engine runs but wont restart after a short shutdown
 

I have a 1979 911 sc 3.0
It runs fine, and after driving 1/2 hour, can shut down and immediately restart right back up.
Problem: after running, and say shopping for half an hour, it wont restart. But if it sits for say two more hours, it will then start right back up and run fine.
Any ideas? Tired of sitting in parking lots waiting to go home.

Has new plugs, pop off valve has been re-sealed with epoxy to body and is new. Air box is not blown.

Welcome to Pelican.

Can you elaborate about your knowledge of the car ... how long have you owned it? How many miles on it? Any upgrades? Any work done recently? Where do you live (climate)? Have you done any testing (fuel pressures, fuel flow rate)? At a quick glance I'm wondering if perhaps the fuel accumulator might be at fault, but I don't want to jump to conclusions and see you spend $ needlessly.

Give us a full introduction to your 911.

Jason

yes, thanks. I have it about 3 years, 70K orig miles. Its a 76 but was told the motor is a later model 3.0sc motor. no upgrades other than later model engine. Was told it was tuned just before I bought it. I havent done any testing.
I Would love to know myself what year engine it is.....

some recent pics if it helps, also noticed an open fitting on left side of air box....
where could I get a hose or parts diagram of engine? THANKS!!!
http://forums.pelicanparts.com/uploa...1567536235.jpg
http://forums.pelicanparts.com/uploa...1567536235.jpg
http://forums.pelicanparts.com/uploa...1567536235.jpg
http://forums.pelicanparts.com/uploa...1567536235.jpg
http://forums.pelicanparts.com/uploa...1567536235.jpg
http://forums.pelicanparts.com/uploa...1567536235.jpg
http://forums.pelicanparts.com/uploa...1567536235.jpg
http://forums.pelicanparts.com/uploa...1567536235.jpg
http://forums.pelicanparts.com/uploa...1567536235.jpg

Check your residual fuel pressure........
 

Do you have a set of fuel gauge to do a fuel pressure test? When the engine is cold, the CSV (cold start valve) is energized and makes your motor starts and run. Once the motor is warmed up (above 113°F), the TTS (thermotime switch) will cut off the ground contact of the CSV and will be disabled until the motor cools below 113°F.

With the CSV off, your warm engine will rely on the residual fuel pressure to go get it running. If your residual fuel pressure is too low when the CSV is disabled, the motor will struggle to get it running again until it cools down. There are several known culprits causing residual fuel pressure loss. The 2 most common culprits are FP check valve and fuel accumulator.

Tony

I dont have fuel gauges for testing, should I get some?
Should I replace FP check valve?
I do hear the fuel pump running upon warm try restart....

Also, can you tell me on the 7th pic if there should be a hose connected to the bib on the left side of air box? Or should it be plugged? Just noticed it recently and seems would let unfiltered air into intake....

So how do you check for residual pressure?

After shutting your warm engine, pop the engine lid, remove the air filter and put your hand under the sensor plate and push up on it to see if you can feel any resistance. If no resistance then you have no residual pressure and likely caused by a leaky FP check valve.

Cheers,

Joe

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

Read through this - there is a wealth of information contributed by many to this excellent thread.

.. and listen to Tony (boyt911sc) - he is the guru of CIS

Jason

PS - When was the last time that the oil & filter were changed? - the filter looks like it has a lot of years on it ...

will check plate for pressure.... thanks! Where is the best place to find all parts or hose diagrams? I only see the parts here on pellica but no full diagrams....

Can anyone tell me if a hose is supposed to be connected to bib on left side of air box in pic seven above or if it should be capped off?
Seems like unfiltered air can get into intake...

Plug the hole on the airbox in your photo.
Download the parts diagrams directly from Porsche classic.

You are guessing.......
 

Joe,

The FP check valve is one of the culprits. After all these time you are still struggling to troubleshoot systematically. You use a pressure gauge to identify the culprit and avoid doing guess-work troubleshooting. What happens after you replaced the FP check valve without verifying it as the culprit and the problem still there? Change the FP? Change the fuel accumulator? You can not rely on luck all the time specially for correctly diagnosing the problem/s.

Tony

Disaster waiting in line........
 

79POR911,

Do these fuel injection lines been cut and mended? They look very scary to me to have such fuel injection lines in a 911. This is like having a ticking time bomb in your car. Replace them when you a chance before it is too late.

Picts?

Id say 90% chance its the accumulator. the check valve is a crappy job but a good oportunity to change the fuel hose at the tank which is probably nessesary by the looks of your engine bay

I took a look at mine - I think it may be for a hose to/from the charcoal canister, but I'm not 100 pcnt sure.

Jason

I took a look at mine - I think it may be for a hose to/from the charcoal canister, but I'm not 100 pcnt sure.

http://forums.pelicanparts.com/uploa...1567561803.jpg

Jason

79por,

To be clear, boyt911sc is referring to this.



http://forums.pelicanparts.com/uploa...1567582466.jpg

it appears so! Did not realize it when I bought the car and that it was not ok to do. dohhh.....
But seems I have more problems....

thanks. This diagram shows it being plugged, has every diagram and parts numbers you could think of....
http://www.***********.com/porsche-parts/911-78-83/porsche_911_parts.php

Not sure but will add to the list oil filter change....

After reading your links for vacumn leak test, i tried removing the oil filler cap during warm idle, no change in RPM's...... bad
Then I put my hand over air intake breather hole and no suction......no change in RPM's
Obviously this is bad....Any suggestions?

pics of car
 

I really need to get this car right, I love it!http://forums.pelicanparts.com/uploa...1567607714.JPG
http://forums.pelicanparts.com/uploa...1567607714.JPG
just sharin lol

I'm like Tony . i like to use the tools to identify as much as possible before using the parts shotgun ..

But tony i do have one question that maybe you answered here that i'm just missing . Lets say you are measuring residual and it is dropping, much like we suspect. What troubleshooting can you use to isolate whether it is the FP check valve or the accumulator that has failed ?

FP check valve is a huge PITA and the accumulator is expensive . Neither job i would want to do without knowing for sure.

TIA

Had the exact same problems you describe and it was the fuel accumulator for my 1981 SC.

CIS troubleshooting........
 

theiceman,

Identifying the source of residual fuel pressure loss is done by isolating the suspect component and do a pressure test. For example, checking FP check valve in situ:
1). Install a pressure gauge kit with a shut-off along the main fuel delivery line.
2). A suitable location is before the fuel accumulator. Install the pressure gauge with shut-off valve in series.
3). Test run the FP for several seconds and switched it off and immediately shutoff the the valve.
4). Record the pressure reading on the gauge after closing the valve. Record the pressure reading on the gauge after 10, 20, and 30 mins. Refer to residual fuel pressure data in the manual and compare your data.
5). If the residual fuel pressure is below the specification, you found the culprit. However, if it passed the test move on to the next test.

Testing the fuel accumulator in situ:
1). Install the pressure gauge kit after the fuel accumulator. Repeat the above test. If the fuel accumulator is not leaking, you will get the same test results.

The fuel accumulator could be easily tested on the bench too. Place the FA in a glass filled half way with water or enough water to submerge 50% of the FA in water. Manually blow air to one of the top ports and blocking the other one with your thumb or a rubber stopper. Air bubbles will be coming out from the water if the FA is defective.

There is another culprit that you may like to test too. The FD primary pressure regulator. But we will defer the discussion on this because the earlier FD models are different from the later one found in SC’s.

You will often read people saying “I replaced the fuel accumulator and fixed the problem”. That is well and good if the culprit was the FA. I don’t recommend replacing CIS components which are expensive without testing and verifying to be bad or defective. Unless you don’t care to spend unnecessarily.

Tony

great info Tony, so basically you are just moving the shutoff between the accumulator and the FP . very good thanks

i never thought if using my CIS pressure gauges beyond the basic system, pressure control pressure, and residual pressure checks

I will have to keep this on in mind

Thanks again .