1973 911 mfi - NEED HELP!!!!

pistolpete · 04-22-2009, 04:36 PM

1973 911 mfi.
I have been having a persistent problem with this car for a year and no one can help me solve it!!!
Car starts fine and idles fine.
Drive approx 10 minutes and the car starts acting like it is running out of gas. Sputtering missing,won't accept fuel. Pull over and it will start up again but will go very slow and you have to keep pumping the pedal to get it to keep running. Then ,may run fine for a little while longer and repeat all over again. It seems to idle fine but under load is when it seems to happen.
Replaced fuel pump.
checked fuel lines from tank.
Checked tank clean and unobstructed
Checked heater line from heater box to thermostat on mfi pump. clear!
Checked thermostat, not stuck and seems to be working freely.

Any possibilities!!
fuel shut off selinoid?
points?
cd box?

I have racked my brain and called anyone I can think of and no one seems to be able to help. Any help would be greatly appreciated. I have read everything I can and have not been able to find a remedy!!

RSTarga · 04-22-2009, 04:40 PM

did you clean the screen filter at the tank?

the911Tprocess · 04-22-2009, 04:46 PM

Hi,
I had a similar issue when I cleaned the thermsat on the MFI pump, after I cleaned all the disc etc and replaced it, it started doing the same thing. Check to see if all the discs are there and if they have been put back properly. A picture of the discs on the thermosat might help some of the others tell you if they are in the right position.

The key is how they have been put back in and if they are all there. If incorrect, as the engine warms up, the engine will start running richer and richer and then it cant sustain it anymore. (Someone please correct this statement if wrong.)

What the thermsat is suppose to do is adjust mixer as the engine warms up, it leans out the mixer.

Hope this might help as a starting point

FenderBender · FenderBender's Garage

+1

I would double check the tank filter and the thermostat spacers. My tank filter was actually varnished shut, looked fine until I soaked it in some carb cleaner and blew air throught it.

zotman72 · 04-22-2009, 05:38 PM

You have fuel flow issue and apparently you have hit most the big areas (e.g. tank and the tank filter screen), what about the big metal fuel filter in the engine compartment that is very expensive and hard to get now? Has that been replaced? Do you smell gas in the exhaust pipe when it dies? Can you check the fuel flow when the car dies underway at the injection pump? Have a fire extinquisher nearby and container to catch the gas.
I had similar issue with 2.4T MFI and it was traced back to the rust in the tank, but the material had traveled all through the fuel system and clogged up in several places (screen, fuel filter, pump and the injector lines. HTH and YMMV

pistolpete · 04-22-2009, 05:55 PM

Sorry I forgot to mention that I replaced the filter in the fall. The tank was cleaned and sealed a year ago. How would you check the fuel flow at the pump??

Terry Young · 04-22-2009, 06:33 PM

You fail to mention if you have an electronic ignition or a regular coil. If the coil is bad, as it warms up, it can short inside. When you stop and let it sit, It cools and then works right again. I hope this is your problem. Had it happen on a couple of cars, most people never realize it. You can check for spark when it quits or just replace it. \
Terry

signature65 · 04-22-2009, 07:37 PM

+1 on the coil.....sounds like a either fuel or the Coil. I have this happen on three....yes three of my cars. a VW, a Jeep and a 65 Corvette.

69911e · 04-23-2009, 03:55 AM

I would check ignition rotor, CDI, Coil, and battery voltage when hot.

Zeke · 04-23-2009, 07:20 AM

The symptoms at 10 minutes do suggest the t-stat. You can check that rascal static with a hair dryer.

porsche1973911 · 04-23-2009, 07:40 AM

I had similar problems. It turned out that a tuneup fixed it. I believe it was the spark plugs and the ignition points that were replaced. I didnt think that i had that many miles on it but it runs better.

Zeke · 04-23-2009, 08:08 AM

"Pumping" the pedal does little for MFI. Agreed on the tune up as well. When I replaced my spark plug wires, mine ran as good as it was going to given the worn butterfly shafts, etc.

jphillips-998 · jphillips-998's Garage

Mine was the ignition box...sounds like it could be anything.

Good luck.

pistolpete · 04-23-2009, 09:12 AM

I replaced the cdi box and just tuned it up 100 miles ago! I am going to attack this tomorrow with all of your suggestions and let's see what happens! Thanks for your continued postings.

jphillips-998 · jphillips-998's Garage

Yes, mine was a bosch from German Auto Parts and it didn't last from Ohio to Chicago.

David E. Clark · 04-23-2009, 09:55 AM

I agree with the thermostat crowd AND with the tune up folks. I would start there. At least those options are inexpensive and easy to check. Make sure the tune up includes setting the points, adjusting the valves and setting the engine timing. Faulty timing alone can lead to the problems you are experiencing. Have you removed the plugs? You can tell a lot just by looking at the color of the plugs. For example, if they are black you are way to rich and the pump is not leaning out (many possible causes but the thermostat not working properly is one of them). You should also have the coil checked. They rarely go bad but when they do they cause just the symptoms you describe - fine when cool, inoperable when hot. Good luck.

pistolpete · 04-23-2009, 02:38 PM

checked the points -set ok
got stuck again so I disconnected the fuel cut off and it still did not run. so it's not that.
what is the best way to check the thermostat??
I also noticed that there is a lot of black around the exhaust pipe.
I will be taking the thermostat apart tomorrow but would like to check it first.
How do I check the coil??

David E. Clark · 04-23-2009, 03:03 PM

Quote:

Originally Posted by pistolpete

checked the points -set ok
got stuck again so I disconnected the fuel cut off and it still did not run. so it's not that.
what is the best way to check the thermostat??
I also noticed that there is a lot of black around the exhaust pipe.
I will be taking the thermostat apart tomorrow but would like to check it first.
How do I check the coil??

Here you go: Bench Testing Your Ignition Coil.

As far as cleaning the thermostat, simply take it apart and clean all the bi-metal disks and housing with a good carburetor cleaner. Follow the advice in this thread and be very, very, careful to put the disks back exactly as you found them.

Finally, the "black around the exhaust pipe" is a good indication that you are running to rich. There are lots of causes for this. The best place to start is by carefully following the advice in Check, Measure and Adjust, found on this page and in the links below.

Good luck

MURF · 04-23-2009, 03:46 PM

you checked the fuel flow from the tank?did you check the return also? we just went nuts with 77 and found the return was plugged..bought new stainless tank from our host..nice piece..murf

pistolpete · 04-23-2009, 05:58 PM

I just noticed that the fuel lines going and coming from the filter are in different positions than the book says although they are in where they say in and out where they say out just switched around. Could that do this???