I went for a tune not too long ago, and was losing fuel pressure. The tune was adjusted for the lack of fuel. It was thought that my fuel pump was bad, because it was always making high pitched noises and would not stay at a solid pressure while at idle. I replaced the fuel pump a couple days ago, and now, the fuel pressure is a solid 43.5 psi at idle, and I have an aeromotive fuel pressure regulator. My question is: Are boost and fuel pressure supposed to rise on a 1:1 scale, even though my tune is not adjusted for the new added fuel pressure?

You will have to get it retuned. The fuel pressure is supposed to rise 1:1 with boost, to maintain the same 43psi differential pressure across the injectors at all times.

I understand that. I am just wanting to make sure that I am not having any issues with my fuel pressure regulator, so that I will be good to go once I get on the dyno.

Luckybob2485 said:

I understand that. I am just wanting to make sure that I am not having any issues with my fuel pressure regulator, so that I will be good to go once I get on the dyno.

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The FPR is completely independent of the tune.

More fuel was added by keeping the injectors open longer.

You're not going to have issues.

You should find a new tuner. Any tuner that would compensate for a failing part shouldn't be touching your car.

agreed especially for base fuel pressure.

GVR4592 said:

You should find a new tuner. Any tuner that would compensate for a failing part shouldn't be touching your car.

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It's the customers responsibility to make sure the car is in good mechanical condition prior to going for a tune.

If someone shows up unprepared (something the tuner wouldn't know until he started tuning the car) and still wants a tune why would the tuner stop doing his job?

He set the car up safely and told the guy what he needed to fix.

Seems fine to me.

Neither of us knew the pump was going bad until we put it on the dyno, and then it had problems from there on out. He put a safe daily driving tune on there, but recommended that I get the pump installed and get it retuned asap. The question I am wondering is: How do i test to make sure my afpr is still working 100%, and everything else is as well. I don't want to have another fuel issue. Because my fuel pressure didn't seem to rise on a 1:1 scale with boost. I know that I need to have it tuned, but I just want to make sure I won't have any more issues.

you could get an electronic fuel pressure gauge so you can see fuel pressure while driving.

I agree that it is the customers responsibilty to make sure the car is in good condition before he brings it in for tuning.

It's the tuners responsibilty to stop the session when he realizes the most important piece of the puzzle is not working correctly. It would be negligent to continue tuning because he cannot accurately predict what the fuel pump is going to do. If it fails when the customers drives off, he can be held responsible for the damage due to negligence. I've been tuning cars for almost 8 years, I have a a couple of good friends that also tune cars, and none of us would ever continue a tuning session after finding a faulty fuel pump.

BigBeans said:

It's the customers responsibility to make sure the car is in good mechanical condition prior to going for a tune.

If someone shows up unprepared (something the tuner wouldn't know until he started tuning the car) and still wants a tune why would the tuner stop doing his job?

He set the car up safely and told the guy what he needed to fix.

Seems fine to me.

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I do have a fuel pressure gauge. I am asking what to look for to ensure that I have adequate fuel pressure. Such as the 1:1 rising fuel pressure/boost ratio.

Fuel pressure should be 43.5 psi with the fuel pump on and the vacuum/boost reference line disconnected. If you want to verify that fuel pressure is increasing at a 1:1 rate, as it should, you need to apply a specific amount of pressure to the regulator and monitor fuel pressure. The easiest way to do this is to turn the fuel pump on with the engine off, and connect your boost leak tester, and pressurize the system to the same pressure your boost controller is set for. If fuel pressure increases by that amount, then everything is working correctly.

With any change in fuel pressure, you will need to have the car retuned.

it's just simple math. say if you run 15 psi of boost and your fuel pressure is 43.5 psi base, then when boosting 15 psi it should read 58.5 psi on the fuel pressure gauge. i can't tell you what it should be under vacuum because there is no such thing as negative pressure.

You can convert in/hg to psi. If your vacuum gauge is registering -20 in/hg. that is roughly 10 psi. So fuel pressure would be about -9.8 psi lower than the base, or 33.7 psi.

they should just make boost gauges that go clockwise in psi 0 -> atmosphere -> boost

It seems that right now, my fuel pressure is at a steady 43 psi at idle. When I give it gas in 3rd gear, my fuel pressure immediately shoots up to about 50-51 psi, then starts dropping as my rpm goes up. What would be the cause of this? I just installed a brand new fuel pump. Could my fpr possibly be on the fritz?

What is the fuel pressure when you disconnect the vacuum line? Does it come up 8-10psi?

It went up about 4-5 psi when I disconnected the vacuum line.

jeffo said:

What is the fuel pressure when you disconnect the vacuum line? Does it come up 8-10psi?

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it should be at 43.5 psi with the vacuum line disconnected. this is the base number you are shooting for and you always adjust the base with the line disconnected. when the line is connected is when you are trying to figure out if it's 1:1. when you connect the vacuum line it should go down about 10 psi assuming you are pulling 20 inHg of vacuum. in boost it should rise as i explained earlier.