When is a "check valve" not a check valve???
 

I guess when it's for a 77-79????

So experiencing hot start problem and little/no residual pressure, I figured I'd replace the fuel pump check valve.

Just happened to have a new one in the tool box.

p/n 91160821100

http://www.pelicanparts.com/cgi-bin/PartsLookup/search.cgi?command=show_page&Catalog_Name=911_USA_ 78_83_KATALOG&Illustration=201-10&Line_Item=2


Got down there removed the skid plate and removed the 30 year old "check valve" but it WASN'T a check valve. Just a fitting!!

Looked at the new part and sure enough not a check valve either!!!

So what holds the pressure? Just the fuel accumulator?? It does have the bottom return line that is not present in 80-83 version

Does 77-79 really not use a fuel pump check valve because of the different accumulator design?

The check valve screws into the neck of the fuel pump.

The 1973.5 T and 1975 through 1979 CIS systems have the check valve built into the pump. In 1974 the check valve is in an external banjo fitting mounted on the pump output and starting in 1980 the check valve was again in an external fitting mounted to the pump output.

Here's an illustration to go with Jim's answer.

The fitting on the right is the adapter which accepts a 10 mm banjo. On the left is the check valve (12 mm) used from '80 onward.

http://forums.pelicanparts.com/uploa...1204514648.jpg

Like tsuter, I would be very interested in a solution to the leaking internal check valve that did not involve replacing the fuel pump.

Install a 1974 banjo fitting; see this thread for more information:


http://forums.pelicanparts.com/porsche-911-technical-forum/277703-fuel-distributor-check-valve-73-5t.html?highlight=1974

So I would cut away the crimped furrule securing the current banjo and install the '74 banjo/check valve. Any issues using a hose clamp (Norma Schellen, not cheapo spiral drive) on the high pressure side of the CIS?

Thanks for pointing this out, Jim. I thought I had researched all the 78-79 check valve alternatives (1- JW's in-line check valve on the back of the CIS distributor, 2- Upfixin's 944 check valve on the pump and 3- switching fuel lines to work with the later (12 mm) pump).

Interesting. 77-79 have fuel pump internal checkvalves......not external like 80-83???

That explains why the replacement part is just a fitting.

Time to see if that's the issue or fuel accumulator before I go cutting off banjo bolts....

Hot start vapor lock. :(

So some follow up notes for future:

Low residual fuel pressure after a hot run. Wait four-six hours all OK!!!

I had removed one injector (while hot - engine would crank but not start) and lifted the sensor plate. Great fuel pump running but only an air hiss at the injector. No fuel!!!

When cold, no issues starting. Everything was fine Normal cold start fast idle..... pressures good. Injector out, lift sensor plate - nice fuel spray at injector.

Vapor Lock!! on Hot restart.

Replaced Fuel Accumulator - problem solved. Internal diaphragm failure/leaking.