1976 911S No Start Flooded

[unzio]

Hi everyone!

I've been dealing with this intermittent problem for 3 years now! I've had enough!!! Every once in a while, it won't start. It doesn't matter if it's hot or cold, if the engine is warm or not. You turn the key, it cranks but doesn't start. It has good spark, is cranking relatively quickly, but I smell raw fuel. I pulled the plugs quickly once to see if the cylinders were filled with gas, but they were not wet.

The car has the pop-off valve installed, and it is not loose. The car also has a Jacobs Ignition system, but as I said before, spark is not the issue.

The funny thing is that it will actually start if you get a good bump start. Then it runs like a bag of crap for a few seconds while (I'm assuming) the plugs clean up, and it's fine after that. Eventually it will happen again, but it could take hours, or days. Help!

[bassfishman]

Check for leaking injectors, cold start valve and WUR control pressure. My car had the exact same problem and it was a combination of all three.

Runs great now.

[boyt911sc]

Originally Posted by bassfishman

Check for leaking injectors, cold start valve and WUR control pressure. My car had the exact same problem and it was a combination of all three.

Runs great now.

Check the fuel pressures (control, system and residual). Check for air/vacuum leak/s. You could do an effective troubleshooting if you eliminate the guess-work. Test and confirm. Bad fuel injector could be the culprit, so test and verify.

Tony

[Targalid]

Tony said it. You need to do diagnosis. These are great cars because the fuel injection is all mechanical with few electrical parts that fail. It is simple if you check the fuel pressures and eliminate air leaks. Good luck!

[Walter_Middie]

The funny thing is that it will actually start if you get a good bump start.

I think this may be a clue. If your starting circuit is drawing too much juice, it can interfere with the ignition. A weak spark may be your issue. Is the battery old? Could the starter be drawing too much current?

I'd put a volt meter on it next time it doesn't start - if it is intermittent, hook up a volt meter inside the car so you can monitor it all the time. If the voltage drops a bunch and you can't start the car - you either have a bad battery, bad starter, or a bad connection somewhere.

[NeedSpace]

When does it happen? Is it after the car has been sitting for a while or is it the next day after running it?

[unzio]

Thanks for all the replies everyone. NeedSpace, the car could act up at any time.

I'll fill everyone in on the latest developments. I had the starter bench tested, and although it still worked, my rebuilder strongly recommended freshening it up. It only cranked at 200 rpm prior to the rebuild, which I felt was a little slow. It also drew 150 amps of current, and the voltage was good, so everything pointed to a worn out starter. Anyway, I've installed it, but it hasn't fired yet because the plugs were very fouled from all the previous attempts to start the car. At least it sounds like it's cranking a little faster.

I removed the plugs and now I find them slightly wet with fuel, but once again, maybe because they were so fouled that they don't fire anymore? I'm not sure. I am sure that I have a decent spark, so it should catch. We'll see.

Now, to muddy the waters even further, while the plugs were out I decided to do a compression test. Here are the results: cyl1- 110psi, cyl2- 150psi, cyl3- 170psi, cyl4- 140psi, cyl5- 70psi, cyl6- 150psi

So.....perhaps I've wasted my time on this engine?

[unzio]

Just a quick question...should the fuel pump run with the key in the on position? Or should it run only when the air flow meter moves?

[boyt911sc]

Originally Posted by unzio

Just a quick question...should the fuel pump run with the key in the on position? Or should it run only when the air flow meter moves?

Unzio,

The FP should not run @ ON position (ignition switch) but if the AFS (air flow switch) is either disconnected or open, it would cause the FP to run at ON position. There is a very simple test to find your problem. Check for ground at terminal #85 (FP relay socket). Keep us posted.

Tony

[unzio]

OK guys, here's the latest; my fuel pump was running with the key on. By accident, I stumbled across the fact that it should not operate in "run", as well as boyt911sc stating that as well. I diagnosed the circuit and found that the relay was inoperative. Because of the quirky, yet brilliant design of the fuel pump circuit, a dead relay will turn the pump on in "run" when it should only turn on in "start" (until the engine fires up of course).

So, I swapped the horn relay for the fuel pump relay and now it works the way it's supposed to. So, my theory is that the engine floods because the pump turns on and injects fuel into the cylinders prior to the engine cranking. Now, that doesn't seem like it should be a huge issue, but perhaps because I have a couple of weak cylinders, and because of slower than normal cranking due to a worn out starter, this causes the the flood and no start that I experience.

Of course, God had a hand in testing my theory, as my freshly rebuilt starter has a defective solenoid and doesn't always crank the engine. When it doesn't crank, I hear the pump turn on, and of course then it will not start when it finally does crank. I then pull out the fuel pump relay to clear the flood, it fires and dies when it runs out of fuel. Then I plug the relay back in and it starts right up. Confusing enough for you?

The question is...should the injectors spray fuel into the cylinders with the pump running and the engine not running. Does the fuel distributor not hold the fuel back until airflow is sensed? The switch in the air flow flap is working, by the way.

[psalt]

No, your theory is all wet. No fuel should be spraying into the engine at rest with the fuel pump running. If the FD is working properly, the air flow sensor must be lifted for fuel to get to the injectors.

What does happen is that every time you turn the key to "start", whether the defective starter cranks or not, the CSV is spraying fuel into the manifold. It is "normal" and "expected" to flood the engine on repeated crank attempt with a intermittent solenoid. The thermo time switch is not "fast enough" to disable the CSV with intermittent current.

[unzio]

Thanks psalt

To clarify, I was wondering if this fuel pump always on situation would cause the flood and no-start with a working starter, because that was what I experienced for the past little while (before the new starter).

I could see how it would happen if the engine did not crank after repeated attempts, but my starter worked properly before today.

[psalt]

Only if you have another problem, like a misadjusted air flow sensor, stuck plunger, or leaking CSV. My advice is to correct your relay/wiring problem and test the safety contact switch. How long are you cranking the engine, it should fire almost immediately ? Have you tested the CSV for leaks and the thermo time switch ? If you have poor compression, weak vacuum, incorrect timing and /or weak spark, you could be flooding it just from multiple prolonged starting attempts. Has this car been driven under load until hot in the past three years ? If you have pushed that much raw fuel through the engine without running it under load, your oil is probably contaminated.

[unzio]

Paul, the car is pretty much a daily driver unless there is snow on the ground! It usually runs well, save for this intermittent no start/flooding issue.

I'm waiting for my starter to come back tomorrow, then I'll put some miles on it and see if the relay did the trick. Thanks for all your help everyone, I'll keep you posted.

[boyt911sc]

Originally Posted by unzio

OK guys, here's the latest; my fuel pump was running with the key on. By accident, I stumbled across the fact that it should not operate in "run", as well as boyt911sc stating that as well. I diagnosed the circuit and found that the relay was inoperative. Because of the quirky, yet brilliant design of the fuel pump circuit, a dead relay will turn the pump on in "run" when it should only turn on in "start" (until the engine fires up of course).

So, I swapped the horn relay for the fuel pump relay and now it works the way it's supposed to. So, my theory is that the engine floods because the pump turns on and injects fuel into the cylinders prior to the engine cranking. Now, that doesn't seem like it should be a huge issue, but perhaps because I have a couple of weak cylinders, and because of slower than normal cranking due to a worn out starter, this causes the the flood and no start that I experience.

Of course, God had a hand in testing my theory, as my freshly rebuilt starter has a defective solenoid and doesn't always crank the engine. When it doesn't crank, I hear the pump turn on, and of course then it will not start when it finally does crank. I then pull out the fuel pump relay to clear the flood, it fires and dies when it runs out of fuel. Then I plug the relay back in and it starts right up. Confusing enough for you?

The question is...should the injectors spray fuel into the cylinders with the pump running and the engine not running. Does the fuel distributor not hold the fuel back until airflow is sensed? The switch in the air flow flap is working, by the way.

Unzo,

For fuel to be delivered through the injectors, the following should occur:
1). FP running and delivering sufficient fuel prressure.
2). FD's plunger is displaced (moved) upward by the air flow sensor plate.
3). For sensor plate to move upward, the engine must be starting/running to develop the suction force to lift the AFS.

The above are the ideal conditions for fuel delivery for CIS through the injectors. But other scenarios where fuel could be delivered by the injectors are:
1). FD plunger stuck at open position with FP running.
2). FD plunger overly adjusted (RICH) with FPrunning.

So in summary, for fuel to be delivered by the injectors (engine not running) needed two (2) conditions:
1). FP running (normal condition or defective FP relay).
2). FD's plunger is RAISED/LIFTED (either stuck OPEN or overly rich setting).

Tony