mtcookson Posted June 27, 2004 Share Posted June 27, 2004 For those who don't like to read, cliff notes are on bottom right above my questions. I just recently bought a 75 280z and have been getting it to where it can run again (been sitting for 2 years). So far, I've fixed some wires that a damn pack rat ate through, cleaned up the thing's mess, put in new spark plugs and wires, new air filter (pack rat ate through that and made a nest in the air box which i cleaned up), i drained the fuel tank, put on a new fuel filter, and am getting ready to change the oil and oil filter. I cranked it over early on to make sure it wasn't locked up or anything and it cranked over beautifully. One thing I noticed though was that I never heard the priming charge from the fuel pump. I checked for more wires and looked around for a possible cutoff switch but didn't see any so I went on the tedious task of taking the fuel pump out. Got it out and touched the terminals to a battery... nothing. I was about to give up when all of the sudden I got the bright idea to take it apart. I took it apart and found the part that spins so I tried spinning it with my hand but it wouldn't spin. I put a rag over it and put some channel locks on it to break it free and it did so instantly. I could then spin it with my hands. I hooked it back up to the battery and it spun fine so I put it all back together and checked it again on the battery, still worked. I toss it in the car and turn the key to the on position to listen for the priming charge... still nothing. I got a multimeter out and hooked it up to the pump to see if I was getting any voltage. Turn to the on position and nothing however... when I try cranking the engine the voltage goes up to 7 or so volts, which doesn't seem correct to me at all. Cliff notes: Fixing up car, fuel pump doesn't work, take out fuel pump, its locked up, i free it, test it multiple times to make sure it works, put pump back in, turn key to on position for priming charge and hear nothing, hook up mulimeter and there is no voltage to do a priming charge, when i try starting the car the multimeter says there is only 7 volts being supplied to the pump. I guess my questions are, is there supposed to be an initial voltage for the fuel pump to prime the fuel system, is the voltage supposed to be lower like the 7 I had read or is it supposed to be 12, and I guess lastly could any of you point me to the location of the wires that go to the fuel pump and also the "electron fuel injection relay"? Many thanks in advance if you guys can help me out on this! Quote Link to comment Share on other sites More sharing options...
GrayZee Posted July 3, 2004 Share Posted July 3, 2004 I had similar problems with my 76 280z. The fuel pump was always funny about priming, especially if it had been sitting for a long time. I sometimes would have to crawl under there with a motorcycle battery and some really small cables to "jump start" the fuel pump. Once the engine was running it would be fine unless the car sat for several days. I always assumed that something was wrong with the fuel pump relay but I never did get around to changing it. Instead I did a turbo swap, used the zxt relay and never had a problem since. The original fuel pump relay is located under the dash above where the hood release cable is. Not a very easy thing to remove. If I had to fix that problem now, I think I would just find out which wire from the ECU triggers the relay and wire up a new relay with a feed wire coming from the battery (with a fuse) and straight under the car along the brake lines to the fuel pump. With a ground wire running back up to the battery. Quote Link to comment Share on other sites More sharing options...
Sumo Posted July 4, 2004 Share Posted July 4, 2004 I have never heard my 75 Z prime the pump on the "on" position, i usually hook power directly to the pump when it has sat long for a couple of months or years, just to run fuel thru the system. It usually cranks up right away especially after it has been running, but let's say after a couple of days of just sitting around not running, it takes about two to three cranks before firing up, but the pump never makes noise when just left on the "on" position. Quote Link to comment Share on other sites More sharing options...
GrayZee Posted July 4, 2004 Share Posted July 4, 2004 Hmm.. that's interesting, maybe the old 280's never did prime the fuel lines? If that's true it's a crappy design if you ask me. I would definatly re-wire the system like the 280zx's if that is the case. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted July 6, 2004 Share Posted July 6, 2004 Yah, I had issues with mine.. it would prime for about 5 seconds, then the car would fire up... but if the car stalled, it would keep running! I think it was a problem with the afm, but I have since ditched my FI in favor of SU carbs. I still have the whole harness, sensors, ect in a box... if you figure out what you need, I'll see if I have a replacement for ya.. I'm not looking to make money here BTW.. just seeing if I can help out...let me know. Quote Link to comment Share on other sites More sharing options...
sims76 Posted July 6, 2004 Share Posted July 6, 2004 The fuel pump only gets voltage when the engine is cranking or running. More specifically, whenever air is going through the air flow meter. Check out this page (not mine). http://www.atlanticz.ca/zclub/techtips/ Quote Link to comment Share on other sites More sharing options...
mtcookson Posted July 11, 2004 Author Share Posted July 11, 2004 I got some files from a Z guy and it said in there that there is no priming and that the pump will only run when air is going through the afm (as said above). Its a safety setup to where if you're in a wreck and a fuel line breaks it won't keep spewing gas out. The engine has to die but it most likely would if a fuel line broke. I worked on it some more and found the problem to be my fuel pump. It is either internally or shorted or just plain fubar. I took it apart once more and tried to take it fully apart but had no luck so I put it back together. I hooked it to the battery again and it sounded as normal running at like, 50%. All of the sudden some dust came out and the thing just started moving real well. I hooked it up to some gas in a gas can and it kind of gurgled. I figured it did that since its a pusher pump and not a puller so I hooked it up to the car. Pushed in the afm and it ran and everything but wasn't getting any fuel. I thought about it for a sec and got the idea to flip the wiring around on the fuel pump. Sure enough once I did that the thing pumped fuel perfectly. I'm not sure what the hell happened to make it do this as I'm pretty sure i put it back together properly. I'm going to see if I can at least get the car started this way even though I don't like it. I'll just grab an aftermarket pump in the next day or so. Next thing I need to figure out is my injectors. For some reason they aren't firing so that appears to be the last step before getting this thing running again. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted July 11, 2004 Share Posted July 11, 2004 If the injectors arn't firing, they might just be cloged from old gas... you said the car sat for quite a while right? If you have the FSM there should be a test for the injectors too.. I cant remember, but it's a simple resistance reading.. between two values its good, above or below, no good. I have the book so let me know if you need the info and I'll look it up for you. Quote Link to comment Share on other sites More sharing options...
mtcookson Posted July 12, 2004 Author Share Posted July 12, 2004 Yeah, the car had been sitting for 2 years and had some real nasty gas in it. I tested the injectors and they still popped but I never checked the resistance. Earlier today after my last post I went back out and messed with it. The injectors started firing when the engine was cranking over. I either didn't have the screw driver on good enough the first time or something but they clicked. It still wasn't starting so I checked the spark, it was good. I then pulled the afm off and put my hand over the tb while my dad held the butterfly open and cranked it over and I was indeed getting vacuum so the only thing left was gas (unless the valves got out of adjustment which would tick me off since I've never messed with adjustable valves before). My dad and I thought that maybe the injectors were clogged or something because he pulled out 3 spark plugs and I held it at wot while cranking and there was no gas coming out at all so I'm in the process of changing them (previous owner bought a spare set of them). I noticed while I was changing them that there was still bad gas in there so I did some crazy hose setup to where I could have fuel flow freely through the lines and clean out any old gas there. I also thing the FPR might not be working properly so I'm going to put the spare on one there. Hopefully something will come out of all this that I've done tonight. Datsunlover, if you could send me or post up the resistance values that would be awesome. Thanks for all of the help everyone! Quote Link to comment Share on other sites More sharing options...
Mr.INSANE Posted February 25, 2006 Share Posted February 25, 2006 Yeah i really doubt the 280z primes. My fuel pump didnt work when i bought it. When i replaced it i still never heard a prime but it still runs so what the hell. Quote Link to comment Share on other sites More sharing options...
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