75_yellow

So I installed a fuel pressure guage on the 75 right before the carb. It wont hold a pressure it jumps around and wont stay on a set PSI it jumps from like 8 or 9ish to 0 really fast so I cant get a set level . What could cause this a bad fuel pump?

vetteguy75

If the engine runs perfectly (idles smoothly, not running rich or lean, etc etc etc), then chances are, it's the gauge that's defective and not the pump. I know my gauge "loses pressure" when the engine gets up to operating temp (goes from 5 lbs to 1 lb then -0- lbs)but the engine's performance stays the same....went through 3 gauges..all did the same thing...finally decided that whatever the gauge shows at startup, that's what the fuel pressure is...apparently that's pretty common in fuel pressure gauges.

Good luck!

75_yellow

uh... ya this is my second gauge but it sounds like yours show something at first start up. Mine does it from the get go

Mike Ward

Do a search of the archives on this subject. Many people have observed one or both of the described problems.

My standard advice is to put black tape over the gauge face, problem gone!

75_yellow

lol so what your telling me is that my fuel pump is good and i shouldnt worry about it

justaguy10825

Is there a difference between the pressure reading with an electric pump vs/ mechanical? My pressure gauge jumps around also but I just assumed it was because of the pulses from the mechanical pump...

ShinodaVette

My understanding is that it is due to the pulses from the mechanical pump also. I've never had a fuel pressure gauge before but we finally started my engine last night. The gauge goes nuts and is pretty much worthless. My neighbor thought it might be a little better if it was liquid filled but he figured even with that it wouldn't be very useful on a mechanical pump.

justaguy10825

That's what I figured...

Thanks

JimT

Less expensive fuel pressure gauges over-react to the pulsing action of a mechanical fuel pump. It will bounce all over the place. I purchased a more expensive gauge from Summit and although it does still bounce it doesn't do it as bad. Good luck.

Jim

Dantana

same problem, I put up a video about a week ago. Thought maybe I had a bad pump too... think the real problem is ignition for me though. I may just toss the gauge ina drawer until I get an electric fuel pump.

DIPPOLD

A mechanical pump will pulse at idial because the pump diaphram is moving in and out, but as you rev the motor it should show a consistent presure (6 - 7 lbs) because the presure is constant. I have no experience with a electric pump but would assum that because it uses a rotating pump there should be constant pressure right from start. Maybe the guys with electrical pumps can pipe in.