Resolved 1g base fuel pressure.

[BIRDCLAWTSi]

i have read the forums and i am getting 37 psi with vacuum lines connected as the proper base pressure for a 1gT, what should i have at base vac. line on and off?

What is the base fuel pressure for 1g. auto, and n/t. My book says something totally different.
Will a n/t, or an auto fpr fit the fuel rail?

i am confused here. i just got a new sending unit and i am going to install it tomorrow. i am not sure what pump is in my car, the line is too rusty to touch and my base pressure is way higher than it should be.

thanks in advance.

 

[govproperty]

I'm a little confused. Are you asking about a stock fpr? With my aeromotive the 37 psi is taken when the vacuum hose is disconnected from the fpr. Setting an afpr is covered in this post at the bottom. http://www.dsmtuners.com/forums/articles-engine-fuel/338084-aeromotive-afpr-install-install-kit.html I saw a good explanation of it earlier when I was trying to troubleshoot my car but I lost it switching between all the forums.

 

[BIRDCLAWTSi]

I'm a little confused. Are you asking about a stock fpr? With my aeromotive the 37 psi is taken when the vacuum hose is disconnected from the fpr. Setting an afpr is covered in this post at the bottom. http://www.dsmtuners.com/forums/articles-engine-fuel/338084-aeromotive-afpr-install-install-kit.html I saw a good explanation of it earlier when I was trying to troubleshoot my car but I lost it switching between all the forums.

no, i am talking about the stock fpr. thanks though.

 

[NOSLO2PT0]

Stock pressure on a 1G manual with the hose OFF should be 37psi. On a 1G auto and N/T it should be 43psi with the hose OFF.

 

[BIRDCLAWTSi]

Stock pressure on a 1G manual with the hose OFF should be 37psi. On a 1G auto and N/T it should be 43psi with the hose OFF.

does the n/t fpr fit the turbo fuel rail? i never tried. but that sounds alot more like my base pressure hose off. like i said i do not know what pump is in my car, it might be a bigger pump on the stock fpr. an that would bump it up, or it might be a n/t regulator. i guess ill find out tomorrow.

 

[steve]

does the n/t fpr fit the turbo fuel rail?

Sure, it fits. It's the same fuel rail.

 

[BIRDCLAWTSi]

Sure, it fits. It's the same fuel rail.

that would explain alot. Thanks

 

[jeffo]

I believe the NT FPR is actually ~48psi. Everyone else is right about everything else though, the base fuel pressure is tested WITHOUT the vacuum line attached to the FPR:
1G MT = 37psi
1G A/T = 43psi
1G NT = 48psi
All 2G turbo cars are 43psi also.

 

[NOSLO2PT0]

From what I remember, I believe the NT FPR return nipple is oriented differently than the turbo one.

 

[BIRDCLAWTSi]

I believe the NT FPR is actually ~48psi. Everyone else is right about everything else though, the base fuel pressure is tested WITHOUT the vacuum line attached to the FPR:
1G MT = 37psi
1G A/T = 43psi
1G NT = 48psi
All 2G turbo cars are 43psi also.

so these numbers are with the vacuum line off? thanks.

 

[steve]

so these numbers are with the vacuum line off? thanks.

Base pressure is always with the reference port vacuum line off and plugged (so you don't have a vacuum leak).

 

[BIRDCLAWTSi]

Base pressure is always with the reference port vacuum line off and plugged (so you don't have a vacuum leak).

well i swapped sending units today and i was right about my fuel pump, according to the numbers on the pump. denso 195130-1020 it is a supra pump, my base pressure is vac on 38 and vac off 45psi. does anyone know what the supra pump is rated at in lph. ?

 

[ramsack]

i thought fuel pressure was adjust with the engine off and the fuel pump jumpered on? this way there is no manifold vacuum to throw off fuel pressure through the injectors.

The fuel pressure regulator maintains the pressure of fuel
delivered to the injectors at a constant level of 335 kPa (47.6
psi) (Non-Turbo models) or 255 kPa (36.3 psi) (Turbo models)
higher than the manifold internal pressure, thus keeping the
volume of fuel injected constant regardless of changes in the
manifold pressure.

i dunno how anyone else reads this but to me it means it doesn't matter if the vac line is connected because the engine should be off. how would you calculate inHg of vacuum against psi of fuel pressure to get it right? if the manifold pressure is 0 (engine off) then you adjust the fuel pressure to 36.3 psi.

 

[BIRDCLAWTSi]

i thought fuel pressure was adjust with the engine off and the fuel pump jumpered on? this way there is no manifold vacuum to throw off fuel pressure through the injectors.



i dunno how anyone else reads this but to me it means it doesn't matter if the vac line is connected because the engine should be off. how would you calculate inHg of vacuum against psi of fuel pressure to get it right? if the manifold pressure is 0 (engine off) then you adjust the fuel pressure to 36.3 psi.

that is why you remove the vacuum line from the fpr. to set you base pressure. i never heard of anyone turning off the engine to set pressure.

 

[ramsack]

yes but the injectors are pulsing and there is still manifold vacuum. the manual says fuel pressure should be 36.3 psi (or whatever for the application you are doing) ABOVE manifold pressure. it just doesn't make sense to me to adjust it to 36.3 psi with the engine pulling in around 20 inHg of fuel through pulsing injectors. is this loss in pressure just not negligible?

 

[BIRDCLAWTSi]

yes but the injectors are pulsing and there is still manifold vacuum. the manual says fuel pressure should be 36.3 psi (or whatever for the application you are doing) ABOVE manifold pressure. it just doesn't make sense to me to adjust it to 36.3 psi with the engine pulling in around 20 inHg of fuel through pulsing injectors.

the manifold vacuum/pressure has no effect on the injectors ever, it does not pull fuel through the injectors. fuel is forced through them by the pump,that is the only pressure that effects them, however vacuum/pressure does have an effect on the fuel pressure through the fpr. when the vacuum is removed from the fpr there is no manifold pressure effecting the fuel or the injectors. that is why you set your base pressure with the line disconnected and plugged.

well i swapped sending units today and i was right about my fuel pump, according to the numbers on the pump. denso 195130-1020 it is a supra pump, my base pressure is vac on 38 and vac off 45psi. does anyone know what the supra pump is rated at in lph. ?

280lph? is that right? i have a stock fpr. the pump is not re wired though.

 

[ramsack]

if the fuel pressure is the only pressure that affects them then why do they not have a fixed regulator that never adjusts for manifold vac/pressure? the 1:1 rise or fall is to keep a constant 36.3 psi of pressure against boost or vac inside the intake manifold. if you set up a rig for an injector that the spray side had vacuum and the supply side was simply placed in a dish or something of liquid then the vacuum would most definitely pull liquid through the injector. even if the supply side had pressure, the vacuum would pull more liquid through than to have no vacuum on the spray side. same with pressure but less liquid.

 

[jrohner]

Fuel pressure goes up with boost / down with vacuum to overcome the difference of the pressure. If boost goes up and fuel pressure stays the same, you'll go lean. Things need to be balanced out.

 

[ramsack]

yes correct. i am just overthinking this i think. i guess no matter what with the vac line disconnected and the engine at any rpm a functional regulator should keep base fuel pressure, right? you could test base pressure with the engine off, idle or 7000 rpm and it should stay the same.

 

[BIRDCLAWTSi]

yes correct. i am just overthinking this i think. i guess no matter what with the vac line disconnected and the engine at any rpm a functional regulator should keep base fuel pressure, right?

yes correct. i am just overthinking this i think. i guess no matter what with the vac line disconnected and the engine at any rpm a functional regulator should keep base fuel pressure, right? you could test base pressure with the engine off, idle or 7000 rpm and it should stay the same.

correct.

 

[steve]

the manifold vacuum/pressure has no effect on the injectors ever, it does not pull fuel through the injectors. fuel is forced through them by the pump,that is the only pressure that effects them, however vacuum/pressure does have an effect on the fuel pressure through the fpr. when the vacuum is removed from the fpr there is no manifold pressure effecting the fuel or the injectors. that is why you set your base pressure with the line disconnected and plugged.

While the vacuum in the intake doesn't directly change the fuel pressure it has quite an impact on the fuel delivery rate of the injectors. It's the difference in pressure between the inlet and outlet (delta pressure) that's creates the flow through the injector. So the manifold vacuum/pressure does have an effect on the injectors.

Controlling the delta pressure is what the FPR does and why it tracks the reference 1:1. We set the base with the reference being atmospheric pressure and when under vacuum both the fuel pressure (inlet) and manifold pressure (outlet) drop the same to maintain the delta pressure. Under boost the pressures rise but we get the same delta.

If it didn't work this way, under vacuum more fuel would spray and under boost less, until boost = base pressure, where no fuel would come out. Having the injectors always deliver the same amount of fuel over unit time makes calculating the pulse width much easier. Keeping the injectors from pinching off under boost tends to keep the engine healthy.

You can set the base pressure with the engine off. We don't because the pump flow rate is dependent on the system voltage and there is a several volt difference between the running /charging and not. With a good regulator the difference in flow rate shouldn't change the pressure but with the factory regulator it can make the difference between overrunning the return and not.

 

[DSMopar]

Ramsack fuel pressure is always set with engine running, the fuel flow rate used by the engine with no load is almost negligable at about any RPM.

The only way the fuel pressure would be affected is if the fuel flow rate through the injectors is at or greater than the flow rate the fuel pump can supply at that pressure (I.E the FPR bypass is closed). Otherwise the FPR will bypass the correct amount to keep the fuel pressure constant.

also:

1G A/T = 43psi

You sure about that?

 

[ramsack]

1g non-turbo (auto or manual) is 47.6 psi
1g turbo auto is about 43 psi
1g turbo manual is 36.3 psi

2g ALL (420a auto or manual, 4g63 auto or manual) is about 43 psi. part number for fpr is the same regardless of engine.

 

[BIRDCLAWTSi]

i have a base pressure of 38psi vacuum on, and 45 vacuum off. as far as i know it is a stock 1g manual trans. turbo fpr. i also just discoverd that i have a supra mkiv fuel pump. i am running pte 680cc injectors, i am obviously way higher than i should be. my questions are,

1. is my pressure so high because of the pump?
2. will a non turbo regulator help?
i know i need a afpr and will get one as soon as i can afford one. i just need some input. thanks.

 

[gofer]

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1. yes
2. no

agreed. you need to get a afpr ASAP.