Fuel Pressure Gauge on A-Piller what does your read at Idle

[03mmmonroe]

I have a fuel Presure gauge on my a-piller auto meter with elec. sender and I am wondering what you see at idle. I am from 24 psi up to 32 psi at idle. Under WOT it will go up to 40psi. I am NA. and no boost a pump. Any information would be helpfull. I was told that I may have a fuel pump concern due to my air fuel Gauge on Piller also will read 14.7 under WOT and was told with my tune should stay at 12.9.

[Fourth Horseman]

I've wondered about this type of thing myself. This is the only AutoMeter gauge I've added to my car that I'm not sure about. It never has shown what the computer shows for pressure. It goes up when the computer readout (via ScanGauge II) goes up. It goes down when the computer readout goes down. But they never agree on actual pressure. The AutoMeter gauge is always like 10 - 12 psi lower than what the computer says.

Now, the computer takes its reading on the passenger fuel rail and the AutoMeter sender is plugged in to where the shraeder valve was, the last spot on the drivers side rail. Could it be that pressure really does drop off that much by the time it gets to my Autometer sender? Or is my gauge/sender wonky? I'm leaning toward the latter explanation.

[Vortech347]

The pressure "should" be equal reguardless of what side the sensor is on.

Your fuel pressure will fluctuate alot. MM's obviously have a different setup than my foxbody but at idle and "coast" my FP drops quite a bit. At full throttle N/A it would go to about 39psi. Most of your Ford fuel injectors are calibrated at 40psi if I remember correctly.

[Marauderjack]

I went around and around with the AutoMeter "LOW" pressure readings and finally got an answer!!:beer: The OEM sender shows "Gross" fuel pressure (actual fuel pressure plus atmospheric pressure) so it reads about 14 PSI higher at the OBD II port than the AutoMeter gauge does!!:argue:

The EEC has to make adjustments as atmospheric pressure changes (altitude) thus the higher reading from the OEM sender??:confused:

I got rid of the AM gauge and use the ScanGauge II exclusively now....Idle pressure is 38-41 PSI as opposed to 24-26 PSI the AM gauge showed!!:cool:

My $.02.....

Marauderjack:bandit:

[03mmmonroe]

Thank you all. The information on the 24-26 at idle is what I needed. And yes working with ford the differance from acutal from the auto meter to the FRP on the fuel rail is normal. But my car concern is it will start at 24 psi and then to up to 35 psi while sitting at idle. This is the concern I am trying to track down. I have been watching the duty cycle on the fuel pump and it will change from 22 % up to 35% and load and engine temp, maf v. does not change. It may be a fuel pump concern. I have installed new fuel filter and did not change. Thank you agian for your information.

Russ 03MM A.

[frdwrnch]

Could this be a strategy to save wear and tear on the injectors? Possibly by boosting the pressure and reducing the injector on time to prevent the injectors from hammering themselves to death?

[Marauderjack]

Thank you all. The information on the 24-26 at idle is what I needed. And yes working with ford the differance from acutal from the auto meter to the FRP on the fuel rail is normal. But my car concern is it will start at 24 psi and then to up to 35 psi while sitting at idle. This is the concern I am trying to track down. I have been watching the duty cycle on the fuel pump and it will change from 22 % up to 35% and load and engine temp, maf v. does not change. It may be a fuel pump concern. I have installed new fuel filter and did not change. Thank you agian for your information.

Russ 03MM A.

Russ,

That is normal due to engine heat...the pressure rises to keep the fuel from boiling in the fuel rails!!

Mine will go to 50+ when idling in traffic or a bank drive through.....seems the AutoMeter gauge went to 35 or so idling hot!!

Marauderjack

[Fourth Horseman]

I went around and around with the AutoMeter "LOW" pressure readings and finally got an answer!!:beer: The OEM sender shows "Gross" fuel pressure (actual fuel pressure plus atmospheric pressure) so it reads about 14 PSI higher at the OBD II port than the AutoMeter gauge does!!:argue:

The EEC has to make adjustments as atmospheric pressure changes (altitude) thus the higher reading from the OEM sender??:confused:

I got rid of the AM gauge and use the ScanGauge II exclusively now....Idle pressure is 38-41 PSI as opposed to 24-26 PSI the AM gauge showed!!:cool:

My $.02.....

Marauderjack:bandit:

Wow! I had no idea. I guess I should have called them or asked here first. Thank you for the information. I appreciate it! :beer:

[jdenning002]

I was watching the same thing, the difference between the AM gauge and the ScanGauge... I read a lot about it on here and found the same answers above.

I do have a different question/ issue,

I tried to reload my tune after my SC re-install and the file was bad, Dennis sent me a new file and now the ScanGauge FPR is blank.... If I go back to stock I can read the FPR again, but not w/ the tune...

Any ideas on this???? THANKS!

[JohnE]

The factory fuel pressure reading is the differential pressure across the fuel injectors. The Autometer fuel pressure is only the fuel rail compared to atmospheric pressure. You can use a vacuum/boost gauge with a fuel pressure gauge simultaneously and to know the pressure across the injectors. I did this on the Grand Marquis, which has a mechanical return system. It's easier to read data from a factory DPFE.

[jdenning002]

i was watching the same thing, the difference between the am gauge and the scangauge... I read a lot about it on here and found the same answers above.

I do have a different question/ issue,

i tried to reload my tune after my sc re-install and the file was bad, dennis sent me a new file and now the scangauge fpr is blank.... If i go back to stock i can read the fpr again, but not w/ the tune...

Any ideas on this???? Thanks!


any ideas on this????

[1stMerc]

Russ, if i may ask. Did you install your A/F gauge yourself and if so which wire off the o2 did you ty into?