65 305e Fuel Pump Question

[melmashman]

My 65 GMC V6 305e engine needs a fuel pump. I think a Carter M3955 fuel pump is a replacement, but I am not sure.
Does anyone know if that is the correct replacement? I can purchase it via Amazon from a vender.
Thanks for your help.

[FetchMeAPepsi]

I used Precision part number M20021 from O'Reilly's Auto Parts. Lifetime warranty too.

[melmashman]

I used Precision part number M20021 from O'Reilly's Auto Parts. Lifetime warranty too.



The photo of M20021 is different than what my current fuel pump looks like. My current pump looks more like the Carter M3955 with a high cylinder shape above it rather than a nut on top. Are you sure that fits the 305e rather than the 305c? Thanks for your help!



Sent from my iPad using Tapatalk

[melmashman]

My current fuel pump looks like this.

[FetchMeAPepsi]

That's what my old one looked like. Here's the thread with a bunch of pictures

https://6066gmcclub.com/showthread.php?p=59047&highlight=m20021#post59047

[melmashman]

Your pictures are great. It looks just like my fuel pump. The picture of the Precision M20021 on the oreillyauto.com web site is very different at first glance. I realized my mistake. The Precision photo shows the underside of the filter. Daaaaah. I will order it for my 305e. Thanks for bearing with my quick observation mistake.
Question: Is there any position the pump’s cam area has to be in when you remove and replace it? Can I just pull it out and stick the new one back in? Does it go in guided or do I have to be precise when sticking the cam arm back in? Sorry - so many questions:-(

[FetchMeAPepsi]

Your pictures are great. It looks just like my fuel pump. The picture of the Precision M20021 on the oreillyauto.com web site is very different at first glance. I realized my mistake. The Precision photo shows the underside of the filter. Daaaaah. I will order it for my 305e. Thanks for bearing with my quick observation mistake.
Question: Is there any position the pump’s cam area has to be in when you remove and replace it? Can I just pull it out and stick the new one back in? Does it go in guided or do I have to be precise when sticking the cam arm back in? Sorry - so many questions:-(


Thanks!
There's nothing special you have to do. Just pull the old one out, slide the new one in, and off ya go! You may have to prime it if it's been dry for a while.

[zoulas]

What is the best recommendation if you don't use the truck virtually at all with just some starting periodically to circulate the fluids? I am averaging one failed fuel pump per year. There has to be some solution. I have been using the NAPA unit. Going to try the Oreilly one this time. Can't be any worse.

[zoulas]

The oreilly warranty carried many contingencies, this is from their web site:


Fuel Pump Warranty
Fuel pumps carry a limited lifetime warranty when the fuel filter and strainer, if applicable, are replaced with the pump. In order to validate the warranty, O'Reilly Auto Parts and the pump manufacturer(s) require proof of purchase and installation of the filter and strainer; otherwise, pumps installed without the previously mentioned items carry no warranty.

[Jeannie]

Hi Zoulas!

The OReilly printed warranty may be nuanced, however I have never had a warranty replacement rejected by the boys behind the counter. Simply bring the old pump with you and explain that it carries a lifetime warranty. You should receive a new pump without hassle. I have on occasion watched them pull the purchase up on the computer to verify but never has that affected my returns.

I hope this helps!

-Jeannie

6066 GMC Club

[zoulas]

Sorry to ask the same question again:

What is the best recommendation if you don't use the truck virtually at all with just some starting periodically to circulate the fluids? I am averaging one failed fuel pump per year. There has to be some solution. I have been using the NAPA unit. Going to try the Oreilly one this time. Can't be any worse. Are there some pumps that are better than others?

[AZKen]

To answer completely this time:
1. You don't use it very much, so it's not "wearing out".
2. There is no way to know if one is better than the other. They are all made in the same Chinese factory.
3. I would have to know, how you know, the pumps are failing.
4. If it is failing, it's possibly because the diaphragm is drying out or your environment there is causing deterioration to it. Maybe too much moisture instead of drying out. Some kind of damage/blockage due to condensation.
5. If you don't start it much, all the fuel in the carb and in the pump will dry out. The procedure for infrequent starts is to put fuel down carb throat to help truck start for 5 seconds at a time, and save long cranking of starter to get fuel up to carb thru pump. What is your procedure and what happens? Won't even fire once? Won't stay running? Sputter/backfire? Runs rough? You may want to put Sta-Bil in your gas tank, which needs to be circulated into all the of fuel system before shutdown.
6. Funny things happen and make us think it's one thing when it's another. Example: A person thinks his motor won't start because of the fuel pump, but does not test properly. Buys a new fuel pump and filter. Then it starts. But the problem was the filter....... but it's never discovered.
7. What motor do you have and what is the Napa part number of your pump?

[FetchMeAPepsi]

If it IS the fuel pump and not a filter or something else, just start the truck more often to keep it from drying out. set up a reminder on Alexa, Siri, or Microsoft outlook and have it say "start ol' Bob today and listen to some oldies!" every 2 weeks or so. You don't need to run it dry, just give her 15 minutes while you drink your morning coffee.

[Clarke]

Does your fuel pump have a weep hole? If so, and the pump has failed, I’m assuming you would have gas or oil leaking from this weep hole.

On my ‘62 305, the rubber diaphragm consistently tears near the pump housing body flange where the diaphragm is pinched. Mine has a bolted body flange so I can disassemble and inspect the internals. To me, it seems the rubber is poor quality or not the right kind of material for it’s application. When mine starts leaking it sprays fluid all over the passenger inner wheel well and under the hood, because the weep hole is on top of the pump.

I have tried pumps from multiple places and for the most part, they have the same casting numbers on the housing body. Could be same manufacture; just different packaging? For me, they all perform the same.

I continue to use O’Reilly because they have lifetime warranty and are easier to find when traveling and they stay open later than most places. I tried several Napa pumps and no different; just more of a return hastle.

In general, I think these replacement pumps are junk and we all seem to have different opinions. I’ve had multiple diaphragms tear within 100-200 miles while on road trips runner my 3200-3400 RPM, so I think the diaphragm is the wrong material and possibly a poor design. I plan to install an electronic pump, but I haven’t pulled the trigger yet.

[zoulas]

I have a clear fuel filter between the carb and the pump. When I crank the engine for 15 or so seconds, the filter goes from close to empty to about half full and the engine starts (when the pump is working.)

Since I now crank the engine for 4 x 15 second intervals and the filter is still empty, I think the fuel pump is at fault.

Makes sense, no?

[zoulas]

Also, I disconnected the output of the pump and cranked the engine. No fuel came out.

I then disconnected the input of the pump and installed a temp fuel line . Put the temp fuel line into a gas can. Cranked engine. Still nothing.

[Clarke]

Assuming you have good fuel flow from gas tank and frame mounted fuel filter, I guess it could be a weak pump.

One time when we were out of town, the same thing happened to us... No gas squirting in the carb when rotating the carb pump. I didn’t find any leaks and I knew the rest of the fuel system was good, so I went across the street to a gas station and put some gas in a water bottle. While my better half was cranking the engine I poured some gas down the carb and she lit. Took a couple tries but she stayed running and got us home. My tank is still behind the seat, so some gravity feed assistance and I’m assuming it was a weak pump that needed to be primed. And no, it did not start after returning home and sitting overnight.

Replaced the pump the following day and fired up after a few seconds of cranking.

I have probably replaced my fuel pump about a dozen times due to diaphragm fatigue/tear with fluid leaking from weep hole. The scenario above only happened to me one time.

If you have a weep hole and not leaking, it does seem strange that you would get multiple weak pumps with low mileage. But again, mine is an older model, so there may be some differences?

Is your tank still behind the seat? Have good fuel flow to inlet side of fuel filter? No sediment from tank in fuel filter? Any unusual marks on the pump arm inside the block? Should have a small polished spot.

FYI, unrelated to our GMC I have seen gas caps that seal so tight that are not vented or a plugged vent, that did not allow enough fuel to pull from tank (too much vacuum). Loosen up cap and full fuel flow.

[zoulas]

This is a 2500 panel truck, so the tank is under the truck ahead of the rear drivers side wheel. There is no 'other' fuel filter under the truck that I know of . Good advice, in the meantime, I will try another pump and see how it goes.

[AZKen]

If you hooked up a temp line into a gas can and observed the outlet and no flow, you did a good job at testing pump. You are correct, the pump is no good. As said, it must be the diaphragm. To the Chinese Peoples Fuel Pump factory, rubber is old flip flops, dog toys and recycled soccer *****.

I have not experienced all this trouble with fuel pumps.

BTW, Ethanol is the enemy of many "rubber" products. If you can somehow avoid Ethanol, you all may be much happier with your pumps.

Looks like the word B A L L S is prohibited.

[Funky61]

Look under the passenger side seat area (under the truck, inside frame rail, to see if you have one of these canister filters.

[Ed Snyder]

In my 50 years of driving V6 powered GMCs, I've only experienced one fuel pump failure while driving. I credit most of that good fortune to using nothing but ethanol-free gasoline. The one failure I did have happened in stop-and-go traffic on the interstate in Seattle. Pulling onto the shoulder would have been difficult at best due to vehicles all around me. Fortunately I overcame my initial panic and remembered to flip on the toggle switch for my backup electric fuel pump. The engine restarted before I had even coasted to a stop, so I didn't even get honked at.

Thus, my recommendations -- use ethanol-free gas and install a backup electric fuel pump for emergencies.

[AZKen]

Look under the passenger side seat area (under the truck, inside frame rail, to see if you have one of these canister filters.

Good idea to check for the original style filter, but remember he bypassed everything when doing the gas can trick. That is how you troubleshoot. Isolate a part so as to either eliminate it as a cause, or prove it is the cause.

[LEWISMATKIN]

fellas, the original AC-Delco fuel pump # for all 305-432 & 478 gas pumps are as follows: 1960-65 4755; 66-74 40050. This was the only two numbers we stocked at the dealership and for years afterward. I hope this helps with the identification process.:thumbsup::thumbsup::thumbsup:

[AZKen]

Unfortunately, most, not all, A/C Delco parts are made off shore. Mostly China. Only N.O.S. will be USA. N.O.S. fuel pump can have a dried out diaphragm.

[ronn]

Just installed this weekend, Precision #M20021; fits as advertised!

[LEWISMATKIN]

azken, I only provided the ac/delco #'s for a reference point and where the break in production was in the pumps.

[snazzypig]

Lewis, Just to avoid any confusion, wasn't the 60-65 fuel pump #4754?
Thanks.

[LEWISMATKIN]

you are right, snazzy. I have fat-finger syndrome again.