More MFI questions

Hello again,
After doing a rebuild on the motor in my '72T, (which had been sitting for 3 years), I am only getting fuel out of my MFI pump to the #3 cylinder. Any ideas? Is there a kit available to rebuild the pump?
It has been suggested to me that since the car was sitting so long, there might be blockage in the fuel lines/filter. Would that explain the fact that I only get fuel to #3, (the closest cylinder to the MFI pump)? The fuel pump seems to be working okay, pressure wise, so I'm at a loss right now.
Thanks, Jim

Jim,

If you don't aready have metric flare-nut wrenches, I suggest you get a set, ASAP! And, a gallon of B-12 Chem-Tool as well!

The following procedures require EXTREME CLEANLINESS with respect to any dirt or particles getting into the injectors, hard fuel lines, AND the fuel ijection pump itself!!! Temporary fuel connections should be made with clean, fresh fuel hose, and a filter for all fluids introduced into the fuel supply side of the injection pump is MANDATORY! If you don't have a clean workbench in your garage, use your dining table for assembly of the test setup! Then take it outside for actual fluid testing.

After you have removed all six 'hard' lines to the injectors, and all six injectors ... first clean the external surface of all lines and injectors VERY THOROUGHLY, then soak all in B-12 Chem-Tool for at least 12-16 hours. If you have access to an industrial ultrasonic cleaner, it would speed up the process!

I don't really expect any problems with the lines ... after soaking, blow them out with compressed air, and note any differences in the volume of air flowed thru each line. The injectors are the most likely culprit at this point!

If you wish to take the injectors to a dealer or authorized Bosch service station for testing, do so, or you can do your own complete test for operation and spray pattern on your bench. Remove injection pump, drain out all fuel and any old motor oil in the pump.

Refill oil supply with 1 pint fresh motor oil. Assemble all six hard lines to the injection pump, then bolt the injectors to the ends of the lines ... use the same layout as on the engine, and you have a mechanical 'insect-like' piece of artwork!
Rig up temporary fuel supply and overflow lines making sure that the overflow line is plenty long and can be elevated to act as a vent line. With a Coleman filtered funnel (for their gasoline lanterns) or equivalent ... fill fuel inlet with 1 cup of B-12 Chem-Tool and BE SURE it has been filtered ... you don't want any rust particles getting into the injection pump!

Newspapers/rags under this 'test assembly' might be a good idea for protection of anything in the vicinity from the effects of the Chem-Tool solvent. With the assembly complete with all 12 flare nuts TIGHT, and fuel test fluid in the injection pump, manually turn over the cog drive pulley for several revolutions, until [hopefully] fuel is being sprayed out of all six injectors. When all air has been bled out of the lines, a sequence of 'chirps' will be heard as the pulley is turned over and each injector is sequentially 'pulsed' with fuel. Examine/watch the spray pattern for each injector. It should be conical and completely uniform, with no breaks or uneveness visible. Assuming your cleaning and testing has been sucessful, break down the test assembly and replace everything on the engine in the reverse order you took them off. If any questionable injectors or lines were found ... my condolances! Output of fuel at each outlet 'port' of the pump can be noted as a small spurt with the lines removed.

Any questions ... just ask away before you start this critical procedure? By the way, I have done the exact procedure above, at home, and with perfect results, too! A 'chirping' test assembly means good music later ...

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Warren Hall
1973 911S Targa

hi, i'll ask the easy question first. did you time the injection pump when you put the belt on it?

Speaking of timing the pump, I read that the factory race guys found litle or no difference in power/running if the pump was timed correctly or not. They should know!
Can anyone verify this?
Doesn't sound like a timing problem anyway (if there is such a thing). Try Warren's ideas. Always a good rule of thumb.

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'72 911 TE

Matt,

I suspect what you read is quite true, for the simple reason that the 3.2 Carrera (and probably all later Motronic engines, as well) have 6 injectors in two groups of 3 that fire simultaneously!!! That is to say, at least 4 of the 6 cylinders have their injectors timed most definitely at the WRONG time, with no reported problems I have heard about in the press! And, apparently this has been quite thoroughly studied and tested by Bosch for over 32 years, since the Type 3 VW engine of 1968 with D-Jetronic injection was split the same way, as were all other users including Mercedes, Volvo, BMW, and others! The reason for these shared injectors? It is cheaper to build two driver circuits, instead of 4, 6, or 8!

That said, I still like the idea of MFI engines being timed at exactly the right time on the FE mark on the pulley ... good 'vibes' for a perfectly tuned engine!



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Warren Hall
1973 911S Targa