DDK - Die Deutschen Klassiker

porscheplus.co.uk · Post by **porscheplus.co.uk** » Fri Jan 20, 2006 9:31 pm

can somebody explain to confused of eccles the difference between mfi.K jetronic and L jetronic.
REGARDS

1972_911t · Post by **1972_911t** » Fri Jan 20, 2006 10:16 pm

MFI is the earliest form of fuel injection. It similar to the system used on older diesel engines. It uses a belt driven fuel pump to inject fuel at very high pressure (115psi if i remember right) directly into an open valve and is a syncronised injection system ie the injection is timed to the open valve the pump delivers the exact amount of fuel required based on engine speed and throttle position. K jetronic or CIS which is also mechanical fuel injection of a sort in that the injectors are opened by mecanical forces relies on a electronic fuel injection pump to build up the pressure, air flows through a metering plate which is connected to a fuel valve, this regulates the injector pressure which inturn increases or decreases the fuel flow. In CIS Continuous Injection System the injectors are permanently open even when the intake valves are closed. Fuel delivery in CIS is directly propertional to the air flow past the metering plate. MFI was only used by porsche uptill 74 I think was the last engine, CIS was used from 73 to 83 or even later on the turbos. As far as L jetronic I wasnt aware it was used on porsche engines but I belive its a more recent electronic injection system.

Hope this helps Steve

davidppp · Post by **davidppp** » Sat Jan 21, 2006 8:16 am

Good stuff.

L-jet was as far as I know only fitted to the 1972075 1.8 L 914 engine for the USA..

The other thing you need to know is that MFI ise Veery spensicve to mend..and wears out rather often..but makes a lovely noise..and is ubercool

Kind regards
David

Ian Donkin · Post by **Ian Donkin** » Sat Jan 21, 2006 4:40 pm

I think L-Jet also made it onto the 912E - perhaps Nige can confirm?

davidppp · Post by **davidppp** » Sat Jan 21, 2006 4:49 pm

Mmm..

I got a fiver that says it reckons that Nige has the old D-jet like the 2L 914..right?

Kind regards
David

Derek · Post by **Derek** » Sat Jan 21, 2006 5:51 pm

I'll have your fiver, I think he's on carbs

porscheplus.co.uk · Post by **porscheplus.co.uk** » Mon Jan 23, 2006 7:40 pm

thanks for the info.
i consider myself mfi'd
regards david

912uk · Post by **912uk** » Thu Jan 26, 2006 10:03 am

just seen a 2.2 mfi pump in Porsche post for £50 if any one is interested as i think these go for alot more money..

tel number 07770 821246
01691 774288

good luck

Nige · Post by **Nige** » Thu Jan 26, 2006 10:12 am

davidppp wrote:Mmm..

I got a fiver that says it reckons that Nige has the old D-jet like the 2L 914..right?

Kind regards
David

Well you're both kinda right, its J-jet, which from what I understand is a mixture of both D and L-jet. L-jet was used alot on later VW injected stuff, vans/buses.

the E in 912E stands for Einspritzung its German for Injection, but I guess you knew that.

Do I get the fiver thats being banded around then?

KS · Post by KS » Thu Jan 26, 2006 11:05 am

For a full, detailed explanation of MFI fuel systems, read my Carte Blanche column in this month's 911 & Porsche World! :D

2.4TE · Post by **2.4TE** » Thu Jan 26, 2006 1:15 pm

Yes, nice article Keith. Very appropriate timing for me as I'm 'tweaking' mine in prep for the rolling road next week. I missed you in the previous issue!

DarrylD · Post by **DarrylD** » Sun Apr 30, 2006 4:28 am

I took the time to animate a CIS and MFI 911 motors if you're interested in watching the difference:

http://members.aol.com/darryld/mfi.gif

http://members.aol.com/darryld/930.gif

Can you see the basic difference? Hint: The 'C' in CIS.

I've noticed people really like to use my artwork as their avatars... very flattering, thanks!