MicroSquirt.com read only forum (Jan.15,2018)

Over at Shop Talk Forums we are discussing the possibility of using MS as a controller for a CIS or CIS-E system. One guy already is using some rigged electronics to control a CIS-E frequency valve, but he wants to move to MS control down the road. My ideas are more ambitious: get rid of the CIS air meter component and just use the fuel distributor. This is mainly to allow mounting of a CIS system on air cooled VW's, which are space challenged. Here are my thoughts:

First, get rid of the air meter. The highly calibrated cone, plate, and arm need to be replaced by something. I was thinking a simple spring. This would allow all flow adjustments to be made on the other side of the fuel distributor. This would be accomplished by:

1) Regular CIS uses a piston controlled by a Control Pressure Regulator to trim fuel flow for warmup, etc. It routes fuel pressure to the back side of the piston and modulates it - it it reduces pressure on he back side, more fuel flow through the distributor and the mixture is enriched. So one option is replace the control pressure regulator with a PWM or other variable valve driven by the MS. The "VE" map would basically just be a duty cycle map for the valve. This would translate to pressure on the piston, which, counterbalanced by the spring on the other side, would control flow to the injectors.

2) CIS-E uses a PWM frequency valve in place of the piston in basic CIS. It is uses to trim injector flow in response to an O2 valve, via a controller. So if the controller is replaced by MS, it could control the mixture directly.

Questions:
1) Is the frequency valve capable of full range flow adjustment?
2) Anybody got an appropriate PWM valve for controlling regular CIS?
3) Does anyone know the forces applied to the piston in the fuel distributor? Or have a reference?

Open for comment.

The Bosch CIS system is a constant injection system. The quantity of fuel is MOSTLY determined by the air meter/fuel distributor, and the Lambda (freq valve) was added to later systems only for fine tuning the AFR.

It is my understanding that the CIS injectors offer superior atomization over even the newest EFI injectors. Therefore it may be *possible* to use very low pressures (and resultant low flows), if the freq valve will produce them, and maintain acceptable atomization.

I investigated this very problem several years ago. The main problem with controlling the distributor plunger directly is trying to find a servo that would move both fast enough and precisely enough that didn't cost $4000. You can get fast, you can get precise, but both together require lab-grade stuff that was not only really expensive, but probably not up to the rigors of a hot, vibrating engine bay.

There are actually two "frequency valve" controller setups on K-Jet. Both vary the control pressure (effectively altering the resistance offered by the air flapper to air flow, and thus the airflow to fuel curve). The earliest just used a fuel injector as a PWM valve. The later systems used a more sophisticated servo valve. Both systems, however, require the airflow meter remain in place. They don't control the plunger directly. I'm not certain a PWM valve and a spring are sufficient, but it's worth trying.

If you want to experiment, the place I'd start is to set up a good measurement system that doesn't restrict flapper movement, to measure plunger movement. Using a magnet on the meter arm and a pair of Hall sensors differentially should be sufficient. This will give you an idea of how far and how fast the plunger needs to move, and if you combine logging of this with logging a few other variables, like throttle position, RPM, and manifold pressure, you should get a good curve to start with for an initial map. You'll also get the data you need to design an actuation mechanism for the plunger.

Best of luck. I thought it was a fabulous idea then, and still do, but it was beyond my abilities.

I'm home for the holidays and I dug up my Bosch FI book by Probst. The "frequency valve setup actually does control the plunger position, but indirectly. It alters the control pressure, which moves the plunger a small amount to trim the AFR.

KE jetronic doesn't regulate control pressure at all. It uses an electromagnet to drive a valve with a variable milliamp signal. In addition, it has an o-ring in the fuel distributor to provide a bottom stop for the piston. It also has a potentiometer on the AFM that could be used for your logging idea.

I think the K-Lambda, with the frequency valve will be the one to play with. One simple test would be a static test: fire up the fuel pump and measure the force required to move the plunger. Then, figure out the deltaP between system pressure and control pressure to move the plunger full range. Then it becomes a pressure regulation problem.

Hmmm... I have played with a few cis systems and can think of another possible and dirt simple method.

Why not create a simple manifold for the fuel supply and have a PWM valve feeding this? Then it wolud be a PIS system!

Yeah, I know cis works so well due to its atomization as its runs continously. But I bet if you insreace the fuel pressures and have an accumalator attatched to the manifold that it would reatain enough pressure to never fully turn the fuel flow off to the injectors.

Best part is you could build a setup to test for SUPER cheap. Here is a cool place with lots of valves that could well perform this job and not break the pocketbook doing it! http://www.stcvalve.com/I-Solenoid.htm#0

I was considering a simple approach.

Let the airflow plate make the 'macro' fueling adjustments, and use MS to control the DPR for 'micro' fueling adjustments based on where you are in the VE tables. We just need to produce a 0-20mA signal to send to the DPR.

I know that this leaves the big nasty air plate in the system, but I am really just looking for a better way to tweak fueling than sticking a resistor on the coolant temp sensor (and the ignition control will be nice too).

Thoughts?

Honestly I am still for getting rid of the airplate all together. Its the biggest restrictor in the CIS setup. I am sure somebody more electronics savvy than me could creat the 0-20ma setup your thinking about. In fact I know that there is actualy a programable setup out there that does this. I think if one were to go MS with a CIS car, do it all the way. Figure out how to get the MS controlling them CIS injectors.

The setup doesn't have to be hard even. Simply gut the air-vane and some other parts out of there, then I would retain the fuel manifold with possibly some bits inside removed. PWM a solenoind feeding it and your pretty much done. Plus your retaining the look of having a CIS setup in the car.

A tangential comment...

With CIS, you can't really control the amount of fuel going into individual cylinders. Doesn't that somewhat defeat purpose of EFI?

No, L-Jet doesn't do this, either, nor does MS. Even full sequential systems usually don't control fuel to the cylinders individually, they just calculate a value for the whole engine and divide by the number of cylinders (conceptually).

To get per cylinder fuel control, you need to measure each cylinder individually, either using an O2 sensor per cylinder, or some other measurement method.

This is still on the drawing board even for OEM systems.

As for controlling CIS without the plate. You can simply use a MAF sensor in place of the plate. However, you still need some way of controlling the plunger through it's whole range of movement, which leads you straight to needing a fast, accurate servo with the appropriate stroke, which costs big money.

The CIS injectors are 70psi pop-off valves, and the system pressure is roughly 100psi. So, the injector pressure is between 70-100psi. This is better than the 45psi used by most EFI injectors, but it's not a gigantic improvement. Direct injection systems use far higher pressure. You could also get much higher pressure by electronically controlling Bosch MFI or SPICA mechanical injection, which use system pressures in the 1000psi range. They're also genuinely sequential at all engine speeds. You still need a fast, accurate servo (again), this time to replace the logic section on these units.

I am just finishing up replacing the CIS injection system on my 1980 mercedes 450slc with a megasquirt setup. Good ridance to the CIS! The hardest part was crafting the fuel rails and fuel plumbing. I was able to turn down the lower diameter of Ford 19lb injectors a couple thousands of an inch on my lathe and they fit perfectly in the CIS pockets. I don't know what CIS looks like on a VW as far a injector mounting but I have never been happier with my Mercedes!