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Fuel pressure

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hi guys

stupid question my brains not working to well atm lol, base fuel pressure if we want 44psi setting of the base pressure (running a fpr 1200) fuel pumps running disconnect the vac line adjust the screw until we see 44 psi lock the nut, obviously when we connect the vac line again the and the engine running the fuel pressure is going to drop, now my silly question if we want a base pressure of 44psi is that with the motor running and everything hooked up or is it 44 psi without the vac line hooked up

only asking as when I got my car back from the tuner a couple of years ago I'm sure with the car at idle i was seeing 44psi on the gauge now after a the cars hot I'm seeing 30psi mayb I was seeing things lol


The 44psi "base" should be gauge/differential to atmosphere, so with the vac line off the reg, pump running.

If you have significantly changed ignition timing and removed idle load vacuum could change a decent amount but that sounds like something isn't right. Is the car fitted with a wideband? Is it reading the same as when tuned? Does it still run ok?

at idle the car is pulling 20inhg of vacuum

haven't changed ignition timing or anything, cars running a wideband I did notice it jumping around at idle the other day but in saying that the car has developed a shocking idle on e85 when it used to be smooth as but that's a different issue I know I have

I would be checking over the reg adjustment and making sure there weren't problems with the filter/pump. If it has developed a missfire.

Are you talking about a mechanical burdon gauge or a transducer to digital gauge?

There was a guy on rx7 clib with a TI/haltech pressure transducer which was reading low with higher ethanol content, as he was running an adaptronic with pressure compensation is caused it to run rich on ethanol and miss.

Yeah it's running mechanical gauge straight off the reg, has new pumps carter black lift pump and a Bosch 044 main both 2 months old just re wired them aswell both getting battery voltage and I removed the fuel filter and ran it same thing

I must be missing something tho because if I set the base pressure with the vac line disconnected to 44psi once the vac line is hooked back up its going to pull roughly 10psi out of it which is what it's doing giving me around 30 psi, so shouldn't I be setting the base pressure to 54psi without vac line then when vac line is hooked up it will give me 44psi?

If it is tuned for a 44psi differential then you set it without vacuum unless you are going to set it by adding the manifold vacuum reading at idle to the gauge pressure to atmosphere. You are setting differential pressure across the injector.

With it reading 30psi while the rnginevis running the pressure differential across the injectors is 44psi.

Yes correct, it's just spinning me out as pretty much all cars I've worked on with a return system are around 40psi I'll message the tuner and ask him if I'm seeing things lol