1973 MFI Electric Fuel Pump questions

[lyon]

Hi,
I have been restoring a car that has been sitting for 20 years. It is in very nice shape, I have been trying to get it started and I am having some problems.

I am not getting any fuel into the engine, when I tried to turn the engine over, the electric fuel pump made a humming sound, it seemed to work, now it doesn't. I think it might be seized up. Is there any way to rebuild this pump? Any suggestions as to the steps I need to make to get this engine running?

[RoninLB]

Rebuilding the rotary Bosch fuel pump is not recommended.

[lyon]

Ok, So I guess a new one is my best bet, what would my next move be? To clean out the Fuel Pump?

[RoninLB]

I have no experience w/ MFI.

I would consider a complete fuel system cleaning and check of fuel lines. I would pull the fuel level sender and give a good eyeball in there. There may be a screen on the fuel drain plug under the tank. Mine has one. The mesh disintegrates over time. If you go there get the rubber gasket up date for the plug and sender. Also old gas turns to a type of varnish coating.

[svandamme]

speaking of mfi electic pumps

i can get one 911 640 110 02

PET says that's for the 911 T-K model ???

note , there is another one for the 911 T model
and for the E/S model

the T-K is on another page in PET...


does anyoen know if that pump would work for an S ?
not that i need one now , but with these pumps beeing pricey
if i can get one for cheaps... migth be a good spare to have , no?

[RoninLB]

I pickeled my used spare w/10W and Marvel Mystery Oil 50/50 to keep it from drying out.

[svandamme]

the one i'm after is never used...
just don't know if it's a suitable pump for a 2.4S

[Andy Ring]

I would bet that its not your pump that's broken, but that the fuel line is clogged somewhere. I went down the same road with my 72T and finally discovered the gas tank had sediment in it that was clogging a screen on the bottom of the tank. This was after I had installed a new fuel pump that didn't fix the problem. Others with cars of the same vintage have had the same problem. Not sure what the right procedure is to confirm that this is your problem, maybe others can help...

[lyon]

Well,
I cleaned out the fuel tank, I removed it and it still had about two gallons of gas in it. I drained and cleaned, no sediment, so I thought things were looking up. I will take out the lines and clean them, I am wondering, since I do not hear the electric pump, how do I know if it is working or not?

[Jandrews]

Have you verified that you actually still have power to the pump?


JA

[lyon]

I am heading out to get a 12v tester, to see if power is getting to the pump.

[Grady Clay]

Lyon,

The critical place is the filter screen located as part of the
outlet fitting from the fuel tank. Here is one with some
of the sediment scraped off. This filter screen still passed
some fuel, enough to run the engine poorly.


Here is the same filter screen after cleaning.

Remember, there is an aluminum or copper crush
sealing washer between the screen fitting and
the fuel tank.


The banjo at the fuel tank should also be removed
and cleaned. Sediment on the bottom of the tank
can restrict the return and can get stirred up to re-
contaminate the screen filter. Removing the fuel
thank for a through cleaning is best.

When you cleaned your tank, did you remove the
fittings?

All of the fuel pipes and hoses are suspect. Now
would be a good opportunity to replace all the
rubber hoses. Note my admonition in the below
link about the hose clamps – very important detail.

Here is a link with the hose measurements:
A really good thread on MFI fuel supply:
”Braided Fuel Hose for a 72T MFI”

There has been a lot on this subject, do some Pelican
searching and post more links.

The electric fuel pump for all MFI is:
901.608.105.00 (Bosch # 058097 0001), it is rated as
1.0 bar (14.2 psi), 125 liters/hour, 3.5A @ 12V, 2800 rpm,
safety pressure relief at ~2 bar (28 psi).

For reference the pump for carburetors is:
901.608.107.00 (Bosch # 058096 0009), 0.3 bar (4.3 psi),
80 liters/hour, 2.5A @ 12V, regulating pressure relief at
0.2-0.3 bar (2.8-4.3 psi).

These two pumps appear identical and are physically
interchangeable. The pressure relief in the MFI pump
is a safety only. The pressure in the circulating system
is determined by the restriction fitting at the fuel filter
console.

The pressure in the carburetor system is determined
by the pressure relief in the electric pump.

The ’71–’75 911s had the fuel pump in the rear very
near the waste hot air outlet from the heaters. This
is not a good place for a fuel pump and caused many
failures. This might be an opportune time to move the
pump back to the cool front as were the ’69-’70 911s
and all since ’76.

Best,
Grady

[lyon]

Grady,
Thanks,
I will get cleaning. I took my fuel tank out and I did not see the filter screen you show, I will take it apart again and look for it.

[svandamme]

thanks GRady, i suppose the 110 02 pump i saw, with T/K listed
is for the 73.5 K JEtronic T's?

[lyon]

ok,
I found the fuel screen, it was clogged up. I re cleaned the fuel tank again. Hopefully that will clear up the problem. I was wondering if there is a specific technique for replacing the fuel lines?
thanks,

[Bobboloo]

Originally posted by svandamme
thanks GRady, i suppose the 110 02 pump i saw, with T/K listed
is for the 73.5 K JEtronic T's?

The T/K pump is for carbs. In 72' the ROW T had carbs. The US ver. had MFI.

Lyon, no special technique replacing fuel lines. Now that the tank is off is a good time to replace all the lines. I just bought fuel lines of the proper diameter in bulk and then just cut to the appropriate length and clamped.

It's a good idea to run a little fuel through the lines into a jar or can at the end of the line before you hook up to the injection pump to make sure there is no debris left in the lines.

It would also be a good idea to run some B-12 Chemtool through the injection pump and injectors before you hook up the fuel lines. This will help remove any old fuel left in the line. Chances are you might have to have the injectors cleaned but atleast try and get the motor run before you go there.

[69911e]

Originally posted by Grady Clay
Lyon,

The critical place is the filter screen located as part of the
outlet fitting from the fuel tank. Here is one with some
of the sediment scraped off. This filter screen still passed
some fuel, enough to run the engine poorly.


Here is the same filter screen after cleaning.



Best,
Grady

Grady; I just cleaned mine for the first time and found a fine mesh filter over the one coarse one shown in your pictures. Is it possible you scraped off this fine filter? It is very, very thin. If so what did you put in it's place?
Thanks
Ed Bogue

[RoninLB]

Originally posted by 69911e

and found a fine mesh filter over the one coarse one shown in your pictures. It is very, very thin.

my stock one was a "very thin" screen. The replacement is same.

They are known to disintegrate after 100k miles.. sometimes.

[Grady Clay]

Ed,

I’ll get the guy who owns that filter screen to bring it with him to the Gmund event Sunday. I have only seen those images. This was off a ’68 911. I know there are several variations including a plastic 914 one and two different size outlet pipes.

Does anyone have images of a new or perfectly clean part?

Best,
Grady

[RoninLB]

can't find mine


pelican has mine listed for '74-'89 911 & turbos

Pelican calls it a "Fuel Tank Screen"
My microfiche calls it "Fuel Filter"

Both pn's correspond as 91120114100 for $34

I couldn't find a listing for an earlier yr pn