87 IROC Z28
5.0
Automatic
87,000 miles

Ok,
Car turned off I turn on key to prime electric fuel pump.
Pressure reads 38 pounds at fuel rail
Pump is still on
after 5 seconds the pressure bleeds off fast to 0

If you try to start the car it always does start and will hold 38-39 pounds of pressure running.

Replaced a new Precision Pump that was bad out of the box with a new Delphi high dollar pump. That's what's on it now and it's new.

Fuel regulator on the manifold holds vacum fine and does not bleed off

Should system hold pressure with key ON and car NOT running for more than 5 seconds?
Sooo, how do I test the regulator?

We tested the NEW pump AT the tank and it held 80 pounds of pressure for over an hour.

UPDATE!
I go out this morning and the car won't even fire.
The fuel pump runs for 1 MINUTE before it shuts off. Not the 2 seconds it should cycle but 1 minute.

Could this be an messed up relay that works part of the time?

UPDATE!
After I try to start it and it doesn't fire I turn the key off and I hear a loud 'hissing' sound for about a minute coming from from the area UNDER the intake somewhere. Vacuum leak? what sits under the intake?

The filler neck on this car has always been bent up from someone trying to pry off the gas cap. Should there be a good tight seal on the cap to build pressure in the tank?
Or should I say, if the cap fits loose, the fuel system won't let the car run right?

UPDATE!
Twenty minutes later I walk out and it starts almost before I turned the key, that fast. Still heard the the hissing under the intake for 30 seconds when I shut it off. I did however see some smoke possibly when it started.

If you're just guessing and really don't know please don't chime in.

Thanks!

 

There might be a injector bleeding down & I wouldn't rule out the pressure regulator. You need to pinch off the return line & note the pressure drop, then prime & pinch off the feed too.

 

How do I do this?
I see on the drivers side left engine compartment where the supply and return lines are.

So the regulator can still be good even tho it holds vacumn?

 

Seems to me as fast as it bleeds down from 38 to 0 after it holds steady for 5 seconds it would have to be a major leak.

 

Also I don't think the 305 is supposed to hold 43 and up all the time. All manuals I see saw 31-40.

 

How long is the system supposed to hold the full 38 or so pounds of pressure with the key on and NOT running?
Anyone really know?
Most people I've talked to say their system bleeds right off also so whats up?

 

It should hold for atleast an hour before starting to slowly drop, this means it looses pressure but not draining the fuel rail. When it drops fast it drains the fuel rail.

 

I had a injector leak on mine. I replaced all with Bosch III'S. Are yours all original? One other note, check and make sure the fuel flex line connections are tight in the engine compartment. Possible cold start injector leaking.

 

I'm going to find out from somewhere how to check the regulator before I go broke replacing a bunch of parts I don't need.

 

Is that an hour on any fuel injection system? Or just this system. Since it always starts and runs I know I can drive it until I hear what to test next. I know these early GM injection systems aren't that advanced like on our BMW.
Thanks

 

Generally port inj. systems hold pressure, most tbi sytems don't.
The fuel plumbing on these older cars isn't much different the newer cars, it when you get into returnless style & direct injection that the systems are more complex.

 

Thanks ex-x-fire!
So is mine the port injection or the tbi?
Should mine be holding pressure?

 

Like I said, pinch off the return line at the rubber section, fire it up & shut it down. Does it hold pressure? If not it could be the fuel pump check valve, a fuel leak in the rubber hose that hooks tthe pump to the sending unit, a leaky line, a leaky injector (cold start too) or regulator. Pull the vacuum hose off the regulator, prime it & watch for fuel to come out of the regulator nipple.
With it primed(you need someone to help to do this), pinch off both return (first) & feed lines, & it still leaks down, this will tell you if the leak is at the rail & not in the tank(pump valve or hose) or feed lines.

 

Thanks,
Whats the odds I got 2 bad pumps out of the box new in a row with the newest one being a Delphi?

 

1st one is tbi The other is tpi.

 

Great, it's TPI.
I'll run those checks.
Think I could have got 2 bad pumps in a row?

 

As far as you know for the 305 what should the pressure be key on NOT running and than running?

 

38-45 psi.

 

I did forget to add that we tested the NEW pump at the tank and it held 80 pounds of pressure for 1 hour at least AT the tank so I doubt the pump is bad.