For your car to run as it should, fuel pressure as well as fuel volume need to be up to proper specifications. If you have fuel pump problems, either or both of these could be a factor. Fuel pump problems can lead to a vehicle sputtering on acceleration, under load, or at a relatively high constant speed. They can also lead to sudden unexpected surges in power, which are particularly disconcerting and potentially dangerous.
To check for proper fuel flow volume, the fuel line is allowed to drain into a measured container. Accepted practice is that the pump should deliver a quart of fuel in 15 seconds, a pint in about 7.5 seconds. If yours is notably less, you have fuel flow problems. Check the fuel filter for any restricting blockage, change the filter, and test your flow again. If you still have inadequate flow, your fuel delivery system’s pick-up screen may be partially blocked, or the fuel pump could be failing.
When checking fuel pressure, the first thing is to determine the right testing instrument to use. Older carbureted engines have mechanical fuel pumps that produce less pressure (psi) than fuel injected engines with electric fuel pumps. The normal range for most carbureted vehicles is between three and seven pounds, but check you vehicle’s specifications to determine its proper fuel pressure. If your fuel pump is supplying inadequate pressure, you will experience problems, and eventually, if the pump fails completely the car will not run at all. Pressure that is too low can starve the carburetor. Too much pressure will cause flooding. We have found that many new fuel pumps deliver too much pressure. In this case, the problem can be rectified by installing a pressure regulator.
After the appropriate testing apparatus is determined for checking fuel pressure, connect it according to the instrument’s instructions. Most are installed between the pump and the carburetor to measure pressure from the pump. Others are equipped to clamp on the inlet side of the pump to measure its suction.
On high performance engines, maximum fuel pressure can only be determined with the engine under load. Check the manual for your engine to see what pressure is being quoted, at idle (minimum), free-revving (near maximum), or under load (maximum), or the overall range.
Customer Questions:
Question: The fuel pump is new but vehicle sat for 4 years, is it possible that the pump has gone bad? By the way, there is plenty of fuel in tank. I do appreciate any response and/or information you provide. I am a loyal customer of mikes carbs sales for if I need parts in future, I will definitely order via your website as I have done before.Yes it could have gone bad. The ethanol may have damaged it. You should do a pressure test on the pump. If you replace it, be sure to test the new one. They aren’t always what they should be. Should be around 4 lbs, check your owner’s manual to be sure.
