Added a fuel pressure gauge between filter and carb and noticed the gauge read very erratically (see first video). Gauge was moving between 0 and 3 psi at idle and would increase to 4.5psi as I raised RPM. I know pressure will bounce somewhat with a mechanical pump and carb, but this was extreme. I took a vise grip and pinched the return line and the pressure increased to around 6psi and was much more steady - more of what I expected to see (see second video). What would cause this? I understand A/C equipped cars require the return line coming off the filter, but based on this configuration it looks like the pump is trying to feed the carb and pumping directly back to the tank at the same time. Is there a check valve in the filter which only bleeds fuel back to the tank over a certain pressure? A little background about my current configuration: 65' Riviera with 401. Factory main and return lines with stock replacement fuel pump and fuel filter. Carb is Edelbrock 750cfm. Fuel pressure gauge is mounted between 5/16 rubber line coming off fuel filter and 3/8 hard line coming out of carb inlet. http://vid1175.photobucket.com/albums/r639/kdml1/fuel pressure 1_zpsu9vbye9e.mp4 http://vid1175.photobucket.com/albums/r639/kdml1/fuel pressure 2_zps8x0ufjam.mp4 Thanks Doug
Do you have any problems that might be related to poor fuel pressure? Seems like the pump is reacting to pressure pulsations normal with a mechanical pump. As speed increases the pulsations are more frequent and the needle appears to be more steady. This also increases flow which is needed to create pressure.
There is NO restriction for the vent line in the end of the fuel filter. Probably the wrong replacement. Since you crimped the return hose & things got better, try crimping the return metal outlet until the pressure is steadier & correct. Worse you can do is have to buy the proper filter.
Other than what I described seeing on the fuel pressure gauge I don't see anything else questionable in relation to fuel pressure. The engine only has a couple of hours run time after rebuild and the idle is a little rough (currently set at 600 rpm in gear/700 in park). Engine is smooth anywhere above idle. Can't test the engine under load as the car is still in pieces. I am checking all the simple things first (timing, fuel mixture, float level, etc), just trying to get the engine in tune. Fuel pressure was just another item I was checking. Pinching off the fuel return line did not change the idle characteristics, but does steady the pressure gauge, so I don't believe its the source of the rough idle. I may just need to get a few more hours on the engine. Other than the slightly rough idle engine runs great. I just checked the fuel filter part number and it appears to be the correct filter (Purolator F21117). Thanks
I would get a knocking or tapping noise at idle by passenger rear wheel on my 64 Riv with ac. Never checked fuel pressure at idle. I put a ball bearing in rubber return line by fuel filter, no more noise. I have not tested it in hot weather and the ac is currently inoperative.
Bigcat, the tapping you are describing is common on Rivieras with a return line. I sleeved mine with a rubber hose by the passenger rear tire to prevent it Vacuum gauge reads fairly steady 14-15 inches at idle
Cam is custom grind from Comp Gross Lift .505 Intake/.489 Exhaust Duration @ .050 218 Intake/230 Exhaust Lobe Separation 110
Doug, glad to see you got it up and running.600 rpms in drive is a little low for that cam. Closer to 650- 700 should be good, should smooth it out a little. There is a lot of exhaust duration, gives it that lumpy idle.
