77 Engine Runs Then Doesn't
 

I have reading posts about CIS and just discovered Jim William's CIS Primer but thought it would get some head-start advice from some CIS experienced people.

1977 911S that is being revived after no use for 18 years (indoor storage). Fuel tank and filter are new. The engine takes a few cranks to start when cold and runs well when it does. 1500 RPM, revs strong and snappy no backfires. Warm up seems normal and the idle gradually settles to about 750. Then the engine acts like its running out of gas then stalls. It will restart right away but won't hold an idle. After a few times of starting and stalling, it won't start at all unless it sits for 5 minutes. After the short wait, it starts up and will run for about 5 minutes then stall again and not start. BTW, on the initial cold start, it idled fine and did not stall until fully warmed up. I checked if the fuel pump is getting power during the no start period and it is.

My initial thoughts are a clogged fuel filter. I cleaned out the lines when I replaced the tank but maybe some junk loosened up. I'll get one today and check that and check fuel pressures. But it also seems like the issue is temperature related because it will run a long time when cold but not when warm. Thanks for any help.

Basic tests..........
 

Avanti,

From your description, I did not notice any major problem to get this '77 back running well. Go test the fuel pressures (control, residual, and system) by running the FP only. No need to run the engine. If you are not yet familiar about this procedure (FP test run) let us know. BTW, lately people are always blaming the fuel filter for their CIS problem/s. And they replaced good working fuel filter because they think or suspect it. Get a set of fuel pressure gauge kit and use it.

Could you check also the ID numbers of the WUR and FD? And don't forget to write down the ambient temperature (approx.) when you measure the cold control pressure (WUR electrical plug disconnected) over a time span of 5 minutes.

Refrain and resist the temptation to tinker the mixture setting at this point. No need to touch it yet. Keep us posted.

Tony

Just to reetirate what Tony said, DO NOT DO ANYTHING ELSE UNTIL YOU HAVE A CIS PRESSURE GAUGE. Without it and associated numbers it will provide you the likelihood of a wild goose chance are very likely.

Thanks for the replies.

I am NOT familiar with the FUEL PRESSURE TEST RUN. I have quite a few books from the seller, some that appear to be copies of the shop manual. I'll look through them but if possible, please explain or direct me to the instructions if they are available. THANKS!

CIS troubleshooting 101.............
 

Avanti,

If you have the desire to learn and work on your car, you found the best place to start your quest. Everything you wanted to know is available at the tip of your fingers. There are no CIS problems that these guys can not diagnose correctly provided you communicate well. Feedback is critical. Since you are doing the work, we rely mostly on your feedback to get to the bottom of the problem.

Start reading posts, technical bulletins, books, etc. There is no substitute for knowledge. The more you get informed the better you will be able to ask pertinent questions. There is no such thing as stupid questions only stupid answers!!!!!!!

Your priority now is to get acquainted and familiarized yourself with different parts of the engine and its CIS (constant injection system) components. Search for ACRONYMS such as WUR, AAR, TTS, FD, FP, etc. these are the lingo for which we will be using regularly. Don't hesitate to ask. Use the PM or email to contact anyone of us here. Have you posted a picture of your car? That's a common protocol being observed in this forum. So let's go back to work and get started.

Tony

Ok,

I'm back after a few life distractions.

WUR # is 033
FD is 050954 and the three following numbers alone in a silver framed area of the tag look like 525 or 528.

System pressure: 4.5 Bar

WUR pressure 4.5 Bar - cold 70 degrees f and WUR unplugged

WUR plugged in after 5 minutes 4.2 Bar and gauge needle flutters a little.

Ran engine for 15 minutes, WUR pressure at 3.9 Bar but engine did not stall this time and and act like it was running out of gas.

Residual pressure: Zero. Drops like a rock to zero immediately after shutting off the engine. Same with pressure gauge valve open or closed. Check valve?

When running system pressure is 4.5 bar.

Also, the engine did not drop to 750 rpm automatically when warmed up (like it did earlier). After 15 minutes of running or longer than it took for it to stall the last time I ran it, I revved the engine to "kick" the idle down which it did and then it would not hold an idle. But it would restart if I held my foot lightly on the throttle. The earlier time it would not restart. Different from my earlier post. The engine does not run well when cold but does when warm. Takes a few tries or cranking sessions for it to start when cold. BTW, I'm in San Diego so "cold" is 65-70 degrees :)) Got dark and I had to stop.

So... I think I may have more than one problem.

Bad WUR and/or power supply? It does not get warm or hot at all. After reading what it does, I would expect it to get hot. Or could it be gummed up and varnished from sitting and old gas?

Bad check valve? I have read the fuel pump check valve is on the output side of the fuel pump. If it is the part that the fuel line banjo fitting connects to, mine has no guts or innards.

Need to check for vacuum leaks. Likely culprits?

Is there an idle air control valve or similar or a solenoid throttle stop/idle compensator that could not be holding the throttle open enough after warm up.

Need to read up more on this system. I know modern fuel injection but not CIS. I have the CIS Primer, the Probst book and Watsons book.

Thanks for any suggestions.

Paul

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

CIS troubleshooting........
 

Paul,

Look again at the FD name tag just behind the air box. It is the printed number like 0-438-100-??? Which is not easily visible. These are not the stamped numbers but the lightly printed part number on the name tag. Use a pen light to get a good look of the name tag and view at an angle. What was your cold control fuel pressure?

You have residual fuel pressure problem based from your information. Three (3) likely culprits are: FA (fuel accumulator), FP CV (fuel pump check valve), and FD CV (fuel distributor check valve). You could test them individually and do not replace part/s unless tested and verified defective.

Fuel accumulator is easy and simple to test. Remove it from the car and don't worry if you notice some small amount of fuel coming off the bottom fuel hose. That's normal and commonly mistaken as the culprit. You need to test it. Remove the fuel inside the FA and allow to dry. Use compressed air to dry the interior of the FA (top and bottom sections). Pressurized the bottom port lightly about 5 to 7 psi. There should be no air leak coming throught the diaphragm (membrane). Another test is to fill up the FA with liquid (water or alcohol) and watch out for any sign of seepage.

You should not step on the gas pedal to help the engine to run during the start phase. It should start and idle after turning the ignition switch to START position. No assistance needed unless you have a severe mixture problem like a big vacuum leak some where. If you have any question, ask.

Tony

Thanks Timmy for the Dummy thread. Good Stuff.

Tony, the accumulator is good, I tested it when the fuel tank was replaced.

Still curious about the check valve. As mentioned, if it is the fitting the fuel line supply hose attaches to on the fuel pump, mine has nothing inside.

i don't think you are checking the pressure right.
the hose with the vlave on it goes to WUR.

warm pressure should be 3.6bar. there is also a vacuum hose that goes to the WUR. if you remove that the control pressure should drop to 2.8bar. or if you check the warm pressure with the engine off it should be 2.8bar.

i don't remember system pressure but 4.5 seems low.

Control fuel pressure chart..........
 

Paul,

Test run the FP and measure the cold control fuel pressures till it stabilizes to WCP (warm control pressure). Measure and record the control pressure at:

Start (WUR electrical connection unplugged) @ zero. Take the pressure reading and record. Plug th electrical connector of the WUR and start the count (time)...........record the pressure readings:
After 1 min.
After 2 mins.
After 3 mins.
After 4 mins.
Stop after 5 mins.

Perform the above test using the FP and make sure you have a fully charged battery. No need to run the engine for this particular test. I am interested how your WUR behaves during the first 5 mins. during a cold start. Make sure the car has not been started atleast 8 hours before. Please post your data. Thanks.

Tony