Help required: 1975 911s not starting due to petrolover flooding the engine.
 

Hi,

I had bought a porsche 911s Year: 1975. Th car was in bad shape and required a lot of mechanical and body work. I believe most of the work is done. However, The engine needed a rebuilt as the Rocker Arms were broken and the exhaust and intake valves were bend, so i bought new ones and replaced them, next issue was the timing chain adjustment and that was one of the most hardest tasks so I had to call in one of the porsche experts to do the job and that job itself cost me a fortune. I have put the engine back and rewired everything, but the car fails to start as every time I try to switch the ignition ON I have noticed the engine cylinders are flooding with petrol and leaking out of the exhaust.

Can someone please tell me as what might be the cause for this? what part could be faulty or what do i have to look into? Any suggestion or help will be appreciated.

First of all, welcome to the forumSmileWavy.

Your 75 does not have a fuel pump relay set up like later cars, so the fuel pump will start to run as soon as the key is turned on. Fuel, however, should not be emitting from the injectors even with the pump running--it should be circulating back into the tank. Typically, a problem like yours is caused by 1) the plunger on the fuel distributor not being fully retracted because the arm of the sensor plate is not fully resting on its stop or the arm is hung-up , 2) the plunger itself is stuck inside the bore of the fuel distributor, or 3) the 3mm screw which is used to set the fuel mixture is out of spec.

If this sounds like "Greek" to you, it's because you may not be familiar with the components of CIS. Go to the linked site and do a little reading as it will help you understand your engine and benefit you greatly now, and in the future. 911 CIS Primer - Index

Regardless of you understanding, your issue sounds like a problem with the fuel distributor. If your mechanic is knowledgeable about CIS, he should be able to diagnose the problem fairly easily. If he isn't, you may have to help so don't be shy in asking specific questions from all here.

One more thing. Your problem can lead to hydro-lock of the cylinders so be sure all gas has been drained from the cylinders before you try to turn the engine over with the starter. Remove the plugs and turn the engine over by hand to remove the gasoline. You will have to change the oil as it is now contaminated. BTW, all the damage to the engine you describe in your post can be attributed to hydro-lock. Not saying is was, but don't risk having to repair the same damage again.

First guess is plunger in the fuel distributor is stuck open. Don't try to start until you've got it fixed or you risk setting it all on fire.
-C

Preliminary investigation........
 

You could confirm this "stuck FD plunger" by pulling a couple of injectors out and run the FP. Place the injector still connected to the fuel line in a suitable container to collect any fuel coming out. If fuel is coming out from the injector/s with the FP running, two (2) most likely culprits: stuck FD plunger at its open position or a leaking injector. Keep us posted.

Tony

To be clear, are your cylinders flooding with gas with the key only to on or are you also cranking the engine?

YES! This is a very important clarification^^.

Please reply to the above post before proceeding further as it may change the diagnosis.

Hi, that was the case earlier. When i would simply just turn the key ON the cylinders will fill up with petrol. But that issue was later resolved. After reading the feedbacks I opened the cylinders to check the injectors and noticed the petrol was being "showered" through 5 injectors into the cylinder. I have disassembled them and opened the bosh jetronic injector system. Upon further investigation by taking the set to a shop that specialises in fuel injectors servicing and repairing I was informed the seals and ruuber rings were worn out and the parts/piston needed polishing to avoid getting jammed. I have got new seal/ring kit installed and serviced the injectors. also I have drained out the old oil and put the new one. I will be installing the injectors again tomorrow and check if things have improved.
Any thing that I need to recheck or please correct me if im going off track?

Also just adding that the petrol was not leaking in one of the injectors upon initial inspection and i believed rest of them were fine too. But opon removing all of them it was noticed that the others were leaking upon just switching it ON I believe it is due to the distributor seals and valves being worn?

It sounds like your are getting the fuel distributor rebuilt. If that's the case, and it is done by someone who is familiar with CIS, then that should take care of your problem. After re-installation of the fuel distributor, however, you might wait before you install the injectors and test the system to see if the injectors still spray with the pump running. Put each injector into a glass container, have a fire extinguisher handy, and test the system. Your 75 should have the pump running without lifting the sensor plate, and there should be no fuel spewing from the injectors.