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[Methodical]

I have fuel a pressure question. I have an adj FPR and a 255lph fuel pump. When I let the car sit without starting for a day or two, the car acts as if it is hard to start. I have to pump the gas pedal a little. I have an autometer fuel gauge and when I turn the key on, engine off, to prime the fuel pump the fuel pressure is only about 35psi. I turn the key several times to try and get the pressure up past 38psi (per Ford) to have an easier start. Now once she fires up the fuel pressure gauge shows 40psi. After the initial start I can just turn the key and she fires right up - no problems for the rest of the day. Now when I rev the engine the fuel pressure gauge goes down (about 38psi) and when I let off the gas it goes back up (40psi) I thought it should go up when revving the car. What's wrong?

Also, what is the proper way to adjust the fuel pressure, with the vacuum line on or off. It seems that I may need to make some adjustments. Thanks for any help. Peace

 

[95strokerPSU]

My car tends to be the same way if it doesn't get driven for a couple days. I'm getting an SCT tune next Monday and I'm hoping that will help it a little.

 

[CManT1914]

If you let your car sit for a couple days, it's gonna be hard to start no matter what. It will take a crank or two. That's strange that your fuel pressure drops when the engine is under load. I can't remember for sure, but when I checked my pressure I thought it increased to like 50psi while under load. Not to sure though.

 

[yellowstang1994]

Are you still running stock injectors? And the proper way to read the fuel pressure is with the vacuum line off.

 

[HISSIN50]

The pressure can dip for a second when going from idle to WOT as you transition (more fuel demand but there is a slight lag in fuel delivery as manifold vac diminishes while steppin on the pedal).

when you remove and plug the vac line, pressure should shoot up 5-8 PSI (i.e. if idling at 32 PSI, when the vac line is removed and plugged, the reading should go up to ~38 PSI).

A lot of aftermarket FPRs bleed pressure off pretty quick, which is alright (dont want the lines staying pressurized for no reason). the pump has a check valve which can seep as well. I would not sweat the issues you have, unless it affects drivability or bothers you.

Good luck.

 

[go-stang5.0]

If your just tapping the pedal and the FP drops but then comes back up over 40 psi then its fine. There is a slight lag when you press the pedal. However if it stays at 38 psi when you hold the gas pedal down...then I would think that you may need a new fuel filter. Or the pump may be going south. But I bet your pump isnt that old. I'd replace the fuel filter if it hasn't been done recently and go from there.

 

[94-302-vert]

Is the fuel filter old? That could definitely cause a delay in building up pressure / keeping up with the engine.

Chris

 

[Methodical]

Yesterday, I started the car after it sat for 2 days. My observations. When the fuel pump primed, the pressure was at 38psi - No problems. When I cranked the car (I did not pump the gas pedal just let it start on its own), the pressure was maintained, however, the car was still hard to start (not the winding of the starter motor issue). It seemed as if it was gasping/stumbling for something. After about 5-10 seconds, she came to life and idled with no problems. I revved the car and the fuel pressure jump up to 40psi (psi setting with vacuum off) and back to 38psi. I shut her down then turned the key - VOOOOOM - she fire right up with no hesitation at all. Let sit for a few hours, turned the key - VOOOOOOM - she fire up again. Let it sit over night. Turned the key, it hesitated to start again (not as bad as the 2 day sitting) - again it seems like its gasping/stumbling for something. Reminder: It's a new rebuild and has new fuel injectors (FMS 24lbs), fuel pump (255lph), spark plugs Autolites, fuel filter. Thanks for any help. Peace

 

[CManT1914]

I really don't think it's a problem. Every car hesitates for a bit before starting after it's sat for a day or two. The fuel pressure bleeds off after sitting, and even though the fuel pump primes the system when you turn the key on, doesn't mean there's fuel actually flowing. So when you go to crank it, it starts the fuel flowing, so of course it takes a second for it to start. Mine sometimes will start, but only rev up to like 400 rpm, then after half a second or so, it will fire the rest of the way and be fine. I wouldn't worry about it.

 

[cavscout371]

Mine does the same thing I'm not to worried about though.

 

[Methodical]

Update: Yesterday I did some diagnostics and discovered that the Ignition Coil was the culprit. Put the stock unit back on and VOOOOOM she fired right up. Went to start it up this morning and VOOOOOOOOM she fired right up. Will check again when I get home today. Thanks all for the responses.