KEIII fuel distributor 101....somebody 'splain how this thing works!!! - PeachParts Mercedes-Benz Forum

Cap'n Carageous · #1 07-15-2003, 04:39 PM

Ok so it's an electromechanical device and can work without electronic help. So...how does it do that? Are the injectors always under pressure and 'firing' all the time. Is there a little man inside there that decides which cylinder needs fuel and how much?? How does it work?? And what are the symptoms of a defective one??

mbdoc · #2 07-15-2003, 05:41 PM

"Constant injection" is another acronym for CIS as well as KE.
Yes, the injectors spray ALL of the time. The quanity of fuel injected is controlled by the fuel distributor.

I know that is a VERY simple answer for a complex question but that is how it works.

sbourg · #3 07-15-2003, 05:59 PM

The fuel flow to the injectors is metered mechanically in the fuel distributor by a linkage from the airflow meter. Additionally, it is fine-tuned electrically via the electro-hydraulic actuator valve (mounted on the side), which is controlled by the ECU depending on various inputs - primarily the lambda sensor (O2 sensor).

Note too each injector has a mechanical pressure-actuated check valve. Dropping the fuel pressure to them cuts off the fuel flow completely.

Steve

Cap'n Carageous · #4 07-15-2003, 07:07 PM

So, let's say we're at 3000rpm. The cycle is happening so fast that the motor is consuming this constant spray. I understand that. But if I remove all of the fuel lines from the top of the distributor, then turn the key, gas will spew out of ALL of the holes at the SAME time?? Remember, I'm thinking distributor here, as in only the cylinder that needs fuel is getting it. Like the spark from an ignition distributor. Is that concept wrong?

Duke2.6 · #5 07-15-2003, 07:43 PM

CIS stands for Continuous Injection System and the fuel "distributor" distributes fuel to each cylinder, but it it continuous, not timed. The German work for continuous begins with a "K", like compressor/kompressor.

The fuel flow is actually not purely continuous as the injector valves are designed to "dither" rapidly when sufficient pressure is available to overcome static seating pressure, and this "dithering" feature improves fuel atomization.

The CIS system is conceptually similar to the vintage Rochester Fuel Injection systems used on fifties/sixties vintage Corvettes and some other GM models, but the Rochester system is a little simpler. A pump driven by a cable off the distributor generates fuel pressure that is approximately proportional to engine revs. A spill valve that bypasses excess fuel is driven by a vacuum signal from a venturi on the air meter, and the linkage is designed so pressure to the injectors is proportional to air flow. The injectors do not have valves to overcome, and actual delivery pressure ranges from near zero to about 200 psi.

The CIS system's basic metering device is a "momentum plate" that can sense actual mass flow, so it self corrects for altitude to some degree. Movement of the momentum plate, which is usually referred to as an air valve operates the equivalent of a spill valve, and rather than fuel pressure being a function of engine speed, the CIS system uses an electric pump and regulator to maintain constant inlet pressure. Then the momemtum plate provides a basic setting for the spill valve, which is fine tuned by the EHA driven by the electonics, which uses engine temperature, ambient pressure (for more refined altitude correction) and O2 sensor output to drive the EHA correction signal.

The CIS-E is a nice system, but very complicated as it is a complete mechanical system and also has nearly all the elements of an EFI system.

Duke

sbourg · #6 07-16-2003, 10:44 AM

"...gas will spew out of ALL of the holes at the SAME time?? Remember, I'm thinking distributor here, as in only the cylinder that needs fuel is getting it. Like the spark from an ignition distributor. Is that concept wrong?"

Yes. Actually, the fuel distributor allows individual metering of the differential fuel flow rate to each injector, but I have seen no posts here implying anyone has tried to fiddle with this. I imagine the new ones are pre-adjusted for equal flow rates. In any event, there are numerous minute passages and slits, sliding and valving parts, and strainers inside. Lots to gum up and wear.

Note that in the same way, exhaust headers could be referred to as an 'exhaust distributor', i.e. a pressure flow-tuned distribution system.

Steve

Cap'n Carageous · #7 07-16-2003, 10:49 AM

Note that in the same way, exhaust headers could be referred to as an 'exhaust distributor', i.e. a pressure flow-tuned distribution system.

And an intake manifold on a carburetored engine is filled with mixed fuel/air waitng to bre sucked into the cylinder....ok I get the picture... sorta.

richard28 · #8 07-16-2003, 11:10 AM

Given the apparent importance of the O2 sensor, would you suggest routine replacement after a number of years or miles,even without the dreaded check engine light, given that so much hot gas and possible contaminants pass over it?

Arthur Dalton · #9 07-16-2003, 11:48 AM

A Distributor would generally take a single flow source and distribute it to different cylinders..
..like a spark distributor takes an electrical signal and distributes it
to many plugs.. [ through the cap/rotor].
..Same deal with a fuel distributor, but you now talking fuel vs. spark..
A Manifold also is used to do the same , but is more of a Collector vs a Distributor in the sense that it does not involve any Timing configurations in its workings..

On the exhaust, we have the opposite of distributor in the sense
that you are now taking a flow from many sources [each cyl., in this case] and bringing then into one artery [ [the exhaust]
So, this is a Collector vs. Distributor..
On small Aircraft engines , they are actually called exhaust Collectors...vs, exhaust manifolrds..
Anyway , something of interest...

dpetryk · #10 07-16-2003, 06:26 PM

Actually, the fuel distributor is a very simple device. Many people here seem to be of the opinion that they are full of parts. That is not the case. Its a simple pressure differential operated system to meter fuel, from all ports at the same time. They are easy to disassemble and clean. Parts like the diaphram and springs are not available, at least I have not found a source. I have yet to need anything other than O rings to repair one. I have done three of them.

Anyway, I thought you might find a photo of one from a 300E interesting.

dpetryk · #11 07-16-2003, 06:29 PM

Another photo - this is the top half.

dpetryk · #12 07-16-2003, 06:30 PM

And of course, last but not least is the diaphram.

richard28 · #13 07-17-2003, 10:33 AM

Could someone please indicate where the o-ring is? Thanks

dpetryk · #14 07-17-2003, 10:40 AM

Picture #1 the oval shaped black dudes.

JBoggs · #15 07-21-2003, 12:00 AM

I am very curious to hear of the procedure-I have received a diagnosis that mine is causing my rough idle and since all I've read indicates that they can't be serviced by anyone other than a Bosch tech, I am truly intrigued by your statement that they are not complicated.

Can you walk us through the cleaning/ servicing procedure please?

Thanks.

J. Boggs