Redtop SR Fuel Pressure Issues

[Quiche2192]

I have an AEM 340 fuel pump and have the following questions:

I tried the nismo fpr and found that it pulses the fuel pressure instead of having a smooth flow of fuel as soon as I adjust it to over 40 psi. Is that normal? I decided to run the stock FPR just in case.


Is it normal for fuel pressure to drop as soon as I turn off the car? Especially with the AEM fuel pump. Does it like backflow and then relieve the pressure once it's off, somehow?

Thanks.

[jr_ss]

If there are no check valves inline, pressure will bleed off.

You need a pulsation damper to relieve the pulses caused by the pump/adjustable FPR.

[Quiche2192]

Ok perfect. There are no check valves, so I don't have to worry about the pressure dropping. As for the pulsing, I'll take a look at the damper but honestly, I'm fine running the stock fpr for now.

[dorkidori_s13]

you cant run a stock FPR with an upgraded pump. the base pressure will be higher than factory and you will run rich.

highly recommend going with either a Tomei Type-S or Aeromotive A1000 FPR with gauge. this will allow you to set base fuel pressure (or add more depending on tune).

yes OE FPR is a rising style regulator, but the factory diaphragm isnt setup for fuel pressure beyond stock fuel pump.

also, if youre running an AEM 340LPH, did you rewire your sending unit to push more than 10v? S13 wiring does not run a full 12v to pump from factory (S14 does not have this problem). outside of Walboro 255lph (which has a built in amplifier), any other pump requiring a full 12v to run properly wont function right an you wont be able to achieve constant fuel pressure (i figured this out with an Aeromotive 340lph pump via my fuel PSI gauge).

[burnsauto]

While we are on the discussion of adjustable fpr's..


Do I even really need one? What situation makes me need to replace the OEM one? I loosely understand that you can kind of "cheat" smaller injectors into thinking they are larger ones by bumping up the pressure differential between the fuel pressure and the manifold pressure, but if I'm already running large enough injectors, do I really need to bump up the pressure?

[Quiche2192]

Originally Posted by dorkidori_s13

you cant run a stock FPR with an upgraded pump. the base pressure will be higher than factory and you will run rich.

highly recommend going with either a Tomei Type-S or Aeromotive A1000 FPR with gauge. this will allow you to set base fuel pressure (or add more depending on tune).

yes OE FPR is a rising style regulator, but the factory diaphragm isnt setup for fuel pressure beyond stock fuel pump.

also, if youre running an AEM 340LPH, did you rewire your sending unit to push more than 10v? S13 wiring does not run a full 12v to pump from factory (S14 does not have this problem). outside of Walboro 255lph (which has a built in amplifier), any other pump requiring a full 12v to run properly wont function right an you wont be able to achieve constant fuel pressure (i figured this out with an Aeromotive 340lph pump via my fuel PSI gauge).

Oooh this is some good info. Thank you! Also, big fan of your work!! I have an S14 so I would say I'm ok on the 12V to the fuel pump. I was planning on wiring a relay directly from the battery to the pump, but now that I know that the S14 doesn't have the problem, I guess I won't need to.

About the FPR, it actually makes sense what you're saying. I've read everywhere that normal pressure should be around 40-45 psi. With the new pump and stock FPR, I'm running at 50 at "idle". Luckily I have a Tomei type S here, so I'll try and run that. I just really liked the simplicity of the nismo one. If anyone has any suggestions on what to use to get the nismo one working, I'd appreciate it.

[Quiche2192]

Originally Posted by burnsauto

While we are on the discussion of adjustable fpr's..


Do I even really need one? What situation makes me need to replace the OEM one? I loosely understand that you can kind of "cheat" smaller injectors into thinking they are larger ones by bumping up the pressure differential between the fuel pressure and the manifold pressure, but if I'm already running large enough injectors, do I really need to bump up the pressure?

Like dorkidori said, you'd need one when you run a larger fuel pump than stock. And as far as I've seen, all aftermarket FPR's are adjustable.

[Kingtal0n]

For fluid systems it is best to run minimum pressure
I always run 34-38psi baseline for my cars
For example 1000cc injectors 35psi baseline I can fuel maybe 800rwhp using some alcohol fuel

Lowest pressure for all fluid systems: Blood, oil, water, air, etc... The least pressure is the least stress on fuel system components. Lower pressure also carries myriad benefits for fuel:

reasons to
Run the lowest fuel pressure possible with a referenced regulator because
1. Keeps fuel cooler
2. Pump will last longer
3. Pump flows the most fuel
4. Easier to idle tune large injectors
5. Takes stress off all fuel system components
6. Allows low base pressure to be adequate for boost setups
7. ____________________ <--- there has to be more


You throw all of that away by using high pressures unnecessarily or counter intuitively. Using high pressure instead of upgrading the injector for example, results with hotter fuel, less overall fuel pump flow, more strain on the pump and parts associated. And is completely avoidable when the system is designed properly.


--------Next Issue--------
I've melted the plastic tank S14 topper using the OEM plug for the fuel pump, aeromotive / AEM 340LPH fuel pump. Even if the wires leading to and from are upgraded, the plastic plug part can't take the current those pumps draw. I had to install 'bulkheads' just a bolt through the plastic to carry current.

[dorkidori_s13]

Originally Posted by burnsauto

While we are on the discussion of adjustable fpr's..


Do I even really need one? What situation makes me need to replace the OEM one? I loosely understand that you can kind of "cheat" smaller injectors into thinking they are larger ones by bumping up the pressure differential between the fuel pressure and the manifold pressure, but if I'm already running large enough injectors, do I really need to bump up the pressure?

with your stock injectors, yes you can eek out a bit more fuel... but basically youre just making things richer by adding more fuel pressure and this will max out the injectors fairly quick. i would HIGHLY recommend hooking up NISTUNE to your car if you choose to go this route and monitor what your injector duty cycle is for the fuel pressure range you choose to run versus how much boost you are pushing.

stock SR redtop/blacktop injectors are really only good for around 12psi of boost on an S15 Spec R T28. anything passed that and youre pushing 100%+ (which is bad thing). the SR ECU is already tuned very rich in high end from the factory as it is (this was to prevent fuel starvation in higher RPMs, but also makes for less power).

fuel pressure passed stock setup really boils down to your tuning and fuel setup. im not 100% sure as to when you would need to really start bumping up fuel pressure... im sure more experienced members on Zilvia can answer this. but if youre running an aftermarket high pressure fuel pump, it is advised to get an aftermarket adjustable unit WITH GAUGE. on my walbro and stock FPR, my base fuel pressure was around 48-50psi at idle. shouldnt be anything more than 40psi (especially on a fairly stock setup)

[burnsauto]

So I'm in the middle of putting together my setup.

So far I've collected a tomei arms 7960, tomei 740's, and a Link G4+. I ran the stock t25 for a long time, while throwing tons of other bolt on parts at it, and currently the tank just has a walbro 255 in it. I'm considering making it flex fuel, so possibly upgrading that to an aeromotive stealth 340. The car already has a fuel pressure gauge in the interior, and I've never seen much fluctuation in the pressure, but I was never one to push stock parts that far anyway (I always drove the car at wastegate pressure).

What it's sounding like to me, that an adjustable fpr would really benefit a build like mine for only small adjustments to get everything just right, not for trying to manipulate injector flow, and push them beyond their limit.

[dorkidori_s13]

Originally Posted by burnsauto

...for only small adjustments to get everything just right

thats always the hard part

my current SR setup mimics my last S13 from the late 00s in terms of upgrades and such because i knew it all WORKED have made a few minor changes from then though (like running an OE S13 Silvia drift shaft that only uses u-joints instead of that hockey puck bullshit)

but yeah, unless youre going all out for competition... a street car should be built for fun and reliability IMO. figuring out a good all around setup where nothing outshines anything else and everything works in harmony is the difficult part. but, once you get it figured out with tinkering and swapping parts to experiment with, theres nothing better!

[jr_ss]

Originally Posted by dorkidori_s13

you cant run a stock FPR with an upgraded pump. the base pressure will be higher than factory and you will run rich.

This is incorrect. I ran a Walbro 255 on my stock S14 FPR for years and my base pressure was normal.

[burnsauto]

Well most of my parts selections are around my target power levels. My plan is to put it together, make sure all the systems are operational (power, fuel, etc) then tow the car to MA motorsports for tuning, so this isn't going to be something I'm going to be screwing with too much. I've got my specialty, and tuning isn't it. I just don't want to get to the tuners, and find out I need xyz. I'd rather have all my ducks in a row, and have it be a painless process.

This is purely a street car, but my theory is to overbuild it to a certain degree, to ensure reliability for the long run.

[jr_ss]

Originally Posted by burnsauto

Well most of my parts selections are around my target power levels. My plan is to put it together, make sure all the systems are operational (power, fuel, etc) then tow the car to MA motorsports for tuning, so this isn't going to be something I'm going to be screwing with too much. I've got my specialty, and tuning isn't it. I just don't want to get to the tuners, and find out I need xyz. I'd rather have all my ducks in a row, and have it be a painless process.

This is purely a street car, but my theory is to overbuild it to a certain degree, to ensure reliability for the long run.

When are you planning on getting tuned? I?m 30mins from MA-Motorsports and I?m actually trying to setup a dyno day with my tuner.

[burnsauto]

Originally Posted by jr_ss

When are you planning on getting tuned? I?m 30mins from MA-Motorsports and I?m actually trying to setup a dyno day with my tuner.

Oh this is probably 2 years out..lol. I'm just a squirrel shoving parts in a giant pile in my in laws basement. They love it.

This is an old photo, I've added more crap to it. Its a sickness....

[dorkidori_s13]

Originally Posted by jr_ss

This is incorrect. I ran a Walbro 255 on my stock S14 FPR for years and my base pressure was normal.

*shrugs* i hooked up a fuel pressure gauge to see where mine was at and i was up around 48-50psi. swapped out to an Aeromotive unit, never looked back (as id had this unit before).

[jr_ss]

Originally Posted by dorkidori_s13

*shrugs* i hooked up a fuel pressure gauge to see where mine was at and i was up around 48-50psi. swapped out to an Aeromotive unit, never looked back (as id had this unit before).

I?m not saying you are completely wrong, just that not all pumps are going to cause this. If you have a 300+lph pump in there, I would expect the restriction to increase dynamic pressure.

[Quiche2192]

Ok so I now have a stable fuel pressure of 40psi. But I have another issue that I'm working on figuring out, but I thought I'd ask here as well:

I'm checking if the injectors are firing by turning on ignition and wiggling the CAS back and forth. I've done this before and was able to see all the injectors fire before. But now, only injector 1 is firing and it's stuck open.

- Is my test method stupid? I think I read somewhere to do it this way.

- Not sure if this is a wiring issue. I have a new wiring specialties pro harness. And I'm sure I've connected and grounded everything. I noticed no continuity between the alternator case and the chassis so I quickly ran a wire between them but still nothing.

- The other reason I'm thinking wiring is because my starter is not turning. I hear the solenoid click, but no rotation. New battery and everything. I'm pulling the starter out tomorrow to test that by itself. I'm also taking the injectors to get checked in order to rule those out.

Sorry for chaning the topic a bit, but would appreciate some advice.

[LoSt180]

Something that no one ever seems to acknowledge is that a lot of these "builds" are simply over sizing their fuel pumps in general. Figure I'd share some of the items I've come across over the years.

- Deatschwerks has a few fuel calculators on their website to help you figure out how big of a pump and/or injectors you'll need based on fuel and HP goals.
Found it interesting that even with a 500HP goal on gasoline, the max flow you need is 208 LPH. Meaning the ever popular Walboro 255 or a DW200 is really all most people need with plenty of overhead. Now, things change if you want to run E85 so you'll need to plug that info into the calculators and don't come at me with "bUt yOu'Re RoNg aBoUt MaH fUeL." Yes I know E85 requires more fuel.

- Base fuel pressure is set with the FPR vacuum DISCONNECTED. Stock is set at 43 PSI. So at idle with vacuum connected, you should see about 34 PSI and it ramps up with boost.

- The factory fuel return line has a brass restrictor "pill" in rubber hose right after the FPR. From what I can tell, it helps keep fuel pressure stable with the stock FPR. Debatable if needed on adjustable FPRs. Might be worth looking into more if you're getting fluctuations.

- I've found wires flipped around on two wiring specialties harnesses now. So if something isn't acting right, time to bust out a FSM and a multimeter. Too many variables here. If you have a relocated battery, you may need to run a dedicated ground from the engine to the battery due to too much resistance trying to rely on the chassis.

[dorkidori_s13]

Originally Posted by LoSt180

- The factory fuel return line has a brass restrictor "pill" in rubber hose right after the FPR. From what I can tell, it helps keep fuel pressure stable with the stock FPR. Debatable if needed on adjustable FPRs. Might be worth looking into more if you're getting fluctuations.

never heard of this before. S13 and S14?

but then again, if you run an aftermarket unit with a nipple fitting, youre gonna wind up replacing the fuel hose anyway... so im guessing this is why ive never run into the problem.

[Kingtal0n]

Originally Posted by LoSt180

Something that no one ever seems to acknowledge is that a lot of these "builds" are simply over sizing their fuel pumps in general. Figure I'd share some of the items I've come across over the years.

There are three issues to consider that most will not realize immediately
1. Boost pressure reference causes fuel pressure to rise with boost- which will reduce pump flow capacity. SO a 500hp pump at 40psi is only like a 400hp pump at say 60psi or whatever. The HP supported drops with boost increasing.

2. Voltage is a powerful influence on pump HP supply. Most people assume they always have 14.5v or so at the pump but it might only be 12.5v usually once warmed up fully. Fuel pumps produce heat and will heat the fuel gradually.

3. Fuel pump heating is a potential problematic for large pumps and especially dual pumps. A single aeromotive/AEM 340lph pump for example over the course of an hour can raise 10 to 15gallons of fuel temp significantly even with engine off. I recommend PWM control for primary fuel pump to reduce heating for daily drivers. But this is extra cost and complexity unwanted in a majority of 4-cylinder sub 500hp setups which typically use small enough single pumps to run constantly just fine.

Finally a tuning tip. I always tune the engine using lowest voltage at the fuel pump possible. Always turn off alternator during WOT to achieve this conditional.
The reason for this is, you want the fuel system tuned to alternator failure just in case the alt actually does fail at WOT you won't lose the engine. If the pump can't support the power at 12.0 or 12.5v then its too small. People often rely on and tune their power output using 14v or even 16v at the fuel pump are asking for catastrophic failure which happens eventually.

I always configure alternator "turn off" at WOT for every engine now,
its a default setting for some stand-alone computers


We target 12.5v at WOT using alternator duty control. Makes the engine safe even if the alternator fails, pump output drops to a pre-determined safe level.
This is also important in general for other electronics such as injectors. An alternator at high RPM may provide constantly changing voltage... e.g. 14.54, 14.46, 14.39, 14.52, 14.42, etc... The voltage is changing rapidly over the course of RPM change, it is not constant or stable. This will influence all other systems, coil dwell and injector delay to name the important two. This leads to 'wavy' torque curves, oscillations in the engine output to the tires, instead of a clean smooth curve. Once you lower the voltage demand to near battery voltage (often 12.45 to 12.55v) the system voltage can remain steady, and clean, using the battery as a high capacitance (large capacitor) which stabilizes the injector delay and coil dwell targets... resulting with a much smoother running engine if the alternator is incapable or somehow unable (it happens frequently on custom setups, not so badly with OEM nissan stuff) to maintain a steady voltage. SR20 I don't generally have a problem letting the alt work like stock but its still a valuable tuning tool to keep the pocket, be aware of the influence of wavering/wavy changing voltage signals and how that will scale non-linearly between intervals of ECU cell to cell programming. In other words, no injector delay map is going to perfectly correct for offsets, it might be close but there are still non linear differences cell to cell. So anytime the cell moves from one to another such as during changing voltage, it will "step more and more" Into a neighboring cell value, the imperfection is included in the step quantity as error. if the signal is oscillating each crossover will generate error term component with a direction in the new cells value, leading to a frequency response dynamical system of dependency for which state space vectors are ultimately defining system behavior, they can be predicted and compensated or neglected causing overshoot and possibly increased oscillation frequencys, uncontrolled frequency oscillation in voltage systems where it isn't wanted. Which is why I think many OEM alternators and current control strategies work well and custom versions fall apart quickly: The late model OEM likely fine tunes their frequency response characteristics for current and voltage regulator systems, whereas a hobbyist is more likely to attach a random alternator on something with questionable ground pathways and perhaps poorly insulated and expect the ECU to regulate it properly, automatically at high RPM to maintain a steady voltage. Even if the alternator is capable of such a thing the very installation influence is such a large part of that possibility it is never safe to assume it's going to work properly without being tested and verified first. And that it can't possibly fail or that the fuel pump can support the engine in case it falls to 12.0v one day unexpectedly. Which will happen eventually, all alternators eventually fail, they can't last forever. The baseline assumption from engineering safety point of view is that, the alt can fail at any minute, so our entire system needs to be configured to allow the engine safe operation when this event happens.

[Quiche2192]

Thank you all for the wealth of information! I managed to finally get the engine running after building the car and engine for two years! What a moment it was to hear it run again!

I have another question. This one is about timing.

-I am unable to run the engine with the CAS in the middle. It has to be turned fully clockwise in order for the engine to run normally.

- I am 95% sure I set mechanical timing correctly. I will verify the 5% next time I have the chance to work on the car.

-According to the marks on the damper, timing is highly advanced. Almost 30 deg btdc

Are these indicators of incorrect mechanical timing?

[Kingtal0n]

Originally Posted by Quiche2192

Thank you all for the wealth of information! I managed to finally get the engine running after building the car and engine for two years! What a moment it was to hear it run again!

I have another question. This one is about timing.

-I am unable to run the engine with the CAS in the middle. It has to be turned fully clockwise in order for the engine to run normally.

- I am 95% sure I set mechanical timing correctly. I will verify the 5% next time I have the chance to work on the car.

-According to the marks on the damper, timing is highly advanced. Almost 30 deg btdc

Are these indicators of incorrect mechanical timing?

Something wrong if the Cas can't be nearly center.

The timing light can fool you, the pickup is often directional. In other words if you flip the pickup on the coil wires 180 degrees it could give you the *correct* timing number. This is often the issue when people find their engine timing needs to have the CAS way off center, they are looking at the incorrect pickup signal through the timing light.

Here we go blast from the past, picture and details showing the light and explaining the directional pickup
https://zilvia.net/f/showpost.php?p=...7&postcount=19

[LoSt180]

Originally Posted by Quiche2192

Thank you all for the wealth of information! I managed to finally get the engine running after building the car and engine for two years! What a moment it was to hear it run again!

I have another question. This one is about timing.

-I am unable to run the engine with the CAS in the middle. It has to be turned fully clockwise in order for the engine to run normally.

- I am 95% sure I set mechanical timing correctly. I will verify the 5% next time I have the chance to work on the car.

-According to the marks on the damper, timing is highly advanced. Almost 30 deg btdc

Are these indicators of incorrect mechanical timing?

Not running unless CAS is fully turned to one direction or the other is a classic sign that you are off by one tooth.

The notch on the CAS lines up with one dot and when it's stabbed in place the notch lines up with the other dot.