Fuel pump woes

[Alfadog]

My car has been reasonably trouble-free since I bought it, but one thing that continually seems to stuff up is the fuel pump. I've bought 3 new ones now... but it's having the same problem again. It's weird, I'll describe it.

Upon starting the engine (seems to be the same whether its cold, warm or hot) the fuel pump will pretty much immediately start leaking fuel. I was told the first three times it was just a broken seal so I have just replaced it but come on, the problem must be originating elsewhere, surely?

As soon as you start driving, the leaking stops. When idling at traffic lights or in a car park it seems not to leak either. Just on startup.

Do you guys have any thoughts, ideas or solutions?

Note that I have 240Z round-top hitachis on an otherwise standard L24 in a 240K. And yes, I did search the forums first.

[sakijo]

Sounds like it's flooded. Is the return line to the gas tank clogged, blocked off or disconnected? I say this because when you shut off the motor, if the excess gas in the fuel rail (which is under pressure) has nowhere to go, it could backflow to the fuel pump. Hmmmm . . . maybe that's why sidedraft Webers tend to puke gas . . . .

[aarc240]

Lachlan, I would agree with Miles.

The fuel return is most likely the culprit, and assuming you are using a 240z fuel rail set on the motor, blow it clear both ways with high pressure air. Then blast air through to the tank with the filler cap OFF.

If you haven't got the 240z fuel rail set on the engine, go get a set. The 260z is identical with addition of heat shield wrap. You MUST have the fuel rail set connected to both the supply pipe and to the return pipe with the Hitachis as per a 240z or you will always have trouble with them.

Have you considered an electric pump?

The wiring is already there in all GC110 harnesses. About 9cm from the alternator wiring branch towards the firewall you will find a short stub of two wires, one black and one black/white. The black/white has a wide spade connector which you will probably have to replace (it's a bastard size unique to Nissan or maybe Mitsubishi Electric) and that is powered from the ignition and fused. The black is ground.

Use a low pressure pump, 3.5psi maximum, particularly with Hitachi SU's. Facet make a decent one at around $80 new. Genuine SU pumps are available again but count on $270. The OEM Mitsubishi Electric part for the 240K GT hardtops delivered here in Australia is still available but is over $300.

Questions? Feel free to ask - our 240K GT hardtop has a similar setup to yours judging by your description, apart from the electric pump.

Miles, got it in one!

You need a GOOD pressure regulator allowing excess fuel to dump back to the tank. Fixes the fuel puking Webers right smartly. This is just like a modern injection system, allowing full flow to the carbs but keeping the pressure under control. A good ratio on a race car with triple Webers is 10mm supply and 8mm return lines with a regulator having a flow rate of 70 litres per minute or better.

Art

[Alfadog]

Thankyou Miles and Art.

I do have a 240Z fuel rail. I disconnected the fuel return line just above the fuel pump just then - it didn't spurt out any fuel or anything (I would imagine that's normal?). Fuel was there though. So if it is blocked, it would be further towards the tank, right? Might have to get someone to look at it if this is the case. I don't anything here that could blow high pressure air through..

I have considered an electric fuel pump - that info is fantastic and only sways me more towards converting. I will put it on my list of "things to do"!

[sakijo]

The black/white has a wide spade connector which you will probably have to replace (it's a bastard size unique to Nissan or maybe Mitsubishi Electric) and that is powered from the ignition and fused. Art

I'd try to shave or trim the spade to make it fit before replacing. FWIW

[beandip]

The 240 rail has at the end of the return line just a small hole that allows gas to squirt out but restricts flow to maintain pressure to the carbs. Have a look at the end of your metal fuel line and make sure it is not plugged . Gazza , Also if you have any RX-7s in a bone yard down there in the '80 here they were carbed and the fuel pumps work vary well in a Z . I have been using on for years . $15.00 at the Bone yard . They are quiet also and will not over power your carbs.