Frequency valve behavior...

[sboesch]

Hello,
I just tried to check the o2 system of my 1980 911SC.
And I wonder about one thing:
Condition for one check: O2 disconnected - that results in a dwell angle of 50% at the frequency valve.
Now I want to check the "enrichment switch" at the throttle housing:
Ignition on, lift the air measurement plate a bit and now I hear the frequency valve and see teh 50% on my dwell meter.
Now I lift the throttle above the 35 degrees - I expect a higher duty cycle of the frequency valve to enrich the mixture but unfortunately the dwell meter shows me 35%.
How could that be? Is it possible to connect the frequency valve wrong or do I misunderstand something.

Thank you very much for answering

Soeren

[wswilburn]

It's been a while since I had an SC, but if I remember, the FV dumps fuel back to the tank to lean the mixture. If so, it's going in the right direction.

[Bob Kontak]

Originally Posted by sboesch

Ignition on, lift the air measurement plate a bit and now I hear the frequency valve and see teh 50% on my dwell meter.
Soeren

Welcome to the forum, Soeren.

When you lift the air measurement plate is the engine running or is the key only in the on position?

If the engine is not running the loud noise is not the frequency valve.

[boyt911sc]

Originally Posted by Bob Kontak

Welcome to the forum, Soeren.

When you lift the air measurement plate is the engine running or is the key only in the on position?

If the engine is not running the loud noise is not the frequency valve.

Bob,

The frequency valve operates in conjunction with the FP & ECU. When the engine is cold, the ECU controls the operation by using its default values. As such, the FV relay is powered by the same power going to the FP @ 30.

As an example, when you test the FP similar to those non-lambda engines, the FV will operate as soon as the FP is energized. So it is not necessary that the engine has to be running to make the FV operate. However, you need the engine to be running at operating temperature to test the OXS.

Tony

[sboesch]

hello again,


@wswilburn: I think when the FV is on high duty cycle the system tries to enrich the mixture - but unfortunateley the duty cycle goes down when the throttle position goes above 35 degrees, that means that the system is trying to get the mixture lean... and I think that is a wrong behaviour.

@ Bob: The buzzing starts when the ignition is on AND when I start lifting the measurement plate - It should be the FV, because furthermore I can see it on my dwell meter. It shows 45 (50%) - I think that is right.

@ Tony: engine is out, but it is warm - I just drove the car...

The other thing is: (now o2 is connected). The more I enrich the mixture (with the little syrew on top of the K-Jetronic clockwise) the higher goes the duty cycle without dropping back again towards 80% or more . And the more I lean the mixture beyond one point the lower goes the duty cycle and again with no stop again to nearly 3%. It is not possible to adjust it to e.g. 65% because it runs towards one direction :completely lean or comletely rich.
So my question could it be that the FV is connected wrong or that something else is connected wrong (plus to minus or so).

Thank you very much for helping me

Soeren

[psalt]

Soeren,

The cold open loop duty cycle for a 1980 is 85%. Once the engine warms up above 15C, the system should go closed loop and the needle should fluctuate between 45-65% duty cycle, based on the O2 sensor signal, but most will fluctuate in a much narrower range, more like 10 %. If the meter needle is not fluctuating in closed loop, there is a problem. When you turn the mixture screw in closed loop, the duty cycle will reduce as you richen the mixture. You are looking at the "effect", as the system tries to lean out the "too rich" mixture. The O2 sensor is ignored in open loop. The 1980 does not have the cold enrichment switch, just the WOT open loop switch. You can test this switch with a meter at the main temperature switch wire.

Paul

[sboesch]

Paul,

are you sure that the FV does not enrich the mixture when passing 35 degrees throttle position. You think that the system is only going into open loop and enrich the system this way.
But how could this be: Engine is out but warm - O2 disconnected - Ignition on.
Now I lift the measurement plate a bit the dwell meter shows 50%.. that is okay because the system is in open loop anyway (o2 is disconnected). And now the following happens: I lift the plate above 35 degrees , the dwell meter shows immediately the exact value of 35. So the FV regulates the mixture passing 35 degrees throttle position though the system is in open loop anyway (because o2 is disconnected). Nevertheless the FV regulates to the wrong direction - I would be happier when it shows 65 % or so.


Soeren

[Bob Kontak]

Originally Posted by boyt911sc

Bob,
So it is not necessary that the engine has to be running to make the FV operate.
Tony

Howdy Tony - I was thinking the noise Soeren was referring to was the screeching when you lift the sensor plate with the engine not running but with the ignition on.

I should have provided more data as to where I was going with that.

[psalt]

Soeren,

Do you have a manual that explains the lambda system ? The open loop WOT switch has nothing to do with the air flow meter plate. My advice is to hook up the dwell meter, and start the engine from cold. The meter should show a steady 85% duty cycle ( 75 dwell on the 4 cylinder scale). After a few minutes, the needle should start to fluctuate around 50 % duty cycle when the system goes closed loop. What does your meter show for these tests ?

[sboesch]

Paul,

sorry you are absolutely right. I wrote it wrong in my previous posts. I mean of course the throttle. I have to lift the MEASUREMENT PLATE only a little bit to start the FV working with the ignition on... Than I bring the THROTTLE towards 35 degrees or more so that the switch goes in WOT or open loop. And than the FV dwell angle changes as discribed in the posts before (O2 not disconnected)

Soeren

[boyt911sc]

Originally Posted by sboesch

hello again,


@wswilburn: I think when the FV is on high duty cycle the system tries to enrich the mixture - but unfortunateley the duty cycle goes down when the throttle position goes above 35 degrees, that means that the system is trying to get the mixture lean... and I think that is a wrong behaviour.

@ Bob: The buzzing starts when the ignition is on AND when I start lifting the measurement plate - It should be the FV, because furthermore I can see it on my dwell meter. It shows 45 (50%) - I think that is right.

@ Tony: engine is out, but it is warm - I just drove the car...

Thank you very much for helping me

Soeren

Soeren,

I'm a little bit lost in your statement highlighted above. What do you mean 'the engine is out, but it is warm'? And just drove the car (???). Do you actually have the engine out of the car and sitting on a test stand doing the test? Please help me follow the logic. Thanks.

Tony

[sboesch]

sorry,
sometimes I use wrong words (I am not from USA - I am german)
I do not mean the engine is out - it is off (not running).