MFI and Relay HELP!
 

I have a bad relay, which has something to do with a mechanical switch on the MFI of my 73 911S. It sits on the board next to the rear window defroster relay. On deceleration, the little mechanical switch closes and the relay is supposed to cause a change in the fuel/air mixture. My relay failed, and now my beautiful car (with a brand new $1000 Leistritz muffler) backfires constantly like an old jalopy. The part number is 901 615 113 00. Porsche lists it as a good part number, but no one seems to have one. Do any of you have a source for one of these parts?

Silver Surfer
'73 911S Sunroof Coupe

Did you try Stoddard? They can probably get it if it is available.

Good luck.

I tried Stoddard, but they did not have it in stock. They were willing to order it, but Porsche did not show any in stock either, so it is uncertain when, if ever, I will get a part.

Read these three threads and fix it yourself:
http://forums.pelicanparts.com/showthread.php?s=&threadid=68529&highlight=MFI+Rel ay

http://forums.pelicanparts.com/showthread.php?s=&threadid=8074&highlight=MFI+Warn ing

http://forums.pelicanparts.com/showthread.php?s=&threadid=81574&highlight=MFI+War ning

Man, this is a favorite topic on this board. The archives have TONS of stuff about this, Warren even reverse-engineered the circuit diagram.

That speed switch/speed relay/rpm transducer is $300.10 from Stoddards ... BUT, it can be repaired, as I have written much on the topic in the past two years ... and, I published a schematic diagram!

There have been SEVERAL success stories repairing the speed switch among Pelicanheads, and there isn't any reason why yours can't be another one!

http://forums.pelicanparts.com/search.php?s=&action=showresults&searchid=283513&s ortby=lastpost&sortorder=descending

What's wrong with a few backfires? My 930 pops on decel (normal behavior without cat) and I kinda like it. Sets off plenty of car alarms in the parking garage at work (if the burble doesn't get it first).

My '72 has some slight popping, and it will, on occasion, backfire severely on startup. Its a lot of fun just starting it in the parking garage and hearing the backfire echo throughout the lot. :)

Its constant backfiring, not "a little." Also, see reference to $1000 brand new Leistritz muffler, above. Anyway, this board is GREAT! I found a cheap reconditioned unit, so I should be back in business in a few days.

Silver Surfer
'73 911S Sunroof Coupe

Warren -
Does your schematic allow someone with some electronics know-how to construct a new board, possibly using more modern (hence available) components?

Obviously not me, since I tried to swap out the transistors on my unit and failed miserably.:D

But it would be nice to know a solution is out there waiting when original units become unobtainium.

Thanks!

Kevin,

Stoddard's price is quickly approaching 'UNOBTANIUM' levels ... at least to me!

Yes, a 'new' speed relay could be built for probably somewhere in the vicinity of $50 - $60 cost in parts including military-grade semicondutors, metal-film resistors, a high-quality, silk-screened G-10/FR-4 PC board, replaceable 40 Amp icecube relay. Strangely enough, though ... designing it for 'maintainability' and reliability would make it larger than the original 1966 Bosch design! Probably only slightly smaller than the CDI-unit ... at least in my mind!

I have toyed with the idea, as has Companzer's brother-in-law ...

Speed Switch/RPM Transducer
 

Thanks to the great people on this board, I have located a source for good reconditioned RPM transducers. If you need one, PM me and I will be happy to share that source with you. Thanks to everyone for making this such a great place to get help!

Silver Surfer
'73 911S Sunroof Coupe