Fuel pump oil leak - advice please!

Tony 260Z

Club Member
Hi all,

I discovered tonight that the Nikki fuel pump on my 240 (L28 with 240Z Hitachis) is leaking oil. It's probably only a teaspoonful but that's enough to produce a dirty mist on that side of the engine and spots on my windscreen where it's blowing out through my bonnet vents. I can't tell whether the leak is at the wider part of the pump where the diaphragm is or where it's bolted to the engine itself. That bit looks as if it might have been siliconed before so I'm wondering if it's the problem spot.

So... three choices... (1) take the pump off, clean up the outside and reinstall it with a better gasket to see if that cures it, (2) as number 1 but try for some sort of rebuild/repair as well, or (3) bin it and fit an electric pump and pressure regulator. I have a Facet red top and a Malpassi Filter King in the garage somewhere which helps.

I'm tempted by option 1 as a fingers-crossed option but have also noticed that when I accelerate hard in first gear, and again in second, when I go into third I get to about 4,000 revs and the engine starts missing. If I then change into fourth it's fine. Feels like fuel starvation to me. Could it be that the pump is failing and the hard charge drains the float bowls? Then the change into fourth and lower revs lets it catch up? Or could it just be that the carbs need setting up properly?

Does all that make the electric pump option the best bet? To be honest I've done most jobs on my Z's over the last fifteen odd years but I'm not a fan of working on the fuel system and I'm not as mentally sharp as I once was so I'm a bit cautious of fuel plus electrics.

All advice very welcome!
 

jonbills

Membership Secretary
Site Administrator
I'd forgotten all about it, but when I used to have a mechanical pump I had that oil leak problem. As I remember it, there's a ball bearing sealing a hole in the body of the pump, and I think it was the source of the leak. I never figured out what it was for, and switched to an electric pump.
I'd be inclined to agree with your misfire diagnosis, but a session on a rolling road would be the way to know for sure if it's going lean.
It could be fuel pump pressure, float inlet valve restrictions or some other restriction.
If you accelerate less vigourously in 2nd, is it ok when you go into 3rd?
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
If you want the minimum work, try option 1 first and also check your fuel filter for sediment.

I'm sure a standard pump will supply enough fuel if the 'system' is clear.

If that fails go for Option 3, where will you mount the electric pump and filter?
 

nospark

Well-Known Forum User
I would buy a new pump. Your existing pump is likely to be tired with either the rubber affected by ethanol or the internal spring not as springy as it was when new and failing to do its job properly. I recently bought a GMB pump from USA and am happy with it. It also comes with two gaskets. The pump is not expensive but the 'extras' (customs etc) pushes the cost up.

Whilst you wait for the pump, clean the fuel filters in your hitachis and blow compressed air through the fuel rail.
 

johnymd

Club Member
You could fit an Electric pump in the factory position, by the fuel tank. The wiring will already be there and you just use a short jumper wire by the radio to make it all live from the ignition. This is what I did to the silver car. I also fitted a cheap inline clear plastic filter on the fuel tank outlet to prevent any rust comeing from the tank.
 

anthon51

Well-Known Forum User
I'd forgotten all about it, but when I used to have a mechanical pump I had that oil leak problem. As I remember it, there's a ball bearing sealing a hole in the body of the pump, and I think it was the source of the leak. I never figured out what it was for, and switched to an electric pump.
I'd be inclined to agree with your misfire diagnosis, but a session on a rolling road would be the way to know for sure if it's going lean.
It could be fuel pump pressure, float inlet valve restrictions or some other restriction.
If you accelerate less vigourously in 2nd, is it ok when you go into 3rd?
Hi Jon.I hope you got my message of thanks when you gave me some advice about the fuel pump.
I have replaced mine with one from the states as MJ did not have any at the time.It seems to be working very well now with the replacement.I also put in transparent fuel hoses in the engine compartment just so that I could keep my eye on the fuel delivery.
I have kept all the old hoses and the old fuel pump just in case they are need later to authenticate the Zs history.of originality.
 

anthon51

Well-Known Forum User
Hi Tony 260Z. I hope this will help in some way as I had a problem of the same nature with my fuel pump some while ago. I think that you will find that the oil is coming from the pin that holds the arm to the petrol pump. If this is the case then the oil must be coming from the gasket were the arm goes into the petrol pump. Although I know the authenticity of your car will be lost by replacing the pump I think you will find it is the easier option. Just dont throw your old petrol pump away as you may want to try and repair it with new gaskets and seals,it is part of the original anyway. Regards Tony 448.
 
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