Engine bog only when I drop to 2nd gear?

Sonny

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Engine- 440, msd coil and msd 6efi ignition box, msd atomic 2 efi, headers, rpm air gap, mild comp cam, 1800 rpm stall converter, Holley dropped air cleaner with 14”x3” filter, Mopar original electronic distributor from a guy named Joe White who rebuilds them.

If I get on it from the line it runs great through the gears but going 55, drop into second to 3500 rpm or so then nail it, it bogs and tries to throw me through the windshield and doesn’t clean up with time. I let off and back to cruising. Nail it in 3rd it’s fine. Seems to happen only when you jump quick to 2nd gear to instant high rpms. Air fuel ratio doesn’t change and car never looses spark. It’s like it can’t get enough air? Does it with vacuum advance on or unhooked. Timing 18/35. Any ideas?
Sonny
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pnora

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What is the fuel pressure? Does it change when this is happening?
 

Sonny

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What is the fuel pressure? Does it change when this is happening?
Good question. It’s fuel injection with pump in tank. I’ll watch it next time and see but it’s not engine driven. It’s Electric.
 

AR67GTX

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Don’t know anything about EFI systems but I assume they have some sort of provision for richening the fuel mixture upon a sudden throttle opening. Maybe it’s not quite calibrated rich enough for second gear, assuming there is some sort of feedback on the transmission gear operation to the computer (which there may not be on aftermarket conversions). However, I would think after an initial breakup, the fuel flow would catch up and the miss/bucking go away.
 

pnora

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Good question. It’s fuel injection with pump in tank. I’ll watch it next time and see but it’s not engine driven. It’s Electric.
EFI does not work well with low fuel pressure. You need to know what pressure the system is designed to work under. Then you need to monitor it between the pump and the injectors. EFI fuel pressures are extremely critical. Do not blame anything else until you monitor it in the correct test port.
 

Sonny

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EFI does not work well with low fuel pressure. You need to know what pressure the system is designed to work under. Then you need to monitor it between the pump and the injectors. EFI fuel pressures are extremely critical. Do not blame anything else until you monitor it in the correct test port.
Called MSD and they solved the issue. There is a separate setting for the accelerator on the hand held controller. It was set to 49lbs/hr and after a few tweaks settled on 67. Bog is gone and it hauls. :)
 

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