Fuel pressure test

[Ares3985]

So my tuner says I have a lean condition. Told me to smoke test. I did that and came up with nothing. Next he wants a fuel pressure test. So I ordered a test kit and it should be here tomorrow. He says I should be looking for a 1:1 ratio with manifold pressure while going to full throttle. So from my understand I should tee into the feed line after the reg on my fuel. Mount my gauge so I can see it and then monitor manifold absolute pressure on my accessport. So if I get 45 psi let’s say on the fuel pressure gauge then I should see 45 psi absolute manifold pressure while increasing throttle?

 

 

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[awfulwaffle]

No. In that case, you should see manifold pressure equal to the difference between 43.5 psi nominal and what your fuel pressure actually reads. The regulator has a nominal setting of 43.5 psi (41-46 psi range), and subtracts 1 psi for each psi of vacuum or adds 1 psi for each psi of boost.

 

You can also pop the manifold reference line off the reg to simulate being at ambient. Your idle fuel pressure should come up to 41-46 psi if your regulator is working right.

Edited September 12, 2019 by awfulwaffle

[Ares3985]

Alright thanks. My gauge comes tomorrow so hopefully it tells me something

 

 

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[Tehnation]

https://legacygt.com/forums/showthread.php/comprehensive-fuel-pressure-thread-109863.html

 

This thread should answer all your questions!

[Ares3985]

https://legacygt.com/forums/showthread.php/comprehensive-fuel-pressure-thread-109863.html

 

This thread should answer all your questions!

 

 

 

Yeah I read that a few times. A bunch of people w different answers. Vacation pics show to tap into the top line closest to the front for the pressure test.

 

This is where it says to put it but other guys are talking about the return line. Which is bottom of the stack

 

 

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[BrandonspecB]

The feed line is the correct location. You want to measure fuel pressure upstream of the regulator. Fuel pressure after the regulator means nothing.

[Ares3985]

The feed line is the correct location. You want to measure fuel pressure upstream of the regulator. Fuel pressure after the regulator means nothing.

 

 

 

But wouldn’t that be what the injectors are seeing?

Before the reg would just be the max power of the pump right?

[BrandonspecB]

The injectors see the max power of the pump. The regulator is after the fuel injectors.

[Ares3985]

Do need to be moving or can I do this in my garage. Just tried and it went from 38psi to 40 at 4000 rpm parked.

When I first start it I get like 51 psi and then it drops down to 38. Not a cold start. Hot start.

 

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Edited September 14, 2019 by Ares3985

[BrandonspecB]

You need to drive it and build some boost.

 

At work we have a pressure gauge with a hose long enough that we can tape the gauge to the windshield and then go for a drive.

 

Your base fuel pressure with the vacuum line unplugged should be around 43 psi. For every pound of boost you should see one pound of fuel pressure over 43 psi. So, at 7 psi boost your fuel pressure should be 50 psi. At 15 psi boost you should have 58 psi fuel pressure, etc.

[Ares3985]

 

Your base fuel pressure with the vacuum line unplugged should be around 43 psi. For every pound of boost you should see one pound of fuel pressure over 43 psi. So, at 7 psi boost your fuel pressure should be 50 psi. At 15 psi boost you should have 58 psi fuel pressure, etc.

 

 

 

I got like 62-63 at 19lbs of boost.

 

 

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[BrandonspecB]

That's perfect. Exactly what it should be.