Lean CIS

[560]

I am running a MillerFI CIS on my car with a 2175 mild hydraulic cam, semihemi 42x35 heads, stock rockers and a late T-1 FI intake type of setup, and stock H2O injectors. I think it is running a bit on the lean side going by plug readings and was wondering if there was a simple way to get more fuel to the engine? I am thinking about the cold start injector running full time or would rather go with larger (more fuel) injectors to keep it simple. Gary is on the East coast now and would not be of much help now.

I also have run my 2276 race engine with same setup that ran good but had other issues I am dealing with now.

Mike

[560]

Any ideas at all?

Mike

[Piledriver]

To make CIS-basic or CIS-+Lambda richer, you lower the control pressure, making the meter vane easier to move by the air flowing past, more motion, more fuel.

Making the control pressure regulator (CPR) adjustable is ~trivial, it's a very simple device. Google is your friend.
I would mod a spare just in case as a hammer is involved.

Stock control pressure (hot) is usually around 52 PSI. I would try ~45 as a starting point, and only change a tiny bit when adjusting, it's VERY sensitive.
(You need to make up the gauges to tune CIS, spare Banjo bolts with added fittings work great for this)

One can also alter the cone profile etc. to alter fuel flow vs load.

Strangely, CIS injector flow is mostly determined by the meter, not the injectors.
Same with injector-injector flow uniformity, it's USUALLY the meter. Some are adjustable.

I ran a CIS-E and CIS-M meter on my setup the last year or so I ran CIS which can be trivially controlled with a potentiometer.
These can move a LOT more fuel vs. the CIS-basic meters and are ALMOST drop in replacements, the cold start injector uses a different size banjo.

CIS is a great, pretty much bullet proof system once you get it sorted out.

It doesn't have the fine tuneability of Megasquirt, but OTOH that can be a feature.
The only big downside of CIS is the physical space the flowmeter takes up.

[560]

Thank you Piledriver, I was hoping you or Mr greenwood would chime in on this.
This gives me a good place to start. Gary DID modify the meter and cone area of airflow other than that I think the rest is basic "stock" modified to fit in my car.
Now that I have a basic baseline I will try and learn what the parts are and find out what they really do. I know this sorta makes me sound stupid but I never got into the R&D with him, I was his grunt and most of his notes and talking with him went a bit over my head.
Thanks again for the help.

Mike

[Piledriver]

CIS is a (fundamentally) simple system, but you could never tell that from the manuals.

The only thing "difficult" about it is as it's basically an analog MAF computer with no baro or RPM correction (at least in -basic trim), it's VERY unforgiving of worn out parts, air leaks or funky fuel pressure.

There are a few excellent books explaining it, I'll have to look for links when i get home.

[Piledriver]

Google for this:
"bosch Gasoline Fuel-Injection System K-Jetronic"

Pretty good pdf of the K-Jet inner workings.

My 30,000 foot view:
Air mass moves flap in a profiled cone, linked to a piston in a pressure regulator that varies the fuel output to fine atomizing spray heads.
Control pressure on piston pushes back on flap, allowing fine control of flaps response to airflow using an external regulator which can be temperature or electrically controlled.

In a way it's could be seen as highly refined, mass airflow version of a Hilborn FI system.

[560]

Thanks for the homework...
I found a book, how to tune & modify BOSCH fuel injection, any thoughts about this book?

I think my biggest hurdle is learning the terminology and understanding what the parts really do.
Like you said, this IS a simple setup. I am probably over thinking this.
Again thanks for the help and info.
Now back to my homework..

Mike

[Piledriver]

The only thing "missing" from CIS is MAP load sensing enrichment.
It DOES have accel compensation via the overshoot of the air vane/mass (which is tunable)

A $30-50 SMC pressure/vacuum switch would be trivial to integrate with CIS-E or -M systems to provide MAP based enrichment.

Then you could run you base tune leaner, and it would fatten up ~instantly at a defined MAP value programmed into the switch.
(could be thought of as an advanced Hobbs switch)

Not as flexible as MS etc, but very simple and reasonably bulletproof.

[560]

Thinking the first thing I really need to do is buy a good quality air/fuel ratio gauge. going by plug reading alone has only given me more questions to ask.

Thanks again PD for all the help and info you have shared with me.

Mike

[Piledriver]

You are welcome.

Plugs readings are of very limited use, and with modern fuels/additives, probably not worth the effort.
You can get an excellent WBO2 setup pretty cheap these days, or even rent one if you have the means to adjust everything in place.

The units at 14point7.com have extensive logging capability, and would be an excellent match for a CIS based system lacking that.