Help! My 1972 911 T w/MFI won't start

[rcs hawaii]

HI,

My 1972 911T with MFI won't start. I has been sitting for a long time. I have new batteries will charge again (I guess I tried to turn it over to many time and the batteries got a bit drained) still running the 2 6 volts, changed the fuel filter. The pump is vibrating and humming so I believe it is working. Will the fuel pump vibrate and hum if the fuel pump relay is not working???

What else could it be. I have poured gas down the carb tubes and the engine turned over until the gas ran out.

I believe the gas tank has about 4 gallons, but the gas gauge doesn't register any gas, could be the gauge or?

Any ideas of what I can do to make the car run again.

Thanks in advance for your assistance.

Russell

[Grady Clay]

Russell,

Welcome to the Forum.
You will find a lot of help here.

First, you said “…still running the 2 6 volts….”
I hope the two batteries are each 12 volts.
The proper configuration is two 12 V batteries in parallel.

OK, on to diagnosis.
Does the starter crank the engine?

If so, is there any sign of it trying to start?

There is a sequence you can follow that leads you to a solution.
We can help.

Best,
Grady

[rcs hawaii]

Hi Grady,

Thank you.

I thought they were 2 6 volts? I have to new Interstate U911 batteries.

Yes, the starter cranks. I poured gas into the carbs stacks and the car ran until the gas in the carbs ran out.

The car turns, but so far doesn't seem like the gas is getting into the engine.

Can there be air in the fuel lines? If so, how do i purge the fuel lines to get the air out of the lines.

Again thanks for the welcome and possibly the solution to my problem.

I am not a mechanic but do work on cars.

I look forward to more replies. I would real like to get the car started and drive and continue to fix any other items that need to be addressed. The car is complete and in very good condition. I would like to keep the car all stock with the exception of some updates to make the car run better.

I have previously had a 1984 911 Carrera Euro Spec. Unfortunately after a few years I needed to sell it. This time I won't let this one get away.

Again Thank You

Russell

[Jim Richards]

Russell, can you hear the buzz of the electric fuel pump when the key is turned on to the position just prior to the starter being engaged?

[DonDavis]

Hello Russell, welcome aboard! As a new member, you must post a pic of your car or you'll get keel-hauled by the Off-Topic crew!

Now, about your car, SLOW DOWN! Be VERY careful pouring fuel down the stacks! The last thing you want is an engine fire.

You also mention carbs. Is this car original with MFI or has it been changed over to carbs? If it's still Mechanically Fuel Injected, there are a whole host of things that can prevent the car from starting.

Let's find out what your configuration is before we go any further.

Don't do any other disassembly until we know exactly what you have.

We are going to get your car running and will continue to help with all other "projects". And there will be more!

[Grady Clay]

Russell,

I agree with Don, quit pouring gas in. Gasoline is one of the most dangerous substances we normally come in contact with.

From your description it seems fuel is the issue.

Per Jim, can you hear the fuel pump?

Do you have a fuel pressure gauge capable of measuring 15 psi? The place to measure the fuel pressure is at the fitting/hose on the fuel filter console closest to the rear of the car. Spec is 11.8 ± 3.0 psi.

Your MFI has three separate fuel systems
First is cold start enrichment. There is a solenoid valve on top of the fuel filter console for this function.

Next is a cold running thermostat. This is the device on the MFI pump and has a paper/plastic hoses coming from the tin alongside the left side of the engine.

Finally there is the main running MFI. There is the low pressure circuit that circulates fuel from the tank, through a filter screen fitting, the electric fuel pump, fuel filter, the inlet side of the MFI pump, past a pressure valve and finally returns to the tank. You should be able to hear the electric pump running when the engine is not running but the key on.

There is the high pressure fuel path from the MFI pump, past a check valve in the top of the pump, through the steel pipes to the injection nozzle.


There are two basic tests of the low pressure circulation fuel circuit.

First is pressure as I noted above. Second is a fuel flow spec. I prefer to do this with a long piece of fuel hose where the fuel returns to the filler on the LF fender. Spec is 900 to 1000 mL (cc) per 30 seconds.


A not uncommon problem is rust in the fuel tank. The usual symptoms are that the engine will start and run but quit after some driving. It will only restart after sitting for a while. A way to inspect this is to remove the fuel level sender (get a spare gasket first) and wipe the bottom of the tank with a long home made Q-Tip. If this is a problem you need to clean the tank and the screen filter fitting.

If the electric fuel pump isn’t running, check the electrical connection. Is there power?

Best,
Grady

[lyon]

I ran into the same problems last summer when I was getting a 73t running after 22 years of storage.
I suggest that you take out the fuel tank, clean it and coat it. There is a little fuel filter that leasds from the fuel tank to the fuel lines, it is probably clogged and is not letting gas into the lines. You should also replace the rubber fuel lines. Make sure you connect everything up correctly.

good luck and lets see a picture...

[rcs hawaii]

Hi Everyone,

Again thanks for all the assistance.

I'll try to answer all the questions.

First, I thought it had two 6 volt. I was one who read and was miss informed. I will charge up the U911 batteries again. They are only about 3 months old. I bought them from my Intersate battery center locally. I did read about some FZ75 gel batteries. Next time I may try those.

I believe my 1972 911 T is original. I did mention carbs again my miss understanding. To the best of my knowledge every thing is stock and the MFI is in.

How much gas should I put in the gas tank. I believe it was very low before. I put in about 4 gallons recently.

Yes, the fuel pump is vibrating and humming. Good sign.

I noticed that when I turn the key the buzzing alarm sound goes on the fuel pump is vibrating and humming. The engine turns, but I think I tried to much and need to just charge up the new batteries again.

I also noticed that after I turn the key off I hear a gurggling sound from inside the car. I believe it to be the gas in the tank.

If there is air in the lines how do I go about bleeding the air out of the fuel lines???

I will try to get the batteis charged up fully again this weekend and try to crank it over again. I will also put in more gas.

I went to my local Porsche dealer today and talked with the parts department. They mentioned that they do not stock any vintage Porsche parts. Everything for the car is special order.

Again thanks for all the information and assistance. I can't believe I don't even have any pics of the car yet. I believe my brother took some before, but I never got around to it. I will take some pics and post as soon as my wife will. She great at the computer stuff. I'm ok.

Thanks again.

Russell

[Gasman59]

Russell, are you sure you are geting a spark?

[David E. Clark]

This article is from the February 1977 issue of Porsche Panorama magazine. It addresses many of the issues you are facing. I hope you find it helpful.


© Porsche Panorama. Posted here for educational purposes only.

[David E. Clark]

These three pages on troubleshooting MFI systems are from the Factory Workshop Manual. They might also help.



© Dr. Ing. h.c. F. Porsche A.G. Posted here for educational purposes only.

[Jays72T]

Nice David, good article.

[David E. Clark]

One more article that might help. The Diagnosis of Sick Porsches Up-Fixin der Porsche, Volume IV, page 270 .

© Porsche Panorama. Posted here for educational purposes only.