[Ceenit]

Three things I would check/change first are the DME relay, fuel filter, throttle body sensor/throttle body cleaning, or battery ground.



Over the years i have had the issue on a few different cars and one of the three items above have solved the problem for me.

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[968Bud]

I swapped out the coil with another "known good" coil. Drove for 5 days. Car shut down again. Engined died for a full 10 seconds and re- fired on it's own while the car was in motion. So it is not the coil! Today I'm going to take out the DME and reflow all of the solder joints. We will see how that go's!!!!

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[jfrahm]

It's very easy to make a DME relay jumper wire also:



http://www.clarks-garage.com/shop-manual/fuel-05.htm

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[Eric_Oz_S2]

My bet is either a faulty DME, cold solder joint as mentioned earlier, faulty coil or poor wiring between the DME and ignition coil.

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[968Bud]

Problem still exists. I have done these two things since my last post: 1. Reflowed all of the solder joints on the DME. Ran the car for 4 days. On day 4 the car died at 70 mph! I let the car coast for about 9 solid seconds. (Down to about 50-55 MPH) and then it just resumed as if nothing happened! 2. Decided to replace the whole DME with a know good working unit. Drove for 1 day and car died on me. My wife was driving it with me. We were doing about 45mph car coasted for about 10 seconds and it then resumed as if there was no problem. Any new thoughts guys. .... again... no check engine light no sign of it comming on!

Oh... and I did replace the coil with a know good working coil.

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[flash]

does the dash go dead, or does the engine just stop running?



is it a tip or manual?

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[968Bud]

Manual transmission ! The dash does not go dead. The check engine light does not come on. The voltage stays constant... maybe a little drop if the lights are on.. The engine just stops running... but engiine is rotating because it is still in gear at 55mph!

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[flash]

if it were a fuel source issue, it would come and go, as the fuel rail filled and emptied and filled. it would also sputter, and not just "shut down"



it's electrical and probably one of 3 things:



1. ignition switch is not staying in the "run" position. i've seen this happen, especially with people who have a lot of keys on their ring.



2. voltage failure from DME fuse, DME relay, or DME



3. fuel system failure, i.e. pump not getting power. this one is less likely, as it should give a less sudden failure.



i recommend making up some test lights and putting them in line to see where the problem lies. this may involve cutting into the harness to gain access to a wire.

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[vliegwielolaf1234]

It could be fuel related . my car has a kill switch for the fuel pump .

Takes about half a sec , after you flip it to stop the engine instant . no sputter and when you turn the pump on again , it wil pick up instant as wel with no sputter .

My guess bad pump , or wires damaged .

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[unknown4u]

my sugest is to replace the wiring from the dme till the fuelpump. why? this because there is a connector 50 centimeter from the fuelpomp what could be the problem. you have to measure the voltage at the fusebox. and then measure the voltage at the pump. Is there a difference from 1 volt then there is a resistance in the connectors. The connector is getting hotter and the clamp from the connector opens inside. When it opens the pump shut down due to a failure in the harness. When the connector cools down the fuelpump starts to work again. It is hard to find. I have had the same problem in the past with my tiptronic. The harness from a tip or a 6 speed is equal. You can also do a small test. put a fuelgauge at the fuelrail at the injectors. jumer the dme and let the pump run as long as it quits. You don't have to start the engine anyway. But connect a extra source for the battery because this will drain your battery. If the pump don't stop after half an hour you have to look elsewhere.

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[flash]

view - are you sure that is a kill for the pump, or the relay to the DME? there should still be fuel in the rail, and power to the injectors if you only kill the pump, and it should still run for a few seconds after it is shut off.

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[vliegwielolaf1234]

[quote name='flash' timestamp='1352386599' post='134591']

view - are you sure that is a kill for the pump, or the relay to the DME? there should still be fuel in the rail, and power to the injectors if you only kill the pump, and it should still run for a few seconds after it is shut off.

[/quote]

!00% sure it turns the pump off directly followed the wires so know they cut of the pump and not the dme relais , the wire and switch came with the car and they used a rear wiper switch to mask it , it is a bit odd since there is an alarm system installed .



I was acctually very surprised that the engine would die that quick after the pump stops , no sputter nothing .

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[flash]

followed them all the way to the pump? if they only go to the ECU, you may not be turning off only the pump, but the injector power too. the fuel pressure in the rail should continue to run the injectors for at least a few seconds if only the pump is disconnected.

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[unknown4u]

My 968 dies immidiatly when you turn of the pump. it doesn't run for a few seconds..... it stalls directly.

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[flash]

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.

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[PorschePilot]

Very interesting... My car did the same thing a couple times within a few days about 3 months ago. Didn't occur again until this week, and now it has done it three times. So far, it has always happened at speed, and the engine has started making power again while the car is in motion. I'm thinkiing if it was just ignition, the engine would load up with fuel, and when the ignition resumed, it would do so with a bang, but the engine "dies" and then comes to life again very smoothy, with no sputtering or other indication at either end of the event. I thought I'd get on the forum and see if anyone else had experienced the problem, and low and behold, it's the first topic!

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[vliegwielolaf1234]

[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 cutout switch wires tap into the wire to the pump , so like i said it turns off the pump , and it dies almost instant with no sputter .



When you think about is , most of the fuel lines are metal so no flex , only a few drop's of fuel without the pump running wil drop the pressur to zero .



I have disconcted the fuel lines at the valve cover a few times just after the car was shutdown , hardly an fuel comes out under pressure .

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[flash]

lol - i am swapping injectors back and forth right now. i can tell you for certain that at least 10cc comes flowing out of there each and every time. the spec for the system is something like that it should hold at least 20lbs of pressure for at least 20 minutes after shut down. it takes my car about a half hour to drop the pressure. the fuel rail should always remain full though, even after the pressure drop. there is something very wrong with your car if there is no fuel in the rail when you open it up after shutdown.



there is no reason i can see that would allow the engine to shut off completely if the injectors are still powered, and the ignition is still on, unless the injectors are acting as a check valve somehow, and require a minimum amount of pressure to open. then the engine would run that long and then shut off. the operating pressure is 3.8 bar. if the injectors require say 3 bar, then it would only run for a second or two.

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[vliegwielolaf1234]

[quote name='flash' timestamp='1352477289' post='134646']

lol - i am swapping injectors back and forth right now. i can tell you for certain that at least 10cc comes flowing out of there each and every time. the spec for the system is something like that it should hold at least 20lbs of pressure for at least 20 minutes after shut down. it takes my car about a half hour to drop the pressure. the fuel rail should always remain full though, even after the pressure drop. there is something very wrong with your car if there is no fuel in the rail when you open it up after shutdown.



there is no reason i can see that would allow the engine to shut off completely if the injectors are still powered, and the ignition is still on, unless the injectors are acting as a check valve somehow, and require a minimum amount of pressure to open. then the engine would run that long and then shut off. the operating pressure is 3.8 bar. if the injectors require say 3 bar, then it would only run for a second or two.

[/quote]





Go drive your car and turn off your fuel pump , see what happens .



Also i said , only few drops wil drop the Pressure to zero , and hardlty any fuel comes out UNDER pressure , i did not mention draining the sytem or fuel rail .



I do not think the car wil run without the pressure in the sytem .







Bear in mind i am dutch so english not alway so easy to explain .

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[flash]

lol - that would mean i need to get under there, cut the power wire, and install a switch. then i would have to get back under there and splice that wire back together. doesn't sound like happy to me.



what i do know for sure is that there is absolutely fuel in the rail after the pump shuts off. i also know that the injectors still get power independent of the pump if you only disconnect the pump. i also know that the ignition still gets power independent of the pump if you only disconnect the pump. compression and spark will continue to ignite any fuel introduced to the chamber. the only question remaining is how much fuel is in the line, and how long it will run.



i have confirmed this now with arguably the best injector company in the country. they said that it will absolutely run for a couple of seconds. it is somewhere between 2 and 5 seconds, based on the pressure and length of the fuel lines.



it sounds to me that your cutoff point is including the ignition system or injector power, which would make it shut down immediately.

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