[vliegwielolaf1234]

I am sorry , i give up after this one .







I know where the wires coming from the switch are connected in my car , and what happens when i turn ONLY the pump off in my CAR , it dies almost instant , but i'll make it a 1.5 sec to be on the safe side(just for you flash) , regardless of what any expert might say or think .







Now I think you are going to connect wires to your fuel pump and find out , why , because you won't get any sleep until you know for sure .(LOL)

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[flash]

funny - not likely though. too many other fish to fry.



all i can suggest is that there is something wrong with your car, because the physics say it should run for a few seconds, as there is absolutely fuel in there. it sounds almost like the check valve is stuck open, and the fuel is going back into the tank, when it should be staying in the lines and rail.

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[PorschePilot]

[quote name='flash' timestamp='1352485474' post='134656']

funny - not likely though. too many other fish to fry.



all i can suggest is that there is something wrong with your car, because the physics say it should run for a few seconds, as there is absolutely fuel in there. it sounds almost like the check valve is stuck open, and the fuel is going back into the tank, when it should be staying in the lines and rail.

[/quote]



And the check valve is where? In the fuel pump? So you're saying the check valve sticking open would dump enough fuel back into the tank to starve the engine? That would be very similar to turning the FP off. I'm looking to see what a new FP costs.

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[flash]

it's back there near the pump.



this is a theory as to how the engine could shut off more immediately. basically somehow the fuel that should be still in the rail, seems to be gone, otherwise it would continue to run a few seconds until it used up that fuel. it's the only explanation i can think of that would explain that.



an abrupt shutoff, barring something weird like that, would be electrical in nature. the issue with the OP i am almost certain is up front in the DME powering circuit. it would be incredibly likely to be the fuse that powers the DME. the fuse box is extremely well known for having bad connections. it could also be the socket for the DME relay. i've seen that quite a bit. i've had to lift up and clean out a few fuse boxes over the years, to resolve issues exactly like this.

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[unknown4u]

[quote name='flash' timestamp='1352471502' post='134638']

how exactly do you turn off the pump? it doesn't make sense that it would not run for a few seconds. there is still fuel there, the ignition power is still on, and the injectors are still powered.



the only way to turn off the pump, is to cut into the wire at the pump, and disconnect it. i'm going to look at the wiring diagram, but i am pretty sure there is no point under the dash that you can disconnect it.

[/quote]





The connector in the harnass is under the car, just 50 or 60 cm, 20 or 25 inches from the pump, you don not have to disconnect the electrical connectors from the pump. You can just extract the connector. :-)



And buy the way, my pressureregulator is in good shape. Just replaced it a year ago and the testresults are that the pressure stays for more than a day at the top fuelrail.

Porsche said that 15 minutes is ok. So the system and injectors are in pretty good shape :-)

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[flash]

the next time i'm under the car, i'll conduct this test. i am certain as to the result though, as i replaced my check valve, and i know how long my car holds pressure. using some basic math based on the fuel at idle setting, relative to maximum flow, the car would require about 7cc/sec at idle. the lines and rail should hold a total of at least 18cc. that should be at least 2.5 seconds that it would run before it ran out of the fuel in the line.

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[vliegwielolaf1234]

oke did a test : idle it takes 2,5 sec to die .

2500 rpm 6th gear less than 1 sec .



But not reallly a sputter . idle it just drops the revs and dies , driving it feels like instant death .

Pump filter checkvalve are three months old , system was pressure tested at that time also .

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[flash]

lol - that matches my math above. nice to see that i can still crunch the numbers.



if you've never had an ignition system cutout, then you may not know what "instant" is relative to an engine dying. it's pretty violent. the nose dives and everything. it almost feels like somebody slammed into the car. a fuel cutout is less abrupt. it can be quick, but the time it takes to burn through the fuel absorbs some of the impact. it's kind of like the difference between jumping down off a fence on to concrete in dress shoes versus onto a lawn in sneakers.



whether or not it sputters on the way down would be due to the load on the engine at the time, as well as the condition of the components. the higher the load, the less sputter, the leakier the injectors, the more sputter, yada yada

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[vliegwielolaf1234]

Topic starter should check his fuel supply unit , all components , could be his problem !!!



Mine runs fine , as long as i don't push the wrong rear wiper switch .

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[flash]

lol - now THAT"S funny



i'm still betting on something in the fuse box. i have yet to see or hear of a problem with these fuel pumps, or their wiring. i have seen and heard of dozens of problems with the fuse box and its related components. the DME fuse is one that is constantly missed. people are constantly blaming the DME relay, but forgetting about the fuse, and it often turns out to be the fuse.

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[flash]

DME fuse is #7



fuel pump fuse is #34



i would clean both of those connection points

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[unknown4u]

The topic starter is very quiet...........

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[PorschePilot]

I mentioned this issue to my brother in law at Christmas and he said he had the exact same problem with his BMW. He said the ECU/DME monitors some signal that indicates the engine is running, and if it senses the engine is not running, it shuts off power to the fuel pump. The idea being that in an accident, you don't want to keep pumping fuel. Whether all that is true or not, I don't know. Seems to me it would be better to use whatever signal trips the airbags to shut the pump off. At any rate, he worked around his problem by running 12v to the fuel pump with a switch in series. Whenever his engine would die while the car was in motion, he would flip the switch on, and the car would start running again. He said he would leave the switch on for a minute or so, then turn it back off.



I'd like to find the root cause of the problem, but given the highly intermittent nature of the thing, I may never get there; so I want to try his band aid solution and wait for it to happen again. What is the easiest way to run 12v to the pump? Can I find 12v on the fuse panel somewhere and jumper it over to one side of the fuel pump fuse, with a switch in between? Any recommendations? Thanks!

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[flash]

there are unused fuse connectors in the fuse box. i would say you could lift up the box, disconnect the wire on the bottom that feeds whatever accessory not being used, and run a new wire into that and on back to the pump, and then button it back up and install the fuse. it's a long run, so be sure to run a heavy enough wire. i would also use a relay, as any switch you use could easily fail by running that much current through it all the time.

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[PorschePilot]

Thanks, Flash. I just found some troubleshooting info at http://www.clarks-garage.com/shop-manual/fuel-16.htm which confirms an engine running signal is necessary to keep the fuel pump powered.



"For the fuel pump to start and remain running, for the ignition coil to develop secondary voltage, and for the injectors to fire, the DME computer must see an engine start signal or an engine running signal (greater than 200 RPM). When it does, it completes the circuit for the Fuel Pump / DME Relay secondary coil and the fuel pump starts."



And if the "engine running signal" is the same thing as the "engine cranking signal", then it is produced by a combination of the speed and reference sensors; which means either one of those sensors, or perhaps more likely their related wiring/connections, could be the root cause of the problem.



"The engine start signal is normally generated by a combination of voltage from the ignition switch to the starter solenoid and a signal from the reference sensor. However, if the starter solenoid signal is not present, an engine cranking signal can be generated by the combination of the speed sensor and reference sensor signals."



I have to work on the car outside, so as soon as it warms up to something bearable, I'm going to run the jumper wires and switch. Then it's just a matter of waiting until it acts up again...

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[PorschePilot]

Finally got it! Sometime around mid-January, I soldered two wires inside the DME relay, corresponding to terminals 30 and 87b, and then ran the wires up to the rear wiper rocker switch in the console (since I never use the rear wiper anyway) and verified that I could turn the fuel pump on with the rocker switch. Then came the waiting game. As I mentioned before, the problem occurs very infrequently; but yesterday, it finally happed again. On the way home from work, doing about 70 down the interstate, the engine suddenly quit. I hit the rocker switch and it immediately made power again. I only left it on for a few seconds, and then turned it off. Again no power; switched it back on, and immediately had power. This time I left it on for about 15 seconds before turning it off, and when I did turn it back off, the engine kept humming right along. So, although I haven't found the root cause (I suspect crank sensor) at least I know I can get the car going again on the fly.

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[Grandpa#3]

Check the connection plug for the Reference Sensor located at the driver side rear of engine. Some times it will lose contact inside and this will cause the DME Relay not to turn on the fuel pump. You can jiggle the connection and it will make it reconnect the signal. The below shows the connection plugs.



http://www.944online.com/cgi-bin/forum/f...1298927600



Cheers,

Larry

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