2G How to set fuel pressure with an AFPR?

[dboyle23]

So I installed an Aeromotive AFPR, but how do I set the pressure?

The nut on top doesn't change anything.

 

[snowborder714]

You have to loosen the nut, as it just locks the threaded rod it's around in place. Crack the nut loose then use an allen wrench in the top of the rod to move it in and out to change pressure. Make sure the car is up to temp and the vacuum line is pulled and capped (either with a cap or just your thumb).

 

[dboyle23]

ok thanks a bunch.
I was having trouble tuning and it seems it was from fuel pressure, which right now is at 30 with vac and 40 without.

35 with vac and 43.5 without for a 2g IIRC.

 

[overkill]

Do you have a bigger fuel pump than stock as your regulator may have been getting overrun? What tuning symptoms are you seeing?

 

[9!'clipseDOHC]

An easier way since you have DSMlink is just leave the engine off, with the key in the "On" position (so that DSMlink can connect) and select the "Activate Fuel Pump" under the "Misc tab". This way you can leave the vacuum line connected since the engine isn't on and isn't pulling any vacuum and the gauge will be easier to read since there are no engine vibrations. Loosen the retaining nut like Brian mentioned and turn the adjustment rod with an allen wrench to raise or lower the fuel pressure. All 2g cars are set to 43 psi from the factory.

For others searching in the future:

1G MT = 37psi
1G A/T = 43psi
1G NT = 48psi
2G ALL = 43psi

 

[Red 4G63]

Like Dboyle23 said... should the pressure go down once the car is started? Mine reads 43 when off and the Fuel Pump activated through ECMlink V3. But when it's on, it reads more like 30... should that be right? Thanks!

 

[sbailey11]

Do you have a bigger fuel pump than stock as your regulator may have been getting overrun? What tuning symptoms are you seeing?

I am wondering what you mean by this?

I am planning to buy a car that is running lean and the owner has put a Walbro 190 in with 850cc's and hasn't had the car tuned using the DSMLink (the car does have DSMLink).

Would the bigger pump make it run lean?

 

[boost97gst]

At idle 30psi is way way low.I see 40 roughly. Now i have cams so i idle at around 13 in/hg. If you idle at -22 or even more vac it still shouldnt drag your pressure down 13psi. Thats sounds like somethings wrong.

 

[WES_393]

I am wondering what you mean by this?

I am planning to buy a car that is running lean and the owner has put a Walbro 190 in with 850cc's and hasn't had the car tuned using the DSMLink (the car does have DSMLink).

Would the bigger pump make it run lean?

No, the pump will not make it run lean unless it's faulty. Overrunning the regulator means the pump is flowing more fuel than the regulator can bleed off, which makes the engine run rich.

With those injectors and no tune it should be running pig rich. I wouldn't even expect it to start.

 

[sbailey11]

yeah the car starts right up, runs fine then randomly goes lean, runs fine, then go leans again. The car also only reads 10psi of vacuum and only boosts to 7psi (with a 20g turbo) and runs lean. i feel like one dumb problem is causing all of this.

SORRY THIS IS OFF TOPIC, but im panicing

 

[delta448]

Trilogy, the FPR's job is to keep the difference in pressure between the fuel rail and the intake manifold the same at all times. It's reference line must be connected to the intake manifold behind the throttle plate, where it will see both vacuum and boost. When there is vacuum in the intake manifold, the FPR needs to be able to drop pressure and bypass more fuel back to the tank in order to keep the injectors flowing the same amount of fuel per time. We all should know that raising fuel pressure makes an injector behave as if it has a larger flow rate.

sbailey, it's time for a real boost leak test.

 

[Trilogy Turbos]

As I said before this is something that I discuss with everyone. It's my opinion regarding the pressure side reading. FPR will always open at the baseline letting the fuel bypass.
Clean injectors? Clean fuel filter?

TRILOGY TURBOS

 

[ishnish]

Does anyone know if my fuel pressure for my AFPR is too high when at idle?

When I adjust the AFPR with the vac line off, I got it to 43 psi. When I attached the vacuum line and the car idles, it goes down to like 41psi.. I'm not sure if that's too high or what. I idle around -18mmHg to -20mmHg

Air fuel ratios and fuel trims are in line though..

 

[delta448]

Nope 41 is about right. 20mmhg in vacuum is slightly less than a half a psi.

 

[import solutions]

2 vacuum units equals a psi.

 

[delta448]

https://www.convertunits.com/from/mmHg/to/psi

 

[ishnish]

Welp, I deleted my last post because this issue/question still remains. I drop to about 41psi or so when the car is at idle and vacuum is applied to my AFPR, but I completely misread my gauge

The units I previously stated were mmHg when in reality my gauge reads in inHg

Nope 41 is about right. 20mmhg in vacuum is slightly less than a half a psi.

So, because I idle at around -21inHg, I used the conversion website delta448 gave me and that was roughly equal to 10psi or so.. This means my AFPR should be idling at -33 psi I'm assuming, right?

 

[delta448]

What size is the return fuel line from the AFPR to the tank?

With a 450lph pump, you might be seeing regulator overrun if you're using the stock fuel lines. Are you running E85 exclusively or could the ratio be a little less? What speed does the engine idle at?

You have a lot of vacuum, even for stock cams, which is a good thing in most cases and can indicate a healthy engine, but it concerns me a little. None of my stock cam turbo DSMs ever had more than 12inHg of vacuum unless engine braking. With 264/272 cams I never saw much over 6-7inHg.

 

[ishnish]

From the AFPR to the tank is all the stock line.

I am using all stock fuel lines. Also, I am not running e85 at all. That is a future goal though. I'm in Cali so I'm running 91 gas.

Well, I would love to think of that as a compliment but with all of the little issues I've been having after installing modifications as carefully as possible, the last think I need to do is hold my breath.

 

[Mello]

I've been following this thread & something's a miss. Your measurement numbers seem sort of close but a little extreme to me. I work in a quality relate field. When we see things similar to your situation the first thing we will do is check the measuring equipment. Are the observed measurements accurate & can they be relied on? What are you using to measure your vacuum/pressure values? Is it of suffiencent quality for what is being checked and for decision making? Check you measuring equipment then double check your mesurements.

 

[ishnish]

I've been following this thread & something's a miss. Your measurement numbers seem sort of close but a little extreme to me. I work in a quality relate field. When we see things similar to your situation the first thing we will do is check the measuring equipment. Are the observed measurements accurate & can they be relied on? What are you using to measure your vacuum/pressure values? Is it of suffiencent quality for what is being checked and for decision making? Check you measuring equipment then double check your mesurements.

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This is what I'm using to measure the fuel pressure. It's brand new so I'd really assume it can be relied on. My boost gauge is also brand new and accurate (I'd assume) but is there an absolute way of making sure through link? I'm not sure if there may be some discrepancy between my boost gauge and link..

 

[Mello]

That's a lot of assumptions. New does really mean much. After all my new Harbor Freight stuff is still a crap shoot.

I checked your profile & went to Prosport Boost Gauges. I also checked Fuel Lab accessories for your gauge (71501). Quickly I would classify them as "generic" as neither make a "statement of accuarcy" for their products. Simply put you do not know how good your measurements are.

Maybe try approaching this from a tuning perspectve & monitoring AFR's. If you're running good, AFR's steady & reasonable, tuning adjustments responding as expected, & not leaning out or run rich, etc.; it's possible your guages may be inaccurate enough to not be realiable. I first suspect your boost gauge may be off from the -21inHg at idle. The only way I can suck that much vacuum at idle is by adjusting my cam gears down to almost zero overlap (largest lobe separation angle possible) which is way less OEM cam overlap.

BTW my MAP accuracy statement is: "Accuracy: +/- 0.5% Full Scale over -40C to 105C includes Repeatability, Hysteresis and Linearity". This is really accurate & I would not easily believe your Prosport is as good without documented proof. You need a statement of accuracy from the manufacturers before you can truely rely on your measurements.

 

[ishnish]

I agree, it is a lot of assumptions. But I did ask if there's anyway of making sure because assumptions aren't good enough.

Yeah, I won't disagree with you there. The fuel lab part I feel is good quality but the prosport gauges are nothing more than glorified glowshift gauges..

The thing is, after dialing in my injectors, then yes I am running pretty good at idle. By this, I mean that I got my fuel trims in line along with my AFRest and wideband within +/- 5% or so. The car doesn't sound stock at idle though and I've had this issue ever since putting in the 2150s but I've read they should idle like stock while others have stated that they don't like pump gas and it's hard to get them to idle like stock. So idk there
But as I've said, link shows good numbers and I won't mind posting up a log when I get the chance.

First thing I should've stated is I just did a boost leak test and fixed a lot of the leaks and now my car idles at -18inHg! So by that, can I then assume my boost gauge is pretty accurate?

I also got a good look at my afpr again and honestly I feel like what I've seen before as 41psi was wishful thinking or something because looking at it very closely at idle with the needle bouncing, it honestly doesn't seem to change from 43 psi with the vacuum line on or off

Is there a checklist I could start from? What is the first thing I could check? Would this be more so likely an issue with the fuel lines or from the afpr itself?

 

[Archer Fabrications]

An easier way since you have DSMlink is just leave the engine off, with the key in the "On" position (so that DSMlink can connect) and select the "Activate Fuel Pump" under the "Misc tab". This way you can leave the vacuum line connected since the engine isn't on and isn't pulling any vacuum and the gauge will be easier to read since there are no engine vibrations. Loosen the retaining nut like Brian mentioned and turn the adjustment rod with an allen wrench to raise or lower the fuel pressure. All 2g cars are set to 43 psi from the factory.

For others searching in the future:

1G MT = 37psi
1G A/T = 43psi
1G NT = 48psi
2G ALL = 43psi

Buddy of mine was looking at this thread and I have to correct this, car has to be up to temp, and running to set a proper base fuel pressure, with the car off, the injectors are not pulsing which would subtract pressure that you are not accounting for If you simply activate fuel pump via link. You will end up with a higher base then you should if you do it that way. I know it’s an old thread, but people still search and come across old Information.

best way is what @snowborder714 said in post #2

 

[steve]

Buddy of mine was looking at this thread and I have to correct this, car has to be up to temp, and running to set a proper base fuel pressure.

I'm not sure I agree with your assessment.

The point of a FPR is to maintain a set pressure even with changes in the incoming feed pressure and the variable demands from the injectors. Some amount of pulsation is going to result from both and the dynamic response of the FPR but if the pressure changes when the voltage is higher and you have low duty cycling of the injectors from what you set with the car off I suggest you have other things also going on.