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Nettlez

Differential Fuel Pressue

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So I have an issue with my fuel pressure no rising linearly with boost pressure. I am monitoring the fuel pressure with an AEM 100psi brass pressure sensor but I have since noticed they have a tolerance of plus or minus 3%, so 3 psi is 20kpa so that's a total tolerance of 40kpa. Does anyone have experience in using a bass one and noticed they aren't very accurate?

I have attached a log, the fuel pressure is always out around 40kpa but then does vary more than this as well. So I am wondering if the fuel pressure sensor is just around 40kpa out (calibration wise) and then is varying by its tolerance rather than my fuel pressure regulator actually being no good?

link for log

http://s000.tinyupload.com/index.php?file_id=94442381336288492771

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Accuracy and repeatability are two different things.  The absolute accuracy may not be too great as they probably dont go through any type of calibration check against a known standard at the factory but I would expect being a solid state device the repeatability to be good.

Your dif fuel pressure seems to sit consistently around 295-300Kpa for the vast majority of your log, the only times it drops is when MAP increases so I think the sensor is reading fine and it is showing you have a control problem.  It could be a regulator issue or the pump not keeping up.  Note dif fuel press will never be dead flat, all regulators have a "gradient" and never control fuel press at exactly 1:1 with boost, however some are much better than others.  You are seeing about a 30kpa drop in differential for less than 100Kpa increase in MAP so that is worse than I would typically see.

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6 hours ago, Adamw said:

Accuracy and repeatability are two different things.  The absolute accuracy may not be too great as they probably dont go through any type of calibration check against a known standard at the factory but I would expect being a solid state device the repeatability to be good.

Your dif fuel pressure seems to sit consistently around 295-300Kpa for the vast majority of your log, the only times it drops is when MAP increases so I think the sensor is reading fine and it is showing you have a control problem.  It could be a regulator issue or the pump not keeping up.  Note dif fuel press will never be dead flat, all regulators have a "gradient" and never control fuel press at exactly 1:1 with boost, however some are much better than others.  You are seeing about a 30kpa drop in differential for less than 100Kpa increase in MAP so that is worse than I would typically see.

Right ok, I do have the ability to check the pressure sensor for calibration but I guess it doesn't matter if it reads spot on, just so long as the repeatability is good as that's what your actually monitoring.

So just to clarify what I am looking for is as the map reading goes up I am looking for the fuel pressure reading to go up the same? So for example if at tick over map is 50kpa and fuel is reading 240kpa then when map is 150 the fuel should be around 340kpa?  If this is right how close should it be when varying?

Or another way of working it out would be fuel pressure minus mgp and the result of that should pretty much stay the same regardless of map?

Edited by Nettlez

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