fuel pressure problem

[screamindemon2]

My fuel pressure changes after i set it. I have a walbro 340, hot wire &aeromotive afpr.I set it no vacuum 45 then drive awhile & it change up to 10psi , no vacuum 55.New pump,hotwire,& ajfr

 

[suicide six]

Try setting with car warmed up,may or may not help,gauge inaccurate?Battery voltage low initally then once car is driven awhile and charged,pump sees more voltage?Bad FPR?

 

[screamindemon2]

thanks i'll try setting it warm

 

[suicide six]

Dont forget the fuel filter if it hsnt been changed in awhile.

 

[screamindemon2]

fuel filter

Thats whats got me everything is new, ajfpr , fuel pump 12-914 force induction from holley, & fuel filter .The injectors set for 5 yrs after install ,but it runs fine

 

[suicide six]

After you set FPR at say 43lbs,vac line reconnected,car running then shut off,how long does gauge pressure maintain running pressure?

 

[screamindemon2]

the pressure maintains for a good while maybe an hour before it slowly starts coming down

 

[suicide six]

Could also be air in the gauge,the sealed portion.Once it heats up,the readings change.Try another gauge,or install abraided hose to gauge.A hose that reaches the windshield is a plus.Less vibration submitted to indicator equals longer lasting gauge.Spend the $ for a good gauge.

 

[screamindemon2]

pressure gauge

I have a braided line from fuel rail to my autometer carbon fiber 2 5/8 0-100psi that is mounted on the hood in the windsheid so you can watch while your drivin

 

[suicide six]

holding pressure that long is good,that takes the leaky injectors out of it.The 55 reading after inital setting is after running pressure has bled off,vac line off again and key turned on? Or is gauge showing 55 after shutting car off immediately with vac line off.

 

[screamindemon2]

say you set no vacuum 45psi & make a pass come back to the pits pull the vacuum off it'll be 52-55 psi at idle.Then sometimes you shut it off let sit for an hour it will be alright

 

[suicide six]

Yes,do this,set initially then go for a drive making sure car runs good,good O2s at WOT.Fuel pressure at WOT should be inital setting plus boost pressure.Come home,shut car off for an hr or till gauge falls below inital setting on FPR.Take vac line off,turn key to run and see if inital FPR reading is @ what you set it at.

 

[screamindemon2]

ok ,but my scanmaster will be wednesday, so currently no scan tool

 

[suicide six]

Ok,you gotta have a scan tool w/these cars.Just keep your foot outta of it till you get some readings.At 45lbs you should be ok.But tool will let you fine tune your car.Good luck I think you were reading gauge either too soon or with vac line still attached.Even after intial setting,once vac line is reconnected,fuel pressure will change.Tye wrap vac line at FPR nipple.

 

[screamindemon2]

ok thanks