Fuel Pressure Measuring?

[doubleyellow]

Been having trouble with the engine. Runs great at idle, but as I accelerate from about 2500 RPM and above, the engine bogs down badly and loses all power. But then back to smooth running at idle.

Please note: in the driveway, when I pull the throttle and get above 3000 RPM I do not hear or notice any obvious power loss

I’ve changed out many obvious things (carb, distributor, coil, plugs, plug wires, checked main grounds) which I may need to explain later, but thinking it may be a fuel starvation issue, I’ve been trying to measure the fuel pressure.

I first borrowed a fuel pressure gauge from the local O’Reillys. Think I hooked it up properly just outside the card (AVS2). The gauge really was more for fuel injection so the range on the dial was up to 100psi. Since I’m trying to read mine to be about 6 psi, the small dial was hard to read. Anyway, fired it up and the dial read about 9psi steady at idle.

9 psi seemed strange. So I dug up my Vacuum Gauge which is also a fuel pressure gauge. Hooked it up in a T-configuration.

Started the engine. At idle, the dial needle started jumping around between about 2 and 9 psi. As I increased the RPM the needle started to stabilize at around 4.5 psi plus or minus 1 or 2 psi. This seems low, but the needle was very erratic and not stable, so hard to tell what the average pressure was.

Shut it off and said have to ask the experts:

- Am I measuring the psi correctly? Correct gauge connections? Could both gauges be bad? What RPM’s do you check the pressure? Is pressure supposed to be stable at all RPM’s?
- Do I actually have a pressure problem? Bad fuel pump? Faulty vapor separator (its my original 1970 unit)? Something in the feed or return lines? Plugged sending unit (it’s new)?

Thanks for the feedback

 

[doubleyellow]

OK, I just realized the hose to the gauge is too long and filled with air. The air pocket is like a spring and causing the dial bouncing. I’ll try again with the shortest length possible.

In the meantime any advice on the fuel pressure is highly welcome, Thanks

 

[doubleyellow]

OK, so I shortened the tube going to the gauge. Ran it again. At idle the needle still bouncing a bit, but averaging about 4 psi. As I increase the RPM the pressure starts to drop below 4 and head toward 3 psi.

Is this running too low? Maybe I still am not measuring the pressure properly with my setup?

Would lower pressure cause the loss of power I am experiencing during acceleration?

 

[Xcudame]

Try this. I used this setup to fire up my 64 Imperial I bought the January that was sitting for 12+ years without running as I didn't want to pump any goo from the tank into the carb. Take a cheapo electric fuel pump and a gallon gas can and hook them up to the carburator fuel inlet. You should be able to cram the gas can somewhere under the hood and secure it. Hook the electric fuel pump to a 12 volt source, stick a rubber fuel line in the can hooked to the pump and take it for a test drive (don't go far or get too crazy!). If my suspicion is correct, you have either a bad mechanical pump or fuel pump rod wearing out. You're running a new metal canister fuel filter, right? What ignition are you running (i.e. electronic or points)? If electronic, what is your control unit? Could also be an ignition problem at higher rpm.

 

[doubleyellow]

I may not try the gas can method so I don’t fry the Chally, but I did order a new Carter mechanical pump to try.

My original vapor separator may also be the culprit, so I will try to bypass it and go direct from the pump to the carb.

I did switch between a mechanical points distributor and an orange box electronic. The higher RPM power loss was still happening, but both distributors could be off. I do have a new electronic module I could try.

As far as the fuel pump rod. Can I pull that out with a magnetic probe easily for inspection?

Still looking for if 4.5 psi at idle, with the fuel pressure dropping as RPM goes up, is not what should happen on a stock 440 set up?

 

[Xcudame]

I understand about the gas can method. I've always been a little crazy! With the fuel pump off, there's a pipe plug just underneath the opening for the fuel pump arm. Take it out and then you can get the rod out. Like you said, you'll probably need a magnet to get it out, but the dang thing will naturally slide out with gravity when you put it all together. Rod should measure 3.220". Pressure should go up some with higher rpm, yes!

 

[doubleyellow]

I understand about the gas can method. I've always been a little crazy! With the fuel pump off, there's a pipe plug just underneath the opening for the fuel pump arm. Take it out and then you can get the rod out. Like you said, you'll probably need a magnet to get it out, but the dang thing will naturally slide out with gravity when you put it all together. Rod should measure 3.220". Pressure should go up some with higher rpm, yes!

Thanks X