Best guess for negative fuel trim problem ?

[bmwdirtracer]

Sorry, kaivon, that's just not the way it works. Fuel pressure RISES when vacuum is removed or lessened. Only a dumbass would REDUCE fuel pressure when the car needs more fuel, and BMW engineers are not dumbasses.

The rating (3.5 bar in this case) is BASE pressure, at idle and high vacuum conditions. Manifold vacuum is more than TWICE the 8 "PSI" (SIC) stated, at idle, and vacuum is quoted in inches of mercury, not psi anyway.

Let me just ask you this: HOW MANY fuel pressure tests have you done on BMWs? I've done hundreds. This isn't a damned garden hose, let's stop screwing up the equation by pretending it is.

Here....I just looked up a basic test......see step # 7.

https://www.2carpros.com/articles/ho...-and-regulator

[kaivonp]

Sorry, kaivon, that's just not the way it works. Fuel pressure RISES when vacuum is removed or lessened.

That's actually what I said: Reducing vacuum increases fuel pressure.

Manifold vacuum is more than TWICE the 8 "PSI" (SIC) stated, at idle, and vacuum is quoted in inches of mercury, not psi anyway.

Well MrSkarZ is the one who kind of said that idle manifold vacuum was 8 PSI. His language was unclear, but what he meant was that the vacuum at idle reduces fuel pressure by about 8 PSI compared with no vacuum. I realize you disagree with that, but his statement wasn't nonsensical.

You know the cheapo method for a lawn irritation system--poking pinholes in a garden hose? If you just let water run straight through, you won't get much flow out of those little holes. But if you put your thumb over the end, you'd create enough pressure to force water out of the pinholes. An FPR on the end of the fuel rail is a lot like your thumb on the end of that garden hose.
Later BMWs with the 3/2 control valve might be different--as early as the M54, the FPR isn't even controlled by manifold vacuum. But I'm talking about the M50 that MrSkarZ has.

[MisterM52]

this ever get solved? i am getting some fuel trim errors..

[kaivonp]

I messaged the PO, MrSkarZ, but never heard back.

[deme]

can someone help me with this fuel trims?

[bmwdirtracer]

You can't judge much of anything about fuel trims when the engine is free-spinning with no load.

Short term fuel trim is basically for idle and near idle conditions, although it might just continue if there's zero load, like a car that's not moving. However, your bank 1 STFT isn't doing a thing, while your bank 2 is changing. The LTFT will hopefully change when the car is under cruise conditions.

You'd do better by looking at the primary oxygen sensor numbers; see if Bank 1 sensor 1 is even working. Your fuel trim numbers revving in neutral are pretty meaningless, except for Bank 1 doing nothing while bank 2 changes.

What's the actual problem you're trying to solve here?

[freestyle31225]

can someone help me with this fuel trims?

Have you fixed that?