What powers the frequency valve in an '87 930?

[PcarPhil]

Hey guys,

I'm doing some maintenance on my '87 930 and currently have all the electronics under the driver's seat disconnected and a jumper on my engine wire harness similar to below that bypasses those 3 boxes. My engine runs the exact same with this jumper hooked up as it did with all 3 boxes plugged in. I haven't been running an O2 sensor so this sort of makes sense.

What I'm wondering is what is now controlling (powering) the frequency valve? Is there simply 12 volts powering the valve or is it perhaps not being powered at all and the engine is no longer using it?

I know I can simply disconnect the valve and see if the engine runs differently however I figured I'd run this past you guys first.

Thanks for the help!

Originally Posted by billjam

[billjam]

Scott,
The frequency valve is "timing valve" at C49 below. It is connected to other devices that you have already disconnected, so it isn't doing anything.

[JFairman]

The frequency valve is an inline electronic fuel injector. It has a hose on each end so instead of injecting fuel somewhere it lets varying amounts of fuel flow through the hoses depending on the frequency or amount of times it opens and closes per second.

It's controlled by the k-jetronic lambda box under the driver seat on your '87.
The middle of the three boxes under the drivers seat is the enrichment relay. Depending on the temperature feedback from the right side chain case cover sending unit and the throttle position switch on the throttle body the enrichment relay disables the lambda emission system and the pulse rate of the frequency valve is set to a certain frequency.

The frequency valve is allowing varying amounts of fuel pressure from the lower differential chambers of the lambda fuel head to the return to the gas tank via the return line. That causes the diaphram in between the upper and lower chambers to raise or lower against the fuel heads final metering orifices in the top of the upper chambers and that makes small changes in the amount of fuel getting by those 6 orfices.
From there the fuel goes up and out the 6 banjo fittings on the top of the fuel head and on to the fuel injectors.

If you remove the lambda system you have to adjust the 6 seperate little spring tension adjusters under the button head screws next to the injector line banjo fittings to get the correct amount of fuel injected. This is tricky and it's one of the things done on a flow bench by CIS Flowtech when they modify a fuel head for more flow.
Brian Bodart described parts of that procedure in another thread.

CIS is a complicated mechanical fuel injection system that just gets more complicated and unreliable as time goes on with the post 1986 electronic lambda system added on to it.

[PcarPhil]

Originally Posted by billjam

Scott,
The frequency valve is "timing valve" at C49 below. It is connected to other devices that you have already disconnected, so it isn't doing anything.

Originally Posted by JFairman

If you remove the lambda system you have to adjust the 6 seperate little spring tension adjusters under the button head screws next to the injector line banjo fittings to get the correct amount of fuel injected.

Bill,

Thanks for the clarification. I confirmed this morning that the frequency valve isn't doing anything on my engine. There's no power to it and now for the time being the harness is disconnected.

JFairman,

My lambda system has been disconnected for quite some time. When I disconnected the lambda system of course the engine went very lean (confirmed by my Innovate MTX-L WB02). When I disconnected it I simply tuned around it by adjusting WCP and CCP via the WUR until the AFRs were back where I wanted them.

Interestingly enough I have never needed to adjust the 6 separate spring tension adjusters on the fuel head. I'm a bit surprised by this as I've read many times that when disconnecting the frequency valve you must adjust the 6 adjusters on the fuel head but I didn't have to do that. Weird.

[JFairman]

It's not weird, you just raised the control plunger hight exposing more of the metering slits in the sides of the control plunger cylinder in relation to the airflow meter position.

It's not the right way to get more fuel when disconnecting the lambda system and it's probably not linear throughout the rpm/load range. Of course there isn't anything linear about CIS anyway.
Call Larry Fletcher at CIS Flowtech and get his opinion. Brian probably has an opinion on it too.
Whatever works for you and in the end it's your car and if you're happy that's all that matters.

[bpu699]

Subscribed . Suspect I will need this info soon...

[RarlyL8]

Manually matching the default frequency valve duty cycle is most simply (and probably most often) done via the mixture screw. You can also compensate via the WUR (if adjustable) or more accurately by balancing each cylinder as Jim suggested. CIS uses rich default settings to keep your engine safe but there is power and fuel mileage left on the table. It is very tedious to balance the cylinders which is why most don't bother.

[PcarPhil]

Originally Posted by Kaefer

Interestingly enough I have never needed to adjust the 6 separate spring tension adjusters on the fuel head. I'm a bit surprised by this as I've read many times that when disconnecting the frequency valve you must adjust the 6 adjusters on the fuel head but I didn't have to do that. Weird.

Originally Posted by RarlyL8

You can also compensate via the WUR (if adjustable) or more accurately by balancing each cylinder as Jim suggested. CIS uses rich default settings to keep your engine safe but there is power and fuel mileage left on the table. It is very tedious to balance the cylinders which is why most don't bother.

Time for an update...

I did end up adjusting the 6 adjusters on the fuel head to balance out AFR/EGTs in each cylinder. By doing so on my engine the adjustments produced a smoother idle and allowed more timing advance to be dialed in.

It is a tedious process (make very small adjustments, then test) but the end result is (IMO) worth it.

[T77911S]

you are playing with dynamite.
you might want to explain in more detail how you did this.

i would put the box back in that controls the FV.
as jim said, the big problem with the way you have done this is that the sensor plate will no longer be in the position is suppose to be at a given RPM. (a bit more confusing than the way jim said it).
with a electronic FI system the AFR's are mapped out on a chip for a given RPM. idle , lean for mid RPM cruise then rich at WOT. (carbs do this too) but with CIS this "mapping" is done with the shape of the AFM. narrow at the bottom for idle, then it widens at a bigger rate to lean out the mid cruise then gets narrow again to richen WOT. (along with boost enrichment in the WUR).
if the sensor plate is in the wrong place the car may not run like it should.
the REAL bad thing with this is you could be leaning out the top end too much.

if you removed the speed relay what are you doing for a rev limiter?

there are 2 options here.
you can use a rev limit rotor or like i did install an MSD with a rev limiter.
instead of jumpering the pins, take the connector apart and jsut solder together the wires needed to make it run, which is really just the FP.

if you want to remove the FV, send the head to flowtech.

[boosted79]

I've been researching this K-jet crap on my '88 and came across this thread. Can anyone give me an idea of what kind of control pressures to use to allow me to run this car temporarily with the frequency valve disconnected? I just want it to run, I don't even need boost. Just need to be able to drive it about 45 miles. The wiring on this car has been hacked and I just want to install the jumper described and get it to run. When I get it to my shop it's going to rebuilt and the fuel head will be sent to CIS Flowtech for non-FV conversion. Thanks. I just rebuilt the fuel head, it was clean and in good shape with the exception of the diaphram which was badly wrinkled from the corn juice.