Leaky mechanical fuel pump

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hgraham
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Leaky mechanical fuel pump

Post by hgraham »

About a month ago, I put in a Facet electric fuel pump to solve a long-time fuel starvation problem. I've since been on several lovely drives covering a few hundred miles without incident... until last weekend. I went on roughly a 100 mile drive yesterday, then parked in my garage. I went out today to get some wrenches for something else and noticed a heavy gas smell as soon as I opened the garage door. A quick search found a big puddle of gas under the driver's side front wheel. I quickly wheeled the car out by hand and cleaned up the puddle, then went to work finding the leak. It turned out to be the mechanical fuel pump and, apparently, an approximately 1mm diameter hole under the top. Is this problem being caused by excessive fuel pressure from the new electric pump, or is it a sign that the mechanical pump now needs rebuilding? I'm not sure if this is related at all, but on the last drive I noticed very low oil pressure (never went above the 2.5 line on the gauge) which has never happened before.
1966 330GT #8553
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hgraham
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Re: Leaky mechanical fuel pump

Post by hgraham »

I forgot to mention that the top of the little glass sediment bowl was also damp and had some old residue from prior leakage around the gasket. In my mind, that supported the "too much fuel pressure" theory.

Hudson
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John Vardanian
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Re: Leaky mechanical fuel pump

Post by John Vardanian »

Hudson, if that is the likely cause, it's pretty easily verified, just put a low range gauge on the line.

john
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Re: Leaky mechanical fuel pump

Post by 8339 »

Hudson, make sure you check the oil and to see if it's "gasified", the mechanical pump may have pumped some fuel into to the oil sump.
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tyang
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Re: Leaky mechanical fuel pump

Post by tyang »

You may have had a weak seal to begin with, but it's possible with the new fuel pump putting more pressure into the system.I agree, if you can put a gauge on the line, it would tell.

Knock wood, I have a similar set up on my car, and have been running it like that all summer, and it has yet to leak. I'm going to the garage now to check!

Tom
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330GT
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Re: Leaky mechanical fuel pump

Post by 330GT »

That hole is a vent hole that vents the cavity between the block and diaphragm in the mechanical pump. If the O-ring around the push rod in the block leaks, you will get oil out of this hole (that was my failure case). If the diaphragm is leaking, then fuel will come out. So I think that you probably have a leaky diaphragm, but whether it's due to age or pressure is unknown. In any case, you need to take the pump off and replace the diaphragm and check valves.

If you replaced the original electric pump with this new one, then the check valves in the mechanical pump would have to be bad to have that pressure inside the mechanical pump. If you put it inline with the mechanical pump, then too much pressure might have caused the problem.
Regards, Kerry
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tyang
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Re: Leaky mechanical fuel pump

Post by tyang »

A bad diaphragm would have leaked anyway regardless of the added pressure, but it didn't help the situation!

Tom
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Re: Leaky mechanical fuel pump

Post by 250GT »

If the original configuration is still there.
I would suspect the Fispa pressure/filter regulator.
so check pressure between mech. pump and regulator.
I suspect you blown up that regulator and this will break down those very fragile pump valves.

C.
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hgraham
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Re: Leaky mechanical fuel pump

Post by hgraham »

Thank you all for the suggestions.

The new electric pump is installed inline with the old, although the power to the old pump is disconnected so that fuel is only flowing through it. I did it this way to avoid cutting the hard lines and retain the ability to go back to stock. I would imagine that the pressure regulator isn't doing too well because there are obvious leaks around that. I'll pick up an inline gauge on my way home from work and see what I can find, then report back.

No matter what I find, it sounds like I'll need to rebuild the mechanical pump. I read through Tom's article in the restoration diary and it doesn't sound like a consensus was reached about what parts to use and how to fit them. While I plan to use the electric pump full-time, I'd like to have the mechanical pump functioning correctly in the event that I switch back to stock configuration, so if anyone has had good luck with a particular product or method I would appreciate any advice.

Hudson
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330GT
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Re: Leaky mechanical fuel pump

Post by 330GT »

Hmmm,

If the new pump is inline with the old electric pump, then the new pump is pumping into the rear of the fuel log with the pressure regulator between it and the mechanical pump.

So i think that it was just time for the mechanical pump diaphragm to give up the ghost.
Regards, Kerry
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hgraham
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Re: Leaky mechanical fuel pump

Post by hgraham »

Kerry: The modern fuel pump was fit in place of the short soft hose between the original electric pump and the hard line running to the front of the car. I really have no idea, but I thought that this line ran to the mechanical pump and not the fuel rail. While I did select a modern pump with the recommended output pressure, I'd think it would be counterproductive to send the fuel directly to the carbs, then have the pressure regulator set a new pressure and send it to the mechanical pump to be pumped back to the tank. I have little experience with these cars or this "advanced" of a fuel system as I'm used to 50's British stuff, so please correct me if I'm mistaken. It will certainly help in solving this problem!

I had a bit of trouble finding a place with fuel gauges in stock, but finally located one before 5pm at a drag racing shop. I now own a cheap Chinese fuel gauge with high priced anodized aluminum race fittings to adapt to the Ferrari. Cool! However, when disconnecting the old hose to fit the gauge, the 40+ year old part threw in the towel, so I'll have to wait until tomorrow to buy some 3/8" hose to test the pressure. Better to have that happen in the driveway than miles down a country road!
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hgraham
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Re: Leaky mechanical fuel pump

Post by hgraham »

I picked up some new fuel hose on the way home from work today and hooked up the gauge between the mechanical pump and the pressure regulator. It didn't register any pressure because all of the fuel was coming out of the mechanical pump. It was difficult to tell exactly where it was leaking, but it's either the overflow hole underneath or the seal between the top piece and the body of the pump. Is there anything else I should check before rebuilding the mechanical pump? I will probably order a kit to rebuild the pressure regulator at the same time.
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John Vardanian
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Re: Leaky mechanical fuel pump

Post by John Vardanian »

Check your engine oil for gas contamination before you start up.

john
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hgraham
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Re: Leaky mechanical fuel pump

Post by hgraham »

Thank you John. I was reading about the great potential for an engine fire if gas gets into the oil. I did take a sniff of the dipstick and didn't detect gas, but will get a few samples along the way before firing up the car.

Hudson
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Steve Meltzer
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Re: Leaky mechanical fuel pump

Post by Steve Meltzer »

I rebuilt the mechanical pump on my GTC, using parts from "Then and Now", 781-335-8860, www.then-now.com, Weymouth Mass. They can also rebuild the pump. Be aware that, over time, the top of the pump and the body, can warp, so they might need some gentle sanding. For the fair price they charge, i'd let them do it next time. Got the regulator parts from GT part in Az. steve
(disclaimer: "Then and Now"kick me back $500 for every new customer I send!) s
steve meltzer,
"I've spent all of my money on wine, a beautiful woman, and stunning cars. Then, squandered the rest."
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