PORSCHE 996 Slow to Fire Up (Sometimes)

Porsche Puzzle Anyone? If anyone is willing to try to solve this one I promise to share the answers. Hopefully, it�s something common we can all learn from. This 2001 Carrera 3.4 was my first engine rebuild and a great education in the magical world of mechanics. Here is a link to the video in question: You Tube The problem the car is having is the slow-to-fire and slow-to-idle issues shown in the video. To give you an idea of how common the issue is, out of 30 starts at various times over a few days the car said tarted normally 20 times, was slow to start 5 times, and was slow to idle 5 times. It rarely does it on the first start of the day, it rarely does it if previously started within the last 20 minutes. If it has ran already and then sat for 1-3 hours, it�s more likely to have the starting problem. So far I have tried a few things in an attempt to resolve or diagnose the issue. What I have tried already: 1. I threw a new Crankshaft Sensor at it, no improvement. 2. I threw a new Duralast Gold 730 CCA battery at it, slight improvement, maybe. 3. Vacuum System tested with smoke, no leaks. 4. Purge valve disconnected from intake (Holes Plugged). No Improvement. (what I�ve learned is that it can be possible for the purge valve to get stuck open causing excess gasoline vapors into the mix on startup) 5. Activated Secondary Air Blower using a Durametric, sounds like a hair dryer on high. I think that means it�s good? 6. Using a cable clamp meter I did a �Starter Current Draw Test� across the positive cable in the frunk with the Fuel Relay Removed. The result was 160 amps with the new battery. What I have not Tried: I have not done a voltage drop test to check the Y-Cable, does anyone know how to do that?? What I think it might be: 1. The Y-Cable that connects between the B+ junction box, Alternator, and starter seems to be a common issue due to voltage drop as a result of inner corrosion. I feel this cable or some other grounding/electrical issue might cause the starting issue and possibly the faults. 2. Fuel Pump or Relay - Prior to install the tank was drained using the car's own pump, the rate was within spec though I have not tested the Fuel Pressure while functioning? 3. Perhaps there is no electrical gremlin and the codes are accurate, throwing a new secondary air blower and bank 1 variocam solenoid might fix it? Other things that may not be related: Other electrical issues that make me suspicious of some rogue grounding point are as follows. 1. The rear Engine Hatch button always works, the frunk button sometimes does nothing, if it doesn�t work, pressing the button will cause the interior lights to shut off? 2. The door locks behave strangely? When I first put the engine in and powered the car up the door lock button (Dash) would not do anything plus there was an error code in the durametric. Now, for no real reason the error code is gone and the button on the dash kinda does something (Clicks and lights) 3. The blower fan for the heat and ac does not run. the fuse is ok, the screen and dash button work but no fan. Just for clarification, this car was non running when I purchased it. I don�t know if these problems have any history prior to the engine rebuild. Wow! thank you for reading to the end 🙌 I appreciate any insight you can provide to solve this issue, You Rock🤘😎

one question, slow cranking ? or normal cranking ?

Very recent thread with similar symptoms - applying gas helps the car start: https://rennlist.com/forums/996-foru...ard-start.html I think it's time for you to start monitoring your fuel pressures.

Thank you for your help 🙌 The cranking is generally a decent speed even when it does not fire up. here is a video that shows the good the bad and the ugly. You Tube

Yea sounds like that other thread. Since its cranking strongly I'd not suspect the Y cable or ground strap or other major electrical things, that should give you a slow crank that isn't fast enough to start the engine.

Awesome Thank you!! That was a great threat. I rented a fuel pressure tester from Autozone this morning, I'm hoping to play with it tonight 🥳

Y cable and starter, the other guy hasn't replaced his starter yet either and I am yet to be proven wrong that is not the problem.

Starter...do it first.

Quotes source posts: 18247794, 18248241

I'll take that bet and give 10 to 1 odds...

Leaking injectors I think (as I did in the other thread). I base this on the observation that A little gas (=more air into the cilinders) helps. It gets the mixture less rich just enough for the fuel that has dribbled into the intake from bad injectors to burn together with the injected fuel. In case of a bad fpr that no longer holds pressure after engine shut-off, then the pressure is built back up during cranking but during that time the injectors (also in-spec ones) will inject too little fuel to ignite. This fuel overrichens the mixture just like the droplets from leaking Injectors do. A little gas in this latter case has the same effect as described above. Of course it could be more than 1 thing wrong but based on the speed the engine is turned over I see no symptoms of bad starter or voltage drop due to a corroded y-cable.

+1.

Had a similar issue, turned out to be the coolant sensor.

Quotes source post: 18250204

Interesting and very plausible. Any details on the before and after test data?? Or was this a SWAG method that worked..lol

After much troubleshooting, Jake mentioned it as a possibility.

Fuel pump check valve, leaking injectors, or coolant sensor come to mind. You can put to rest the leaking injectors or check valve with a simple fuel rail pressure check, turning the key on it should prime to 60psi and hold. If it drops quickly either the check valve in the pump is bad, or possibly the in tank feed line is partially ruptured. If it drops slowly a leaky injector may be the culprit, although the car may run rather rough in the first few seconds of operation with too much fuel in the cylinders affected. Coolant temp sensors are relatively inexpensive and probably not a bad idea to replace if that is a concern. When I have a temp sensor failure it seems to flash a red light in the temp gauge and starting is difficult when warm.

Quotes source post: 18252831

So SWAG ..... I gotcha..

AHA!! I was hoping you might reply to this post UPDATE Hello Everybody!! - Thank you all for your help 🙌 Many of your pointed to the fuel system. After renting a Fuel System Pressure Tester I found that there is a pressure drop that is certainly contributing to these issues. Left overnight the Fuel Pressure drops to zero, When Cranking the system can momentarily achieve 55 PSI Idle pressure is 48 PSI After shut down the pressure immediately drops to 43 PSI The fuel pressure drops 10psi after 60 minutes My understanding is the fuel pressure should be around 55PSI when sitting and 48 PSI at idle. The fuel pressure should drop a maximum of 2PSI per hour. Reading a post on Rennlist from Porschetech3 explained that when the fuel is hot and does not have enough pressure it boils away creating a hard start. I�m learning about the different parts within the fuel system. Here are the items that have been checked or replaced within the last 1000 miles. FUEL VOLUME - CHECKED OK FUEL QUALITY - 3+ Tanks of Chevron since rebuild FUEL FILTER - REPLACED FUEL INJECTORS - REBUILT & TESTED (Witch Hunter) Based on all fo your advice I think that leaves: FUEL CHECK VALVE / FUEL NON RETURN VALVE (Are these the same thing?) FUEL PRESSURE SENSOR SPLIT HIGH PRESSURE HOSE ON FUEL PUMP SEND I should also mention that the car will not let you fill past 3/4 tank in case that�s related.

Thank you for your help 🙌, As you can see from the update below, you are right on the money. Is there a test for the check valve? Here is the update... UPDATE Hello Everybody!! - Thank you all for your help 🙌 Many of your pointed to the fuel system. After renting a Fuel System Pressure Tester I found that there is a pressure drop that is certainly contributing to these issues. Left overnight the Fuel Pressure drops to zero, When Cranking the system can momentarily achieve 55 PSI Idle pressure is 48 PSI After shut down the pressure immediately drops to 43 PSI The fuel pressure drops 10psi after 60 minutes My understanding is the fuel pressure should be around 55PSI when sitting and 48 PSI at idle. The fuel pressure should drop a maximum of 2PSI per hour. Reading a post on Rennlist from Porschetech3 explained that when the fuel is hot and does not have enough pressure it boils away creating a hard start. I�m learning about the different parts within the fuel system. Here are the items that have been checked or replaced within the last 1000 miles. FUEL VOLUME - CHECKED OK FUEL QUALITY - 3+ Tanks of Chevron since rebuild FUEL FILTER - REPLACED FUEL INJECTORS - REBUILT & TESTED (Witch Hunter) Based on all fo your advice I think that leaves: FUEL CHECK VALVE / FUEL NON RETURN VALVE (Are these the same thing?) FUEL PRESSURE SENSOR SPLIT HIGH PRESSURE HOSE ON FUEL PUMP SEND I should also mention that the car will not let you fill past 3/4 tank in case that�s related.

Hello John, Thank you for your help, here is an update UPDATE Hello Everybody!! - Thank you all for your help 🙌 Many of your pointed to the fuel system. After renting a Fuel System Pressure Tester I found that there is a pressure drop that is certainly contributing to these issues. Left overnight the Fuel Pressure drops to zero, When Cranking the system can momentarily achieve 55 PSI Idle pressure is 48 PSI After shut down the pressure immediately drops to 43 PSI The fuel pressure drops 10psi after 60 minutes My understanding is the fuel pressure should be around 55PSI when sitting and 48 PSI at idle. The fuel pressure should drop a maximum of 2PSI per hour. Reading a post on Rennlist from Porschetech3 explained that when the fuel is hot and does not have enough pressure it boils away creating a hard start. I�m learning about the different parts within the fuel system. Here are the items that have been checked or replaced within the last 1000 miles. FUEL VOLUME - CHECKED OK FUEL QUALITY - 3+ Tanks of Chevron since rebuild FUEL FILTER - REPLACED FUEL INJECTORS - REBUILT & TESTED (Witch Hunter) Based on all fo your advice I think that leaves: FUEL CHECK VALVE / FUEL NON RETURN VALVE (Are these the same thing?) FUEL PRESSURE SENSOR SPLIT HIGH PRESSURE HOSE ON FUEL PUMP SEND I should also mention that the car will not let you fill past 3/4 tank in case that�s related.

Your absolutely right! 🙌 Here is an update.... UPDATE Hello Everybody!! - Thank you all for your help 🙌 Many of your pointed to the fuel system. After renting a Fuel System Pressure Tester I found that there is a pressure drop that is certainly contributing to these issues. Left overnight the Fuel Pressure drops to zero, When Cranking the system can momentarily achieve 55 PSI Idle pressure is 48 PSI After shut down the pressure immediately drops to 43 PSI The fuel pressure drops 10psi after 60 minutes My understanding is the fuel pressure should be around 55PSI when sitting and 48 PSI at idle. The fuel pressure should drop a maximum of 2PSI per hour. Reading a post on Rennlist from Porschetech3 explained that when the fuel is hot and does not have enough pressure it boils away creating a hard start. I�m learning about the different parts within the fuel system. Here are the items that have been checked or replaced within the last 1000 miles. FUEL VOLUME - CHECKED OK FUEL QUALITY - 3+ Tanks of Chevron since rebuild FUEL FILTER - REPLACED FUEL INJECTORS - REBUILT & TESTED (Witch Hunter) Based on all fo your advice I think that leaves: FUEL CHECK VALVE / FUEL NON RETURN VALVE (Are these the same thing?) FUEL PRESSURE SENSOR SPLIT HIGH PRESSURE HOSE ON FUEL PUMP SEND I should also mention that the car will not let you fill past 3/4 tank in case that�s related.

UPDATE Hello Everybody!! - Thank you all for your help 🙌 Many of your pointed to the fuel system. After renting a Fuel System Pressure Tester I found that there is a pressure drop that is certainly contributing to these issues. Left overnight the Fuel Pressure drops to zero, When Cranking the system can momentarily achieve 55 PSI Idle pressure is 48 PSI After shut down the pressure immediately drops to 43 PSI The fuel pressure drops 10psi after 60 minutes My understanding is the fuel pressure should be around 55PSI when sitting and 48 PSI at idle. The fuel pressure should drop a maximum of 2PSI per hour. Reading a post on Rennlist from Porschetech3 explained that when the fuel is hot and does not have enough pressure it boils away creating a hard start. I�m learning about the different parts within the fuel system. Here are the items that have been checked or replaced within the last 1000 miles. FUEL VOLUME - CHECKED OK FUEL QUALITY - 3+ Tanks of Chevron since rebuild FUEL FILTER - REPLACED FUEL INJECTORS - REBUILT & TESTED (Witch Hunter) Based on all fo your advice I think that leaves: FUEL CHECK VALVE / FUEL NON RETURN VALVE (Are these the same thing?) FUEL PRESSURE SENSOR SPLIT HIGH PRESSURE HOSE ON FUEL PUMP SEND I should also mention that the car will not let you fill past 3/4 tank in case that�s related.

Your barking up the right tree for sure, thank you for your help Here is the update. UPDATE Hello Everybody!! - Thank you all for your help 🙌 Many of your pointed to the fuel system. After renting a Fuel System Pressure Tester I found that there is a pressure drop that is certainly contributing to these issues. Left overnight the Fuel Pressure drops to zero, When Cranking the system can momentarily achieve 55 PSI Idle pressure is 48 PSI After shut down the pressure immediately drops to 43 PSI The fuel pressure drops 10psi after 60 minutes My understanding is the fuel pressure should be around 55PSI when sitting and 48 PSI at idle. The fuel pressure should drop a maximum of 2PSI per hour. Reading a post on Rennlist from Porschetech3 explained that when the fuel is hot and does not have enough pressure it boils away creating a hard start. I�m learning about the different parts within the fuel system. Here are the items that have been checked or replaced within the last 1000 miles. FUEL VOLUME - CHECKED OK FUEL QUALITY - 3+ Tanks of Chevron since rebuild FUEL FILTER - REPLACED FUEL INJECTORS - REBUILT & TESTED (Witch Hunter) Based on all fo your advice I think that leaves: FUEL CHECK VALVE / FUEL NON RETURN VALVE (Are these the same thing?) FUEL PRESSURE SENSOR SPLIT HIGH PRESSURE HOSE ON FUEL PUMP SEND I should also mention that the car will not let you fill past 3/4 tank in case that�s related.

10 Psi per hour is not terrible, the other guy has a 26PSI pressure drop in an hour so two and a half times worse. The 2 psi per hour is the Gold Standard and has been ever since Bosch invented the Electronic Fuel Injection ( 40+ years ago) . But I don't think quality control is what it used to be as I see many cars/parts that just cannot achieve this... Some will hold strong pressure for days even weeks and some struggle to hold any pressure for 30 min , with all new parts...the quality control sucks, it's a hit or miss thing..

Fuel check valve and fuel non-return valve are the same thing and internal to the fuel pump itself. There's no fuel pressure sensor on the M96. What you probably mean is the fuel pressure regulator (#2 in the diagram below). You can check whether its internal membrane is fine by measuring fuel pressure at idle and compare it to the pressure when revving the engine by snapping the throttle wide open. Manifold pressure will mementarily equal ambient pressure and your fuel pressure should increase to 55 PSI momentarily too. You could instead also remove the vacuum hose (#14) from the fpr (pinch the hose to avoid a vacuum leak) to see if 55 PSI are achieved. Check if fuel drips out of the vacuum connection on the fpr. If it does, the membrane is ruptured. Schematic cross section of an fpr similar to that on the M96 I don't see a way to differentiate between leaking injectors and a leaking (into the fuel return line) of the fpr easily. One way might be to observe whether further fuel comes out of the fuel return hose on bank2 crossing over to bank1 after the initial spill when removing it from the rail on bank 2. I think it will be hard to tell, however. Perhaps removing the fpr and applying vacuum/suction to the inner, central opening of the fpr might reveal a bad seat by allowing air to be sucked through it. If you can't suck air through it then I'd say the fpr does not leak but holds pressure as intended and the injector(s) is/are leaking, resulting in the pressure drop you've observed. Perhaps removing the injector rail from bank 2 in its entirety would show dry injector tips thereby indicating the fpr must be leaking. Unfortunately the opposite (wet tips) may still mean the fpr is faulty too. Personally I guess I would buy a new fpr and see if fpr drop after shut down is back to spec or at least lessened massively and then take it from there and move on to the injectors.

The 03 996.2 doesn't have the Fuel Pressure regulator mounted on the fuel rail like pictured above. That is for the 996.1 fuel system. The 996.2 has a return-less fuel system meaning the fuel pressure regulator is a little plastic one mounted inside the tank right above the fuel pump.The fuel pump still has the check valve and the fuel pressure regulator still holds the pressure in the line just like all systems do, it just does away with the external return line...Same principals apply.

Doesn�t sound like a check valve or fuel pressure problem. Should start right up at 48 psi.

Quotes source post: 18253683

True but in his first post he states his troubles are with a 2001 carrera (2WD) that's why I referred to the 996.1

Quotes source post: 18253957

I stand corrected...lol ....BUT someone has a 03 996.2 ..lol or else my old age is just getting to me...lol

Thank you very much, I printed this out and will ad it to my list of things to check. This Sunday I'll have time to work on the car again and see what comes up.

Seems to be normal??

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.

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.

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.

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 You Tube The slow start and the fueling issue could be related??

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! You Tube

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.

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