No fuel pressure with new pump & gauge???

spaman · 07-26-2009, 10:19:37 AM

I posted up a few weeks back about issues I was having with loss of power at the top end of the power band. Still having same issues,, Heres what I tried so far.
Many of you guys said the problem sounded like the pump could be the culprit. I replaced the pump with a new mech holley, & also a new liquid filled pressure gauge. I fired the motor, pressure came up to 3# & kind of faded back down to 0#. I then bypassed the tank (ran line from a gas can) still no pressure. I went ahead & test drove the car anyway since it idled fine. When car gets to high end of 3-4th gear it still noses over.. Came back pulled pump & fingered the pump rod while turning over motor. The rod is only moving about a 1/4inch. It is a hardend rod looks fine. I had someone tell me the rod should be moving 1/2in or more to activate the pump properly. He thinks I've wiped the lobe on the cam... I'm at a loss here. Whats your thoughts on what could be going on here? Thanks

Damon · 07-26-2009, 11:29:12 AM

1/4" of movement doesn't sound like enough to me. I think you're buddy is probably right. But wiping a fuel pump lobe is kinda odd- nowhere near as much pressure on the fuel pump lobe as on a lifter lobe, plus it's not really a lobe at all, but and eccentric circle- no pointy "nose" to wipe off of it.

Also see if you can look up through the pushrod hole to the fuel pump lobe on the cam (good luck doing thaqt with the engine in the car!). Maybe something is obviously wrong with it.

The simplest fix here if you can't figure it out might just be to return the mechanical pump for an electric one and a regulator.

theflash · 07-26-2009, 12:12:23 PM

the rod will only move so far depending on where the lobe on the cam is. I'd try another mech, or electric pump before tearing in to the motor.

Ted · 07-26-2009, 04:21:13 PM

Just wondering if your gauge was the type that needed to be vented. Most liquid filled require the internals to be at atmospheric pressure to read properly. Possibly the gauge could be bad.
Can you rig a way to fuel the carb by gravity long enough for it to run 2 minutes. That way you could see how long it would take for your pump to fill a gas can.
Should be less than 1 minute for a gallon.

80-z28 · 07-26-2009, 05:42:18 PM

Can you take the push rod out of the block and measure it?

80-z28 · 07-26-2009, 05:43:16 PM

Hope it is not a bronze tip rod.

spaman · 07-26-2009, 06:59:42 PM

Its a hardened rod,but its been running fine for about 3000 miles

1972L · 07-26-2009, 07:25:08 PM

I measured an old cam
The fuel pump lobe is round,
It ground on an offset.
I measure about .400" lift
If you are only getting .250",
You have a problem.

spaman · 07-27-2009, 12:11:45 AM

thanks for the help..