Phil Silano

Hi all,

I'm looking for some info from the fuel injection experts in the group.

Assuming that the mixture on the car is set properly, what should happen to the idle speed if you manually activate the WOT switch??

I know that this will drive the system open loop but will it drive the mixture too rich at idle and cause the speed to drop, increase the mixture just enough for the speed to go up, or have no effect at all??

This is for an 83 928S US spec car.

All info, opinions or test data would be greatly appreciated.

hacker-pschorr

Unplugging the idle switch on the 81 does nothing. I have a air/fuel gauge on the car, no changes. Yes it is a functioning switch.

Phil Silano

What idle switch are you refering to?

hacker-pschorr

On the side of the throttle body.

Phil Silano

I assume you are talking about the WOT switch. There should be two switches on the left side of the throttle body. The lower one is the idle switch. it is electrically closed when the throttle plate is closed.

The upper switch is the WOT (wide open throttle) switch. It is electrically closed when the throttle is about 72 degrees (?) open. There is a lever on this switch that is contacted by a cam on the throttle linkage. This lever can be reached and activated by hand, without opening the throttle, thereby enriching the mixture and driving the system open loop.

What I was asking was; What happens to the idle speed when the WOT switch lever is depressed? When the wires are disconnected at idle nothing will happen because the switch is "open" at that point anyway.

hacker-pschorr

No, I am talking about the idle switch. Disconnected at idle, nothing happens.

John Speake

Hi Phil,
At idle speed, if you trigger the WOT switch you will get a mixture enrichment of about 10%. This will not trigger an off O2 loop situation because you are not pulling enough air through he engine to trigger it.

On my test jig, I can't have closed throttle switch plus WOT at the same time. If I hold idle speed and then trigger WOT I get a transient enrichment for about 1/2 sec.

The effect of this on idle speed is not clear, it is too fast for the O2 loop to respond. My best estimate is that the idle may "stumble" for a monent, and then recover.

Phil Silano

John,

Interesting. When I activate the WOT switch by hand the idle speed goes up and stays up for as long as the switch is "closed". If I adjust the mixture rich enough the idle speed will drop under the same conditions.

I'm just trying to understand which condition is the right one.

justin

I can trigger my WOT switch when the car is at idle and nothing happens.

PorKen

Are you certain that your idle switch is working? (Rev to 2000, trigger idle switch, revs should 'hunt' 1000-1500.)

hacker-pschorr

Porken - at what RPM is the WOT switch normally triggered - in neutral, under no load.

PorKen

~30° throttle, regardless of rpm.

I would like to find an adjustable vacuum switch (vac open/atmo closed), to use instead of the mechanical WOT switch.

Interestingly, the L-Jet service manual says the WOT switch enrichment (+12%) is not for power, but to keep the exhaust temp down for the O2 sensor, and cat!

hacker-pschorr

I know the 30 degree part, just curious what RPM your car triggers the switch when sitting still in neutral.

PorKen

That's what I thought you meant, but I think my neighbors would object to finding out.

I think it will redline before 30° in neutral?

IcemanG17

Porken
Hmm....this sounds like Hacker speak for "Go blow up your engine and tell me about it"