gmanatc97 Posted June 17, 2012 Share Posted June 17, 2012 I have a 78 280z with a stock L28e that I have been working on here and there for about three years. When I got the car, it would not run. So after trying different things I found that it was just a rusty old fuel tank and rust in the fuel system. But during this process I bypassed the relay under the passenger seat going to the fuel pump. So now the fuel pump runs constantly when the key is in the on position. I have not done any other wiring adjustments, but that doesn't mean someone else hasn't. Here are my questions: A. What is the exact function of that relay? B. Is that relay the reason for the pump running constantly or is that a function of the fuel pump relay under the dash? C. Is there any problems with the pump running constantly? Other than possibly overheating. Quote Link to comment Share on other sites More sharing options...
OldAndyAndTheSea Posted June 17, 2012 Share Posted June 17, 2012 There are two main functions of the fuel injection relay. Its overall job is to provide reliable current to both the fuel pump, and the injection system. This relay controls when the fuel pump will actually run. The fuel pump runs at two intermittent times: First when you are CRANKING the motor, and only then. Then once the motor starts the fuel pump power signal is based on the Air Flow Meter flapper being open. This is done this way so in case the car wrecks, or you stall the car out, subsequently the AFM flapper closes, shutting off the fuel pump. This eliminates the possible, and expensive need for a casket should you wreck, and break a fuel line. If you are going to run a straight new line to the fuel pump, most recommend using at least a 20 amp relay either way, for reliable constant power. Then they will hook the fuel pump power to the oil pressure switch, so when the motor sees 0 oil pressure the pump shuts off, much like the AFM controlled switch in the stock wiring harness. Here's the link to the fuel injection bible. Read it, if you haven't. It's full of valuable information. http://www.xenons130.com/files/280zfuelinjectionbook.pdf Quote Link to comment Share on other sites More sharing options...
gmanatc97 Posted June 17, 2012 Author Share Posted June 17, 2012 Okay so I have read and understand the Fuel Injection Bible. But no where in there does it mention the relay under the seat. I know the function of the relay above the ECU, so that might be causing the fuel pump to run constantly. Either that or the connection on the AFM. On the relay under the seat in my car there were only four connections. One for the positive and neg going to the pump. I can only assume since the pump works the other two were the power going into the relay and a ground going into it. Am I wrong in that? Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 17, 2012 Share Posted June 17, 2012 Read the FSM, it has more detail specific to 1978. Fuel pump relays are probably described in Body Electrical or Engine Fuel. Somewhere out there on the internet is an account of how the 1978 safety system of the oil pressure switch and the alternator output can actually fail itself and cause the fuel pump to run continuously. If I find it I'll post a link. Quote Link to comment Share on other sites More sharing options...
gmanatc97 Posted June 17, 2012 Author Share Posted June 17, 2012 Thanks NewZed. I agree fully with Andy, I don't really want the fuel pump to run constantly and especially in the event of a crash. I am still at least a few weeks out from getting her back on the road, so I would like to solve this problem before then. Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 17, 2012 Share Posted June 17, 2012 Somehow I found that link. It's buried on the Atlanticz.com page, the only place I've seen it. Might not be your problem but still very informative. http://atlanticz.ca/zclub/techtips/fuelpump/moreinfo.htm Quote Link to comment Share on other sites More sharing options...
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