1972 911E MFI Problem?

Jimal92 · 09-13-2004, 03:30 AM

I have a 1972 911E that when run for long periods of time starts missing so bad you can only reach about 20 miles an hour. Runs fine when cold but after about 30 mins of highway speeds the missing would start. If you shut down let it cool for 5 mins or so you could start it back up and problem would be fine for awhile. The car had the MFI pump replaced with a rebuilt one from Einmalig Porsche 3 years ago less than 2000 miles. Fuel filter replaced one year ago. Tried a different CDI, new points, new fuel pump. This problem has been getting worse (showing up sooner) and friday when i took it out for a test drive after replacing the fuel pump it occurred in under 10 minutes of driving. Turned around an headed for home but never made it down to 20MPH with accelerator to the floor and missing badly. Pulled over to the side and shut it down to cool. Well this time it would not start back up. Checked for spark and that was fine. After having it towed home tried about 4 hours later and it started right up. Any help appreciated.
Thanks
James

jpachard · 09-13-2004, 03:46 AM

James,
I would start by checking the hose that runs from the Heat exchanger to the thermostat on the back of the MFI pump. if this slips off it can cause problems. Also, has it ever worked correctly after the rebuild? You might also try disconnecting the hose i mentioed above completely and see how it works. The MFI pump might be adjusted incorrectly.

Cheers, James

Jimal92 · 09-13-2004, 05:21 AM

The pump worked fine after the rebuild. I checked the thermostat hose and it looks fine. How often do these MFI pumps need to be readjusted?

POKDUB · POKDUB's Garage

I had similar bad running after warmup (1969 911E) after just buying the car. The idle mixture was too rich.
When starting cold, both idle and main mixture were rich, so the car was well nourished.
After the thermo heated up and the main mixture leaned, she would stall once the foot came off the pedal, and she was difficult to get revving again. I leaned off the idle and this sorted my poor running.
Although this is probably not your problem, the stop solenoid also interferred with the smooth running until the car actuallly warmed up. I have since run a manual switch to the dashboard to over ride this.

Grady Clay · 09-13-2004, 08:53 AM

James,

Do a fuel flow test. I’ll bet you have junk in the fuel tank and the filter screen in the tank is restricting the flow during your drives.
Do some searching on Pelican.

Read here:
“MFI thermostat spacers”
p. 1 end has CMA extension, p. 3 has nozzle, fuel flow, and fuel pressure.
MFI thermostat spacers

Do you have a copy of CMA?
Here:
Check Measure Adjust (CMA)
http://www.scatliff.mb.ca/pelican/MFI_Check_Measure_Adjust.pdf

Best,
Grady

Jimal92 · 09-15-2004, 05:10 PM

Well looks like Grady is right on this one. After reading all the post on here about rusty tanks i decided i was going to drain my tank and take out the sump screen filter. Well I went to use the pump on the car and took the inlet line to the MFI pump off and ran it to a gas can. Well that screen must be about plugged cause ther is only a little amout of gas coming out be forever in a day to do it this way. So now i am siphooning it out through the sending unit hole. The sending unit came out with a rusty residue at the bottom. Got about 6 gallons out so far car had 1/2 tank. Well before quiting for the night i took a bright flashlight and shined it throught the hole looks like alot of rust particles in the bottom. So going to have to get this tank flushed out or get a new one. Anyone know of a place for good used ones?

Lukesportsman · 09-15-2004, 05:30 PM

I'd post here for WTB. Some of the racers may have one left over from a changeover to fuel cell. May not have any luck, but more likely to get a good deal for a clean tank than a junk yard.

Jimal92 · 09-16-2004, 05:30 PM

No sump screen in my tank. I can shine a flashligh down through the sending unit hole and see the supply and return line and a plug but no screen.

Grady Clay · 09-16-2004, 05:41 PM

Clean the tank and go buy a new metal screen-fitting.

I’ll bet some PO had the screen get restricted and took off the screen. I’ve seen several just sitting in the bottom of the tank.

You now need to look at the fuel pump, hoses, and MFI filter.

Best,
Grady

72doug2,2S · 72doug2,2S's Garage

Grady is right on. I just replaced my tank with a repro, new intake plug and screen. This solved my problem, my old tank (Damaged from a road hazard) had some rust and the screen was filthy. Now my pump humms happy. At any rate, drain your tank and clean or replace the intake plug screen ($10.00)-called a "gas cap" on our hosts site.

thastings · 09-17-2004, 04:22 AM

Having finally given in to Grady's pressure, I checked mine (after considerable manhours and dollars on EVERYTHING else) and checked mine. He was right again. I am now looking for a replacement so I won't have to use a homemade one.
Doug, I could not find it under "gas cap", or any other combination of words. Part Number?
Terry Hastings

72doug2,2S · 72doug2,2S's Garage

901-201-023-02 8mm gas cap 72 sc
$9.50

There seems to be some problem locating this on the site. Call the 800 number and make sure you get the sealing ring too. I bought 2 one for myself and one for a friend.

I believe there is also a 7mm (Connecting line size) for the "T", I wasn't sure which one to get since my car was a "T", but had an "S" motor. I got the 8mm which worked well for me. Bigger is better right? Well so far so good.

I hope your pump is fine, sounds like your may want to replace the expensive fuel filter again, once you get the tank cleared.

Best of luck,

thastings · 09-21-2004, 04:08 AM

Doug,
How long ago did you buy this filter from our host? According to their online catalog, they do not carry it and the replacement # part is special order for $40. ?????????????????????????
I am waiting for their telephones to open at 7am Pac time.
Terry

72doug2,2S · 72doug2,2S's Garage

Here is my order. I bought 2 at $9.50 each. The other one was for a friend. I did order over the phone.

Tuesday, July 6, 2004 Doug 1089127113-316

Order Id: 1089127113-316 Customer:
Doug

--------------------------------------------------------------------------------

Status
Part Number
Description
Qty Price
Total

Packed 901-201-023-02 8mm gas cap 72 sc
2 $9.50
$19.00

Packed 900-123-007-60 sealing ring
2 $2.50
$5.00

Packed 900-123-011-30 O-Rings
1 $0.25
$0.25

Packed 900-123-011-60 sealing ring
2 $.10
$0.20

Packed C-631-115-02 Headlamp to Fender Seal, 911 (1965-94)
- This part is in stock and typically ships out the same or next business day.
2 $4.35
$8.70