codyace

Ah derrrrrrrrrrrrrrrr. Homer moment.


I understand this: What I'm saying is that a weak pump would not 'magically' get better by using more fuel. Remember at a certain PSI, that's all the more the pump is flowing...him tuning it rich is not using any more flow from the pump itself (as it's regulated by the FPR). If the pump was weak then, it should be weak now.

I know it may be redundant, but have you rewired the pump?


On the contrary, if it's throwing MORE fuel at it, it could be a sign for the duty cycle. I doubt this as well though as your car would be exceptionally rich.

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jspaeth

Haha no biggy on the homer moment.

Haven't rewired the pump, but here is an interesting tidbit, which may be relevant.


Occasionally, at idle, I see my fuel pressure drop down to like 30 psi (normally it's at 36 psi).

This happens maybe 1/50 times that I look under the hood while it is running, even with a brand new fuel filter.

So, I figured maybe something is up with the pump voltage.

Checked voltage from hot side of pump to ground side of pump and hot side of pump to chassis, and both give 12 V.

I then repeated this when I "caught" the car at low fuel pressure at idle (30 psi) and the voltages were the same.

So I don't believe it's a voltage to the pump issue.

Really strange here...

EDIT:

as for the weak pump....I am saying if the pump is weak up top to the point where it is unable to still provide enough flow/pressure to keep the pressure in the rail at say 62 psi, then you will have to use more injector duty than you thought you would have had to.

This might be wrong, but it seems like a possibility to me. I really need a digital FP gauge, but don't feel like spending the $$$.

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slider2828

JSPAETH

I have the same setup but step 1's 264 HKS. Fully built top and bottom... I just run a stock FPR, which definitely works fine. No reason to run an adjustable if you are just going to adjust it to stock. I get about 8PSI at 900RPM on my SR tuned by steve shadows. Now I didn't get 370HP I got about 330 at 17PSI which is a lot for me on a dynodynamics. Stock intake mani, stock exhaust mani on a .84 2871R.

One thing you ARE doing wrong is comparing injector size to the power you make. Really? Come on you know better than that. Power is based on tune, independent on injector size. I ran my DW 600cc's at 330 and it was about 80% and now I am on NISMO/HKS 740's and I think about high 60's to 70%...

BUt really its all in the tune. Put on that stock fpr and see if you have the same problem. The Stock FPR can be used up towards 450WHP... I would trust IT...

Right now you have WAYYY too many variables to tune. You don't trust your setup, so its all hit and miss.... so really just go back to stock FPR. Test on your dyno. Steady state, tune it, check your plugs, and then watch your knock.... Seems like you are rushing things a little....

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jspaeth

Thanks for an input. Car is tuned by an expert ....Jeff Evans....CodyAce can vouch for that.

There really aren't "too many" variables.

I am running an Aeromotive FPR set to 43 psi base pressure.

I am running 740 cc injectors.

I AM comparing injector size to power, bc aside from some minor "slop" in guessing the BSFC, you should be able to calculate a theoretical required amount of fuel based upon injector size and duty.

Like I said (and you validated with your post), most people making 350-370 whp with 740 cc injectors are using NOWHERE NEAR 90% of their injector duty.

My car runs well, the tune is pretty good, and the AFRs are not unreasonable (slightly rich 10.5-11 under full boost).

Nothing seems WRONG with the car, except for the fact that it just is unexplainable why so much injector duty is being required for the AFRs and power level and injector size combination I have.


EDIT:

BTW my 370 whp on dynapack is likely slightly lower on Dyno dynamics, maybe like 340 or 350 I would guess. But still, you said for an (almost) identical amount of power, you were requiring only ~70% injector duty with 740s.

Now, if my tune IS too rich, and I were to make it say 11.5-12 AFR at full boost, I think this might bring the MAX injector duties down some, but not 20% from 90% that I am seeing to the 70% you are seeing.

You say power is based on tune, but given a perfect tune and reasonable AFRs, you should again be able to CALCULATE how much fuel you require for an engine to put out XXX whp.


AGAIN, the car runs fine, the tune is good, there are no PROBLEMS. ......it's just sketchy that my duties are so high.


J

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slider2828

Yeah that is really weird.... but.... At the top end, I get about 10.7 AFR.... Now I believe it should be closer to the 11.5, but I measure pre cat, so its about 11.5 post cat. I think that is most important to keep in mind.....

Just for kicks, try putting in the stock fpr... I seen some weird things happen with adjustable fprs....

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KoukiMonsta

is it possible that there is a voltage drop at high rpm's causing the pump to be "weak"

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slider2828

He said he ruled that out.... but you have to measure at HIGH RPM though...

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jspaeth

This I did NOT measure.....requires 2 people in the car at least, but something I SHOULD do.

Thank you for the idea.


Justin

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jspaeth

My wideband is positioned in my "cat" **wink** in between my test pipe and cat-back.

So I should be getting a really good, true reading there.

Like I said, the tune is safe and a little too rich IMO

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garagelu

I don't agree with the stock fpr being ok for high hp apps especially when running double or triple the boost was from stock. These regulators are 1:1 ratio. So if the stock regulator is designed for stock boost (7 psi), when you hit full boost you should be around 43 psi. Most of the people with 2871r are running around 19-20 psi. At full boost you should see fuel pressure around 56 psi. Are you sure that a stock fpr designed for stock boost is going to hold well when you up the boost to 19-20 psi. Sure, it may do the job but how well?

jspaeth

Wrong. 43 psi is base fuel pressure with no vacuum attached, which is why people typically see 35-36 with vacuum attached.

Thus, with "stock" 7 psi boost, fp would be around 50 psi, and for 20 psi boost it would be ~63 psi.

I do agree with you tho it can't hurt to buy a beefier adjustable aftermarket FPR.

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codyace

We did this forever ago with DSM's and small wired jap cars, so it's something I just natrually do on new cars.

Super easy to do as well. Use the factory fuel pump 'power' wire as the trigger for the relay, battery for power in, ground to the chassis, and run a new power out wire. Easy Peezy. This way you know FOR SURE you'll have good voltage going to the pump at all times.

Another thing to check (being you're not rewired) is alternator output at WOT. Not sure if the ApexI unit does this or not...I know I can log it though with my Conzult.


I can see your train of thought, but to me, 62 psi from the pump is 62 psi from the pump...and shouldn't require any more fuel in the grand schme of things...what you're describing would be in the event the pump is weak, and the regulator is only persay putting 55 psi at WOT to the car...which would then make sense (higher duty cycle) as the injectors are being asked to work faster.

For what? Just put a T in your fuel line, run it up to the window under the wiper. At the other end of the line, just put a gauge in. Crude? certainly...but it's mechanical, and it works.

Another crude mathematical forumula I've used is the following...it's oddly dead on.

Desired whp (or actual whp) X 1.15 (drivetrain loss) = Crank Power
Crank Power/2 = Number then take Number /4 (4 cyl) = Injector size minimum required to run for the power

For example (my car)

400 x 1.15 = 460 415/2 = 230 230/4 = 57.5 lbs (603.75 cc)

THis is about damn near dead on for my car. I have 615's, and my car run low 90% duty cycle for the power at WOT.

It's funny to see how this works on 'most' cars. I'm not sure where I initially learned this little trick (I think it was a street racing thing we used to do, as you'd ask for injector size to determine the cars potential power output...this way you could gauge a cars pwoer without asking hhaha)


I think pre cat measurements would be the one I'm looking for...this way the actual outside air can't change the measurement. 10.7 is very rich IMO.


Agreed. This is why I like Nismo ones.





This has become quite the troubleshooting thread Nice to see some civilized car discussion going on

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KoukiMonsta

i will not even attempt to quote that cody....
intersting equation, seems to be fairly accurate.

but jspaeth, i would wire the fuel pump w/ a relay, maybe try the stock FPR if u have it.

and testing the alternator at WOT, cody how do u suggest one goes about doing this? i am under the impression my alternator is not up to par(yes i kno its unrelated to the thread)

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codyace

I use my consult plug and Nissan Data Scan to log voltage during my pulls. Only reason I even look at this, is due to me noticing very low output during some logging earlier this year. I subsequently got my alt rebuilt, and all is fine now.

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garagelu

You don't need to get all technical on me. I know you are supposed to check fp with the vacuum line detached. I was just trying to get my point across which is when you increase the boost, a stock fuel pressure regulator may not be able to keep up when hitting full boost/max fuel pressure.

And if you are on the dyno or running on the street, you won't be reading with the vacuum detached....it would be attached. So you set it with the vacuum line off, but read it on if you are running the car.

SO YOU ARE WRONG

codyace

I'm pretty sure he's got a good idea on how to set fuel pressure. No reason to get defensive or accusatory.

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KoukiMonsta

good to kno, thanks

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jspaeth

1) My Apex'i Turbo timer can output voltage while the car is running. Usually at idle it's around 13.6-14. Never bothered looking at it under load really, but I will check

2) What you said about injectors working harder is what I am talking about.

Let me explain this (but I COULD BE WRONG).

When the fuel pump can EASILY outflow the amount required, the FPR can maintain 1:1 pressure with boost no problem.

But what I think is happening here, if my pump is weak, is that as boost goes up and hits 19 psi, the fuel pump cannot generate enough flow to create 62 psi of back pressure at the injectors. so they only see something like 55 psi.

Remember there is no "feedback" on an FPR that tells it to close down diaphragm to achieve X psi in the rail. It just so happens to have a spring in it that when it sees Y psi of boost from the manifold, it closes the open in such a way that the fuel pressure goes up by Y psi.

This does not necessarily have to be linear 1:1, particularly if you are greatly overworking the spring or the fuel flow is not even strong enough to create that much pressure

I really feel like I am bullshitting haha but maybe not

NINJA EDIT!:

From fluid mechanics. Let's say that the FPR closes down COMPLETELY, so that all of the fuel is going directly into cylinders through the injectors.

Now, this corresponds to some fixed flow rate moving through some orifice.

There will be some pressure difference between rail and cylinder associated with this.

For fixed cylinder pressure, you can obtain pressure in the rail.

What I am saying here, is that even under full flow scenario, where ALL fuel goes into cylinders, the pressure required to do this could be way less than let's say 62 psi.

Basically, I imagine a scenario where the fuel pump is weak so the FPRs spring no longer produces 1:1 boost:FP increase.

I really do actually think this makes sense.

I would love to hear some thoughts/criticisms

3) I actually was gonna do that with the FP gauge out the window and my friends told me I was retarded.

Will probably do it now though.

4) Yes, I really enjoy this thread when it starts getting down to the details, even though I feel like I am kinda threadjacking.

Hopefully I am contributing though.

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jspaeth

In case you can't read, I was agreeing with you about stock FPR not being able to keep up (even tho time and time again people have shown it works just fine for very high boost applications.

I am not wrong. You suggested that FP under 7 psi boost is 43 psi which is wrong.

Sorry, but good try.

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slider2828

Well I am not sure if you have the fc commander but that will tell you voltage and injector duty cycle as well. How are you getting your read out for the injector duty cycle anyways?

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jspaeth

Yeah I'm running PowerFC D-Jetro (of course i have the commander) and just recently got datalogit.

I can see on the commander from it's peak hold function that the duty peaks out at 91% under full boost at high RPM (7000+).

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slider2828

Hmmm and you I assume you get the voltage and its around 13 to 14... Do you log voltage as well? Is there any dips? Unless the wires are messed up back there in the FP area, a voltage dip is good enough to see if your are having electrical problems.

Can you take a picture of your fuel lines and system? Also I assume you are using a z32 fuel filter? Just ruling out the obvious stuff...

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garagelu

Read my first post about this. I said when you hit full boost at 7 psi not under 7psi boost. Not sure where you got that from....

With vacuum ATTACHED (I am not talking about setting fuel pressure since it should already be set) at idle if you are running stock fuel pressure you should be at 36 psi. Since our regulators are 1:1 ratio, for every lb of boost you should see an increase of 1 psi of fp. So 36 + 7 = 43 psi.

And I guess you are not understanding my logic.....you should keep an eye on the fp gauge to make sure it keeping steady fp throughout the rpm. When you are running on the dyno, the vacuum will be attached which means your numbers don't apply. So WHEN RUNNING THE CAR at stock fp, the gauge should read 36 psi and at full boost of 7psi it should be holding 43 psi to redline.

And I never mentioned anything about you disagreeing on the topic of upgrading fpr in my second post.

jspaeth

WRONG!

THe car reads 36 psi FP because the vacuum is -7 psi. So when you boost 7 psi, that is actuall 36 + 7 psi = 43 psi when the manifold is at 0 PSI (atmostpheric)

......PLUS an additional 7 psi on top of that for the boost!

So it should be 50 psi.

Someone please chime in so it's not just me on this.

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garagelu

Set your fp to stock setting and go run your car on the dyno. Come back here and let me know what your gauge reads.

codyace

When your car is running, and the vacuum line is disconnected (simulated WOT, but without boost) it should read 43.5 psi. Knowing what the fuel pressure is, when idleing, should be somewhere in the 34-38 range...but this measurement is silly as it can be so different. Again, the main measurement should be vacuum line off, car idleing, 43.5.

So at 10 psi of boost you should see 53.5, 20 psi of boost 63.5.

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codyace

I said this before:
It make sense though...it could potentially be a FPR issue (like described, not going perfectly 1:1 in boost). Again, I'd just hook a line up with the gauge on your window. Who cares of it looks stupid and your friends think it's wrong - it'll work, and that's what you wanna know.

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jspaeth

No need to do that. It will read 43.5 psi + boost pressure like Cody confirms below

Agreed. I don't know why this is even debatable to be honest haha.

You say "the measurement with vacuum can be so different".

Honestly, as long as your idle is stable, the FP shouldn't fluctuate at idle, provided your FPR is working correctly.

Mine always reads 43.5 psi - vacuum pressue, which for my current setup, comes out to about 36 psi.


I am gonna do this, I agree it will be VERY enlightening. If at full boost I am only seeing say 55 psi, this could immediately be the cause.


Just did a calculation.....using an injector flow calculator.

740 cc at 43.5 psi is 740 cc

740 cc at 63 psi is 890 cc

740 cc at 55 psi is 830 cc.



So at 19 psi it should flow 890 cc but if it is only flowing still 740 cc, then if someone else (with a "working" setup") is using 70% of their duty, a setup where the injectors only flow 740 cc under boost would use:

70% * (890/740) = about 85%


I am using 90%!!!!!!!!!!!!!

Something is VERY wrong here, and yet the car runs just fine......hmmmm must be fuel pump.

I bet when I do the FP check under full boost, I will find that it's not getting anywhere near the right pressure.

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slider2828

If I remember correctly, you said your car runs at 1250 idle. That is not normal in my opinion and can cover up small minute problems int he setup. what happens when it idles at 900 RPM?

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codyace

Unless it's tuned to idle there. I have mine at 1000, common JWT cam program for idle.

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