Car died while driving, now won't start

This topic was posted in another thread, but since it is puzzling, I decided to start a new one. 1999 996 c2 sat for appx 10 days. When I started it after the layoff, it started normally, and drove off fine (minor stumble on takeoff that lasted for a second). Got to destination, no problems. Started car w/no issue. Drove about three miles and motor quit abruptly. No sputtering, just died, with no restart. After getting it home, I troubleshot the issue, narrowing it down to the fuel pump relay not getting a signal from the dme, preventing the pump from operating. Tested the fuel pump relay and replaced it with a new one. Tested the DME relay, and swapped it with another relay of the same part number. Replaced the MAF sensor. Today it started after an extended period of cranking, and idled fine at 880 rpm (by durametric), until I tried to rev the motor, whereupon it died and would not restart. since it was running normally at idle, that tells me that the CPS is ok (replaced two years ago). No unusual numbers were noted using the durametric actual values page, except the exhaust temp after catalytic converter showing minus 48 degrees c. static. I did get the running number while i had the motor operating: 54 degrees c. Throttle plate angle showed 0 not touching the pedal to 80% with the pedal fully depressed. I have the rest of the numbers if anyone wants to see them, it's a pretty long list though. My next step is to send the dme to a repair shop unless someone has something else that I can check out?

Any codes and what happens when you crank it when cold now?

No codes at all, other than the expected P1602/P0102 after removing the battery and MAF. Cleared those with no recurring code. I'm wondering if the immobilizer might be at fault, and if there are any diagnostics I can run? The box is dry, btw. I replaced the ignition switch a few years ago also. I suspect that there is a wet connector somewhere: the car sat for 10 days outside before this episode (sits outside all the time). Prior to this issue there were no problems at all. The battery is fully charged, I even tried a booster start with no luck.

If the starter spins, the immobilizer is fine. That's why I asked you what happens when you try to start the car now. Assume the starter spins, next is to check for sparks and fuel. Also, have you cleaned the idle control valve and replaced the fuel filter?

Thanks for the info on the immobilizer. I thought that was the case, but wasn't sure. Yes to both. The motor actually started and ran at idle for about two minutes with my foot off of the accelerator. As soon as I touched the pedal and applied pressure, the motor quit. That shows me that the ignition system is ok, the starter is good (replaced a few years ago), and the fuel filter is ok (also replaced a few years ago). My theory as to why it started and ran for a while is that the minuscule siphoning action created by the injectors opening under a vacuum caused enough fuel to start flowing. Maybe a WAG, but that's the best I can do right now. As I said, the fuel pump is inop until I jump the relay, when it runs ok, with no unusual noises/vibration. While aggravating, this is still an interesting problem to diagnose.

What happens if you disconnect the MAF? Note the fuel pump will only keep running as long as the engine is running. I think you need to check your fuel pressure on the fuel rail. There's spec at idle and at some rpm to verify the flow rate and fuel pressure regulator. Sounds like to me you're low in fuel pressure/flow.

Would you know where I can get the adapter for the fuel rail other than oem?

As for the MAF, no change. I replaced it hoping that would solve the problem, even though I prefer to diagnose rather than throw parts at a problem until something sticks

I had issue with mine starting and sometimes dying after idling for a bit. It also would have issues starting and other times it would start right up. The ignition switch was the issue. It was replaced and all is good.

Quotes source posts: 14272932, 14272952

Most fuel pressure tester kit should have the right adaptor. No, I meant completely disconnect the MAF.

http://forums.pelicanparts.com/boxst...re-tester.html

Fuel pressure and flow spec https://www.renntech.org/forums/topi...ove-fuel-pump/

Thanks ,I did disconnect the maf with no change noted. I'm now headed out to pick up a fuel tester (had one, loaned it out, never returned). Looking like a fuel flow/pressure issue: started, ran for 43 minutes. I could gently accelerate to 4.5k rpm. Idles relatively smooth. Soon as I pressed the pedal at all hard, it sputters and won't accelerate. For those interested here's the Durametric numbers for my last run: Durametric Codes Date 6/22/2017 Temp +22 c./75 f. Unit of Measurement Static Cold Operating Temp idle Operating temp 2k rpm RPM rpm 0 880 680 2000 Load Signal ms 0 3.3 2.1 Air Mass kg/h 100 48.75 24.75 Hot Film MAF vdc 1.02 1.79 1.41 Speed km/h 0 0 0 Volts vdc 11.7 14.06 14.6 IATS deg. C. 34.5 30 63 ECTS deg. C. 24 42.8 97.5 Throttle Position Angle % 0 to 80 0 2 Ignition Timing deg. Crk 78 6 32.3 Spec. Air Mass kg/h 0 22 13 Spec. Air Adaptation kg/h 0 0 -2 Ambient Pressure hPa 0 960 1025 Injection Time ms 0 5 4.9 4.1 Exhaust Temp after Catalytic Converter deg. C. -48 54 420 Oil Temp deg. C. 13.5 41.3 87.8 Engine Compartment Temp deg. C. 24.8 34.5 54 Oxygen Sense Cyl 1-3 not spec 1 0.81 0.98 1.02 Oxygen Sense Cyl 4-6 not spec 1 0.88 0.98 1.01 Range2 Cyl 1-3 FRA not spec 0.98 0.99 1.03 1.03 Range2 Cyl 4-6 FRA2 not spec 0.98 0.98 1.07 1.07 Range 1 Cyl 1-3 TRA not spec 0 0 -0.013 -0.13 Range1 Cyl 4-6 TRA2 not spec 0 0 0.1 0.1 Oxygen sense Voltage Ahead of Catalytic Converter vdc 0.44 0.04-0.74 0.04-0.76 0.04-0.76 Oxygen sense Voltage Ahead of Catalytic Converter Bank 2 vdc 0.44 0.05-0.72 0.03-0.77 0.03-0.77 Camshaft Position 1 Deviation deg. Crk 0 0 0 0 Camshaft Position 2 Deviation deg. crk 0 3 3 3 HO2S Heat Res Ahead of Catalytic Converter ohm 1.8 3.4 3.3 3.3 Rough Running Threshold 1/sec squared 0 18.2 12.9-14.9 15.3 Rough Running 1/sec squared 0 2.8 0.0-4.8 0.0-11.3 Segment A not spec 1 1 1 1 Segment B not spec 1 1 1 1 Learn. Progress Sens. Wheel Adapt. not spec 0.0007 0.0007 0.0007 0.0007

OK disregard the numbers above, I've attached the word file:

Are these numbers correct? "Air Mass kg/h 100 48.75 24.75" "Hot Film MAF vdc 1.02 1.79 1.41" "Load Signal ms 0 3.3 2.1" At idle fully warmed up, air mass should be 17 kg/hr +/- 2.5kg/hr. Also MAF voltage should be ~1.3v. Something is not right. Load signal should be 1.3ms +/- 0.3ms Can you also measure what's the air mass when engine is rev'ed to 3k? Should read 50-80kg/hr.

thanks I'll try. I was hoping that you (or someone) would read these numbers and point out the out of spec values. Thank you! I've ordered another fuel pressure tester, along with the adapter from Actron. I'll let you know what I find. I have a cheap Russian fuel filter that I wasn't really enthusiastic about installing, but I might try that next.

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What's the model number of the MAF you're using and is it a Bosch unit?

Quotes source post: 14273958

I'm embarrassed to say it's a cheap chinese copy. I'll install the original back in and try that. Original Bosch pn: 0.280.217.907/Porsche pn 996.606.123.00

Let me know once you got rid of all the Chinese and Russian parts

Done. Gone. Lesson learned. Ouch.

Quotes source post: 14274914

And?

Waiting on the test equipment to get here, then I'll post the results

Just to close this thread: tested fuel pressure with engine not running, 10 psi. Re[laced the fuel pump and filter: pressure within spec (can't remember the exact number). Replaced the MAF sensor and all is well-finally! BTW as a cautionary note: the cheap chinese MAF sensor was showing a reading af 45 (!) at idle, with attendant rough running difficulties for the block or so that I drove it. Immediately threw it away. Note to self, "if it sounds too good to be true, it probably is"..

Glad to hear you got it sorted.

Next time, look up the part number using the Bosch site parts finder, then order that part from Amazon. It's a lot cheaper and the box says "Bosch" instead of "Porsche," but they're otherwise identical. As of 7/14, one specific MAF that is sold both at Amazon, Porsche parts resellers, and the Porsche parts counter was selling for $275 (Porsche parts site in a Bosch box), $713 (Porsche parts site in a Porsche box), and in a Bosch box on Amazon for $155.

Thanks all.