starting problem
 

PLEASE HELP.

I am extemeley frustrated, I have owned my 1975 911 2.7CIS for 4 months now and I still cannot drive it. I have spent over $3500 trying to fix the starting problem and I am not closer to finding the problem !!!!

I have replaced the following:

1)New Fuel distributor Head
2)New Fuel accumulator
3) New fuel filter
4) New check valve on fuel pump
5) New decel valve.
6) New fuel line from pump to accumulator.
7) 6 New fuel injectors
8) New ignition leads,
9) New spark plugs,
10) reconditioned alternator,
11) New Battery,
12) New ignition coil
13) New distributor cap,
14) New points


Last week I took my car to porsche so they could adjust the fuel/air mix on the new fuel distributor. They also did a pressure tests and a leak down test. They discovered that there was a pressure leak and rcomended I replace the injectors. BUT Now that I have replaced the injectors It still won't start.

Just to clarify my problem, the engine keeps turning over but it takes many many goes before it starts, usually draining the battery. Once the car starts it runs o.k now. If you turn the ignition off and let it sit for about 5 minutes it will start o.k but if you leave it for 15 min or longer it won't start.

Check the boot for a leak.

I wonder if it will start right up if you turn the ignition to the "run" spot, and the move the CIS "sensor plate" till you hear injectors squirting..then try to start .............Ron

I have checked all the fuel lines and there are no leaks !

Could a faulty or leaking start valve cause a drop in pressure from 2.0 bar to 0.7 bar in 2 minutes. ?

What about a faulty WUR or Throttle control pressure regulator.

These 3 things are the only things I haven't changed in the entire fuel injection system.

:confused:

check the fuel distributor, there is an o-ring that tends to (like all of them) deteriorate over time, mine was in 3 pieces, and it allowed the fuel pressure to drop dramatically. this o-ring is on the side of the fuel distributor held in place by a screw and some shims, gd luck

Thanks for the suggestion . But i have changed the o-ring and all copper washers on the fuel distributor when I put the new one in.

I don't think the WUR and Throttle pressure regulator can cause problems like this ? can they !!

My guess is the start valve . Thas all I can think of ?

jk911...did you try as I suggested on a previous thread here on this subject.........Ron

Sorry Ron,

Yes this does help get it started. In fact this is the way I have been starting it since I bought the car.

But this doesn't solve my pressure problem. There apears to still be a drop in fuel pressure when sitting.

Leaky cold start valve? I have a motorcylce that with carbs (I know, not related, but..) that have been jetted. When cold it starts fine, when warm, it floods very easily and will take a lot of cranking before it starts if it starts at all. Usually draining the battery a bit, then I let it sit. Anyways, the point is, with all the new parts you listed, you didn't mention the cold start valve. Like you, I have problems with my CIS (78 SC in my 76S), I have checked or replaced nearly all the components, but the cold start valve.

My guess (smack me on the back of the head if this is on the wrong path guys) is that the cold start valve is leaking causing your pressure drop and a very rich condition on starts, hence you nearly endless cranking before it starts. Just a thought. I'm going to try to replace mine soon. (Just got a new bike so it'll have to wait for a couple of weeks).

Souk

it takes many many goes before it starts

Sounds like a cold start problem, so I would concentrate on the cold start valve, thermo time switch wiring, ground and 12V on the yellow wire when the starter is engaged.

Even if none of the major fuel injection components were working, the engine should still fire up briefly from the cold start mixture alone as long as you had fuel pressure.

Cheers,

Joe

I think you guy's are right.

when I unscrewed the old injectors of the fuel line no fuel came out , its as if they were almost dry. The car is oviously leaking fuel. Probably the cold start valve.

would a faulty WUR cause fuel to leak out of the fuel distributor ?


Where is the thermo time switch ?

The thermo time sw is mounted on the left chain cover to the left of the distributor. It has two terminals, one is the ground for the cold start valve, the other terminal is connected to the starter circuit #50(yellow?). The cold start valve needs both the ground and the 12V from the starter to work.

Joe

Stlrj,

Which post/terminal on the t-t-switch is 12V and which is the ground? Or doesn't it matter?

Also, on a 78SC 3.0 and newer (to when I don't know) there is a thermo valve in the vacuum line to the WUR. Which post on the thermo time valve is ground and which is 12V? Again, does it matter. (Sorry jk911, don't mean to hijack you topic).

Souk

When the engine is cold and there is no pressure in the fuel line it would not take too long for the cold start valve to provide a large dose of fuel in the manifold to start the engine. Once the engine is warm the start valve is no longer involved in starting the engine. You said that it will start after being shut off for 5 min. but not 15 min. After 15 min there is no real fuel pressure and the engine is still hot enough to prevent the start valve from helping to dump fuel into the maifold thats why it cranks for ever and doesn't start. What would happen if you caped off the line to the start valve with a pressure guage and started the car to build up the pressure and check to see if it drops off dramatically without the start valve in the circuit. I would suggest the Bosch fuel injection manual to help troubleshoot the problem. I used it and a fuel injection pressure guage kit to troubleshoot my starting problem. I ended up adding an external check valve to my fuel pump to prevent loss of pressure and subsequent warm start problems.

Can I test the WUR and the Throttle pressure regulator by simply disconecting the return lines and seeing if there is a flow of fuel once the engine is turned off??

Should fuel be flowing out of the ruturn lines of these two things when the ignition is off ?

Yes, fuel pressure should be in the lines, but that is not a good check. Order a CIS tester from JC Whitney for $50 or so dollars and you'll be able to know if the system(ss) checks out. Of course with all the replacements you've made on CIS parts, get a new cold start valve and you'll have nearly replaced all the CIS parts. I would still recommend a CIS tester. And the cold start valve is about $100.

Good luck!

Souk

Well porsche have already tested the cis pressure and charged me $630 for it together with adjusting the fuel air mix.
They told me it was the injectors and the wur relay was not working. I changed these but I still have the problem.
I will speak to the mechanic who did the leak down test and ask where he measured this from?

Do you know is a faulty WUR or Throttle control pressure regulator are capable of causing a fuel leak ?? If not then I will just replace the start up valve. I don't want to waste any more money.

Souk,

Put an ohm meter on one terminal to ground. If you read resistance, that one should be connected to 12V. The other one will be grounded when cold or open above 20*C.

Cheers,

Joe