Constantly Needing Primed
 

I'm a long time viewer, but just recently signed up. I'm having an issue that I was hoping someone here might be able to shed some light on a solution, or tips to get things in motion.

I have a 1974 911, with a 1981 3.0. The car starts fine, and runs great first thing in the morning with no issues. BUT...Let's say I start it up, drive to the store miles away, that's when things go awry. It seems that once the engine is warm it just turns over, but doesn't want to start. I have discovered that if I pull off the air filter lid and prime it, the car starts right up again. Additional symptoms that are pointing me towards my guess; not all the time, but on occasion, when I'm above 4k rpm it sputters. For a 81 3.0 it also seems that it doesn't have all of the horsepower it should (or maybe it just seems that way because I'm comparing it to my 480hp Dinan BMW).

Sound familiar to anyone?

Facts:
Cold starts fine
Warms starts require priming
Occasional Pop at high RPMs

What I was thinking:
Maybe the fuel pump

Any help would be appreciated.

911 CIS Primer - Troubleshooting

Good info on this site.

regards,
al

The comparison to the Dinan BMW is not quite apples to apples…the warm start issue could be the fuel accumulator or possibly a check valve if that model has one. I had similar symptoms in my 930. I had the check valve and accumulator replaced. Got start issue went away.

Lots of more knowledgeable folks will likely chime in…

Good luck.

First thing you will need is a good CIS fuel pressure gauge set up.
Then you can begin to troubleshoot properly.
You need system pressure, cold pressure, Warm pressure and residual pressure readings at a minimum to determine what is going on.
Read the CIS for Dummies thread for sure.
Post your results of the tests and help will come your way.
The last thing you want to do is start throwing parts at it blindly.

http://forums.pelicanparts.com/porsche-911-technical-forum/758788-cis-troubleshooting-dummies.html

My 73.5 has an engine from a 3.0 with CIS. When I had this exact problem, a new fuel accumulator from PELICAN PARTS solved my problem.

Sounds like you're loosing residual fuel pressure. You will need a pressure gauge to trouble shoot the problem.

Loosing prime when the engine is warm and the 4k sputter are two different issues that need to be dealt with individually.

Let's start with the prime issue. What your symptoms are pointing to is a lack of prime from the cold start valve which makes you do it manually. You need to find out why you are not getting the cold start valve working during that critical warm period.

After your sort that out, work on the sputter issue...one thing at a time!


Cheers,

Joe

CSV doesn't fire unless car is cold. When warm restart is troublesome, it is usually due to residual pressure concerns. Let's get some test results before steering in different directions....

Thermal/time switch is stamped 45 degrees C which is actually quite warm to the touch for a cold engine IMHO. The popular misconception is that the cold start valve only operates on a stone cold engine.