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6V Fuel Assist Pump for '41 Chrysler


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I have a multi-part question (or maybe just a series of questions) about replacing the electric fuel assist pump in my Saratoga. When I bought the car, it had an electric pump with a kill switch already installed. The pump (not sure of the brand, but has E8011 on it) is located in front of the engine compartment (rather close to the manifold) and the kill switch is also in the engine compartment. The Saratoga is positive ground. So my questions are:

1) Why, if the car already has a mechanical pump, does it need an electric fuel assist? Shouldn't the mechanical pump keep fuel flowing to the carburetor?

2) If it's wise to replace this pump (I've had a couple of episodes of having the car stall after it warms, because of vapor lock), where is the best place in line to place the pump? Closer to the fuel tank?

2a) Best place for the kill switch? Inside the cab?

3) Does it matter that the electrical system is positive ground? Do I need a specific pump? I noticed that this listing on eBay

states that the pump can be used with either a positive or negative ground system. There are other pumps, such as this one on Amazon that don't specifically state pos/neg ground requirements - but there is one reviewer that states that he has installed it in a pos. ground car. (I might be overthinking this...)

Thanks for any help on this - the car will be running great for weeks, and suddenly *poof* it dies in traffic and no fuel is being delivered. Today, I left it for over an hour, and even though the engine temperature had cooled, the car wouldn't start. I couldn't hear the electric pump running, so I disconnected it, put it back, and it started humming again. Turned the key, and the car started right up. Again, thanks for any help.

Dave

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Guest Bob Call

Dave

An E8011 is an Airtex brand 6 volt pump rated at 30 gallons per hour and pressure of 8 PSI. This pressure is a little high for the carb on your car. Better suited would be the E8902 6V, 30 GPH, 4 PSI. Airtex pumps can be purchased at NAPA stores or online at Summit Racing or RockAuto.com.

Most applications like on your car is because of vapor lock problem. The pump should be located near the gas tank not in the hot environment of the engine compartment. Be sure the pump is a flow through type, that is when it's powered off gas will still flow through to the mechanical pump. The switch should be placed somewhere on the instrument panel where it is quickly accessible. Probably powered from the accessory pole of the ignition switch so that if you should forget to switch it off it will be off when you stop the engine. Look at the installation instructions at this link: http://g-ec2.images-amazon.com/images/G/01/auto/Mishimoto/X93272.pdf

If you are having a vapor lock problem, lots of people with old cars say that reducing the gasoline octane helps or cures the problem. When your car was new it was designed to run unleaded gas, called white gas, of about 55 to 60 octane. Suggested additives to unleaded 87 octane is Marvel Mystery Oil, diesel fuel, motor oil, top cylinder lube additives, and others. The lower octane is less prone to boil in the hot fuel line and cause vapor lock.

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Thanks for the links and the pump model #, Bob. Your information helped me confirm that the fuel pump should be placed closer to the gas tank, and the kill switch should be installed in the cab.

I was speaking to a knowledgeable friend, who has worked on many pre-war Chryslers, and told me he has never had a problem with vapor lock on his cars - and has never installed an electric-assist pump. I was considering taking the electric-assist pump out of line altogether and seeing if the mechanical pump would keep the car running, before I re-install an electric pump.

I would think that if the mechanical pump diaphragm is in good shape (I could bench test to make sure there is suction) that this is how the car was designed to run in the first place. My understanding that the higher octane fuels degrade the rubber and might have compromised the diaphragm. If I rebuild the pump with new rubber, I would assume (always dangerous) that modern seals, etc., would stand up better to the higher octane.

Have you (or anyone else) had any luck running their Chryslers in the original configuration? Thanks again!

Dave

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Guest Bob Call

Dave

The problem with modern gasoline is the ethanol additive, up to 10% in most places but up to 15% in a few places. First, ethanol is not compatible with rubber and some plastics. If you rebuild your mechanical pump be sure the parts you get are ethanol compatible. Also, any rubber fuel lines should probably be replaced with ethanol compatible line.

Modern 87 octane ethanol blend gasoline is more volatile than old 50 plus octane white gas and therefore has a much lower boiling point so it is more prone to vapor lock. But, with a proper functioning mechanical fuel pump and adding some diesel fuel to your gasoline to lower the octane you should not have a vapor lock problem.

If every thing is working properly and the gas octane is lowered there should not be a need for an electric pump.

Ethanol has a lower BTU content than gasoline so mileage with the ethanol blend gasoline is not as good as straight gasoline. I have a 52 Chrysler 331 hemi and use only straight gasoline no ethanol. It costs a few cents more per gallon but I don't have to worry about some component not being compatible with ethanol and I get a couple of miles more per gallon. In some regions of the country straight gasoline is not allowed by the EPA. I lived in Houston for a while and Harris County (Houston) and the five surrounding counties all require ethanol blend by EPA regulations. I now live in Oklahoma and about 30% of the service stations and convenience stores across the state sell straight gasoline. The station where I buy gasoline sells about 100,000 gallons of straight gasoline per month; that's a lot of gas.

Anyway, why not rebuild the mechanical fuel pump and try it without the electric pump and lowered octane and see how it works. There have been lots of comments on this site about adding diesel to the gasoline. I would start with a mixture of about 9 parts gasoline and 1 part diesel (10%). Seems like some have said they use up to 4 to 1 (20%).

Good luck.

Edited by Bob Call (see edit history)
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That's very good advice, Bob. I think that's the direction that makes the most sense. Ideally, I'd like the car to run as it was originally designed, and if that doesn't work I can always add the electric assist pump inline. Thanks, I appreciate the input and the idea of adding the diesel to lower the octane. I'll let you know how it goes.

Dave

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If the carburetor and fuel pump are in good shape you don't need an extra fuel pump. There should be a heat shield between fuel pump and exhaust manifold, if it is missing you may have vapor lock. Also the fuel line must be routed away from the exhaust, as it was originally.

Today's fuel is more prone to vapor lock. With fuel injection the fuel is always under pressure and vapor lock is not a problem. As you live in Massachusetts you should not have a problem with excessively high temperatures. Owners of old cars who live in hotter climes like Texas and Australia, add about 10% diesel fuel, kerosene or stove oil to lower the boiling point of the fuel. This reduces vapor lock and makes a low compression engine like yours run smoother, cooler, develop more power and better mileage. There is no down side except a slight diesel smell from the exhaust when idling. If you use diesel.

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