Losing fuel pressure??

[svtcards]

So I was going to start my truck today after I installed a fuel pressure gauge to see what kind of fuel pressure I get.want to know because it seems to start hard if it sits for a while.so when I put key to run position not cranking and I looked at the gauge.it jumped to 30 psi pretty easily.but after that I noticed pressure started to drop pretty quickly.below 20 psi then to 15 psi.took me about 3 or 4 cranks to get it to start.after I got it running psi went to 35 consistently.after I shut it off I lost 15 psi instantly.apparently there's a leak somewhere thats not visible so I'm assuming it's somewhere internal.any ideas what could be causing this? also after it gets running it runs and starts fine.just the initial start up after sitting is a bitch.

 

[rusty ol ranger]

Probably a stuck open injector.

 

[Uncle Gump]

Probably a stuck open injector.

Stuck open would most likely take fuel pressure to zero... it would also have some drivability issue to boot.

I believe a leaky injector... or a fuel pressure regulator.

 

[svtcards]

Well I had it Dyno tuned this past November and it had no issues on the Dyno.if there was he would of said something about it I would think.driveabily part of it anyways.also if it was injectors wouldn't that hydrolock the engine?how can I test regulator to c if that's the culprit?

 

[rusty ol ranger]

Well I had it Dyno tuned this past November and it had no issues on the Dyno.if there was he would of said something about it I would think.driveabily part of it anyways.also if it was injectors wouldn't that hydrolock the engine?how can I test regulator to c if that's the culprit?

3 months or so is plenty of time for an injector to start leaking down. It might have been fine in november but now its not.

The other possibilty would be the check ball that keeps fuel from draining back into the tank when the key is shut off and the pump stops. That would cause no driveability problems besides extended cranking or not starting the first time.

 

[Uncle Gump]

I guess it could hydro lock an engine in extreme cases. But there have probably been way more drippy injectors then hydro lock caused from them.

You would look for fuel in the vacuum reference port on the fuel pressure regulator for testing of the regulator.

 

[alwaysFlOoReD]

Regulator... to paraphrase unclegump... pull vacuum line and smell for gas.

 

[svtcards]

Is check ball in fuel pump?

 

[svtcards]

Regulator... to paraphrase unclegump... pull vacuum line and smell for gas.

Pull The vaccum hose that's plugged directly to regulator? If it's bad I should be able to smell gas coming from it?or fuel will be pouring out of it correct?

 

[rusty ol ranger]

Pull The vaccum hose that's plugged directly to regulator? If it's bad I should be able to smell gas coming from it?or fuel will be pouring out of it correct?

Youll smell gas in it. Might get some dribbles. Usually when these fail though they run rich.

 

[RonD]

Any pressure above 10psi would allow start up, could stumble but should start, so not your issue, on a 1997 or earlier fuel system, i.e. runs at 30-40psi

Could be Choke issue if it only happens on cold starts
That would be ECT sensor, maybe change that sensor, so computer can set correct Choke Mode for engine temp
ETC sensor has 2 wires connected

Dash Temp gauge SENDER just has 1 wire in older vehicles

These look similar but ECT is 5 volt, sender is 12volt so not at all the same

The fuel pump has a Check Valve inside it, a "backflow preventer", these can leak a bit before they close
The Fuel Pressure Regulator(FPR) has a spring valve set for 43psi, these can also leak a bit
For either to be "bad" you would see 0psi after a few minutes of key off

To test FPR remove its Fuel line, thats the Return line, fuel flows back to the gas tank on this line
With fuel line removed, put a towel down under FPRs outlet
Cycle key on one time, that runs fuel pump for 2 seconds, that adds about 10psi to current pressure
See if FPR is leaking fuel
Cycle key off and on again, for 20psi
If no fuel is leaking out then FPR is OK, your pressure is being lost via check valve inside fuel pump

 

[svtcards]

Any pressure above 10psi would allow start up, could stumble but should start, so not your issue, on a 1997 or earlier fuel system, i.e. runs at 30-40psi

Could be Choke issue if it only happens on cold starts
That would be ECT sensor, maybe change that sensor, so computer can set correct Choke Mode for engine temp
ETC sensor has 2 wires connected

Dash Temp gauge SENDER just has 1 wire in older vehicles

These look similar but ECT is 5 volt, sender is 12volt so not at all the same

The fuel pump has a Check Valve inside it, a "backflow preventer", these can leak a bit before they close
The Fuel Pressure Regulator(FPR) has a spring valve set for 43psi, these can also leak a bit
For either to be "bad" you would see 0psi after a few minutes of key off

To test FPR remove its Fuel line, thats the Return line, fuel flows back to the gas tank on this line
With fuel line removed, put a towel down under FPRs outlet
Cycle key on one time, that runs fuel pump for 2 seconds, that adds about 10psi to current pressure
See if FPR is leaking fuel
Cycle key off and on again, for 20psi
If no fuel is leaking out then FPR is OK, your pressure is being lost via check valve inside fuel pump

Remove vaccum line or the actual fuel line? If ect sensor was bad would my electric fan not turn on? because it does turn on. I do see 0 psi after about 5 to 10 minutes just turning key to run with everything still connected.

Youll smell gas in it. Might get some dribbles. Usually when these fail though they run rich.

Don't smell any gas or any fuel In hose either

 

[svtcards]

I was also told If I crimped return line and turned key to run position if pressure holds then regulator is bad.if I crimp pressure side and pressure holds then check valve in pump is good.which would narrow down to injectors.does that sound right to u guys?

 

[RonD]

I was also told If I crimped return line and turned key to run position if pressure holds then regulator is bad.if I crimp pressure side and pressure holds then check valve in pump is good.which would narrow down to injectors.does that sound right to u guys?

+1 ^^^

Thats another way to do it, but carefully squeeze the nylon fuel line, don't want to break it

And yes, remove the "fuel line" from the FPR, if fuel comes out of FPR with pressure under 30psi then its leaking, should hold pressure up to 40-45psi, 43psi is spec, with engine off, i.e. no vacuum

 

[svtcards]

+1 ^^^

Thats another way to do it, but carefully squeeze the nylon fuel line, don't want to break it

And yes, remove the "fuel line" from the FPR, if fuel comes out of FPR with pressure under 30psi then its leaking, should hold pressure up to 40-45psi, 43psi is spec, with engine off, i.e. no vacuum

My fuel line isn't connected to regulator it's on fuel rail on both pressure and return side.im assuming just disconnect it from rail your meaning?my psi only hits 30 psi with key on the run position at the moment.35 max when idling.my fuel lines r braided stainless.not sure if I can actually crimp them without damaging it.your thoughts on that?