Fuel injection guru's...a couple ?'s Options

[biosurfer1]

I tried asking this in another thread but it was an OT question there and didnt get much advice, so I thought I'd try here...

anyways, I was wondering wha part and how does the stock FI hold pressure in the fuel lines when the car is sitting so there is fuel immediatly when started?

I recently fixed my AAR and its working good now and hoped it would solve this other problem but no luck. It seems when the car is cold and has been sitting a while, it takes several cranks to get it going, like these isnt enough gas getting to the engine. After the 3-4th try the car starts and run normally, with the AAR open and slowly closes(as it should). I had a very similar problem in my 911 and there was a part (warm up regulator) that served this prupose and had the same symptoms with it wasnt working correctly. Does the 914 have a part like this, does the fuel pressure regulator handle this aspect? Something else maybe? I was told to check the CHT sensor and have one of those coming, but i cant see it doing much since the problem is right when the car starts and it wouldnt have much time to effect the system, or am I wrong?

any help or direction would be great...thanks!

[dimitri]

3 things that will make starting hard. 1/ defective 5th injecter,sittingin in manifold.
2/ temperature sensor under manifold on top of block: controls 5th injecter.
3/ the cht in the r head, controls enrichment. I sume the pumps cycles on when ever you turn the key on. there is a check valve built in the pump or a fitting on the pump, depends on pump used which keeps system pressure, or a low pressure, depending
on age, to prevent total drainig of supply lines, Dimitri

[JohnM]

" was wondering wha part and how does the stock FI hold pressure in the fuel lines when the car is sitting so there is fuel immediatly when started?"


Fuel pump check valve. Operates on negative pressure/flow ie. stops pressure from bleeding off through fuel pump when it is not powered/operating. John

[biosurfer1]

ok, so as I understand it, when you turn the key, the CHT sensor tells the cold start valve how much extra fuel to inject to help starting?

so if either one (or both) are defective the problem would have have the same symptoms?

[biosurfer1]

thanks johnny, now that is more along my line of work so thats easy to check...its when the problem goes electrical is when I start losing it....

[Dave_Darling]

ok, so as I understand it, when you turn the key, the CHT sensor tells the cold start valve how much extra fuel to inject to help starting?

Nope, two entirely separate systems. The CSV ("5th injector") only operates while the starter is cranking, and only when the temperature of the thermo-switch (thermo-time switch in later cars) is colder than about 40 degrees F. It simply dumps some set amount per second of fuel into the intake.

The CHT tells the ECU (the "brain") to open the main injectors for longer than it otherwise would when the CHT is colder.

A CSV that won't open shouldn't have any effect if the engine is above 40 deg F. One that is stuck open will result in a rich mixture all the time, as well as an engine that may be hard to start.

--DD