Any good recommended sites to visit to learn more about the operation of the MFI??

I understand a cam within the pump helps determine fuel amount, but besides throttle position what else is there??

thanks.....

I had MFI on my previous /6 engine, in the 914, and I learned quite a bit about the system.

There are two basic inputs used to regulate fuel: load, which is measured by throttle position, and RPM. There is also an adjustment for atmospheric pressure.

There is a warm-up enrichment mechanism that uses air funneled from the heat exchangers to "tell" the MFI pump about the temperature of the engine. The warm-up enrichment will require careful thought if it's to be made to work on the 914. I ended up making a heat exchanger on my passenger side header to channel air to the regulator.

There is no adjustment for ambient air temperature or for engine vacuum. (but there is an overun cutoff).

There are two adjutments, one for overall richness which adusts mixture over the whole range of operation, and a separate adjustment for idle mixture.

The pump is engine specific (or rather camshaft specific) because the basic mixture adjustment affects all operating conditions. But two engines that require the same amount of fuel at 3,000 rpm will not necessarily require the same amount at, say, 6,000 rpm. The hot camshaft of an "S" engine and the mild camshaft of a "T", the different compression etc . . . will all affect relative fuel needs under different operationg conditions.

I understand that the real experts are able to open a pump and make some internal adjustments to adapt it to different engine configurations, but that is beyond my paygrate.

I hope this helps.

Oh, and there's quite a bit of documentation available on the Pelican site, see in the technical articles section. Do a search for MFI there, a lot of info is available, several experts who hang out on that board will help.

Michel

It's based on Diesel injection pumps; some research should turn up information on those. I found a book at a library and read through it for an hour or so until I had a vague notion of the concept.

--DD

There are 3 basic types of fuel injection....

1. Mass Air flow systems.
Think L-Jet.. Load is determined by amount of air coming into the engine.
2. Speed Density Systems
Think D-Jet..Load is determined by throttle position and and manifold vacuum.
3. Alpha-N systems.
This is MFI. Load is determined by engine speed and throttle position.


The Alpha-N system is not as efficent as a MAF or Speed Density system. It cannot accurately determine the load on the engine. An Alpha-N system is using a preprogrammed fuel curve based on throttle position and engine speed. Because it does not use engine vacuum, it can be used with very high overlap camshafts that would mess up the Speed density or MAF systems.


What the MFI system does is to use a "space cam" (A 3 dimentional cam) to adjust the mixture in response to some basic, mechanical inputs. There is a pointer that follows the countor of the space cam. That pointer moves the mixture control rack. (I won't go into detail about how that part of the MFI works).

The first thing it uses is throttle postiton. As the throttle is opened, the space cam is twisted on it's shaft to change the location of the pointer on the space cam's sorta egg shaped profile. That richens the mixture to account for the added engine speed.

The second thing is the govenor style centrifegual weights. When the engine accellerates, the weights move outward. This causes the space cam to move forward (in a 914) or backward (in a 911). This also richens or leans out the mixture.

With those two items, the MFP pump can determine the correct mixture for the engine speed and load. It knows you have your foot all the way to the floor, but the engine is only at 1500 RPM because the cam is rotated to max, but the flywheel weights are still in.


Now there are added things to make it more user friendly on a day-to-day basis. There is a barometric cell that leans the mixture out when the car climbs in the mountains by moving the relationship between the pointer and the mixture rack. There is also a warmup thermostat that leans the mixture out as it heats up from air in the heat exchanger.



The MFI's control system can be duplicaed with modern electronic fuel injection. Most aftermarket systems can be programmed to use the MAP sensor for BARO input only, and to use just the TPS and RPM sensors to adjust the base fuel curve.


Ok.. is that clear as mud???

Clay,

Great description of the system. I have always loved driving a well tuned MFI car. Best throttle response I've ever felt. The simplest description of MFI I've heard was that it's a mechanical carb. Fuel is metered by throttle position, not buy the vacuum created by the motor.

I'd look for a system from a BMW 2002tii if you're looking to retrofit a 914-4. At least that was a 4 cylinder system...

But they ain't cheap, and they ain't easy to wrok on...

-Josh2

The BMW 2002 Tii iw easier to setup than the Porsche implementation. It only uses one throttle body. No balancing of airflow needed.

Not an expert, but I work on a 2002 Tii with a buddy a while back and recall a coolant line as part of the system. Could make for some issus on a TypeIV. Also recall parts were hard to find and $$$

the coolant line is used for the same function as the warm air on the Porsche system. You can swap out the coolant warmed thermostat for the air warmed one from the Porsche six. The only difference between the two is the number of cylinders in the rear half of the pump.

Ahh, I see. Do that Mike!

2002 tii used kugelfischer FI

And I believe Bosch bought Kugelfischer somewhere along the line, so that the difference merely became one of branding.

thanks Clay..

I can take some picts of the MFI pump that I disassembled to show all this if it will help....

I believe that the "space cam" is significantly different on the Kugelfischer system; isn't it more like a disk there?

--DD

How would you get a 3 dimentional profile on a flat disk?

Unless they have come up with a new wrinkle on twinkle, it works identically. I am fairly sure the kugelfisher pump has a space cam like the bosch pump...

I was thinking that it was like an old vinyl record (remember those? ) with bumps and grooves on the disk. I see from my research that it is not so. It seems to have, in fact, a cam much like the Bosch one does.

Mike, a little reading for you--
The Kugelfischer system:
http://www.thetiiregister.com/pump/pump_guide_v1.pdf (big file; ~22 MB)
The Bosch version:
http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

--DD

Last time I checked, about 2 years ago, the guy that bought up all the KF FI parts had a few pumps left. There are no service stations left, at least in the US (I called Gus) and you simply wouldn't believe what those pumps cost. You can't get the injectors rebuilt, either. Trust me, he has an idea what those pumps are gonna be worth someday. Might be better off looking into a Spica system from an Alfa Romeo.

The Cap'n