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Z

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Discussion Starter #1
I have installed the HKS Fuel Pressure regulator, now I need to have it tuned in to right pressure.
Supra repair manual says the car should idle around 1.7-2.2 bar(24-31psi), and FPR keeps a constant 2.5 bar (36psi) above intake manifold. so does that mean if I am boosting 1.3 bar (19psi), my fuel pressure at full boost should be at 4.0 bar (55psi)?

I am kinda confused because repair manual measures fuel pressure at Fuel filter, but my Greddy Fuel pressure sensor measures at different spot...
correct me if I 'm wrong.

thanx

Jonas
 

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My fuel pressure at 0psi is about 43psi and at full boost...which is about 20psi...fuel pressure comes in at 65psi. At idle my pressure is at about 32psi. Hope this helps.
 
Z

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Discussion Starter #3
finally...thanx for the info! it really helps to have someones # to compare mine to.
at idle I am about the same as yours, but at full boost I guess I am running lean at only 57psi. The repair manul says FPR should keep pressure 36psi above intake manifold...thats why I thought if I boost 19psi my FP should be about 55psi...guess not!

just for the record, what kind of FPR are you using? are you using it to bypass your stock FPR? what kind of FP gauge are you using?
your stock twin correct?

thanx again for your input...really appreciated.

Jonas
 

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Zerosoul said:
finally...thanx for the info! it really helps to have someones # to compare mine to.
at idle I am about the same as yours, but at full boost I guess I am running lean at only 57psi. The repair manul says FPR should keep pressure 36psi above intake manifold...thats why I thought if I boost 19psi my FP should be about 55psi...guess not!

just for the record, what kind of FPR are you using? are you using it to bypass your stock FPR? what kind of FP gauge are you using?
your stock twin correct?

thanx again for your input...really appreciated.

Jonas
What is your fuel pressure at when you are at 0psi? It should be about 1lb of fuel pressure to 1lb of boost...but I am sure you probably already know that figure.
I am running stock twin turbos with absolutely nothing done to the fuel system yet. I am using DEFI gauges for monitoring. My fuel pressure is tapped into the fuel line after the fuel filter...of course.
 
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Discussion Starter #5
yup...1psi of boost, 1psi of fuel pressure.
I am gonna see where the fuel pressure is at when boost gauge reaches 0psi. hopefully by full boost (18psi) my fuel pressure will be 18psi more.

are you using aftermarket fuel pressure regulator or you just monitoring stock FPR? Defi gauges are nice..I was gonna get them too, but they didnt offer 60mm for fuel pressure that I needed to fit in the air vent, so I went with good old Greddy.
does Defi gauge reads in PSI or bar?

thanx

Jonas
 

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Zerosoul said:
yup...1psi of boost, 1psi of fuel pressure.
I am gonna see where the fuel pressure is at when boost gauge reaches 0psi. hopefully by full boost (18psi) my fuel pressure will be 18psi more.

are you using aftermarket fuel pressure regulator or you just monitoring stock FPR? Defi gauges are nice..I was gonna get them too, but they didnt offer 60mm for fuel pressure that I needed to fit in the air vent, so I went with good old Greddy.
does Defi gauge reads in PSI or bar?

thanx

Jonas
Stock FPR.
All DEFI gauges read in good old American English.
 
Z

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Discussion Starter #7
just checked out your web pages...nice looking supra...and FAST!

what size is your Defi (PSI) fuel pressure gauge? seems like its 60mm in the pictures, but I didnt see 60mm fue pressure gauge offered in PSI readings on Defi website. where did you get them? I know RX-7 store sells Defi gauges...

anotehr thing, where did you purchase your NOS kit? is 100 shot safe with stock fuel system?
thanx

Jonas
 

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Zerosoul said:
just checked out your web pages...nice looking supra...and FAST!

what size is your Defi (PSI) fuel pressure gauge? seems like its 60mm in the pictures, but I didnt see 60mm fue pressure gauge offered in PSI readings on Defi website. where did you get them? I know RX-7 store sells Defi gauges...

anotehr thing, where did you purchase your NOS kit? is 100 shot safe with stock fuel system?
thanx

Jonas
52mm gauges because the fuel pressure does not come in 60mm...which I have no idea why?

I got the gauges at Titan Motorsports...got here really fast.

I purchased the NOS kit at a local store here...KC Trends. 100 shot is fine for the stock fuel as long as you don't go over the hp that everything will handle. I have not used nitrous for about 2 months now because I am making too much hp just on the motor...I am wanting to do my fuel system mainly so I can spray the nitrous.
 
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Discussion Starter #9
i see....oh well, I guess I'm stuck with Greddy gauge then for a while till Defi decides to manufacture 60mm FP gauge.

gonn try my car out with more FP, will let you know how it goes..thanx again!

Jonas
 
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TT_6spd_95, where is your fuel pressure sensor tapped into?
 

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Don't forget!

Your idle VACUUM will effect the pressure reading. Base fuel pressure has to be taken with no line attached. Regulators will lower pressure for vacuum and raise it under boost. Boost tries to push the fuel back up the line, hence the higher pressure to compensate, vacuum will try to suck it out of the rail\injector and this is why pressure goes lower. To really compare BASE pressures you must measure it sans vac connection....
 
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Discussion Starter #12
Defi 60mm fuel pressure gauge

if you do not mind reading the pressure in bar then you can get the fuel pressure gauge(well all of their gauges, inluding tach) in 60mm

Defi gauge list
 
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Re: Don't forget!

BLKMGK said:
Your idle VACUUM will effect the pressure reading. Base fuel pressure has to be taken with no line attached. Regulators will lower pressure for vacuum and raise it under boost. Boost tries to push the fuel back up the line, hence the higher pressure to compensate, vacuum will try to suck it out of the rail\injector and this is why pressure goes lower. To really compare BASE pressures you must measure it sans vac connection....
I have my FPR vacuum line T'ed into the stock FPR vacuum line and
at idle I am set at 2.2 bar. when I pulled the vacuum to FPR which tells me my Fuel pressure at 0 atmospheric pressure I get about 2.9-3.0bar of FP pressure. does that seem normal?

I'm not quite understand what you meant, but are you saying that I should disconnect the vacuum line than set my idle at 2.2bar?
 

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FP setting

The factory likely gives a reading that's set with NO vac line attached. The pressure going UP when the line is disconnected is normal. when not under boost the vacuum in the engine is attempting to suck the fuel from th einjectors and thus the pressure at the regulator is dropped to compensate.

The reasoning this is all done is to make the creation of the ECU fuel maps easier. when they create those maps they'd liek o be able to asume a nice steady fuel suppply. Tuning for a constantly varying fuel supply would be a nightmare! So, they created a system that compensates for variations - boost attempting to push fuel back up the line is one example of a variation. To compensate for that they created a regulator that would increase fuel pressure for every 1PSI of boost pressure and do just the opposite for vacuum conditions. Following me? For instance - if you turbo a carb vehicle and don't compensate for this condition the carb will actually be receiving NO fuel when your boost level passes the base fuel pressure setting - it blows the fuel back down the line! Making sense? when pressure rises under boost you're no actually getting MORE fuel unless the pressure is rising faster than the boost is.

As for the correct base setting, I dunno'. :) I'm not (yet) a Supra owner but I DO know how EFI fuel pressure is supposed to be set and WHY it's set that way. This is true for all EFI vehicles although the new returnless systems are probably REALLY funky (shiver).
 
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Discussion Starter #15
I forwarded yout post to my tuner and he said you're right and my FP is set that way. basically when vacuum line is pulled, the FP raised up to around 3.0bar...which is what I should be getting when intake manifold is at atmospheric pressure at 0bar.
thanx for the information, it is very helpful.
 
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