My2nd 69 442

I have recently put a fuel pressure gauge on my 69 442.
The pressure fluctuates about half scale (0-15 psi gauge) 2 separate gauges tried with same fluctuation issue, although the engine runs fine.
Is this pressure fluctuation normal for the stock engine mounted fuel pump or should it be steady like an electric pump would show?
Thanks for any replies
Jerry

MDchanic

Completely normal.

Every time the pump pumps, the pressure goes up, once every other revolution of the engine.

This, along with those 210° temperatures in traffic, are reasons why sometimes you're happier not having a gauge.

- Eric

classicmuscle442

X2 Completely normal

My2nd 69 442

Thought it might be ok, but I wanted to check.
What should the fuel pressure be?
Thanks guys

MDchanic

5 to 7psi, measured about 16" above the level of the pump, and roughly steady from idle on up the RPM band.

- Eric

ah64pilot

Actually, what kind of guage do you have and where is it?

Liquid filled gauges will read lower fuel pressure once they get hot fyi

My2nd 69 442

My gauge is a liquid filled 0-15 PSI Mr. Gasket gauge.
It is located in the engine bay about 8 inches above fuel pump outlet and 7 inches from carb inlet fitting.
Averaging the fluctuation, pressure is aprox 5-6 PSI. Pressure appears to stay hot or cold and thru the RPM band(with the same flux as described in post 1.
I don't see that I have any problem. I only wanted to get your opinions on the "normal" pressure and the fluctuation.
Thanks to all for your replies
Jerry

rcorrigan5

I'm resurrecting an old post to discuss fuel pressure to the carburetor on my '68 4-4-2. We measured it this morning and it was 9psi which sounds too high to me. What I'm asking is, what is the solution to this too high of fuel pressure? Installing a "new" fuel pump? Or installing an in-line fuel pressure regulator?

I like to keep this car as stock in appearance as possible and I don't like the idea of an in-line fuel pressure regulator. The problem I have with the car is that, at idle, fuel just piles up in the carburetor (you can see it) and the burn becomes so rich I'm pouring black smoke out the back. When I speed up, the carb clears itself and the car runs fine down the road at about 30mph and up. But below 30mph, when I accelerate every so lightly I get a good burst of rich black smoke out the exhaust. And when I'm stopped at a light or stop sign, after a few seconds the idle gets rough and the exhaust just bellows black smoke. When we had the fuel pressure gauge on it this morning, when we reduced the flow of fuel to the carburetor (by pinching the fuel feed line) the idle became normal again after just a few seconds. When we released the pinch, the idle went rough again after a few seconds and the rich black exhaust re-appeared.

The carburetor has been rebuilt and rebuilt by two independent rebuilders and everything appears fine with it. I believe the problem lies with the fuel pressure going to the carburetor.

My 4-4-2 has been like this for about 8 years now and I would sure like to get this problem solved. Any thoughts from all of you will be greatly appreciated!

Randy C.

Fun71

years ago I put a new Carter fuel pump on my car and it flooded the carb. Fuel pressure pegged my gauge at 10 psi. I returned that pump and got a replacement that did the same thing. I gave up and ended up installing an inexpensive Moroso fuel pressure regulator. jump forward many years and the fuel pump failed, and whadda ya know, the new Carter pump had the correct pressure so I was able to take the regulator off.

So I guess my answer would be to get another fuel pump.

jaunty75

From the '68 Chassis Service Manual.




I would replace the pump as the manual says. The car didn't need a fuel pressure regulator when it was new. Why should it need one now?

matt69olds

What are the odds the car is equipped with A/C? If so, is the fuel return line clear and not restricted? The A/C epuipedengines got a fuel pump with a return line. The fitting inside the pump has a small orifice. The idea is to have a small calibrated internal leak back to the fuel tank. That keeps the fuel pump cool under high heat, and bleeds off fuel pressure when you shut off the engine. If the pump couldn’t bleed off pressure, the fuel could boil under a heat soak condition, making the pressure go high enough to push the needle off the seat in the carburetor, causing a flooding and hard to restart condition.

rcorrigan5

My car doesn't have A/C but it does have the heavy duty cooling option (Y72). I believe all of the "high compression" engines of that era had the return line which mine does have. I made sure the return line is clear such that nothing is blocking the fuel from returning to the tank. I also tested the fuel pump by running a hose from the return fixture on the pump to a bucket and the pump is returning fuel. I believe the bottom line is that the pump is just delivering too much pressure to the carburetor so my next effort will be to replace the fuel pump and we'll see what happens. Hopefully I'll get a good one!

Randy C.

matt69olds

I have had good luck with the Airtex 40736. It’s a factory replacement pump for the performance engines. I have had it on several cars, always maintained about 6 to 6.5 psi. It was enough pump to get my friends 66 Olds into the 12.20s. Not bad for a 40 pump!