Jeff HIggins' MFI technique

[wkbergman]

Ref.: Excellence May 2010 p.84 , Karbon Kopy [KK]

I am one of those who annually [analy] struggles with MFI. Belgium's annual tech control requires me to mess up a good setup in order to pass the CO test. Well, maybe not so bad, as my annual fiddling with this keeps me on my toes.
Randy Wells in KK article mentions a "little known" [in my 40-odd years of ownership totally UN-known] technique allegedly documented by Jeff HIggins, which involves screwing around behind the diamond shaped idle screw plate.
I reviewed ten pages in the Pelican Parts Forum, but don't know how to go straight to a topic....
Holy moly, this means removing the idle adjustment screw to remove that plate?
Anyone provide me a bit of detail on this?
Many thanks
WB

[911st]

If you are talking about messing with the adjustment of the springs on the centerficall weights, that is for staging the rate you fueling advances with rpm. I would not touch this on a car that runs well and was built as a factory MFI car. This is for trying to adapt a pump to a motor that it was not intended for.

Better to send your pump in to be freshened and recalabrated properly. This is worth it just for the improvement in drivability.

If you have to you can do some tuning with the normal rack adjustment screw to get your AFR at speed dialed in. The air bypass screews and throtle plate angle for idle. If needed one can also make some effects by playing with the linkage length to the pump if needed but I would avoid this if possable.

I do not know how they test you but MFI cars should not be tested at any rpm over idle unless under the correct load. It must be tested on a dyno.

JMO.

[kenikh]

Search "open heart surgery" on this forum and you will find it. The "Jeff Higgins method" is nothing more than a reverse engineering of the Bosch manual for fine tuning the MFI pump as the factory did in the old days. The screws are simply the means to fine tune the pump's fuel curve for optimal AFRs, which Jeff took one step further to find the edges of tunability to make a 2.4T pump work on his 3 liter motor.

To your purpose, it would highlight how to lean out your pump to pass CO in emissions testing then predictably reverse the process for optimal driving. There is no voodoo involved, just a description of how to tune a good running pump the way the factory recommended back in the good old days.

I agree with the above that if a pump isn't running well, a rebuild is needed, but yours sounds good, so tuning the pump screws is a good option for the short term needs of passing emissions testing.

[kenikh]

The link:

MFI Pump - Open Heart Surgery

[Rich Lambert]

Here's a detail of the master at work.

[Rusty Heap]

lets try wiggling this wire and see if spark bang thingy works then .



"Hey look Dad, a cow"

[wkbergman]

Wow, lotsa great info, and much of it scarier than Open Heart Surgery!
What I finally found were the very German instructions on setting up the MFI, a 1970 2.2L in my case.
Starts with the usual tune up stuff, valve setting etc., then proceeds to a very careful (anal one could say) checking of the lengths of the rods beginning with that 114mm pushrod; and the simultaneous opening of all the butterflies.
Equalize the air thru those six throats.
Do all that before screwing with the adjustment screws.

It took all weekend and produced very sore back muscles, but the result was immediate.

Fuel consumption went from 17 mpg to 22 mpg; a 29% improvement!

Yes, in the past I did find that messing (carefully) with those thermostat washers can help lean the overly rich setup.

Why don't Porsche mechanix do this? Takes a lot of time; the two screws are more obvious; only the Old Guys apply the Teutonic methods these days; new Porsches are all computer and electronics - forgotten skills.
Cheers
WB