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Using a handheld vacuum pump (e.g. Mity-Vac), apply vacuum to the regulator:
for every 2 inHg of vacuum applied, the regulator should drop pressure by about 1 psi;
if it not changing pressure, then the regulator is frozen or leaking.
Also, put vacuum gauge on vac hose from manifold:
you should see idle vacuum (what, about 20 inHg, or similar);
if not, then this hose may be restricted.
(1 psi = 2.036 inHg)
2.91 to 2.85 is about 2%, is not alot.
what is the preferred pressure to set the injectors at?
minimum, maximum, or average?
Hi Mr.Prick,Quote:
Originally Posted by mr.prick
Are you asking: to what base pressure (FP) should the FPR be set in order to get the best injector performance...
<rambling=on, not as good as Led Zeppelin>
I don't know the answer... but it would depend on the injectors' physical characteristics... injectors are inductors (inductance L)... when the PCM grounds the injector (completing the circuit) the current ramps up with a time constant of L/R (the beginning part of the red curve)... when the current is sufficient to magnetically move the pintle, the pintle starts opening (the red dip) 1.2ms after the PCM closed the circuit, and fuel flow begins it's ramp up until it reaches it's maxium flow (at the given rail pressure)... then when the PCM removes the ground the injector's inductance self induces a reverse voltage across the injector in an attempt to keep the current flowing (the blue spike), but the circuit is open so the voltage just ramps down... during this ramp down, the pintle is ramped shut by the spring (during which the fuel flow ramps down), and this induces a small voltage (the blue bump)... so fuel was still flowing for about 0.8ms after the PCM opened the circuit...!!!
<rambling=off>
:Nothing_funny_to_ad
As you can see, it depends on many variables and physical aspects, the question can only be answered by empirical means (doing experiments).
(I have seen large injectors work more "precisely" at lower rail pressures.)
Cheers,
Joe
:cheers:
http://img206.imageshack.us/img206/5...veformsfl6.png
I borrowed the diagram from the picotech site.
i mean when using the IFR sheet.
which logged fuel pressure would be best. (min/max/avg)
the IFR table for 02 fbody OS is static,
i guess i could change it every time i drive though. http://smiliesftw.com/x/deadhorse_1.gif
Oh, I would use the average.Quote:
Originally Posted by mr.prick
I like the emoticon...http://smiliesftw.com/x/deadhorse_1.gif... :cheers:
thanksQuote:
Originally Posted by joecar
i thought it would fit.
Great read fella's
Thanks for the info
Nick--
Good read as I will be changing the stock injectors out in the truck for 8.1 Marine injectors that flow 42lbs @43.5.
Also, I have used the Blue Ford Cobra injectors a lot and even though Ford Motorsports rate them as 30lbs at 40PSI they actually flow 42lbs.hr at 43.5PSI. Note converting them from 40 PSI to 43.5 gives you 40.67 but I have had them tested on a couple different machines and they have always been 42+lbs.:nixweiss:
Moreover, injectors from different manufacturers can both be rated at 43.5 PSI and flow the same yet actually flow different on the vehicle. This is because they are rated based on Open/Static flow(which basically grounds the injector) but you vehicle does not do that it pulses(like stated by Joe) the injectors on/off. So the Pulsed/Dynamic flow is really what the vehicle will see unless your injector is defective and gets stuck open.
In one example I had on injector flow more in open flow yet it flowed less in pulsed flow.
BTW, I have noticed a couple people state that their IDC was over 100% based on their EFI log. How is that possible?
When the IDC is over 100%, it means the PCM is commanding more fuel, but the most the injectors can deliver is 100%.
I figured that since an injector can't flow more than open flow(100%) but thought it was strange that people said their injectors were at 125% IDC.
Joe,Quote:
Originally Posted by joecar
Isn't equal to the pump pressure? (I mean the rail pressure), so if the pump is a stock one, very easy to know its pressure.
What about depending on efilive scan tool, I found the following (in PIDs):
DESCRIPTION PARAMETER
Fuel Rail Pressure SAE.FRP_C
Fuel Rail Pressure (Gauge) SAE.FRP
Fuel Rail Pressure Relative To Manifold Vacuum SAE.FRP_B
Another question, let's say the stock fuel pump gives 58 psig. Is it possible GM designers will rate engine's injectors at lower than that, so we need to correct it when we start tuning??????
:thankyou2:
Stock pump/regulator pressure is qouted by the GM service manual as 58 psi.
But don't assume that... measure it, and measure it thru-out the load range (should measure voltage at the same time).
If you're running an LS1/LS6/LS2/LS7 then the PCM is not measuring rail pressure, it doesn't have a sensor.
GM engineers rate the stock injectors at 4 bar (58 psi); they may or may not have put the correct values in the IFR table.
thx
could someone that knows how this spreadsheet works,(math equation)
create a new column to paste fuel pressure data for each area of MANVAC?
so instead of using a constant fuel pressure for each column of MANVAC
you can scale each separately without doing it manually.
you mean like this?
http://redhardsupra.blogspot.com/200...gged-fuel.html
here is the equation:
new flow in lb/hr = the original fuel injector flow x The square root of ((new fuel pressure+MANVAC) / original fuel pressure)
Example: car with 24lb injectors rated at 40 psig (at the factory) and will be used with 70 psig pump and the MANVAC=0. Take the square root of ((70 psi (new FPR setting) +0 (MANVAC))/ 40 psi (original FP)) = 1.3229 x 24 lb/hr = 31.75 new flow rate in lb/hr
refer to the attached file it includes ur request (MANVAC)
Attachment 3789
wow!Quote:
Originally Posted by redhardsupra
your quick.:hihi:
looks like i need to get out more.:doh2:
well it's been there since December of 2006... catch up! :)
Hi folks,
after reading this thread and letting my head cool down I thought about my conversion.
I have a 2007 5.3 "LMG" with OEM in tank fuel pump of the same application. GM went to a single fuel line without return. So how do they control the pressure in the fuel rails? Where could I start for adjustments of the IFR?
Harald
The 'plumbing' has changed with the more recent systems. There is a return of sorts, however it is not external as the more familiar, previous systems. Not sure how helpful this is, as it is a bit vague.Quote:
Originally Posted by harascho
Hi,
in the '07 system I transfered to my 1997 Tahoe there is definitively no external return line to the tank, only a single line from the pump to the fuel rail on the intake . I don't see any sort of return ??
Harald
Return systems: FPR is MAP-referenced (located between rails), IFR table is flat across, return line goes from FPR (located at the rail) all the way back to the tank.
Returnless systems: FPR is unreferenced (located in tank), IFR table is sloped (i.e. the PCM looks up IFR based on MAP (or rather MANVAC)), return line is at the FPR in the tank, FPR is BARO referenced.
could someone direct me to an IFR spreadsheet? the old link is no longer active.
PM me I may have what you are searching for
This one?
That is the one, thanks :cheers:
Bingo
Please note the following with regards to the 1997-1998 Y-car:
the FPR has a return fuel line and a reference hose, but the reference hose references barometric pressure
(i.e. the FPR is open to the atmosphere, it is not referenced to manifold pressure);
this categorizes this FPR as un-referenced;
this is supported by the fact that the IFR tables are sloped (and calculation shows they agree with the Bernoulli squareroot pressure-flow relationship).
I made suitable corrections to post #1 above.