Fuel Pressure Issue

[Compton74]

So I installed 550s and a Lex AFM, along with the AFPR on my 91 gte. Noticed when i was setting fuel pressure per the tsrm, that no matter if the vacuum was hooked up or not, it still ran the same pressure. So i followed the Vacuum lines down to the VSV, which the vacuum was off. Put it back on and everything worked the proper way. So went to shut the car off to check if it held pressure after the car was not running, and about 10 seconds after the car shut off the pressure went down to 0. I noticed while putting the vac back on the VSV, that there was no filter, from what i can tell this is a source of a vacuum leak, but is it enough to make the pressure drop as stated above. I rebuilt the AFPR with the rebuild kit from aeromotive and got the AFPR install kit from driftmotion. Car also while idling, threw a code 25 which is lean, so could this be the source of my problem or would it be something else? Thanks for all the help.

 

[TurboStreetCar]

My Aeromotive sometimes hold pressure and sometimes doesn't after shutting down.

In the stock setup (witch it seems like your running because you mentioned a VSV) the vacuum goes from the manifold to a VSV and to the regulator. The purpose of this VSV is to help with hot restart. What it does is close off vacuum to the regulator and vents the regulator diaphragm to the atmosphere to bump the fuel pressure. The Filter just prevents dirt and grime from getting into the VSV or possibly the vacuum lines.

If this VSV is defective it may not be allowing vacuum to pass to the FPR. Run a single vacuum line to the FPR bypassing the VSV to rule that out.

If your playing with fuel pressure, I would dismiss any fuel related codes until you get it straightened out. Monitor the VF signal to see if the TCCS is happy with the mixture.

 

[Compton74]

I've read some stuff about VF signals, but would you be willing to enlighten me on how to monitor them?

 

[TurboStreetCar]

In the check connector there's a terminal labled VF1. Check voltage to ground as you drive to monitor fuel trim.

 

[dragracer]

When you bypass the factory jtube return, your pressure will drop after you shut motor off.

Jtube has a restrictor to hold pressure as a backup in case regulator fails.

Since thats gone, fuel drains back to tank pretty quickly. This isnt anything to worry about.

 

[TurboStreetCar]

The j tube wouldn't effect pressure after shutdown.

 

[Compton74]

well does the fuel pump only pump when cranking? or as soon as the ignition is on. This morning i turned the key to on, grabbed something falling on the seat put it back and started her up, and it took way less cranks then normal.

 

[Poodles]

The fuel pump check valve is what holds the pressure after shutdown. Fuel pump doesn't turn on until it's cranking.

Leaking pressure down after shutdown is fairly normal. Some cars hold pressure, others instantly lose it, both will run fine.

If you're getting a lean code it's probably the FPR, you never said what the fuel pressure was.

 

[wardog]

X2 Double check that fuel pressure regulator. If you have vacuume going to the regulator IT WILL ADJUST the pressure unless its bad. What fuel pressure are you currently at?. With the 550cc injectors you should never be at stock pressure, I had mine at 25 with vac on and it ran fine.

 

[Compton74]

well after i got everything properly adjusted, and now the FPR has vacuum fuel pressure with vac on is at around 32, with the vac off around 40

 

[TurboStreetCar]

X2 Double check that fuel pressure regulator. If you have vacuume going to the regulator IT WILL ADJUST the pressure unless its bad. What fuel pressure are you currently at?. With the 550cc injectors you should never be at stock pressure, I had mine at 25 with vac on and it ran fine.

It references to manifold pressure maintaining the "No Vac" pressure differential across the injectors at all times. If your running 550's and LEX AFM you should run stock fuel pressure as the AFM ballances out the injectors. You need a certain amount of fuel pressure to get a proper spray pattern from the injectors.

well after i got everything properly adjusted, and now the FPR has vacuum fuel pressure with vac on is at around 32, with the vac off around 40

How is the VF? Did you reset the TCCS and see if you get any more codes? Does the fuel pressure reference manifold vacuum properly?

 

[Compton74]

Hooked the vf up just at idle and it was at around 0.135 or in simpler terms pig ass rich, do i need to drive the car around with the voltmeter hooked up and see what it does at different RPMS? If so what RPMS? And could you elaborate on the fuel pressure referencing manifold vacuum properly?

 

[TurboStreetCar]

I would leave it hooked up and drive it however you drive it. Though it will zero out when operating in open loop.

Fuel pressure should follow manifold vacuum. If you look at the fuel pressure and rev the motor the fuel pressure should raise and then fall with manifold pressure.

 

[wardog]

Hooked the vf up just at idle and it was at around 0.135 or in simpler terms pig ass rich, do i need to drive the car around with the voltmeter hooked up and see what it does at different RPMS? If so what RPMS? And could you elaborate on the fuel pressure referencing manifold vacuum properly?

Try to adjust the AFPR and you wouldnt happen to have a wideband hooked up to monitor AFRS? If not just monitor with VF if its too rich lower the fuel pressure little at a time. Good luck keep us posted..

 

[Compton74]

no wideband, lll play with the fuel pressure and see what happens with the vf numbers but correct me if im wrong, but running rich is bad but no will not ruin anything correct?

 

[TurboStreetCar]

If its extreamly rich it could dilute the oil to a point that it damages bearings.