Fuel pressure and tach problems

[fe3xclone]

Problem #1:

I'm having an issue with mine lately on the 455. Been trying to get it fired back up since I had it running last fall and its been pretty rough going.

I think one of my problems is fuel pressure. When I turn the key, I hear the fuel pump turn on and run for 2 seconds like its suppose to. However when I go to the passenger side of the car to check the fuel pressure gauge on the fuel rail, I can see it dropping really fast back to zero.

I checked for leaks and tightened all my fittings and everything seems good. In fact, last fall I had a few leaks in the system but it would never lose pressure as quickly as it is now. Would take it at least 10-20 minutes for it to drop back to zero.

Fuel pump is obviously working as I can hear it and have confirmed I have fuel pressure at the rails. So what's left? Fuel pressure regulator? It's brand new and was working fine last fall. What would cause it to fail all of a sudden?

Problem #2:

I seem to be having problems with my tach signal. I can see my tach in the dash registering when I crank the engine over, however when I review my datalog, it shows my rpm as being zero for the entire time I was cranking. A week ago I fiddled with the connection at the distributor and manged to finally get it working and the engine running somewhat. But now its back to doing the same thing before and not registering.
Last fall I didn't have this problem. Could the tach signal be getting interference from the other wires in the wire loom? That's really the only thing that I had changed since the last fire up last fall. I routed the tach wire with the rest of my engine harness and taped it all together.

Little info on the engine:

455 Olds
Multiport EFI
stock HEI vacuum distributor for the moment

Thanks for the help,

[trakkies]

For the pressure to hold after the pump stops relies on the pump, reg, injectors and pipework between all being good. If you have rubber hoses to pump and reg, you can check those by clamping the hose after each one in turn. If it's only just started after a layup - could be rust etc from the tank getting into the pump?

[Matt Cramer]

On the tach issue, are you able to get RPM on a Stimulator?

[fe3xclone]

For the pressure to hold after the pump stops relies on the pump, reg, injectors and pipework between all being good. If you have rubber hoses to pump and reg, you can check those by clamping the hose after each one in turn.

All my fuel lines are brand new EFI rated rubber at the tank to stainless steel lines up to the engine with Aeroquipe Teflon stainless steel braided hoses from the frame to the engine and regulator.

If it's only just started after a layup - could be rust etc from the tank getting into the pump?

My fuel pump has the stock "sock" on the end of it which I assume is used as a prefilter of sorts. Could rust make it past this?

[fe3xclone]

On the tach issue, are you able to get RPM on a Stimulator?

Matt, I'll check it with the stimulator as soon as possible. I just started a new job this past Tuesday and they have us working a lot of hours at the moment. Haven't even had a chance to get out to the barn to work on it.

[LeslieTroyer]

if your loosing pressure it can be one of three places 1) out the injectors (probably not too likely if it starts and run ok hot). 2) Back thru the pump if the check valve there is open (or there is no check valve) and, 3) Leaky pressure regulator. if you can cap the where the fuel comes into the rail with a pressure gauge -- run the pump and see if that hold pressure -- if so it's not the pump. Then cap the return line before the pressure regulator -- if that holds pressure it's not the injectors - and must be the regulator. -- process of elimination.

LEs

[fe3xclone]

Okay, finally had time to mess around with this today after letting the car sit for a week. I decided before I started messing with anything I would reload a tune into the ECU and just try starting the engine.
Didn't catch the first try but cranked it a few more times and finally got it to fire.

RPM's were fine now??? And the fuel pressure was okay as well? Kind of confused why it would have fixed itself.

I noticed though at first if I just turned the key on and let the fuel pump prime the system and it stopped, the pressure would drop steadily back to zero. However once I had the engine running, I had a solid 42-45 psi of pressure and when I would shut the engine off, the pressure would now hold steady.

Can running low on fuel cause the problems I was having? The reason I ask is that last fall I had put 5 gallons of fuel into the tank. My fuel level gauge wasn't working properly so I never really knew how much fuel I had left. This spring here when I went to fire it back up and had it running for a short time, I noticed the fuel pump sounded a bit different and heard some gurggling coming from the pressure regulator. I figured I was low on fuel and went and put another 5 gallons in.

Did it just take all this time for the fuel to recirculate through the system? Doesn't seem like that would be the problem but I don't know what else it could have been for it to all of a sudden be working properly again.