Another P1391 - finally got it fixed

[TXracefan1320]

Hope this helps somebody some day.
97 caravan 3.8 developed a hard bucking problem that got worse with time.
Had the P1391- loss of cam or crank signal
Changed both plus the coil pack and plugs and wires.

Hooked up a dual trace scope to the cam and crank sensors and they looked good and were in proper time so I figured flexplate was good.

A week later I had the scope hooked up again but at night so I could really see the traces and saw random spikes on the cam signal. Figured out they were happening when the coil was firing. (thats when I changed the pack and plugs and wires)

Saw in another thread here about signal noise created by the alternator so I disconnected the field wires and that was it.

New alternator and problem solved.

A bit of irony here: I had installed that alternator in a misguided attempt to fix a different problem a few years ago.

[plymouthsrock]

Great post. Did you ever scope the alternator output (excessive AC ripple)? I wonder if this would have showed up there.

[TXracefan1320]

Early on I had scoped all the voltage supplies and seen a slight ripple but I didn't give it much thought at the time. Sometimes I'm just not paying attention!