Quote:
Originally Posted by montauk
Dan
Did you end up installing a fuel pulse damper on your setup?
I’ve been chasing some odd behavior in my long-term fuel trim table—huge swings between adjacent cells, like the ones in the screenshot I attached. From what I understand, that kind of variation really shouldn’t be happening under steady-state conditions.
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No, I am running the CIS Fuel Accumulator between the fuel pump and the FPR, then the fuel supply deadheads to the fuel rails.
Regarding your long term fuel trim screenshot, do those dips move around from one run to another (that is moving to different rpm / TPS conditions)?
My experience with OEM emissions systems is that long term trim changes more slowly. If the LTFT dip persists, then it would indicate the base fuel trim map is too rich in those areas - 1500 to 2500 rpm at low TPS is like pulling away from a stop with light throttle then cruising around the neighborhood?
Anyway, back to my fuel set up and observed fuel pressure changes. While Gary Bains was running the car on the dyno, I stood at the back of the car and watched the fuel pressure readings (my MegaSquirt 2 doesn't have an input for fuel pressure).
When Gary floored the gas (WOT) at 2000 rpm, the fuel pressure would drop from 50 to 48 psi then recover to 50 psi after 1 second or so and then stay steady at 50 psi through the rest of the WOT ramp run until after 7000 rpm and the fuel pressure would start to drop slightly (not sure of the amount, only that I started to see the gauge slowly moving lower), but then at 7300 rpm Gary ended the ramp run and the fuel pressure went back to 50 psi. That indicates to me that my fuel pump may be getting flow limited above 7000 rpm. If I was a racer, I would be thinking about a higher flow rate fuel pump, but for canyon carving and cars & coffee duty I am okay with what I have.