Have bandaid but want fix - 39 flathead

[adileo]

Hi

First the facts: 1) Mech fuel pump is less than 8 mos old - bought from drakes. 2) I had this problem before putting mech new pump in 8 mos ago 3) have electric fuel pump 4) I only use high Oct gas 5) dual edelbrok 94s 6) I replaced most of the rubber fuel lines (not all)

I have an intermentant problem. Most times car run great idle & all speeds. I like to run the car without the electric fuel pump running and only use it as cure for vapor lock or after car sits for long time.

Every so often (doesnt matter - can be sitting at idle- driving 40-50 or slowing down for light) the car loses fuel pressure and begins to stall. I hit the switch & turn on electric fuel pump and (within seconds) car acts perfectly fine. As soon as it does I shut elec pump off and most times I good to go without problem re-occuring for that drive.

The vacum line from the dist to manifold is mostly a rubber hose - can that be the culprit? Or a simple dirty fuel filter?

thanks in advance Andy

[48 coupe]

Why not just run the elect. pump, and keep on keeping on? That's all I have on my 48.

[adileo]

I could and have run elect pump all time and it is a bandaid fix - but there is still an underlining problem I would like fixed.

Also while rare, as Vic menions here on barn, if your mech pump fails ur elec pump could pump fuel into the crank - and thats not good")

[51 MERC-CT]

How do you know it looses fuel pressure?
Sounds more like a supply problem.
Check float level.
A similar problem was caused by air being sucked in at the filter bowl gasket while being supplied by the mech. pump.

[adileo]

I have a fuel pressure gauge - and once at idle in garage, I saw it drop to zero and car began to stall - I turned on elec pump and car ran normal

[Tony, NY]

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Just thinking out loud. Is the electric pump inline or in a bypass line? If inline it may not be a flow thru type of pump and be a restriction.

[JSeery]

This is a side issue, but why are you running high octane gas? Does your engine have that high a compression ratio?

[adileo]

1) Its inline - Most times I have no issue and can run car alone without elec fuel pump so elec fuel pump is flowthrough

2) Since most fuel is crap these days - I figured high Oct would be somewhat better than regular gas, is only rationale.

[Vic Piano]

Hi Andy, the first thing I would do, is make sure all your lines, fuel and vacuum, are not leaking or letting air into the system. Second, I would replace any and all fuel filters. A good way to prevent air from getting in and/or fuel from getting out of connections where rubber hoses connect with steel, etc. lines, is to coat the end of the line with Indian Head Shellac, before you snug the clamp. As you know, I'm not a fan of using an electric pump in line with a mechanical pump. I've had too many new or rebuilt fuel pumps go bad, to the point where I've changed out almost all of my Flatheads to use an electric pump as the primary. I do gut the OEM pumps and make them 'pass through', so the OEM pump stays mounted on the intake manifold. I also leave the pushrod in the engine and carry a 'known to be good', if not reliable, mechanical fuel pump in the trunk, in the unlikely event that the electric fuel pump has a problem. Hope you get it squared away and drive the wheels off that '39

[adileo]

Thanks Vic - if not resolved....on my next visit to your pondarosa, I may bring a project with me....and if you would not mind - maybe you can show me how to make the mech fuel pump flow through Of couse, I'll supplt all the parts and buy pizza

[Scott H in Wheaton]

The high octane fuel probably isn't helping one bit, just making your wallet lighter and causing the fuel to reduce detonation. If you have no detonation (high compression or severely advanced timing) you don't need the higher octane.
Octane rating is not an indication of the quality of the gasoline.

[alanwoodieman]

according to a local gas dealer, the high octane gas has no ethanol because they cannot get the octane rating with it. these guys "blend in" the ethanol at the pipeline before sending out to stations. experts out there-any truth to this statement?

[30-9]

I'm not as smart as you guys but, I very much doubt high oct gas is causing adileo from losing fuel pressure. If I'm wrong please help me understand how it could

[oldskool]

have you checked gas cap it should be vented

[JSeery]

Originally Posted by 30-9

I'm not as smart as you guys but, I very much doubt high oct gas is causing adileo from losing fuel pressure. If I'm wrong please help me understand how it could

10-4 on that, just thought it was interesting that he would be running high octane gas. High octane burns slower than the lower octane gas and provides no benefits other than the ability to run higher compression ratios. I don't know about the ratio of ethanol in the various grades of fuel, that would be interesting to research.

[Vic Piano]

Originally Posted by adileo

Thanks Vic - if not resolved....on my next visit to your pondarosa, I may bring a project with me....and if you would not mind - maybe you can show me how to make the mech fuel pump flow through Of couse, I'll supplt all the parts and buy pizza

Andy, I'm looking forward to your next visit, and PIZZA Marv (here on the FordBarn) built the first 'pass through' pump for me, we had talked about the best way to convert the OEM pumps. I have made all the others that I'm now using. It is an easy modification. First, you need to disassemble and gut a mechanical pump, removing all the moving parts. Second, you need to create a 'reservoir' for fuel in the top section of the pump. I do this using a (for lack of a better term) thumb pull, the kind that go into pocket doors (available at most home improvement stores), the large ones are almost a perfect fit. I fill in the small gap with JB Weld. Third, I reassemble the pump, mating the top and bottom halves using the OEM diaphragm between the two halves, giving the outward appearance of a stock OEM pump. That way, everything under the hood looks stock.

[adileo]

Gas cap vented ......ummmmm?

I dont see anything that would indicate my gas cap is vented. However, I thought the gas tank had a vent. Am I incorrect? Are the gas caps vented on these cars?

I can take a pic of my gas cap and post if that helps.

[MGG]

Vic - You indicated that you leave the pushrod in the engine with your pass through mechanical pump. Is there still a spring in there to keep the pushrod against the cam to keep it from rattling around? I thought the spring on the mechanical pump did that. I have never had a pump out and don't know how that all fits together. - Thanks

[Vic Piano]

MGG, I've never had an issue with the pushrod rattling but, most of my cars are convertibles so, after a while, rattles go unnoticed...

[30-9]

I am pretty sure your right adileo that gas tanks are vented but can't say with 100% certainty.