Scoped 12v+, Odd transient, Wave form attached

grimreaper

New Member
Jul 2, 2008
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Dallas
Getting used to the new scope and found this on the B+ line at the ecu. Car was at warm idle, minimal electrical load. DC+AC coupled probe with no freq limiting. Its a consistent transient.

DVM measured warm idle is a stable voltage of 13.8-13.9v even with a 30 amp load (headlights,blower,defrost ect..) Increased rpm does not increase voltage or current. It appears that it can sufficiently provide what is needed at idle. Lights dont dim when things are turned on etc...

Higher rpms under heavy load usually show a 3-500mv drop which I believe may be normal.

Does this look like a failed diode? roughly 500mv VPP for the shown transient.










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Dan_Gyoba

Turbo Swapper
Aug 9, 2007
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Alberta
www.gyoba.com
The bulk of the transients is half that. A failed diode will produce much larger values than that.

Automotive DC is notoriously noisy, which is why every circuit that I've ever seen designed for a car has got some sort of filter on the power input.

Oh yeah. Keep in mind that the fuel pump is also on that circuit.