Poss time to change mech fuel pump... - Impala Tech
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post #1 of 6 (permalink) Old 08-16-2019, 10:05 PM Thread Starter
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Poss time to change mech fuel pump...

Hi all.

I tried doing numerous searches and general research but did not find any relevant hits. The mechanical fuel pump on my stock 396/325 *seems* to be on its way out. Two weekends ago I intended to take the car for a cruise. I started the car and noticed it was leaking fuel from what appeared to be behind the pump (think side closer to the firewall/passenger cabin).

I thought perhaps the diaphragm failed, the rubber hose leading to the pump failed, or that for some odd reason it was leaking out of a weep hole. But I didn't get under to investigate at the time, just shut it off and figured I'd look at it next weekend. Took the other classic car out for a ride/show instead. This past weekend, I went back to the Impala. Figured I would start it up, crawl under and see where the leak may be coming from.

Well, there were zero leaks. I could not replicate the problem no matter how many times I started and shut off the car. So now I don't know if this could be an intermittent leak, or if it maybe was somehow leaking out a weep hole(?) - though I do not know how it would have built up enough pressure to do that. The car ran perfectly fine the first weekend while leaking and it was not just drips but almost to a healthy stream that pooled up quickly under the car. Basically it ran no differently when it was leaking than the way it does now.

So if anyone has any experience and has seen an intermittent problem I'd love to hear about it but either way I have decided to replace the rubber gas hoses using teflon lined hoses and a new pump to be safe. But is there a consensus for what pumps are the best/most reliable?

I've been looking at Carter's mainly, but not really thrilled with what I am finding through places like Hubbards, Classic Industries, Impala Bobs, etc. I realize today's replacement parts will never rival the quality of yester-year's parts and standards, but I'd like to find the best one available. Anyone have any recommendations based on their own experiences for which brand to buy? This would be, again, for a stock 396/325 4BBL car so 6-7psi should be fine.

Thanks!
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post #2 of 6 (permalink) Old 08-17-2019, 03:08 PM
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If it is not leaking then it doesn't need replacement, but here is an OEM replacement from Rock Auto dot com:

https://www.rockauto.com/en/moreinfo...84039&jsn=1053

If you have A/C that may just be condensate that hadn't drained until you moved the car.

Big dave
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post #3 of 6 (permalink) Old 08-17-2019, 06:55 PM Thread Starter
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Quote:
Originally Posted by Big Dave View Post
If it is not leaking then it doesn't need replacement, but here is an OEM replacement from Rock Auto dot com:

https://www.rockauto.com/en/moreinfo...84039&jsn=1053

If you have A/C that may just be condensate that hadn't drained until you moved the car.

Big dave
Thanks Dave. Any experience with that Carter unit? I know you typically run hotter setups and use fuel injection but I am hoping to find the best most reliable one I can find, though I was already leaning towards Carter.

I wish it was condensation but I saw the leak, put finger to it and it was gasoline for certain. But it has not leaked since.
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post #4 of 6 (permalink) Old 08-18-2019, 01:07 AM
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I'm not sure what year 396 you have but it's possibly the same pump as the 427 in my 66 uses. I bought an Airtex pump. Someone (who claimed to be in the know) on one of the sites said that Airtex makes the Delco fuel pumps. I'm not sure if it's true but the pump looks just like an original except it doesn't have the AC logo on it of course.

I only have about 200 miles on it since I put it on but it fit fine and works perfect so far. I wanted one that looked as original as possible.
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post #5 of 6 (permalink) Old 08-18-2019, 08:53 AM
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I should add, it's an Airtex 40193. It is the style that uses a male pipe thread 90 degree fitting for the outlet. The fuel line does not have a 90 degree at the bottom. It comes straight down and the flared end of the pipe is straight, it theads into the inverted seat (female 3/8" tube seat) of the fitting. There is no bend at the bottom of the fuel line to go into the pump. I can get a picture of it if you like.
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post #6 of 6 (permalink) Old 08-21-2019, 11:48 PM
 
 
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Marsmann, I have seen fuel pumps beginning to fail, leak and then not leak. Any fuel leak is cause for concern. Find a good price on a Carter M6901 that has the base that you can rotate for better alignment of fuel lines. I use them a lot on mild rat motors. Also, be sure to do a fresh oil change. If the diaphragm is leaking it goes straight to the oil pan. Any time your oil level is higher than it used to be you are in big trouble.
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