# Fuel pressure

## Recommended Posts

My tuner said that I had a problem with my fuel pressure when he mapped the car, he said my fuel pressure wasn't rising at the same rate as my boost pressure. So Im just looking at a  log so I understand it so I know when I might have fixed it. He put a 4d fuel trim table in to compensate for it for now. So my question is how do i work out what my fuel pressure should be? Im guessing its some maths to do with MAP BAP MGP? Thanks

##### Share on other sites

Fuel pressure should maintain a fixed differential above MAP. So say for instance at 100kpa MAP your fuel pressure is 400kpa (that's 300kpa differential).  Then at 300kpa MAP you should have 600kpa fuel pressure (still 300kpa differential).

##### Share on other sites

Ah ok i understand, mine seems to vary by 24kpa at worst, whats a realistic figure it should stay within? 5kpa?

##### Share on other sites

Thats usuall. What I've seen, on most cars pressure drops by 0,25 bar at higher injector duty cycles. Even with new fuel pressure regulator and big fuel Pumps.

If you setup modelled fuel, you can choise FP as a load source, so pressure is compensated by the fuel modell.

##### Share on other sites

Thats usuall. What I've seen, on most cars pressure drops by 0,25 bar at higher injector duty cycles. Even with new fuel pressure regulator and big fuel Pumps.

If you setup modelled fuel, you can choise FP as a load source, so pressure is compensated by the fuel modell.

I can attest to this.

Recently calibrated a R32 GTR.  Was running a nismo pump that couldn't keep up with the required supply.  Had fuel pressure dropping by more than 50kpa.  But with the Fuel pressure sensor wired to the ecu with the correct settings in the modelled equation, you could look at the lambda and wouldn't even notice that the fuel pressure was falling.

I have even had my own car melt the fuel pump completely fail on my own personal car and the ecu was able to compensate enough just based on fuel pressure to keep the car running for about 3-5 mins after all the warning lights on the dash came on with less than a bar of fuel pressure.

##### Share on other sites

oh right, so basically its nothing to worry about then? I was going to be getting either another pump or regulator as I was thinking I may have brought fakes

##### Share on other sites

I would still 100% try to address the mechanical problem as best you can before just letting the ecu make the necessary compensations to be right.

##### Share on other sites

we add a fuel pressure on every second LINK ECU install. I never seen a constant fuel pressure.  It's really usuall to see such a small drop. Think it has to do with the return line flow resistance, which is less at higher INJ Duty cyle.

Brad Burnett, you can use a GP limiter to cut rpm if pressure drops to much. We usually allow a small amount of pressure drop and cut rpm to 3000 or something else if it goes below.

Edited by mapper
##### Share on other sites

Mapper,

Yes on the GTR that we did that had the pressure drop we set up a 3d gp limiter for both fuel and oil pressure.

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.