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Old 08-01-2012, 10:29 AM   #1
Porsche 944
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Cool Porsche 944 N/A fuel pump problem

i have a project porsche 944, and sometimes it starts, and sometimes it doesn't due to the fuel pump which sometimes works and sometimes doesnt.
when i feed current directly to the fuel pump it works so i figured there was a connection problem somewhere, so i tested the wires and they all worked fine, is it a relay or can someone give me some advice??

I was also thinking maybe there is an issue with the wiring from the ignition to the DME

also idk if it is relevant but my fuel gauge reads empty but there is fuel in the tank.

Thanks
Nick
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Old 08-01-2012, 10:40 AM   #2
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It is more than likely the DME relay that is beginning to fail. It is located in your fuse panel. They are around $30 (if you buy online from Paragon, 944 Online, etc), get two and keep a spare in your glove box. Also, change the fuel pump fuse while in there, should be a 16 amp fuse.
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Old 08-01-2012, 10:44 AM   #3
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If you have a factory alarm, check it as well: consider bypassing it.

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Old 08-01-2012, 10:48 AM   #4
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I'm not sure if you have tried this but you can pull the relay and put a wire between 30 and 87B. This will check the connection between the fuse box and the pump. You can also check the voltage and the continuity from this bypass. On my '86 944 NA this relay is in the fuse box in the row closest to the engine and the silver relay 4th (?) from the rear. It will have the numbers under the relay once you pull it.
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Old 08-01-2012, 10:50 AM   #5
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The DME relay actually contains two relays. One turns on the ignition, which then turns on the fuel pump.
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Old 08-01-2012, 12:01 PM   #6
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alright, thanks guys, ill try changing the DME relay and the fuel pump fuse, and yes i did test connection between fuse box and pump
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Old 08-01-2012, 12:20 PM   #7
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Another option is to pull up the carpet in the back. The fuel pump is mounted there along with the electrical connections. With a pair of pliers you can pull the top off the connectors. Mine were green with corrosion and were cleaned. This will eliminate the DME if you want to hot wire the pump itself.
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Old 08-01-2012, 03:18 PM   #8
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The fuel pump is under the car just in front of the tank. The connectors under the rear carpet are for the fuel level sender. There is a filter in the tank (connected to the supply nipple) and a filter in the fuel supply line on the discharge of the pump. If the car has been sitting for a while, either (or both) of these could be clogged. You might also want to check that the "S" shaped hose between the tank and the pump has neither kinked nor collapsed.
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Old 08-01-2012, 03:39 PM   #9
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JWADE944 I appreciate the info. My car has been sitting idle for three years. 4:00 Monday with an hour left of shop time we were trying to chase the problem with pumping the last 2+ gallons of gas out of the tank. The fuel filter was removed and I connected a hose to the fuel line hoping to pump the old gas out. I was unable to activate the pump and finally traced the potential problem to a low 9 volt charge in the battery.

Monday I'll put 12 volts to the battery and go from there.

I don't want to hijack the thread. My tribulations are on my thread "Three years on jack stands...time to fire her up" in this same forum.
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Old 08-01-2012, 05:09 PM   #10
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NC, you have a 1986 with a plastic tank, so sediment in the tank is less of an issue for you. Still, you might want to replace the intank filter as well. The original poster, Nick, does not indicate the year of his car, but if it's older, it will have a steel tank and there could be quite a bit of rust in the bottom. To replace the intank filter, just unscrew the nipple. There is a hex head fitting so you can use a wrench. The filter and nipple are a single assembly.
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Old 08-01-2012, 05:09 PM
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