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Discussion Starter · #1 ·
My question is, is there anything in the TUNE that can cause a lean condition that actually pulsates in a rhythm at that load, becoming worse as the load increases? If you go into open loop it's gone. The trims are pulling fuel out so I know I'm too rich if anything but it still occurs. I've had lean conditions in areas on cars I've tuned but they may hesitate, quit accelerating, even misfire. But they don't act in a perfect rhythm like you're on and off the pedal a bit, 3-4 times per second.

I have disconnected the EGR, monitored fuel pressure, checked many times for vacuum leaks, swapped upper intakes from the JLP back to the C&L, etc. The truck runs great at idle, light throttle, and wot. But at about .70 load and/or 350 throttle position it jumps into a lean pulse swinging from 15:1 to 16.5:1 in an even pattern, 3-4 times per second, with the rpms and blower noise in unison. Almost feels like you're pushing the gas pedal up and down. Once you go beyond to open loop it's fine. It's like the engine will not run happily at 14.64:1, it wants to be in the mid to upper 13 A/F range.

I dropped my open loop setpoints to 350 TP and .70 load and then re-worked the maf transfers and it runs great. My problem is the guys from SCT seem to think it should be happy at 14.6:1 at those loads/throttle position. I'm wondering if you tuners have fought this or can think of anything else that could be causing it. The tune the way I did it seems to fix it, but is it just covering something else?

Here's my mods:

03 Lightning NLP2
ported heads
Stage II crower cams
KB blower at 18 psi
JLP sheetmetal intake or C&L with C&L tube
Accufab monoblade
SCT big air maf
60# injectors
twin 255 pumps
stock manifolds and exhaust (did it with high-flow cats and cat-back also)
alcohol injection

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