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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old May 9th, 2023, 02:29 AM
jgpnashville jgpnashville is offline
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Default 1967 305e V6 Fuel Pump

I think I need to replace my fuel pump - the truck stalls when it's hot (after about 30 minutes of driving). I have searched this forum and find different answers for the right fuel pump model for a 1967 305e V6.

Some people suggest a Carter M3955, while others suggest the Precision M20021 from O'Reilly's. They look similar to each other, but neither comes up in a search for the 1967 305e engine. They look similar to the one that is in the truck, but the pump lever is straight on those units, whereas mine has a curve to it, as you can see in the attached picture.

O'Reilly's suggested a Precision M16105 (shown as correct for a 1968 305e), which is like a Carter M4503, and has a little short, curved pump lever that would not seem to touch anything whatsoever in the engine block on my 305, so I cannot see that being the right pump.

I seem to recall a thread about this very thing a while back, but I cannot seem to find it.

Can some wiser soul shed some light on my search? Do I use a straight-arm pump lever like the Precision M20021 (from a 1966) or do I need a pump with the curved arm that seems to be unobtanium as far as I can see?
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  #2  
Old May 9th, 2023, 02:49 AM
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LEWISMATKIN LEWISMATKIN is offline
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Default Re: 1967 305e V6 Fuel Pump

the AC/Delco p/n on this pump is 40050. it doesn't matter about straight or bent pump arm, either will pump the fuel. this pump has a .375 inlet and a threaded outlet for a brass fitting. if possible, use only non-ethanol gasoline. if not, use a marine grade fuel stabilizer and high test gasoline(needs to be 3-5% ethanol content).
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Old May 9th, 2023, 06:03 PM
jerrspud jerrspud is offline
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Default Re: 1967 305e V6 Fuel Pump

it's really easy to put a fuel pressure gauge on to see if it is a fuel pump problem.

I've had plugged lines and too much pressure out of my fuel pump. I would have had a hard time figuring out with those two different issues with no gauge.
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Old May 28th, 2023, 01:59 AM
jgpnashville jgpnashville is offline
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Default Re: 1967 305e V6 Fuel Pump

I bought a Precision M20022 fuel pump from O'Reilly's and returned it because it was putting over 10psi into the carb. The 2nd unit does the same thing, so I've decided that 10psi must be within the design of the M20022 pump. The only design specs I can find on that unit state a minimum of 6.5psi (which it clearly is doing). It also shows up as being the recommended fuel pump for a Chevy C60 truck from the late 60's, so it doesn't quite match to my 305e in terms of what the Internet thinks is the right model. I cannot seem to locate an original AC Delco 40050 pump anywhere other than on eBay, so I'm wondering about installing a fuel pressure regulator and sticking with the M20022.

Would I be better off installing a regulator (such as a Holley 12-803) and keeping the M20022 mechanical fuel pump, or should I bite the bullet and just install an electric fuel pump? Something about me likes the simple mechanical pump, but I'm ready for the engine to run more reliably and I wonder if an electric fuel pump would save me headaches down the road.

It's a beautiful Memorial Day weekend and I would love to be out driving my old gal, rather than figuring out what the right fuel pump is.
Thanks.
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Old May 28th, 2023, 10:12 PM
jgpnashville jgpnashville is offline
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Default Re: 1967 305e V6 Fuel Pump

After some rest, I went ahead and bought an Edelbrock 17301 Fuel Pump and wired it to switched power. Tested pressure - right around 5.8psi, so it should be in the sweet spot for my Holley 4412 carb on my 305e V6. Started and ran fine, but died about a mile from home, just barely after the engine had gotten warm.
It started back after about 30 minutes and drove home, but it died after pulling into my driveway. This has me frustrated and stumped.
Tested spark plugs with inline light - all plugs are firing. Gas is getting to carb and float level is near perfect (at the bottom of the side weep hole). When I get it to start, I do so by putting the accelerator to the floor and it will idle for 2 or 3 minutes before dying again.
Spark, fuel, and air - I seem to have all three of these. so I don't know what else to check. Does this sound familiar to anyone?
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Old May 28th, 2023, 11:33 PM
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Default Re: 1967 305e V6 Fuel Pump

Hi,

I am no expert on these engines but I ran into an issue with Vapor Lock. My engine was getting so hot it would heat up the fuel in the carburetor bowl and stop running. I would have to wait for the engine to cool down before it would start. Once I upgraded my cooling system, I had no issues.

John
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Old May 29th, 2023, 12:23 AM
jgpnashville jgpnashville is offline
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Default Re: 1967 305e V6 Fuel Pump

How did you determine it was too hot and how did you know you had vapor lock? I considered that, but the water in the radiator isn't unduly hot, so I was figuring it was OK. The heater hoses seem warm, but all heater hoses get warm, don't they? Since I don't have a water temp gauge, can I shoot a infrared thermometer somewhere and see if it's getting too hot? What temp would I be looking for?

I haven't replaced the thermostat or flushed the coolant yet. I'll go ahead and do that. I have new belts and hoses for it that I'll install while I'm at it and see if that changes things.

I guess I have lots to learn, but the truck is a lots of fun. Neighbors stop by and visit when they see me out working on it.
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Old May 29th, 2023, 06:29 PM
jerrspud jerrspud is offline
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Default Re: 1967 305e V6 Fuel Pump

I'm trying to diagnose fuel pump problems as well.
Your original question about different pumps doesn't really matter cuz they're all made by the same one company. Carter, Napa, O'Reilly.. they're all just the same pump still made in one factory. I have replaced mine twice.. one was Carter the other was Napa and they both had the same number stamped on the side.

I have the same symptoms as you but.. in my mind it can't be a vapor lock because it was even a cool day, but it sure seems like it..My PSI was showing one to two pounds after the pump. Checked the tank cleaned all the lines move the fuel filter and I still have the same issue.

It might just be all these pumps are garbage, but if you put an electric one on there and you're still having the same issue... Sounds like something else?

Maybe a spacer on the carb will fix the issue? Or at least help? I'm starting to think more and more it is a vapor lock issue in my situation and probably yours.
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Last edited by jerrspud; May 29th, 2023 at 07:22 PM.
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Old May 29th, 2023, 07:23 PM
James James is offline
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Default Re: 1967 305e V6 Fuel Pump

Quote:
Originally Posted by jgpnashville View Post
Tested spark plugs with inline light - all plugs are firing. Gas is getting to carb and float level is near perfect (at the bottom of the side weep hole). When I get it to start, I do so by putting the accelerator to the floor and it will idle for 2 or 3 minutes before dying again.
Spark, fuel, and air - I seem to have all three of these. so I don't know what else to check. Does this sound familiar to anyone?
There is two things I can think of that could be the problem:

1. If the problem started after installing the Holley carb then when you get the engine running, look down the carb and see if it has fuel dripping out of the booster nozzles when the engine is at idle. If it is, the the engine is running rich. While the engine is cold it can handle the extra fuel, but as it warm up it causes the plugs to miss fire. Pull the plugs and see if they are black with soot. You will need to adjust the fuel level on the carb with the electric pump running. On engine with mechanical pump the engine need to be at idle to adjust the fuel level. It should barely come out of the hole on the right side of the bowl.

2. If you have an electronic distributor (doesn't matter which type), your inductive pickup might be bad after it warm up creating an intermittent problem.

I had experences both problems.
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Old May 29th, 2023, 07:58 PM
jgpnashville jgpnashville is offline
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Default Re: 1967 305e V6 Fuel Pump

James and Jerr - thanks for the ideas. I've been thinking it's running rich, but that makes sense why it would be OK rich when cold, but misfire when it warms up. I'll definitely check that, starting with pulling the plugs.
Meanwhile, I caused a leak in the radiator when draining it today to flush and replace the hoses. The drain plug was seized and turning it bent the copper rad and the female thread for the plug now has a leak around the fitting. I pulled the radiator out and will take it to a shop to be repaired (hopefully) and I'll drop it back in. Got a little more than 6 gallons of nice green coolant out, less than the 8 gallons I was expecting. So, it's not in a running state right now.

A question on the water manifold - if I remove it to replace the short hose between the water pump and the manifold, where can I find the gaskets to seal the water manifold against the head? Anyone know a part # for those gaskets?
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