[Diy_efi] About MAP sensing and it's jitter

[Ludis Langens]

"Tomas Sokorai Sch." wrote:
> 
> Anybody knows how much (KPa, inHg, etc.) should the MAP signal jump at idle
> with a totally stock 1975 Ford 302?.

I was helping a neighbor fix his $85 Ford van.  The EFI 302 had one
dropped/loose exhaust valve seat.  At idle, the exhaust valve wouldn't
properly close.  This resulted in exhaust blowing back to the intake
during that cylinder's cam overlap time.

Ford uses a frequency out MAP, so I hooked a GM voltage out MAP into the
system.  I then watched the GM MAP's output on a scope.  Once per cam
revolution, the intake vacuum would drop to zero (or even be slightly
pressurized).  During the next seven cylinder events, the MAP would
ratchet down to a normal level.  I didn't note exactly how high the
fluctuations were during this time, but they weren't small.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

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