Fuel pressure and hard starting

Truck starts hard once it’s been sitting for an hour or more. It will fire right back up if it’s on sat for 10 minutes. I tested the fuel pressure and when putting the key into the on position, it only went up to about 20 psi. Turned the key off then back on and it went up to about 45lbs. Third try and it makes it to 60-65 psi. After seeing this I replaced both the fuel filter and fuel pump with no change in starting.

After some research and frustration, I’ve moved on to thinking the fuel pressure damper may be bad. The biggest reason I suspect this is that I have a vacuum leak I’ve been dealing with inside the dash and it smells of raw fuel. Apparently if the damper goes bad it can/will allow fuel vapors into the vacuum lines and of course you’d smell it in a vacuum leak.

What I’m unsure of is if the damper would cause these starting and fuel pressure issues as well. My 2nd question is where the heck is it located? I know what it looks like, I would imagine it’s on the fuel rail but I just can see it. Would I need to remove the intake and maybe the fuel rail to get to it?

Thank you for any help you can provide.

Welcome to TRS

Fuel rail damper is on passenger side fuel rail near firewall, it does have a vacuum line attached for safety, in case it leaks.

Check that vacuum hose for fuel before replacing Damper.

Fuel Pressure should hold above 30psi for a few months, so yes you have a pressure leak.
Key on only runs fuel pump for 2 seconds, that adds about 10-15psi to current pressure, each time you cycle the key off and on adds more pressure as you found.

If Damper is leaking, or an injector, then over time it would FLOOD out a warm engine, so it would be hard to start, also cause a fuel smell in the intake as the leaking gasoline vaporized in the warm cylinders and lower intake.

The Amount of fuel it leaks, time wise, would decide when it would be a "hard start".

But you are on the right track I think, maybe not Damper but could be, check the vacuum line to be sure or rule it out

Thank you for the detailed response and good info. I’ll try to locate it again tonight after work and check that vacuum hose as you suggested. It does seem to be flooded when I try to start it because once it finally starts it blows smoke. Once it’s running it usually idles rough for the first 5 seconds or so. If it’s an injector issue, is there an easy way to figure out which injector is the culprit? Thanks again

Fuel injected vehicles usually have a "Clear Flooded Engine" routine
Ford and most others use this:
Key on
Press gas pedal down to the floor all the way, hold it down
(Computer sees 0 RPMs and Wide Open Throttle)

Computer will start "Clear Flooded Engine"
Which means Spark is working but Injectors are shut off
Crank engine over
It should NOT start, or even fire, since there is no fuel getting in

Just air is flowing thru which would dry out a flooded engine

As soon as you release gas pedal injectors will start, even while cranking
If engine fires, because of leaking fuel, and reaches 400rpms, computer will start injectors

There are a few ways to use this Routine.
I have a high mile 4.0l OHV, I use this every morning to get oil circulating thru engine BEFORE it starts up
So foot to the floor and crank for 5-10seconds before releasing gas pedal

You can disable coil pack and crank engine in Clear flooded engine mode then check spark plug tips, all should be DRY, WET tip means leaking injector.

I know the 4.0l SOHC can be a pain to get at some spark plugs, so if engine fires in Clear Flooded Engine mode, then you could disable 1 spark plug at a time, then crank again, when engine doesn't Fire, then the No Spark cylinder has the leaking injector.

But..........you have a Waste Spark system which means 2 spark plugs share one coil in the coil pack
When you disable 1 spark plug you can be disabling its partner spark plug as well, if you look at the coil pack's firing order you can see the "Matched pairs"
3 4
2 6
1 5

So disabling 2 may cause 6 to not spark, or visa versa
But you could narrow it down to 2 possible cylinders and then just pull those 2 spark plugs to check for WET or DRY tips


One heads up, many vehicles can get stretched throttle cables, so foot to the floor won't get Throttle sensor to tell computer its at WOT(wide open), so no Clear flooded engine routine.
Its an easy fix, Google: Ranger throttle cable mod

Also gets you more power back if it was stretched