99 Heat Soak Hard Start

Alright guys. Need some help. I have a 99 996 C2 and when the engine is heat soaked it�s really hard to start but will eventually start. I took it to an reputable Indy in dfw area and they told me it could be 1 of the 3 things. Fuel pump, fuel pressure regulator, or fuel injectors. They couldn�t really pin point the issue (kind of annoying as it�s $160 a hour for diagnostic) told me to run injector cleaner and a fresh tank of gas and see if the problem persist. Well that didn�t fix the issue. I�ve replaced all of the below and I�m still getting the same hard start vapor lock issue. I don�t think it�s the injectors as the guy I bought the car from said he got them �professionally� cleaned. Any other ideas what my issue could be? I�m hesitant to take it back to the Indy to look at it again to tell me what it could �possibly� be for another $160. Pretty sure it�s not the crank shaft position sensor as that�s the last thing I�ve read on the forums about hard start issue when hot. The car starts fine cold. Car also runs fine when I get it started with the heat soak issue. It eventually starts just very annoying to be in a 911 and it not start. The heat soak issue only happens when the car is hot and sits for 20+ mins. If I pump the gas peddle some while starting it will shudder to life after 2-3 long cranks. Any info is much appreciated. I have replaced all of the below. Fuel pump Fuel pressure regulator Fuel pressure sensor Evap purge valve aka regeneration valve in the engine bay

A starter on its way out and/or corrosion in the "Y" cable from the battery to the starter and alternator can cause a hard hot start issue. Corrosion in the Y cable can be difficult to see because it tends to corrode under the insulation.

Can you be more specific on "hard to start"? If it cranks extremely slowly, then the starter / Y cable are the likely sources. If its cranking fine but having trouble catching its something else.

If it's a cable related hot-start issue; more information in this thread: https://rennlist.com/forums/996-foru...l#post10585888 Also recently discussed starting here: https://rennlist.com/forums/996-foru...l#post18175629 I went with a different cable solution using aftermarket cables, and posted detail here: https://rennlist.com/forums/996-foru...l#post18175714

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Not "heat soak". Replace the crank position sensor and call it a day.

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But doesn't a failed crank position sensor lead to no/intermittent cranking and sometimes a fault code? And are those heat dependent, I didn't think they were?

Starter

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Doesn�t crank slow. If I crank it and pump the gas peddle it helps start it which leads me to believe it�s fuel related and not a starter/ y cable issue. Starts normal on cold start every time. Only have this issue when it�s hot and sits for 20+ mins. If it sits for 5-10 mins when hot it will start right up.

I’m still saying starter… mine would behave similarly after filling up with gas. Starters are cheap and easy to replace… not a lot to lose.

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Based on what the OP is describing, my bet is on the crank position sensor. Cheap replacement part and easy for the DiYr to swap out. https://www.fcpeuro.com/products/por...ter-0261210204

I know the suggestions have been all over the place. Spark, air and fuel. When was your last time you replaced your air filter? When was the last time you cleaned out your throttle body?

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airfilter is clean. Haven�t looked at the throttle bottle. I�ll give that a once over and clean it out.

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take it somewhere else. That�s my advice.

i recently had the same issue .. It was the Y cable from the starter to the Alternator .. It's a known issue and it corrodes internally. When it gets hot it let's less voltage through the cable .. It also had a slow to crank on cold start.. didn't realize how slow till the cable was fixed and it's fast as crap now.. The new replacement part has fixed this issue as well. this is for a 997 but the concept is the same You Tube

Sounds like you could have a "vapor flooding" issue going on here. If the "pumping the pedal" truly makes a difference, then as a "quasi-test" try holding the throttle wide open on hot starts. IF the starting improves dramatically, then you have a hot flooding condition. ( by holding the throttle wide open the DME goes into a "de-choke mode" which turns off the injectors while cranking but if the RPM reaches a running state they turn back on. ) Because if the engine is vapor flooded the addition of fuel from the injectors will be so rich it will not ignite, turning off the injectors will allow the engine to start on the vapor alone, then the injectors will turn back on once the vapor is cleared and RPM are at running state. If this turns out to be the case, then a real test of the fuel pressure, and holding time of the fuel pressure is needed to see if the injectors are leaking and flooding the engine.Or if this test proves good, investigation on the carbon canister for fuel saturation is required. Other suggestions here are also good if the "pedal pumping" really doesn't make a difference..

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here is a video on the issue. First crank my foot is not on the pedal. The 2nd crank I have the gas pedal to the floor. Also noticed black soot on the passenger tail pipe. None on the driver side. Not sure if that is part of the issue either. Based on the video think it�s a injector issue or y cable/ starter? You Tube

Not pulling your leg here: Park the car with a hot engine again and let it heat soak the same amount of time again. Start the video camera rolling and upon restart floor the throttle pedal BEFORE you crank it. Crank it till the engine starts, whilst keeping the pedal pinned to the floor. The order of action you recorded in the video dumped fuel into the intake aggrevating any vapour flooding that you're trying to identify. My take on what you are experiencing: After heat soaking the internal resistance of the Y-cable has increased so much that the battery voltage has dropped far enough that the injectors can no longer be controlled properly by the motronic thus spraying too little fuel to ignite and start the engine. (Despite the fact that the motronics compensates for the lower voltage by adjusting the injector opening times). Whilst doing so the engine is actually flooded after some cranking. OR, another scenario: Voltage has dropped far enough for the starter motor being no longer able to spin the engine fast enough to enable it to start (there is a minimum rpm threshold programmed in the motronic for this). Flooring the throttle pedal puts less load on the starter motor which manages to spin the engine just fast enough, despite the low voltage, that it catches and runs. I believe the 2nd scenario is the more likely of the two. Remedial action would be replacing the y-cable. You can dismiss both scenarios when the cold cranking speed is no faster than what you recorded (but I find that quite slow tbh). Testing how long it takes for the fuel pressure to drop when the car is parked with a hot engine and compare that to the spec is how you would identify a leaking injector. Don't know exactly how you check for vapour flooding as Porsche intended but pulling the line that carries the fuel tank vapours to the intake manifold and plugging the hole in the manifold as well as the line immediately after you parked the hot car should work. Start the car after the same time as in the video and DON'T floor the throttle. If it starts normally then the engine suffers from vapour flooding. If it doesn't start but requires flooring the throttle pedal it's back to my scenario 2 or you have leaking injectors that you would diagnose doing the test for residual fuel pressure. Curious to see what you'll find or what the shop you trust with this sort of diagnostic work finds. Please report back the findings!

Watching you start video I think you have a hot flooding condition, most likely from leaking injector(s)..The vast improvement with the DME in "de-choke" mode on the second try is telling. ( plus the sound it made when firing off is indicative of a flooded engine) The cranking speed is fine, so I think the starter and "y" cable is fine. I have seen 996 engines with much slower cranking speed that would still fire up without much fuss.A cranking voltage of 9.6v is all that is needed. Buy or rent a fuel pressure tester and test for pressure holding time. A drop in pressure of 2psi per hour is the factory spec, but in real life I have seen pressure drops of 2psi per 20min and still start fine( but this is not ideal). I suspect your pressure is dropping much more than than that, and the pressure leakage is going into the cylinders and flooding it, plus leaves the fuel rail with bubbles in it and not solid liquid fuel. IF this proves to be the case, then replace ALL injectors. OR pay a competent Porsche Technician to do it..

Got a multimeter and fuel pressure tester and gathered a lot of data. I�m starting to think I might have a y cable issue as my multimeter readings are kind of low. Below is also my fuel pressure readings after an hour. I have videos in chronological order for the fuel pressure test cold start, shut down at operating temp, then 1 hour sit heat soak start. I also have a cold start multimeter video. As you can see in that video car starts right up with no issues. Let me know what you guys think based on all the data I compiled. Greatly appreciate the feedback! Cold start multimeter readings (from what I�ve read these seem low. Thinking it might possibly be a y cable issue) https://m.youtube.com/watch?v=aV_simcI48M Cold start (not running)- 12.2 volts Car running after cold starts (foot on the gas pedal 2k RPMs)- 13.3 volts Car running for 20 mins up to temp (car still running idle)- 12.9 volts Car off for 5 mins- 12.4 volts Car off for 20 mins- 12.38 volts Car off 1 hour- 12.35 volts Volt Readings after 1 hour sit (heat soak) Car off- 12.35 volts Car running(ac on)- 13.1 volts Battery reading on dash is right above 12 (car running) Volt readings after a 2 hour drive After 2 hour drive (car off sat for 30 mins)- 12.6 volts While car is running(car is hot)- 13.2 volts

Fuel pressure test is belowCold start (starts right up easy) https://m.youtube.com/watch?v=U5GQG0AUbfU Fuel pressure readings cold start to operating temp Running (up to temp)- 48 psi Immediate shut off-drops to 42 psi 1 min after shut off- rises to 52 psi 5mins after shut off - 52 psi 10mins after shut off- 52 psi 20mins after shut off- 49 psi 30mins after shut off- 42 psi 40mins after shut off- 36 psi 50mins after shut off- 30 psi 60mins after shut off- 26 psi Shut off after running for 20 mins https://m.youtube.com/watch?v=S_e4qx7IV5I 1 hour after heat soak start readings: Car Running- 48 psi consistent no drop Immediate shut off-drops to 42 psi 1 min after shut off- rises to 52 psi Heat soak start video (hard to start) 1st crank- foot isn�t on the gas 2nd crank- pumped the gas pedal before I started 3rd crank- gas pedal is to the floor https://m.youtube.com/shorts/PvshJopXjU8

If those fuel pressue numbers r correct u have a fueling issue. Fuel pressure should stay steady no matter how long your car runs for. I think it should be 55 psi +-3.

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those #s above are after the car is turned off. Held 48-49 psi while running with no fluctuation from that

My bad, guess the fuel looks good.

Read the last paragraph of post #18 carefully, and compare it to your test values....

Leaky injectors� change them out with new ones (not �re-conditioned�). You�ll be saving yourself a lot more than poor hot starting conditions.

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was hoping that wasnet the case but I�ll get them changed out. Thanks for the help!

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injectors it is. Going to try and DIY it after I get the new injectors. I�ll update the thread when I get new ones and get everything up and running.

Rennlist should put Skip on a paid retainer.

*update finished putting in new fuel injectors this AM. Car runs a lot better but STILL has the heat soak hard starting issue. I�m at a lose of words because changing the injectors was a PITA. What on earth could the issue be now? I�ve replaced everything fuel related the problem could be now�..

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crank position sensor. Change it!

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So ahhhh�. With all the stuff you have done, have you replaced the starter yet ?

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Have not done the starter. To me it turns over fine even when its hot. I did notice when I got it started after the heat soak and the injectors replaced it ran rough like it always does at start up. Going to compile my thoughts on a y cable, Crankshaft position sensor, or starter. Im getting really tired of buying $100+ parts and it not fixing the issue. I thought forsure new injectors was the final fix..... Im going to try and replace one more thing and if it doesnt fix the issue the car will find a new home.

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what makes you think its the CPS? Have you had this issue on your car before? Based on everything Ive read on the forums and such people cannot start their car at all when the CPS is bad. Mine will eventually start if I hold the gas to the floor. After everything Ive replaced this is what Im leaning towards next on replacing. This was initially going to be the first thing I replaced but I thought surely something this simple wouldn't be the issue.

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This. Not unique to Porsche, this sensor is susceptible to heat cycles and, as it fails, shows the symptoms you are experiencing. In our Jeeps, especially the XJ (original Cherokee) it is a must to carry a spare. Even if it is not the cause of your problem, it is 1. cheap to buy and 2. easy DIY to replace, so it would have been first to check if it was me.

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Are you still getting 26psi fuel pressure drop in 1 hour?

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I didn�t measure fuel pressure with the new injectors. I put all brand new bosh injectors in so I wouldn�t think fuel pressure would be bad after changing those, fuel pump, and fuel pressure regulator now. If fuel pressure was bad what else would there be to change?

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I would test the fuel pressure again just to make sure you fixed THAT problem, then I would smell/test the oil for heavy fuel contamination and change it will fresh oil and filter..

Per PT3 check your fuel rail pressure again, then change the Y cable (most likely culprit) crank position sensor (easy change) and then the starter - in that order. Don�t �throw the baby out with the bath water�(ie - get rid of the car)� just eliminate one potential problem at a time til it�s fixed.

Try this for a quick CPS diag, really doesn't sound like the starter/y cable if its cranking strong but not starting. I replaced my starter last year for hot start issues and it would barely turn over once or twice then just give up, even with a fully charged battery or jump pack hooked up. https://rennlist.com/forums/996-foru...-this-cps.html

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Checked the PSI this AM. Basically getting about the same read out as the older injectors which seems weird to me. I highly doubt the new bosh injectors I put in are bad. I put them in myself and they are all seated correctly (would be hard for them not to be seated correctly with the fuel rail bolted back in) but I double checked also to make sure. Is there a break in period for new injectors? I only did about a 15 min drive after I put them in but the car ran really good. My PSI readings after shut off are below. Is there anything else that could affect fuel pressure? Already did the fuel pump and FPR. Just ordered a crank sensor but on the fence about that fixing the problem. I did notice when I got the car started it ran rough at initial start up like it always does then smoothens out after 30-40 seconds. Immediately after shut off - 46 PSI 20 mins after -34 PSI 40 mins after - 20 PSI hour after- 18 PSI

The reason I said to retest the fuel pressure drop is so that you can confirm the ROOT cause of the hot start issue is fixed.. With 26psi pressure drop in 1 hour you have a LOT of fuel going somewhere it shouldn't.. If the fuel pressure lose has been going into the cylinders for a while, the oil will be hearily contamintated with fuel. Heavily contamintaed fuel/oil will put off enormous fuel vapor when hot enought to flood the engine and cause hard starting as a secondary cause. Don't just throw parts at it without testing/good reason. Retest fuel pressure to CONFIRM root cause of pressure lose is fixed, Then finish repair by testing/smell/taste the oil for heavy fuel contamination....

I see you posted the retest right before I reposted.. Yes, it looks like your pressure drop is NOT due to leaking injectors..the retest seems to confim this.. There is a check valve at the discharge of the fuel pump, then the pressure regulator at the other end on a 99 that holds the fuel pressure. A leak at either end or anywhere the middle (injectors)will cause a pressure lose. In an ideal world there would be 0psi pressure drop. This would give instant restarts.The factory gives a specs of 2psi per hour. The reason is that when the fuel and fuel rail/lines/ injectors are hot, then need the pressure to keep from bubbling/boiling.. IF the fuel pressure drops quickly after shut-down when hot, the fuel will bubble/boil in the rail/lines/injectors and cause long crank times. In the real world with aged parts or quality control what it is , 2 psi per hour is rairly achieved, 2psi per 20 min is more realistic. This will give near instant restarts. The further away you get from this the longer the crank times will be.

Since there were no pressure drop tests done before you replaced the fuel pump and regualtor, there is no way to know whether they helped or hurt the pressure drop..Were they Genuine Porsche parts?

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yes, unfortunately I replaced those before I got smart and started running the PSI test. They are genuine Porsche. Thought all these test were for specialized Porsche mechanics but I�ve realized all this stuff isn�t as hard as I thought to replace even though I still have the hard start issue ha

Not sure if you have solved your hot start issues or not, but thought I�d let you know that my �99� has new injectors and the fuel pressure after shutting down engine is about what you�ve reported. My car has no issues starting right up after being driven for a long stretch. You could always check your purge valve again. If that checks out then check your dual element temp sensor. DME might be getting bad temp info.

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Thanks, that is good to know on the injectors! I changed the crank shaft position sensor yesterday and that did not fix the issue. My next change is the Y cable. I'm thinking this might be the fix. My battery gauge stays at 12 or slightly above 12 where as what I've been reading alot of people says theirs is at about the 14 level. If its not the Y cable I'm flat out of ideas. Ill check the dual element temp sensor and see if it looks bad too.

i changed the starter,cable...and did not help,finally the regeneration valve did the trick.not expansive to try.

Just to give yall an update. changed the CPS and Y cable. Neither fixed the issue. Im throwing in the towel and taking it to Mayo performance in Euless, Tx. If I ever get it fixed Ill update the thread.

Hey, I just wanted to see if you ever fixed your hard-start issue. I�m going through the same thing and your thread has been pretty helpful.

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never fixed it. Spent to much time, money, and effort for it to not be fixed. Took it to another Indy and they couldn�t pin point the issue. I�m kind of leaning towards some sort of vacuum leak now. The Indy mentioned try changing the coolant sensor but I�m not changing anything else unless I know 100% it would fix the issue. Hope my thread helps you on trying to fix your hard start. If you do end up fixing yours please let me know what fixed it!

Come on, don't give up! You're close and were able to replace so many components yourself already. Try this: Switch off hot engine, open engine cover and clamp the line shut that's going from the Purge Valve to the throttle body with a pair of mole grip pliers or hose pliers, see the scribble in the foto. Restart the engine after the same amount of time has passed that would normally have resulted in hard starting of the engine.

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I have defiantly replaced a lot. At least I got basically all preventative maintenance done as one perk. I will try that and see what happens. I tested the regeneration valve again recently with a 9v and sprayed brake cleaner all in it. I hear a faint click with hooked up to the 9v so I think it�s working. When I took it to the Indy they mentioned it had a rough idle at start up and to replace plugs and coil packs. I put all new Beru coils and bosh plugs and still have a bit of a rough idle. It�s something to do with vapors or some sort of temp sensor/ possible vacuum leak causing the fuel ratio to be out of wack.

I have replaced mine (also 99MY) recently and it had a faint klick just like yours. That's indicative of it being ever so slightly open instead of properly shut when no voltage is applied. The fuel fumes from the charcoal filter are no longer held back when the engine is off or started but put your air fuel ratio out of wack when starting the hot engine. Cold is not a problem as there's hardly any fuel vapour coming from that line into the throttle body.

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Have you tried another shop?

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both shops I used were very reputable. I think they could find the issue possibly after hours/ thousands of diagnostics fees. Not worth it to me at this point after how much I�ve already spent. Both shops did 2 hours of diagnostics each. I don�t think the issue is obvious or harming the car in any way which makes it tougher to find. No check engine, no codes, etc. going to try the regeneration valve hose clamp soon and see if it makes a difference.

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tapped off the line and it didn�t make a difference. I did notice when it gets started after the heat soak the battery gauge hangs around 12 when it�s normally at the 14 mark. Seems weird since I just replaced the y cable.

Sorry to hear that! But thanks for posting the result nonetheless. Have you reconnected the hose yet? If not then now would be a good time to undo the quick connector on the other side of the valve, disconnect the electric plug and blow through the valve from the quick connector side. It should be shut, no air coming through. Just a while you're in there type of check.