3.2 - Car died while idling, won't start

[david.avery]

Hey guys

I was idling down after a nice drive in today, and just as I was about to turn it off, it died, as if it had been shut off, no drama, mech noise, etc.

It surprised me, so I tried to restart it and could not. I let it cool down, and tried later, and it just cranks.

I went out and checked all the fuses and relays, as well as the connections to the three plugs in the back that hang off near the fuel pressure reg. Everything seated tight, as are all relays, and plug wires.

I could only feel the DME relay seemed seated, I cannot get to it without pulling my seat (corbeau). This is what I think may be the problem. I do not have a replacement (I know, I know)

I am unfortunalty far away from help at work, so I will probably have it towed home to fix.

Sooo... anyone have any ideas? I was thinking of calling a local auto parts store to see if they have a relay. Engine cranks merrily, I do think I cannot hear any fuel pump noise. Thanks

[cbeers]

David,

It sounds like you are on the right track. I had something similar. Went to a shop bought a relay since that was an easy check. No go. Had it towed to the shop and within minutes it was diagnosed as a failed fuel pump. I wish I could tell you exactly how that was checked. Something like jumping a wire from the fuse panel to ?? to see if the pump came on. Nothing. Replaced and it's been golden since.

Hopefully it's something simple like that......

-Chris

[Rot 911]

If you can't hear the fuel pump then most likely is the DME relay as it is also the fuel pump relay.

[MBEngineering]

HI go to the fuse box under the front and check fuse No 16 if ok jump fuse 16 and 17 on the bottom row with a wire (paper clip)and check the fuel pump runs. if not PM me and i will send the
911 carrera dme test plan over.

regards mike

[ruf-porsche]

Could also be the sensors on the flywheel.

You need to check for fuel and spark.. If you don't have fuel it could be the DME or fuel pump.

[david.avery]

Thanks guys, odd thing... I called AAA, and when the tow truck came, I decided to try it once more. It started up. While it was idling, I ran over to tell him I was going to drive it home, and when I returned it had stalled and would not start! Very odd. I have two relays coming in at a local NAPA tomorrow morning, will try that first. I did swap the fuel pump fuse with another just for a test during my diags, so I don't think that it. Oh well!

[jbrinkley]

it always baffles me when someone says they can hear the pump running while the engines cranking on a carrera, I can't hear **** when I'm starting my car. no offense kurt
bad CHT will do the sort of thing you're talking about.

[ZOA NOM]

You should be able to reach the DME relay without removing the seat. Pull the seat all the way back and look under the front edge, there is only one 10mm nut holding the relay in.

[jbrinkley]

here's a pic of jumper on the DME plug to run the fuel pump, with a fuse just in case

[ZOA NOM]

Lose the fuse. It's unnecessary. The circuit is already fused in the trunk fuse panel. Just use the heavy gauge wire between the plug holes.

[dentist90]

Probably unlikely that a dead fuel pump would come back to life, but with electrical.... who knows. I think your idea to replace DME relay is a good one as even if it is wrong diagnosis it's nice to have a spare. Question though: since DME relay controls both fuel pump and Motronic ECU, if it fails wouldn't you lose the module ( computer) as well? Or are there two seperate relays built into one wherein one might fail while other still works? If not you should have no spark either. If no spark and no fuel must be relay. Make sense?

[ZOA NOM]

The DME relay is actually DPDT (Double Pole, Double Throw), which is two relays in one. You can have independent failure, usually found in the form of cold solder joints on the relay circuit board where the contact pins connect. If the coil fails, the whole relay fails.

[david.avery]

Thanks Jbrinkley, more ammunition for later It's freaky how it starts and runs for an indeterminate time. This may take the shotgun "replace all the potential culprits" approach I think, starting with the relay.

[david.avery]

Originally posted by ZOANAS
You should be able to reach the DME relay without removing the seat. Pull the seat all the way back and look under the front edge, there is only one 10mm nut holding the relay in.

Actually, got low corbeaus on there, it's nigh impossible with the way I have them mounted, though this was perfectly possible with stock seats (removed the DME computer several times during turbo install)

Still, it was sad flatbedding it, it's first time in 15K miles since I've owned it. I'm just glad it stranded me right at my office, where I keep the car in full sight.

[ChrisBennet]

Originally posted by MBEngineering
HI go to the fuse box under the front and check fuse No 16 if ok jump fuse 16 and 17 on the bottom row with a wire (paper clip)and check the fuel pump runs. if not PM me and i will send the
911 carrera dme test plan over.

regards mike

I'll expand on what Mike said. This is the pertinent part of the DME test plan.


I actually carry a jumper like this in my tool roll but for testing you can bridge the bottom of the fuses with most anything like a penny or a house key (a Porsche key is not a tool! ).
I can't count to 16 so I start at the other end of the fuse box and bridge the 3rd (aka 17) and 4th (aka 16) fuses from the end. (See picture.)

I don't remember if the key has to be in the ignition (experiment). Open the hood, pop off the fuse box near the left front fender and touch a conductor to the screws at the bottom of the 2 fuses mentioned previously. You'll get a little spark and you should hear a whine from the fuel pump under the car.

The chain of events when starting the car goes something like this:
1. Turn key to Start position, energizes starter and fuel pump directly, 1/2 of DME relay (the part that powers the DME) is switched On.
2. Release key, if DME senses that air is going through motor (and if it gets the right signals from the motor sensors) the fuel pump 1/2 of the DME relay is turned On.
Soooo, if you power the fuel pump directly you bypass the part of the DME relay that powers the fuel pump. If it was just a bad relay, the car will now run.
The ignition switches in 911's can also fail. It's advisable to avoid any sort of heavy key chain as this can exacerbate the problem.
-Chris

[arerrac]

Exact same thing happened to me. I let it sit overnight and the next morning it ran. Drove it up the driveway and it died! Finally had it flat-bedded 112 miles (thank god for AAA extended coverage). Verdict, fuel pump!

Let us know what it was.
-W

[Drago]

Sounds like exactly how my DME relay failed. Sitting at a stop light waiting to turn left...car dies. Won't start again so I push her to the side of the road and call JW.

JW says "do you have a BASD (Big Ass Screw Driver) to hit the DME relay with". I say no. He says "go find a rock, hit the DME relay while cranking her over". I do...and she starts. Only to die again a couple of seconds later. Bang, bang, bang again and she starts, again, only to die a couple of second later. I didn't even have time to put her into gear.

Do yourself a favor and replace your DME relay and while your at it buy a spare for the glove box. (like you've never heard this advice before )

[MBEngineering]

HI thanks Chris i was beginning to think no one was reading my in put/advice

regards mike

[MOMO3.2]

David:

My money is riding on the DME relay. You need an extra any way...

Good luck.

Mike

[ChrisBennet]

Originally posted by MBEngineering
HI thanks Chris i was beginning to think no one was reading my in put/advice

regards mike

When Mike talks, I listen!
-Chris