fuel pump &/or fuel pump relay problem
 

My 911 C4 starts right up but then dies after heating up & running 15-20 minutes. Then it'll crank but won't start. After sitting/cooling for awhile it starts right up but then the same routine persists; it dies after the 15-20 minutes. When you turn the key to the on position you can hear a high pitched humming in the fuel pump for 5-10 seconds before you hear clicking. It's not the normal clicking noise you hear from a fuel pump either. So I'm guessing after it warms up the fuel pump quits working or there's a fuel pump relay that's stops working or both...?

I read some of the hot starting posts but I'm guessing those won't restart after they're hot vs. the car quitting while running & then won't restart...?

Any feedback is greatly appreciated!!!

Thank you,
Dean

Run a fuel pressure test during start up. I'd also check out the crank position sensor, they are famous for causing starting issues.

Thanks JFP. Would a faulty crank position sensor cause the car to shut off while running?

MY is really helpful when trying to find an issue as many times (like this) there are different possibilities.

Anyhow, the 997.2 w/ DFI has a known issue/recall on the HPFP. 997.1 can have issue w/ a short in the fuel pump / sending unit. 997.1's issue is hard to correctly diagnose particularly intermittently until it fails completely.

If you're under a warranty or even if not, next time issue occurs and vehicle won't start, have it towed immediately to a dealer/indy for diagnosis. They can pull the codes and trace back thru starting sequence to see what didn't occur and should have, etc.. Once it does start, the memory of the issue (as I understand) clears.


Good luck :)

Yes; worse yet, when it does it, it does not throw a code .......

Thanks again JFP. There's a high pitched squeal under the front right fender which is where the EVAP Canister is located. Should I start by replacing #’s 2 & 6?
Would #'s 2 or 6 also shut the car off while it's running?
http://www.renntech.org/forums/index.php?app=core&module=attach&section=attach&at tach_rel_module=post&attach_id=8262

1 - EVAP canister purge valve
2 - EVAP canister
3 - Purge air
4 - Tank
5 - Tank pressure sensor
6 - Shutoff valve
7 - Operating purge valve
8 - To intake manifold
9 - Vacuum control valve

If so, where should I order parts?

Thanks a ton, Dean

Possibly, but I would pull the fender liner and look at the hose connections first. In general, the EVAP system can make the car run rough, but should not shut it off.

Thanks JFP...we're getting closer. I have multiple issues. The squeak under the front right fender has turned out to be the brakes so I can deal w/that as a separate issue. The good news is now I know it’s not the EVAP canister or shutoff valve squeaking. I like the idea of blowing compressed air through the EVAP canister purge valve (#1 in the diagram below). I have a pancake compressor. How would I go about blowing compressed air through it (any advice, diagrams or sites to help)?

Secondly, and most important, is the engine shutting off. How do I check the Crank Position Sensor or should I just replace it? If replacement, any tips, diagrams, or sites to help me tackle the beast…?

Thanks again for everything,
Dean

You simply need to disconnect both ends of the line and blow air into it to make sure it is not blocked. Just about any compressed air source will work.

The crank sensor is a simple "Hall Effect" unit that generates a signal if ferrous metal passes near it (like the shutter on the flywheel, which triggers it when the engine is turning). When the sensor fails, the DME thinks the engine stopped turning and shuts off the fuel system. Problem is that what you are seeing is intermittent, making testing problematic as you would need to catch it doing it using a device like an oscilloscope (the factory test procedure) or a data logging system. On the flip side, the sensor is over $100, so you don’t want to go changing it without good reason. Sometimes these things throw a P0336 code, have you checked the DME to see if one is stored?

How about excessive pressure in the fuel system? If the car runs for 15-20 mins, it creates a vacuum in the fuel tank, and reduces fuel flow to the engine? Just a guess.

Try testing the fuel pressure? Monitor it from the time the engine starts until it stalls. At least, that's the next step that I'd do.

Keep in mind I'm only a hobbyist mechanic. So my opinions aren't really worth much. But every now and then, I do say something valuable. ;)

Ah, I see JFP actually recommended the fuel pressure in post #2. See, that's why he's the professional! :)

Hi JFP in PA, Thanks for your patience w/a rookie. Here's my pic of my EVAP canister: http://986forum.com/forums/attachment.php?attachmentid=16295&stc=1&d=13405664 82

Which 1 of the 3 do I blow out w/an air compressor or should I do all 3? And what's the best way to disconnect the lines (they almost look as if they unscrew...)? Do I have to disconnect the other end or can I leave it connected? If disconnect, how do I find the other end?

Have a nice weekend, Dean

Answered in detail in a PM...............

Thanks JFP. What are the 3 lines coming out of the top of my EVAP canister picture? Which one(s) should I blow out w/an air compressor?

Any chance one of you could share this PM with me? I have my car all apart, have the factory diagnostic guides for the codes I'm throwing, have access to lots of info from the PET software, which does have a canister that looks like mine in its diagram but has no info on the hoses and most of the valves, and my canister/hose layout does not match the one in the shop manuals but matches his picture. I have a compressor all charged up and ready to blow, but want to make sure I'm not making this problem even worse. I for sure have fuel and or vacuum pressure problems.

In my translation I want the left-most hose in his picture, but the diagnostic/repair manual says to pull it out there then blow. Nothing about the other end. I tried tracing the lines visually but can't see well enough for that to work. This is a 2000 986 2.7 manual by the way, in case that makes the answer different.