Working on a 96 LT1 Caprice...
Yeah, not quite an F-bod, but posting here since you guys know your stuff
Hopefully someone can help me out.

I first noticed that the fuel pressure was bleeding off after the car sits for a few hours. Goes to 30psi after 1hr, 15 psi after 2hrs, probably 0 after more.

Started to do some investigating:

Ignition ON, prime only = 44 psi
At temp and idle, vacuum tube on regulator = 44 psi <-------?
At temp and idle, vacuum tube off regulator = 48 psi

The vacuum tube has the odor of gasoline, but I have yet to actually see any in it. I'm not sure if that counts

As pointed out above, my fuel pressure isn't dropping at idle. I do live in the mile high city, so I don't know if that is a reason for this or not. But it seems wrong to me.

I'm going to a junkyard tomorrow to piece together some fuel line shutoff valves to check into this more. But at this point, does this scream FPR to anyone?

Thanks for your input.

 

Those pressure readings seem normal. Spec is 43.5 psi with the vacuum hose the fpr off, but GM allows anywhere from 41-47. I don't see anything wrong with it bleeding off pressure after several hours. If it went to zero after a min, then I would be worried. If the pump primes at koeo and the psi jumps back to mid 40's, then you should be fine. What made you start investigating fuel pressure in the first place?

 

I've been getting hard starts lately whenever it has been sitting for more than a few hours.

If I just get in the car and start it right up after its been sitting, it will sputter like its losing gas and then once pressure comes up, it's fine.

If instead of just turning it over right away, I turn the ignition ON and let the pump prime, it will start flawlessly.

This behavior is new in the past couple of weeks.

 

if you smell gas in the vaccum line then the regulator maybe leaking fuel through there. start the car remove the line and watch the regulator no fuel should come out of it. My impala leaked by the regulator i had the same problem, i also had the check valve in the pump stick open which caused it to bleed down.

 

Well the fpr isn't too expensive or difficult to replace. I think there is a write up on testing for pressure loss on shbox.com somewhere. Clamping off lines to tell if the leak is somewher in the supply or return line.

 

Sounds like fpr to me. Strange though, usally see fuel in vac line if this is the problem. What makes you say "when the pressure comes up its fine"? Did you put a gauge on it while it was acting up? The pressure readings you posted are fine. There is a spec and time limit for fuel pressure drop off. I do not know what it is, but most cars will bleed off pressure in that amount of time. When you key on it should prime fast. You posted that you had good KOEO pressure. This is why I asked why you said " when the pressure comes up. Post backsome answers so we can try to help.

 

The Dude: What I was describing was...

With a gauge on it, and the immediate start (not waiting for prime) it will fire right away, but then stumble as the pressure builds up to 44psi.

I cut some quick-connects out of an old Lumina at a yard today and made myself some shutoff valve attachments. Total cost with fittings and hose: $20

Kent Moore/Snap-on wanted $150 for the 'official version'

If the weather holds up this weekend, I'm going to find where the pressure loss is.

Isn't the fuel pressure at idle supposed to be less than the prime only pressure? Makes me think it's running rich which would explain the poor mileage I've been getting lately. Was just blaming winter gas before.

 

I think even if your pressure was running a little high, it wouldn't cause more fuel to actually get into your engine, thats controlled by the computer.

 

I got a chance to hook up the shutoff valves and figure it out today. It was the FPR thankfully. I really didn't want to pull the tank down over this. I guess the smell of gas in the vacuum tube even without the presence of it was a good hint. It must have been a small leak in the diaphragm rather than a complete blowout.

 

I see that at wok all the time