basically its one of the inputs to the DME controller along with the idle switch, cylinder head temp sensor, air volume sensor, engine speed sensor and tdc reference sensor. (Did I miss any?) It uses all these inorder to decide what amount of fuel is injected and when it is injected.

The full throttle switch tells the DME controller that you are 'full throttle' which inturn modifies the mixing/ignition timing appropriately.

Andy

[Victor]

Hi Andy,

Do a search on "throttle linkage adjustment" and you will see this is somewhat of a hot topic. Also, check this link I think you will find some answers here.Finally found what I've been looking for...

[teardrop]

Yep.. I've already read that thread, and every other I can find but no one seems to state just what full throttle really is.

At 'Full throttle' should the throttle butterfly be vertical or not?

If it should then I'd say mine is out like so many others seem to be. I hesitate though because the full throttle switch comes on at about 70 degrees and there is not enough adjustment to make it come on at say 88/89 degrees.

I could adjust my linkages to get the butterfly opening to 90 degrees but the switch would still activate at about 70. Maybe this is how it should be but maybe not.

Wheres a 3.2 injection expert when you need one? :-)

Andy

[marcesq]

I believe, but not sure, that when the full throttle switch is activated, either the head temp sensor or the O2 sensor or both are disregarded by the DME and this allows a rich mixture to keep up with engine speed.

What you find is that the extra opening of the butterfly with allow for more air and therefore more power. Since the full throttle switch is already activated, the extra air just means more ZOOM.

Once you have made the adjustment to the linkage, get ready to shift when she hits 4000 because 6400 is coming reeeeel fast.

Good luck.

[Argo]

I just adjusted my throttle linkage and wondered about this too. Before adjustment, throttle was about 3/4" from the stop with the pedal to the floor and the full throttle switch was already closed. It seemed kind of premature to me, but I figured wth, I'm just getting to the fun section of the fuel map a little earlier.

BTW, add me to the group that gained performance from proper linkage adjustment. Pulls to the red line and beyond (Weltmeister chip) a lot easier and faster. Now I get to think about that whole rod bolt thing ....

Argo
88 Targa

[Steve W]

The full throttle switch sends an input signal to the Motronic box telling it the driver is at full throttle, switching it from the part throttle maps to full throttle fuel and ignition maps accordingly. When you are driving at part throttle, the O2 sensor is active and tries to adjust the fuel mixture to keep it at stoichiometric. At full throttle, with the switch activated, the O2 sensor is ignored and fuel is injected according to a preprogrammed amount. If you look at the fuel map below for an '89 Carrera, you can see these programmable fuel values. That said, I think the throttle valve switch should be adjusted to activate where you normally press your throttle all the way down when you are trying to accelerate at the max.

[teardrop]

All good stuff but my question still remains...

Should the throttle butterfly be vertical at full throttle? My feeling is it probably should (marqesc's and argo's experience seems to bear this out) .

Whats odd (to me at least) is that the full throttle switch comes on at about 70 degrees throttle butterfly opening (0 being closed/horizontal 90 being vertical/fully opening).

As my pedal is only opening the throttle about 70 degrees my full throttle switch comes on right at the bottom of the pedal travel. If I adjust the linkage so I have full 0 - 90 degree travel the switch is still going to come on at 70 degrees.

The adjustment on my switch is as far clockwise as it will go (looking at the switch from the right hand side of the car) and turning it back makes it switch on earlier!

Thanks for everyones input so far...

Andy

PS: Steve : What program did the screen shot come from?

[teardrop]

Just dropped my car off at a well known UK independant to have the rear anti roll bars mounts replaced and took the opertunity to bend the ear of the workshop manager.

He said he'd been brought up on 3.2's and he said that the throttle butterfly should be vertical when the accelerator pedal is fully depressed. He added that the full throttle switch should activate some time before the pedal is fully depressed. Finally he said this was a common problem that they see all the time.

This seems to agree with the experience of people here and my observations of the full throttle switch.

I'm going to replace the bushes on the bell crank and do the pedal cluster at the same time and then adjust the throttle linkage to get full travel 0-90 degrees.

Thanks for everyones input.

Andy

[anil999]

Andy

I would be interested to hear about your experiences after the throttle has been adjusted. I think I may have the same problem...

BTW, which independent do you use?

Cheers

Anil

[marcesq]

Anil:

The only problem that Andy will have is: