89vette

65 365

When I bought my car, it came with a "correct" original AC Delco fuel pump part number 40083 stamped on the flange and "AC" cast into the top. Not knowing the history of the pump, I sent it to Aurthur Gould Rebuilders. They rebuilt the pump and sent it back. I installed it on the car and it flooded the carb with fuel. So my mechanic told me he thought the carb needed rebuilt. He rebuilt the carb and the same thing happened. It even bubbled out of the vent tube. We checked the pressure and it was 15 psi.

So I put a new AC Delco pump on (no AC logo) and it ran fine at 5.5 psi. I send the original pump back to Gould and he said there were some unfamiliar parts in the pump and the guy that rebuilt the pump no longer worked there. So he put all new parts in the pump and sent it back. I installed the pump and the same thing happened. Back to 15 psi.

So now I'm really frustrated. I send the pump back to Gould and he puts it on his car. He calls me and said it is running fine on his car and its putting out 5.5 psi.

So I write to the previous owner and he told me he rebuilt the pump also and it did the same thing when he had the car!

So here is what we know:
1. Pump works on another car
2. Pump does not work on my car
3. New identical pump works on my car (even tried 2 of them)

I am completely stumped. The only thing left that I know to check is the fuel pump push rod. But that still does not explain why one AC Delco 40083 pump works and the other does not.

Does anyone know what this could be?

MikeM

I think you're making an assumption on item #1.

I don't believe pushrod length would be a factor at all unless the pump just wasn't pumping fuel. Could be wrong.

89vette

Correct. I would have to assume that Arthur Gould is lying to me

MikeM

You said it, I didn't.

In case you don't get any more answers, I THINK the max pressure the pump will put out is dependent on the internals of the pump itself and I THINK the minimum side of the pressure is controlled not only by the pump internals but also the length of the pushrod stroke.

That's why I don't think switching the pump from one engine to another has anything to do with high pressure. Maybe low pressure.

It's been years since I rebuilt a pump so I forget what really does limit the pressure.

captcfd23

I had a similar issue, it turned out to be a float issue. Make sure the float is not full of fuel. May not be the case, but thought I would pass it along

66BlkBB

I ran into the same problem on my 327 with a Holley carb. Holley states that their units will not take any fuel pressure over 6#'s. Mine was going up to 14#s so I went to NAPA and got a new fuel pump. It was guaranteed to put out no more than 6#s. I installed a pressure gauge between the pump and the carb and it is running a consistent
5.5#s of pressure with no flooding.

dirkdaddy

That is WAY too much pressure for a carb IMHO. Most run 2.5-5 psi. The float valve is not designed to handle much pressure, its being overwhelmed.

If you are really anxious to figure it out, I'd also check the push-rod stroke on each vehicle if you have one it works on and one it does not. I'd bet you are getting more pushrod stroke on the corvette engine. This could account for the higher pressure.

Why did you have the correctly working pump re-worked by Gould? I am not a pump expert but I think they have a relief valve sort of a regulator. Gould seems like they are screwing it up.

In the end you could test this on the bench manually if you wanted to put some time into figuring out the problem and see what PSI you get pumping it either with a hand held setup or some sort of elaborate eccentric and a drill.

89vette

I was told the pump needed rebuilt. I did not have a working pump taken off my car and rebuilt.

Pilot Dan

If you can run an identical pump on YOUR MOTOR without any problem, then it is safe to say that the problem is in the original pump. Now with that being said, I am thinking your original pump (that Gould rebuilt) may have some incorrect parts in it. If it were me, I would disassemble the problem pump and the one that you have that works and compare the pump arms and other internals side by side. If your original castings are good, the problem should reveal itself and you could even swap out the guts to repair your "AC" logo pump. Pilot Dan

toddalin

Maybe not.

An unregulated pump will build up more pressure into a sealed chamber that offers resistance than at free flow.

Who knows how the pump has been modified.

Perhaps when he put it on and fired up the engine, it was able to "free flow" at 5.5 psi into the fuel bowls and this is when he checked it. Maybe he never waited for it to build pressure against the closed seats.

BTW, my fuel pump puts out 8.5# and the Holley 600 dp has no problem with this.

89vette

I called AG today and they said they put a different style valve in it that has relief holes in it to bleed some pressure. So we'll try one more time. I talked to the former owner of the car and he had the same issue with this pump. It was putting out too much pressure.

MikeM

Great, now how did that pump work on AG's car before they put new vlaves in the pump?

89vette

They apparently didn't put it on their car after the new valves were put in. It ran fine with the existing valves. I fairly confident that they are telling the truth.