[Diy_efi] About MAP sensing and it's jitter
Ludis Langens
ludis at cruzers.com
Sat Jan 17 14:32:18 GMT 2004
"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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