Stumble when Stabbing the Throttle (4.3 w/ bigger injectors)

[thehemi]

Setup: Stock '99 4.3 with Marine MPFI intake and MotoTron 60# injectors
Issue: Stumble when stabbing the throttle. If too quick, it can backfire. Same in Park or loaded.

I'm running stock exhaust manifolds now, but it was a turbo setup in the past. However, the stumble upon stabbing the throttle was always an issue, so I'm sure it's related to the intake/injectors. Otherwise, it runs great in all other situations.

Not sure if this suggests it's lean or rich, but I don't know how to adjust for it?

Thanks,
Scott

[99 Blazer]

Setup: Stock '99 4.3 with Marine MPFI intake and MotoTron 60# injectors
Issue: Stumble when stabbing the throttle. If too quick, it can backfire. Same in Park or loaded.

I'm running stock exhaust manifolds now, but it was a turbo setup in the past. However, the stumble upon stabbing the throttle was always an issue, so I'm sure it's related to the intake/injectors. Otherwise, it runs great in all other situations.

Not sure if this suggests it's lean or rich, but I don't know how to adjust for it?

Thanks,
Scott

Mine has done this in the past due to a poorly sealed intake manifold. Some SOB had used a cookie to grind the intake gasket surface and caused a vacuum leak from #1 to the intake valley. Other symptoms included rattling PCV valve and oil contamination of only that spark plug. Unequal long term fuel trims were also a clue. Good Luck!