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Hey all,
I just joined rennlist today. I came across this site while searching for answers to my 964 fuel pump issues. I recently acquired a 1992 C4 that had been in storage for over 15 years. This is my first Porsche so I have lots to learn but I like learning... I think my C4 will challenge me on learning. It has fresh oil& filter, fresh gasoline and new battery. The engine cranks over but won't fire. I pulled the DME/fuel pump relay and jumpered 30 and 87b which is supposed to turn on the fuel pump. I heard nothing. 30 has the same voltage as the new battery.. I checked the current draw between 30 and 87b and found it to be a steady 13 amps. One site said normal was 10 amps, so this is quite a bit higher and getting close to the 15 amp fuse that drives this circuit. My main question: Is there anything else I should check or do before I jack the car up and dive underneath to pull the pump? Is 13 amps indicative of a problem? Should I be able to hear the fuel pump run? Thanks in advance for any help you can provide.
Cheers
Tom
If you've jumped the relay to power the pump then yes, you should be able to hear it running, all be it quietly. You may have to get under the car to hear it tho.
Be careful if you have gas in the tank when you pull the pump. Be sure to clamp of the supply hose from thee tank, and keep exposed flames or hot light bulbs away.
Thanks guys,
Well I pulled the fuel filter before going underneath to look at the pump. I knew the filter was old. The date said 1995 but it still had flow when I bench tested it. I was kind of hoping it was plugged solid and maybe that is why the pump would not start since it would not be able to move any fuel. Oh well. I had lots of fun wrestling with the fuel filter connections, particularly the front one. Hey does anyone put any anti-seize or teflon tape on the threads to prevent frozen joints on the fuel filter?
Update: I pulled the fuel pump down a few inches, just enough so I could access the terminals. Fuel lines were left connected. I applied 12 volts directly to the terminals of the pump and could hear a humming noise but no fuel arrived at the disconnected fuel filter in the engine bay. I am looking at disconnecting the fuel lines and pulling the pump for bench testing, but have a few concerns like, should I drain the tank first. If so, how? Do I need a special wrench on the fuel pump? The clearance between the electrical terminals and the nut I need to access is so small, I don't see how any ordinary wrench will fit. I have searched for these answers but so far have not found anything useful. If someone reading this has done this before, I would greatly appreciate advice. See attached photo. If the blue plastic part is removable it would help with wrench clearance.
It is possible to clamp off the fuel line from the tank to the pump. One caveat is those old rubber hoses can be brittle. It is fairly easy to suck most of the fuel out of the tank thru the hole the fuel gauge sender goes into. Definitely disconnect your battery before attempting to remove the pump an accidental spark down there could be not good. There is a screen at the out let of the tank prior to the fuel pump I guess it could be plugged. The big nut with traces of red paint on it in your picture is what you remove to disconnect the the fuel line it is a banjo fitting. Simple hose clamp at the other end of the pump. I don’t recall if there is a drain plug for the fuel tank. If no one else replies when I get home tonight I look at my tank I have it out of the car right now
Thanks JohnK964,
Were you able to remove your fuel tank without first disconnected the suction hose to the pump? Also when you look at your tank can you tell me if the return line attachment point is beside the suction hose attachment point. The Porsche parts and maintenance manuals don't have this level of detail at least not that I have been able to find.
I always have the battery disconnected when doing this kind of work, but thanks for the reminder. When testing the pump, I made all my connections to a battery charger and then had an assistant plug the charger in to make sure there would be no sparks anywhere near the fuel pump. What year is your 964?
I just pulled the suction side line from the pump hose clamp end left pump in place I’m at work now but will post up or private message you later what I find at home later my friend 👍
I pulled the suction side by removing hose clamp from the side of the pump and undid the fitting from the return side it’s pretty obvious which is which in the picture the straight line is the return the curve hose is the suction no drain plugs by siphoning from the fuel gage sending unit you can get down into the sump where the suction side of pump is. Good luck and have fun
That photo of the tank bottom is perfect. Thanks JohnK. A picture is worth a 1000 words. Now I know exactly what I need to do when I pull the tank.
This afternoon I removed the sending unit, and siphoned out 10 gallons of gasoline that surprisingly, did not smell totally rank. After 15 years, I was expecting far worse. However, when I went to siphon the last gallon or so out of the well, the siphon plugged with a thick, black goop. I think there is about 1/4" of this goop in the well. So I will pull the tank and give it a good cleaning.
You had a good suggestion about my battery charger, but it is a heavy-duty 15 amp charger that should have ample power for a fuel pump test. The fuel pump circuit is on a15 amp fuse, so I am pretty sure that test was valid. The only other think I can think of is, the fuel pump check valve might be blocked.
I as just about to post this when your most recent post arrived. All good info. I did peer inside with a flashlight and that is how I discovered the well for the suction filter and return line. At this point I am convinced it is the pump or the check valve inside the pump. Either way, she has to come out. Thanks for sharing your "lessons learned". I will do the same if I learn anything new.
Update: I got the fuel pump out and bench testing proves I need a new one. One step closer to getting this baby running again. There could be other things wrong, but without question the engine won't run without fuel.
If anyone else is thinking of removing the fuel pump, be advised that it is a challenge to hold the nut on the back side of the banjo bolt. The only way I can see to do it is to grind the outside edges of your 17mm open-ended wrench to fit, or use needle nose vice grips. An unmodified wrench only engages about one half of the flats of the nut because the wrench hits the electrical terminals. One half flat engagement on the nut is not enough. Trust me. I rounded the corners off mine. See photo taken on bench afterwards.
03-28-2018, 08:16 PM
Fuel pump problem
