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Discussion Starter #1
The mechanical fuel pump on my 240Z is leaking oil from a small vent hole in the side of the pump body near where the pivot pin is. The pivot pin was sealed with silicone by the previous owner (a common remedy), but the vent hole is leaking oil into the prop-wash of the cooling fan and spraying the plug-side of the engine bay. I guess the vent hole was also sealed with silicone because it was fine for the first week of ownership, but now leaks with each drive.

I had a few gear shifts when the throttle jammed wide open :-O until I worked out that it was the aftermarket carpet fouling the pedal and not the throttle linkages. Maybe the 7500RPM blew/sucked the opening clean again?

My previous car, an ugly Datsun 120Y (B210 in US?) with an L16 SSS motor exhibited the same leakage/oil spray (the 7000RPM episodes were always intentional in that car :) so I guess its' a common problem in the L-series mechanical pumps.

Anyway, the vent hole is obviously intentional - but brand new Datsuns didn't spray oil all over the bay, so I guess the Positive Crankcase Ventilation setup is supposed to keep that hole sucking air not blowing oil?

Any ideas on how to stop the leak?
 

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I think you have the answer right in your message, check/replace the PCV valve. The oil is just spray off of the cam chain area and if it's blowing oil you have too much pressure in the crankcase. You might try disconnecting the hose to the pcv for a little bit to see if the leak stops. If the engine has a ton of miles on it and a working PCV than do a compression check to make sure your not blowing a lot by the rings. You might have to rebuild or use a heavy oil additive if you want to cut costs in that area for a while. Hope it's just a stuck PCV valve. Good luck.
Of corse this is all kind of a guess, I've never had that problem with any of my 3 Zcars but there's always a first, don't know if there is just a hole where there isn't supposed to be in the fuel pump, you might try getting another one from a junk yard to see if that's the case. I'm going to go take a look at mine to see about this hole. You can always just get a block off a fuel injected Z motor at a junk yrad and plug that area and get a electric fuel pump instead. If you do that make sure you add a gas pressure regulator. Ok, that's a few idea's to look into... Have fun..

> The mechanical fuel pump on my 240Z is
> leaking oil from a small vent hole in the
> side of the pump body near where the pivot
> pin is. The pivot pin was sealed with
> silicone by the previous owner (a common
> remedy), but the vent hole is leaking oil
> into the prop-wash of the cooling fan and
> spraying the plug-side of the engine bay. I
> guess the vent hole was also sealed with
> silicone because it was fine for the first
> week of ownership, but now leaks with each
> drive.

> I had a few gear shifts when the throttle
> jammed wide open :-O until I worked out that
> it was the aftermarket carpet fouling the
> pedal and not the throttle linkages. Maybe
> the 7500RPM blew/sucked the opening clean
> again?

> My previous car, an ugly Datsun 120Y (B210
> in US?) with an L16 SSS motor exhibited the
> same leakage/oil spray (the 7000RPM episodes
> were always intentional in that car :) so I
> guess its' a common problem in the L-series
> mechanical pumps.

> Anyway, the vent hole is obviously
> intentional - but brand new Datsuns didn't
> spray oil all over the bay, so I guess the
> Positive Crankcase Ventilation
> setup is supposed to keep that hole sucking
> air not blowing oil?

> Any ideas on how to stop the leak?
 

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I had the same problem with my fule pump. Took me a while to locate that leak. I just bought a new pump for around $45 and fixed the problem. That was my fix.

Hope it helps.

Chris
 

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Discussion Starter #4
> I had the same problem with my fule pump.
> Took me a while to locate that leak. I just
> bought a new pump for around $45 and fixed
> the problem. That was my fix.

After Brandon's reply (thanks) I checked out the whole positive crankcase ventilation system. There wasn't too much info in my Hayne's Manual about PCV, but I have a Datsun 180B (610) manual that better describes a similar system.

Without going into it, as long as the rubber seals are good on the Oil Filler Cap and the Dipstick, the crankcase will be under vacuum from either a) the hose going from the rocker cover to the air cleaner box or b) the larger hose going from the crankcase to the balance tube (post-carby inlet manifold). The normal flow actually reverses at full throttle. Anyway, there shouldn't be positive pressure in the crankcase even with a failed PCV valve, although I expect there is a lot of air movement between the cylinders underneath the moving pistons. I have an even 150 compression across all cylinders, so I shouldn't be getting sufficient blow-by to upset the system.

A closer look at the fuel pump exploded-diagram shows an internal oil seal around the diaphragm rod which sounds like the culprit. It looks like there are three regions in the fuel pump:

- the fuel chamber (fuel/wet)
- an airspace on the other side of the flexible diaphragm (air/dry)
- an opening into the crankcase that gets sprayed with oil to lubricate the rocker pivot (oil/moist:)

I suspect the air hole opens into the dry airspace to allow the diaphragm to move, which makes more sense than opening a hole into the crankcase where I first thought it went. I guess you shouldn't seal this hole with silicone!

Anyway, I'll verify all this next weekend when I dismantle it. The fuel pumps in Australia are about $AUD150 from Nissan (about $100 US) so I'll overhaul it if I can - or buy an electric pump instead.
 
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