1976 911 not starting

slippyd · 07:25 AM

I was driving my 911 when it suddenly shut off on me. I still am getting spark but no fuel or instrument gauges.
I first replaced the fuel pump, which was tested and is working, then i noticed that the fuel relay does not click in.
I traced the yellow wire to the ignition and it is okay, then I had noticed there is no voltage regulator and the plug is just dangling.
well i tried tricking the fuel relay in which it gives me fuel and the gauges work but the car will not start. I then ordered a voltage regulator and popped it in and it did not seam to work, I now think that I could have an internal regulator, in which there was a jumper pin in the old connector that had fallen out.
does this seem logical and is there a way to test for it? any help is appreciated. Thanks.

ossiblue · 06-04-2010, 06:49 AM

Just a thought but you might try this: Remove the air cleaner and turn on the ignition. Gently lift the plunger inside the throttle body--that should cause the fuel pump relay to "click" and operate the fuel pump resulting in a squealing of the injectors as they pump fuel. (Only do this test for a few seconds!). It the above doesn't happen, the micro switch in the intake or the connections to it may be bad.

Still, you mentioned you "tricked" the fuel pump into working and still no start. If you have spark and fuel is supplied, there should have been a start unless the system somehow had been depleted of fuel. The test mentioned above will bleed the injectors and you should get a start if you get the response described (squealing injectors.)

slippyd · 06-04-2010, 07:19 AM

We (my little brother, who wrote the previous post, and I) were starting to think the same thing since the wiring diagrams show the relay is wired up to the airflow sensor, but we didn't know what the exact purpose was. We'll try what you mention first thing and let you know what we find in a couple hours from now (he's still sleeping, was up late trying to figure it out).

The little bugger normally works on high-performance Hondas and Acuras, but he's taking a liking to Porsches… he especially admires how well-built everything is on them! I just hope he can get it running and get to drive it before he has to head back home to Wisconsin (he's visiting me out in Seattle).

Thanks so much for your help!

slippyd · 06-04-2010, 10:00 AM

Quick question: Is the “plunger” the same thing as the “butterfly valve”?

slippyd · 06-04-2010, 10:04 AM

Alright, did the test, relay/injectors didn't go. We noticed in the parts diagram that the microswitch was only through '75; is there a different kind of switch from '76 on? Thanks in advance.

FastFrog · FastFrog's Garage

I had the same problem w/ my 76. After a few days of checking everything, it just needed a dab of Boch grease on the points of the distributor. Ran like new

slippyd · 06-04-2010, 11:59 AM

Further inspection… we think it's the alternator (or its internal voltage regulator) on the fritz… would that make sense?

@FastFrog: Would the distributor prevent voltage from getting to the red fuel pump relay? (I understand the wiring diagrams somewhat, but get lost when trying to figure out where the voltage is coming from and where it's going…) Thanks!

ossiblue · 05:10 PM

The micro switch you mentioned that ended in 75 was for the hand throttle cars and it was for activating the cold start valve. The micro switch I was referring to is on the air flow sensor and activates the fuel pump relay.

AFIK, the test mentioned should produce fuel to the injectors regardless of the alternator condition as it is not a part of the test--only voltage from the battery. I'd suggest you pursue the issue of no fuel from the injectors/no fuel pump relay activation first, though you still may have an alternator problem. The alternator must be working for the voltage to the WUR and AAV to be present, however. Try swapping out another relay--a black one will work for the test. Or, you might wish to run the test again but this time, jump the terminals at the fuel pump relay so the pump runs with the ignition switch on. Lifting the plunger should now cause the injectors to squeal. If not, you've likely got a fuel pump problem.

Edit: After some further investigating, it appears the relay is energized when the engine is running via terminal 1 on the coil, according to the Bosch manual. I am no expert so I don't know if that applies to all post-75 CIS cars or just the "early" post-75 CIS that may (or may not) have an air flow sensor switch. Still, your engine should start if you jump the relay terminals and if it does then the fault may be in the relay or circuit to the relay.

slippyd · 06-05-2010, 07:57 AM

Circuit to replay indeed. After futzing with the ignition switch, we got it to start and run, but it still occasionally doesn't work. I just replace the electrical component a year ago with the cheaper aftermarket one available here on Pelican; I guess it's time to try the Porsche-brand one?

Thanks everyone for the help!