Fuel Pump Pressure

[Keith W.]

I need to check my fuel pump pressure on a 1970 with steel lines. Any tips would be appreciated.

[Larry M.]

Re: Fuel Pump Pressure

Keith:

I know of only two good ways:

1. Disconnect and remove the steel line. Install a temporary rubber fuel line from fuel pump to a good gage. Crank engine over until you get a steady and final reading. Probably best to do this after running engine a bit to be sure it is lubed up well internally. Engine may even run for a bit with the fuel still in the carb.

2. Buy a second steel line, cut it, and add a nylon tee or metal tee into the line for the gage. Reinstall line and also attach gage thru rubber fuel line/tubing to the gage. Run engine and record pressure.

Obviously #2 gives a better and more accurate number, as well as the flexibility to alter the RPM to see its effect.

Larry

[Gary B.]

[Larry M.]

Re: Fuel Pump Pressure

Gary:

The GM Service Manual states to measure fuel pump flow with engine cranking and fuel line disconnected from the carb. I assumed the open end would be connected to a rubber hose and bucket. Coil wire pulled (or similar) so engine will not start. It then stated to hookup a gage to the fuel line open end......but it then said to run the engine for a 1/2 minute or so to get the pressure using fuel still contained in the carb fuel bowls. It said RPM should be 450-1000 RPM (idle or slightly fast idle). This is different than I stated in my Item #1, but I also did say the engine would/could likely run from fuel already in carb fuel bowls (if you did not disable the spark). In both circumstances, the fuel pump is dead-headed and has no flow.

When an engine is running (especially at idle) there is very very little fuel going into the fuel bowls of the carb (almost zero). So the difference in pressure between this and being dead-headed (absolutely NO flow) is negligible in my opinion. The biggest difference is likely between pump pressure generated at cranking speed (150-200 RPM) and the service manual specification of 450-1000 RPM. I would think that this difference would also be small for a diaphragm pump at a no flow condition. But I have not tested this.

Best way is to run the engine as recommended in the service manual. Although the time for measurement is short. In my recommendation #2, you have all the time in the world.........or at least until you run out of gas.

Larry

Larry

[Gary B.]

Re: Fuel Pump Pressure

Larry,

Good and interesting info.

Thanks,

Gary

[James G.]

Re: Fuel Pump Pressure

With the TI ignition I do not think you can just pull the coil wire and crank it over.

Keith, are you having fuel issues you believe may be related to your original pump?

If you believe the pump is not operating correctly YET it is not externally leaking, one thing is to check the oil, if the level appears a little higher than remembered and/or the oil smells of gasoline the pump could be leaking into the oil pan through the fuel pump push rod through passage.

[Keith W.]

[Keith W.]

Re: Fuel Pump Pressure

Yesterday I tested the pressure on my fuel pump and it maxed out on my gauge at 10. Obviously that is not correct. Time for a rebuild. Does anyone have references for a good fuel pump rebuilder that will keep it survivor? Thanks

[Dan A.]

Re: Fuel Pump Pressure

The fuel pump off of my 72 LT-1 is presently being rebuilt by Fred Ballard. His email address is fredsclassics@hotmail.com, phone number 661-251-2362. He can do either a restoration or survivor type rebuild. Seems like a great guy to deal with.

[James G.]

Re: Fuel Pump Pressure

I had my survivor pump back from FRED within 10 days.

[Keith W.]

[Richard M.]

Re: Fuel Pump Pressure

Keith, I would try CRC Freeze-Off on the male fitting to shrink it.

It's smelly so back up the area with a rag and wear safety glasses. About a 10 to 20 second shot should do it.

Rich

[Keith W.]

[James G.]

Re: Fuel Pump Pressure

You can get a socket on it.
I think I used a shallow 9/16 with a short extension, I may have used a shallow 9/16 with a universal then an extension.

A little tip for small block fuel pumps. - photo below.

There is a 9/16 head bolt in the hole indicated by the yellow arrow.
This leads directly to the fuel pump push rod galley.
IF you remove the short bolt(3/4") you can insert a round bar magnet or a longer bolt (ideally with a nylon tip) to keep the pushrod from falling down when installing the rebuilt pump. You may be able to get a wire 3 finger prong in there, I haven't ever tried. I typically just use a bolt however have used a magnet more than once.

!!! IF YOU USE THE BOLT METHOD !!!
!!! IF YOU USE THE BOLT METHOD !!!
!!! IF YOU USE THE BOLT METHOD !!!
MAKE SURE TO NOTE IN YOUR CHECK LIST- THAT YOU MUST REMEMBER TO REMOVE THE LONGER BOLT PRIOR TO TURNING THE ENGINE OVER - it will cause problems with the eccentric lobe on the cam which operates the fuel pump if it remains locked.
PICT1096.JPG

[Larry M.]

Re: Fuel Pump Pressure

Here is a "How to do" thread for this job from CF. It is for a C2, but C3 will be similar.

https://www.corvetteforum.com/forums...on-a-63-a.html

I purchased some Snap-on swivel-sockets for doing this job. Makes wrenching from the wheelwell a lot easier.

Larry