Marc280 Posted May 22, 2007 Share Posted May 22, 2007 Hi, i've recently replaced the stock fuel pump in my 280zx with a Bosch 910 as i'm planning engine upgrades and the old pump was dying. The only problem i'm having now is it is really hard to start when cold. I'm pretty sure that it is a pressure problem becuase I have put a gauge in the line after the fuel filter and it goes up to about 35psi when the pump primes but then drops away. In the searches i did, someone mentioned that the stock pump has a check valve in it to prevent fuel flowing back to the tank. I would have thought the bosch unit would have this too? does anyone know whether it should or not? Did anyone else have to put a check valve after the pump when they changed theirs? Just that i've never heard anyone mention this before which is why it seems a little odd to me. Marcus Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 25, 2007 Share Posted May 25, 2007 Usually the check valve is integral with the pump discharge fitting or body. If the pressure bleeds off, look for leaks such as a weeping FPR pintile to the return side, or a dribbling injector pintile dumping fuel to the intake. Either of those would also cause pressure drop after shutdown. You can install a check valve in the line, but if it's one of these other common items, it won't do you any good. Cheers! Quote Link to comment Share on other sites More sharing options...
Marc280 Posted May 26, 2007 Author Share Posted May 26, 2007 Hey thanks for the reply, I've checked for leaks at as many places as i can and haven't been able to find any, so I went ahead and installed a check valve and the pressure now stays up. But it still doesn't want to start when cold.... this has got me a little confused as the only thing that has been changed since it started fine when cold is the fuel pump and pressure regulator. At the moment the pressure goes up to about 40psi when priming and cranking (seems a little high although runs at 32psi when engine is running) but doesn't kick. I've checked that it is getting spark and you can hear the injectors clicking. The strange thing is this only happens when cold, even if it is only run for a couple of minutes it will start fine after that. Anyone got any suggestions, for what I should try. Quote Link to comment Share on other sites More sharing options...
Nismo S30 Posted May 28, 2007 Share Posted May 28, 2007 What do you have to do in the morning to get it to start? It might not even be fuel related! Just a coinsidence. Once you get it started how then does it run? Quote Link to comment Share on other sites More sharing options...
Marc280 Posted May 29, 2007 Author Share Posted May 29, 2007 Basically to get to get it to start i keep priming the pump (turning from acc to on) and eventually it splutters into life. Pretty sure it is back firing out the intake when it first gets going which is what was making me think that it isn't getting enough fuel. Once it is warm it will then start first time without any worries. Quote Link to comment Share on other sites More sharing options...
Marc280 Posted May 29, 2007 Author Share Posted May 29, 2007 sorry also meant to say once it is started it runs smoothly with no other signs of any problem, it is just the cold starting.... Quote Link to comment Share on other sites More sharing options...
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