A different MFI thread - electrical

[rs911t]

This winter my 2.8l '72 911T is being converted back to MFI after spending the last 25+ years with Webers. I've collected most of the parts, have a pump being rebuilt to 2.8 specs and S throttles bodies and mag stacks, etc, etc. All this is looking good.

So, what about the electrical connections? I'm having trouble identifying the MFI bits in the wiring diagrams. In particular, I'm concerned about the relationships between the RPM transducer, shut off solenoid, micro switch (on the throttle body?), the temperature sensor on the breather cover and ignition components. The car has a Crane / MSD ignition. What's the best source of technical info regarding this aspect of MFI? The wiring diagrams?

Also, I still need to source couple bits, specifically the 3 studs used to mount the pump console to the case. Anyone have specs for these?

Thanks in advance!

[Jim Richards]

Greg, if no one else provides better info, perhaps we can use the wiring diagrams and look at my wiring harness. I'll be around most of the time Thursday - Sunday.

[svandamme]

the ignition part is totally seperated from the mfi part, no need to change anything there for the mfi change.
msd's website has diagrams that are very clear

the temp sensor controls the solenoid for the cold start injectors which is located on the top of the fuel filter
the shutoff sensor plugs in to the mfi pump

as far as i know ,that's all there is to it all the rest is mechanical , but maybe somebody else can comment/confirm on this as well

the 3 studs for the pump console : can't find the exact part number
but you'll also need one spacer to support that pump console partnumber is 901110236


i think there's different studs required
one of them is 900061147 8x62 78 in the picture

the other 2 are in the picture of PET , but the no part number for them , 76 and 77 , not in the list

[jpnovak]

Greg, here are the wiring diagrams for a 71. They should be the same with regards to MFI. the legend is below. This should get you started on the wiring. If your electrical panel is stock all the necessary parts should be there. you can trace each component by wire color. I think the Hayne's Manual has a pictoral of the actual component locations.

[derek murray]

Here is a high resolution schematic for my car (albeit its a 1970) that may prove to be of some use to you... good luck in returning your car to mfi

http://www.scatliff.mb.ca/pelican/Electrical_Schematic_SL35(high).pdf

[Grady Clay]

Greg,

I know we have discussed this prior but it is good for all Pelicans installing (or re-installing) MFI. One of your goals is to return it to “stock appearing.” Sherman and several others will benefit.

Starting with the new MFI pump, does it have one or two solenoids on the front cover? Your new MFI system started life as a 2.0-2.2. Two is desirable but will affect how the wiring in done.

Inspect the engine wiring harness for any extra wires taped back to the harness. I suspect we used a ‘71T harness or something modified without any MFI stuff. Ron’s goal was to make a 2.8S appear as a 2.0T.

As far as the wiring goes, there are two possible ways to proceed; first is to manufacture a small custom MFI wiring harness and the other is to replace the existing engine harness back to stock ’72 that has all the MFI wiring. Your choice. I recommend the OE harness.

The RPM transducer and relay should be easy, they just plug in. Does the crankcase breather have the opening for the thermo time switch and oil return from the MFI pump? Does your linkage have the micro switch and hardware?

Do you have the hose and crankcase fittings for the MFI pump oil supply?

I suspect you have a modified (added air duct to cooler) early black fan shroud. Have you found a ’72-’73T MFI fan shroud?

You need the left piece of tin for the thermostat heat hose, the left heat exchanger with the MFI heat outlet, and the thermostat heat hoses.

What are your plans for the warm intake air system?
It depends on how serious “original” you want as the ’73 set-up is preferable with the warm air intake in the engine compartment (’73 only). In any case you will need the ’72-’73 rear tin.

Do you have the two pieces of tin for the MFI Gilmer belt? Reminder; replace the belt and both toothed pulleys as a threesome. Replacing one at a time only accelerates the wear.

From your post, you have the MFI pump support but not the three case studs. Do you have the aluminum spacer?


OK, on to fuel system.

The MFI uses a different (higher pressure) electric fuel pump from carburetors. Where is the pump mounted on our “T”?

You need the fuel filter console and mounting bracket. I’m sure the mounting points are still in the body but might benefit from replacing the rubber parts. I recommend new OEM hoses and clamps everywhere. Where there are assembled fuel lines, cut off the crimped hoses and replace with the OEM hose and particularly the “Norma Schellen” Factory hose clamps. NEVER use worm-screw hose clamps as they damage the hose.

This would be a good opportunity to clean the fuel tank and the fuel pick-up filter screen. A subtle mod would be to return the fuel to the tank via another pick-up screen and just use the bottom drain port for draining the fuel tank. This prevents the return fuel from stirring up sediment between cleanings.

Something to consider is that there appears to be an additional restriction in the return fuel flow in these years. There has been some discussion on the Forum about this.

Be sure and check the electrical connections to the pump, it draws more current.


Had I known 30 years ago that we would be going through all this effort, I would have recommended a slightly different course of action. It is remarkable that this is a 30-year-old 2.8S that has never had the case split.

Best,
Grady

[rs911t]

Lots of info. Thanks!

Jim: I'd love to come over Sunday and shoot some pictures.

Grady: I have lots of answers..

-- the pump has one solenoid and the thermostat.

-- I haven't inspected the remaining wiring yet. But, I'll cast the net for a '72 OE harness.

-- I have a new breather cover w/ thermo switch and the fittings and hoses from the case to the pump.

-- Indeed found a proper yellow MFI shroud.

-- I have all the tin pieces but haven't procured hoses between the exchanger and thermostat. Just recently found a left-side HE, so I'm going the that route for warm air intake.

-- Have the 2-piece belt cover, as well as a new belt and pulley.

-- I do indeed have the aluminum spacer, just lacking the 3 studs.

-- Our "T" has the pump in the engine compartment where the fuel filter used to be. I've procured an MFI pump and located the spot below, forward and left of the engine compartment. The wiring harness is still there! Also, I have the filter console and fittings.

??? The RPM transducer and relay were part of the original question. What do they look like and where should they be? Right now I honestly don't know if they're still in the car....

??? My plan is to skip the cold start injectors. The car sleeps in a garage and is a fair weather driver. The thought was to replace the cold start solenoid atop the filter console with a plug. Any problems with this approach??


I estimate this 30-year-old engine has less than 50k miles on it. Leaks just a few drops of oil, doesn't smoke and has leakdown numbers in the 2-3% range across the board. Seems to me you guys knew how to put'em together!

[svandamme]

them extra injectors, i have em too , and plan on skipping them as well
at least with the thermo switch , if i use em , i'll fire em manually to
i actually flooded my engine badly half a year ago with them cold start injectors : if the engine for some reason doesn't start .. the injectors will dump huge ammounts of fuel , and in the end fill your exhaust to the point where you have to disassemble your muffler to drain it.


and since my harness is shot
i'll be rewiring my engine as well when i finished my rebuild ( but not like it was, stock look isn't that important to me)

[arrivederci]

Greg,

While you're out at Jim's, feel free to swing by my place over the Christmas weekend. My MFI (2.4L) is still in the car and intact. I can't say the same for the rest of the car, namely the suspension.

[derek murray]

Originally posted by rs911t
The RPM transducer and relay were part of the original question. What do they look like and where should they be? Right now I honestly don't know if they're still in the car....

The RPM Transducer (aka Speed Switch) is located on the electrical console in the engine compartment. It is #5 on the photo below.


(C) 1971 Dr. Ing. h.c. F. Porsche A.G.

...and for the archive, here's the complete console layout

1 - Console
2 - Relay switch for single stage rear window defroster (not used with two-stage window defroster)
3 - RPM Sensor
4 - Relay switch for start enrichment (not used in carburetor engines)
5 - RPM transducer (not used in carburetor engines except 911T USA version)
6 - Control Relay for two-stage rear window defroster (not used with single stage defroster)
7 - Radio noise supression
8 - Regulator
9 - Ignition trigger unit
10 - Fuse box III

[Grady Clay]

Greg,

The “Porsche speak” legend for the illustration below is:
The number in [brackets] is the listing in the ’72 wiring diagram.

1) Console
2) Relay switch for single-stage rear window defroster (not
used with two-stage rear window defroster.) [51]
3) RPM sensor.
4) Relay switch for cold start enrichment (not used in
carbureted engines.) [52]
5) RPM transducer (not used in carbureted engines
except 911T USA-version.) [11]
6) Control relay for two-stage rear window defroster (not
used with single-stage defroster.)
7) Radio noise suppression.
8) Voltage regulator. [4]
9) Ignition trigger unit (CDI.) [9]
10) Fuse box III. [80]

Note that #3 is the interface unit for early tachs to
operate properly with the 3-pin CDI.
It is not the MFI RPM transducer.

#5 is the MFI RPM transducer.
There is not a separate relay that operates the shut-off
solenoid in the MFI pump, it is incorporated in the #5
RPM transducer.

#4 is the relay that operates the cold start solenoid on top
of the fuel filter console. It operates via the starter yellow
wire and the thermo time switch [14].

Who knows what the relay is just inboard of #3?
I think this image is for a '70-'71 and the unmarked relay is for
the cold start enrichment solenoid on the MFI pump.
The Porsche manual isn’t clear – help me out.

"
"
(C) Dr. Ing. h.c. F. Porsche A.G.


Greg, do you have the steel air filter assembly with the
cold-start "nozzles" above the intake stacks?
The reason I like the ’69-’71 MFI pump front cover is because
it has the cold start enrichment solenoid that forces the rack
to full rich position while cranking (also has a 2nd themo
time switch.)
This removes the necessity for the nozzles in the stacks or
air cleaner (fire hazard.)
With the two-solenoid set-up, you can fashion a center
off, momentary on, double-throw switch to either operate
the cold start solenoid or the shut-off solenoid to crank
the engine if flooded.

Best,
Grady

[Grady Clay]

Greg,

Here is the correct fuel plumbing diagram for your car.
I am in favor of moving the Bosch electric pump to the front
as was a ’69 E & S and all ‘70s.
There are nice Factory parts to accomplish this where it
appears original.

This puts the fuel pump in a cool location and with a much
shorter suction hose.
The rear mounted fuel pump is at the waste hot air outlet
from the heaters when they are off.
It has to be incredibly hot there in the summer.




"
(C) Dr. Ing, h.c. F. Porsche A.G.





Here is the front mounted pump for a carburated 911.
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.


Here is all the front mounted pump, hoses, and hardware.
"
"
(C) Dr. Ing. h.c. F. Porsche A.G.


In this last diagram, the #43 & #44 bracket fits the tubular
steel front cross member. They aren’t needed for the
aluminum cross member, only #38 and two #40.

When moving the return line #16 to where #7 is, you
use #2 or #3 in place of #7. Then you use #5 for the drain port.
As I said before, this allows any sediment to collect at the
drain and not be stirred up by the return flow.
The only disadvantage is that if you have a substantial amount
of water in the fuel it will sit at the drain port and not be stirred
up in the fuel.

It is easy to fashion the electrical connector as a ’70.

Best,
Grady

[Grady Clay]

Greg,

Please post an image of the engine electric console as it is currently.

Best,
Grady

[Grady Clay]

Greg,

OK, I went back to my ’72-’73 parts manual and the studs (Stiftschribe fur Konsole) you need are:

2 each 900.061.008.02 8 x 25 mm DIN 835 8.8
1 each 900.061.147.02 8 x 62 mm DIN 835 8.8

Who has a derelict case with these studs?

Best,
Grady

[rs911t]

Thanks for the pix and descriptions! I don't have a picture, but upon inspection everything is there except #3 and #6! I haven't inspected the pump carriage with these diagrams, but I don't believe the carriage and bumpers are there. If not, I'll look for the front mounted unit.

Anyone have excess studs ?!

[Grady Clay]

Greg,

I assume your tach works OK. If so, you don’t need #3. That interface was necessary for the early tachs to operate with the extremely short pulse and fast rise-time of the Bosch CDI.

Best,
Grady

[rs911t]

I assume your tach works OK.

Yep, works fine. I believe the signal is provided by the MSD unit.

[Early_S_Man]

The #3 'RPM Sensor' is/was also called a 'Ballast Unit' in some factory references, and is a simple, three-terminal resistive divider ... used with early tachs through 1969 production, and part way into 1970 production, IIRC ...

Three diffeerent ballast units were used, two different versions for battery-coil ignitions, and a third one for CDI ignition of the 1969 'E/S' cars, and into early 1970 production for all 'T/E/S' models, and I believe the last ones were rectangular rather than round.

[Grady Clay]

Warren, you are a wealth of knowledge.


OK, on to some planning for moving the fuel pump to the front.

The fuel pump power in the ’72 comes from fuse 7 on the 10-pole fuse block. It is a red wire with green stripe. This is exactly the same as a ’70 with the only difference being where the wire comes out of the main harness. As I recall, the ’70 has the power and ground for the front mounted pump coming out of the main harness above the pedal assembly. It has a large-diameter rubber grommet where the harness goes from inside the passenger compartment to the cross member area. The reason for the large grommet is that the hole in the chassis is large enough to pass the pump connector.

Please, will someone with a ’70 confirm my memory?

There is a wiring harness (911.612.072.10) to the ’72 rear fuel pump but I don’t think it is long enough for use in the front.

Greg, I think that for your application a small, new wiring harness would be appropriate. Find a salvage 911 and get the red/green and brown wires. If possible, get the fuel pump connector with rubber boot. Inspect your 911 near where the two brake fluid supply tubes go from the reservoir down to the master cylinder. You are looking for a hole that has a plastic plug in it. Anything from 6 mm to 14 mm will do. The routing of this new 2-wire harness should be from the fuse 7 on the 10-pole fuse block and the nearby common ground on the chassis through a rubber grommet, past the master cylinder and to the fuel pump. You should use black heat shrink and have the grommet in place on the harness. You will want a brass ring connector for the ground connection.

I would leave the existing fuel pump wiring in place and just zip tie it to the harness. Don’t do anything to molest the main wiring harness.


When you install the fuel filter console, there is a small ground strap (911.612.009.00) that goes between the console and ground. This is necessary for the cold start solenoid. Even though you aren’t intending to use the cold start, reinstalling it now will prevent possible confusion or a problem later.

I recommend you remove the electrical console and inspect it for all the ’72 MFI features. It is possible we exchanged the harness for a non-MFI one. When someone installed the fuel pump in the engine compartment, where did the get power for it?


All this illustrates how useful a personal “Car specific workshop manual, parts manual, service manual, scrap book” can be. I regret we didn’t start one for Ron in ’74 although I suspect all this was well documented on the original repair order and invoice.

Best,
Grady