PORSCHE 996 Slow to Fire Up (Sometimes)
08-16-2022, 04:20 AM
#31
Track Day
Thread Starter
SECOND UPDATE (for anyone still interested 🤣)
PORSCHE SLOW TO FIRE UP UPDATE AUGUST 2022
The first post had a bunch of problems and fault codes listed. It was a brain dump of everything not right with the car at that time.
The issues fit in two groups.
(1). Slow to Fire up when hot AND left to sit for 60+ minutes (Starter spins Ok)
2. Check engine light with error codes from Secondary Air System and Bank 1 Vario Solenoid.
PROGRESS REPORT ON (1)
STATUS: SOME ITEMS OFF THE LIST
1. Following everyone's advice I rented a fuel pressure tester and found that the pressure is good when running but drops 10+ PSI per hour when shut off.
The assumption here is that the reduced pressure is causing the fuel in the fuel rails to vaporize while the hot engine sits, causing a vapor lock on startup. Cold Starts and restarting the car within 45 minutes are generally trouble free.
So where is the fuel pressure drop coming from?
a. INJECTORS - Many of you mentioned the Injectors. Leaky injectors are certainly one of the 996 horror stories doing the rounds. In this case, the engine was just rebuilt and the factory injectors were refurbished and tested at witch hunter. So yeeees it "could" still be the injectors but they are not at the top of the list due to their recent refurb.
b. FPS - Fuel Pressure Regulator - Some of you had mentioned a possible broken membrane in the FPS. I ran the car with the Fuel Pressure Gauge connected. With the FPS vacuum hose disconnected the fuel pressure went up to 55 PSI which apparently is what is should do 🤓🤞🏻. At the same time I checked for fuel coming out of the FPS Vacuum line and there was none. I think that means the FPS is off the suspect list.
c. FUEL LEAK - Other suggestions on possible leak points are the Fuel Filter connections (Recently replaced it with the engine rebuild) and the pipes/connections that go to the Fuel Tank and the Fuel Rail. My plan is to inspect/ disconnect some of these lines and perhaps run some some SMOKE through them to help see leaks?? This is something I have not had time to do yet. It important to note that there is never any fuel smell, ever. Perhaps the leak is very small and therefore avoids detection?? Perhaps the fuel is leaking back into the tank as in “D”.
d. FUEL PUMP - From the information have received it seems that the Fuel Pump might be running ok but the “Fuel Return Check Valve” might be allowing fuel to leak back into the tank after shutdown. Also, it may be possible that one of the hoses in the tank has a rip or hole in it from age, causing fuel to slowly leak back in to the tank after shutoff.
IS IT ELECTRICAL
A strong contingent of you are leaning more toward an electrical gremlin as the root cause……
a. CRANK SHAFT POSITION SENSOR - This was replaced with the engine rebuild. Some of you have commented that the Rev Counter needle does not bounce far enough on startup.
b. Y CABLE - This is a very popular suggestion - The Y cable is a thick gauge electrical cable in a y shape that join’s the Starter Motor and the Alternator to the car.
c. STARTER - The starter has been replaced at some point, the current one was tested OK by a local auto electric specialist at the time of rebuild.
d. BATTERY - The stock battery was replaced with a CCA half way through diagnosing this issue. It’s probably not the battery.
e. ALTERNATOR - This unit was also professionally tested prior to install.
PROGRESS REPORT ON (2)
STATUS: FIXED👍
1. The blue thread locker on the 10mm bolt holding the ground point of the Vario Solenoid was causing the a grounding issue. After removing the bolt and attacking it with a wire brush both the secondary air AND the Various cam error went away. It also made the front trunk release work every time 🥳
Thank you all for your help, this would be a treacherous and expensive experience without your help 🙌
Let me know what you think? After reading this I’m leaning toward 1D - Fuel Pump Check Valve.
The first post had a bunch of problems and fault codes listed. It was a brain dump of everything not right with the car at that time.
The issues fit in two groups.
(1). Slow to Fire up when hot AND left to sit for 60+ minutes (Starter spins Ok)
2. Check engine light with error codes from Secondary Air System and Bank 1 Vario Solenoid.
PROGRESS REPORT ON (1)
STATUS: SOME ITEMS OFF THE LIST
1. Following everyone's advice I rented a fuel pressure tester and found that the pressure is good when running but drops 10+ PSI per hour when shut off.
The assumption here is that the reduced pressure is causing the fuel in the fuel rails to vaporize while the hot engine sits, causing a vapor lock on startup. Cold Starts and restarting the car within 45 minutes are generally trouble free.
So where is the fuel pressure drop coming from?
a. INJECTORS - Many of you mentioned the Injectors. Leaky injectors are certainly one of the 996 horror stories doing the rounds. In this case, the engine was just rebuilt and the factory injectors were refurbished and tested at witch hunter. So yeeees it "could" still be the injectors but they are not at the top of the list due to their recent refurb.
b. FPS - Fuel Pressure Regulator - Some of you had mentioned a possible broken membrane in the FPS. I ran the car with the Fuel Pressure Gauge connected. With the FPS vacuum hose disconnected the fuel pressure went up to 55 PSI which apparently is what is should do 🤓🤞🏻. At the same time I checked for fuel coming out of the FPS Vacuum line and there was none. I think that means the FPS is off the suspect list.
c. FUEL LEAK - Other suggestions on possible leak points are the Fuel Filter connections (Recently replaced it with the engine rebuild) and the pipes/connections that go to the Fuel Tank and the Fuel Rail. My plan is to inspect/ disconnect some of these lines and perhaps run some some SMOKE through them to help see leaks?? This is something I have not had time to do yet. It important to note that there is never any fuel smell, ever. Perhaps the leak is very small and therefore avoids detection?? Perhaps the fuel is leaking back into the tank as in “D”.
d. FUEL PUMP - From the information have received it seems that the Fuel Pump might be running ok but the “Fuel Return Check Valve” might be allowing fuel to leak back into the tank after shutdown. Also, it may be possible that one of the hoses in the tank has a rip or hole in it from age, causing fuel to slowly leak back in to the tank after shutoff.
IS IT ELECTRICAL
A strong contingent of you are leaning more toward an electrical gremlin as the root cause……
a. CRANK SHAFT POSITION SENSOR - This was replaced with the engine rebuild. Some of you have commented that the Rev Counter needle does not bounce far enough on startup.
b. Y CABLE - This is a very popular suggestion - The Y cable is a thick gauge electrical cable in a y shape that join’s the Starter Motor and the Alternator to the car.
c. STARTER - The starter has been replaced at some point, the current one was tested OK by a local auto electric specialist at the time of rebuild.
d. BATTERY - The stock battery was replaced with a CCA half way through diagnosing this issue. It’s probably not the battery.
e. ALTERNATOR - This unit was also professionally tested prior to install.
PROGRESS REPORT ON (2)
STATUS: FIXED👍
1. The blue thread locker on the 10mm bolt holding the ground point of the Vario Solenoid was causing the a grounding issue. After removing the bolt and attacking it with a wire brush both the secondary air AND the Various cam error went away. It also made the front trunk release work every time 🥳
Thank you all for your help, this would be a treacherous and expensive experience without your help 🙌
Let me know what you think? After reading this I’m leaning toward 1D - Fuel Pump Check Valve.
08-16-2022, 09:01 AM
#32
Rennlist Member
Glad to hear the solenoid issue was a grounding issue. You must have taken the right advice and steps there to avoid a four-figure repair that might not have solved your issue.
The following users liked this post:
Man in a Garage (11-05-2022)
08-16-2022, 06:27 PM
#33
FPR is fine based on your results.
Good detective work on the grounding issue caused by the thread locker, thanks for posting that!
I thought of a way to check whether it's the injectors leaking or something internal to the fuel tank.
Create the conditions that normally result in the hard start.
Connect the fuel pressure manometer, then run your fuel pump but not the engine and get the fuel pressure up to 55psi.
Clamp hose #17 in the diagram I posted above shut and switch off the fuel pump.
Possibilities:
If the fuel pressure does not drop, then the injectors are all leak-free and you can concentrate on in-tank hoses and the pump's check valve (integral to the pump outlet).
If the fuel pressure does indeed drop, then one or more injectors leak.
In order to find out which rail these injectors are in, do as above but not only clamp hose #17 but also both hoses that interconnect the two fuel rails.
If pressure drops then AT LEAST one or more injectors in bank 2 leak. However, you cannot exclude that in addition also one or more injectors in bank 1 leak.
Only when fuel pressure stays at 55 psi whilst it dropped when just hose #17 was clamped shut you can be certain that no injector in bank 2 leaks.
If you can jerry-rig an adapter to fit the fuel supply hose to the schrader valve that the manometer is connected to and also find a way to connect the manometer to the fuel supply connector on fuel rail bank 1 (thereby basically swapping the two), you can do as above and identify whether injectors in rail 1 leak.
Remember, identifying one or more leaking injectors does not exclude that something inside the tank is amiss additionally!
Since starter motor speed is high when engine hot I'd consider the Y-cable to be fine.
Good detective work on the grounding issue caused by the thread locker, thanks for posting that!
I thought of a way to check whether it's the injectors leaking or something internal to the fuel tank.
Create the conditions that normally result in the hard start.
Connect the fuel pressure manometer, then run your fuel pump but not the engine and get the fuel pressure up to 55psi.
Clamp hose #17 in the diagram I posted above shut and switch off the fuel pump.
Possibilities:
If the fuel pressure does not drop, then the injectors are all leak-free and you can concentrate on in-tank hoses and the pump's check valve (integral to the pump outlet).
If the fuel pressure does indeed drop, then one or more injectors leak.
In order to find out which rail these injectors are in, do as above but not only clamp hose #17 but also both hoses that interconnect the two fuel rails.
If pressure drops then AT LEAST one or more injectors in bank 2 leak. However, you cannot exclude that in addition also one or more injectors in bank 1 leak.
Only when fuel pressure stays at 55 psi whilst it dropped when just hose #17 was clamped shut you can be certain that no injector in bank 2 leaks.
If you can jerry-rig an adapter to fit the fuel supply hose to the schrader valve that the manometer is connected to and also find a way to connect the manometer to the fuel supply connector on fuel rail bank 1 (thereby basically swapping the two), you can do as above and identify whether injectors in rail 1 leak.
Remember, identifying one or more leaking injectors does not exclude that something inside the tank is amiss additionally!
Since starter motor speed is high when engine hot I'd consider the Y-cable to be fine.
Last edited by hardtailer; 08-16-2022 at 07:58 PM.
The following 2 users liked this post by hardtailer:
Man in a Garage (11-05-2022),
zbomb (08-16-2022)
11-05-2022, 08:46 PM
#34
Track Day
Thread Starter
Thanks, Mike. Just seeing your reply now.
That solenoid issue has not come back at all since the thread locker fix so I think that was real.
Still working on the slow start, I have thrown a few cheaper parts at it and done some more testing (Work has been brutal)
The time has come to circle back to this issue and learn some more about the Fuel/emissions system.
I'll be running some more tests and cleaning some lines, hopefully, I will hit on the culprit.
Now that the car is on the road I have noticed a fueling issue mentioned in this weeks video
The slow start and the fueling issue could be related??
That solenoid issue has not come back at all since the thread locker fix so I think that was real.
Still working on the slow start, I have thrown a few cheaper parts at it and done some more testing (Work has been brutal)
The time has come to circle back to this issue and learn some more about the Fuel/emissions system.
I'll be running some more tests and cleaning some lines, hopefully, I will hit on the culprit.
Now that the car is on the road I have noticed a fueling issue mentioned in this weeks video
The slow start and the fueling issue could be related??
The following 2 users liked this post by Man in a Garage:
e30rapidic (11-09-2022),
Mike Murphy (11-07-2022)
11-05-2022, 08:50 PM
#35
Track Day
Thread Starter
Thank you Hardtailer!!! You ROCK!!!
Today there was time to go back to this issue and try again. Your information will be valuable in that, I really appreciate you taking the time to type all that.
With the car on the road, I'm having trouble filling a full tank, do you think the slow start and the fuel shut-off issue could be related?? (See Video)
Thank you!
Today there was time to go back to this issue and try again. Your information will be valuable in that, I really appreciate you taking the time to type all that.
With the car on the road, I'm having trouble filling a full tank, do you think the slow start and the fuel shut-off issue could be related?? (See Video)
Thank you!
11-08-2022, 12:39 PM
#36
Intermediate
Hope you figure out the hot start issue! Thinking about trying the coolant sensor for mine. I posted on facebook about my hot start issue and someone mentioned they bought a 99 and the seller said it had a vapor lock issue (similar to our issue). He replaced the starter and never had the issue since. My starter seems to turn over fine but I guess when its really hot things can change. Would be extremely hard to bench test the starter under the heat conditions as I'm sure it probably checks out cold.
11-08-2022, 04:32 PM
#37
Have you checked the fuel return vapor valve?
This one:
https://www.pelicanparts.com/More_In...CABEgKUV_D_BwE
Your symptoms seem very familiar to that valve failing
This one:
https://www.pelicanparts.com/More_In...CABEgKUV_D_BwE
Your symptoms seem very familiar to that valve failing
