1990 3.4L 250hp no-spark on 3 cylinders...

[Capt Randy]

...only at idle and low speeds. When i try to idle I lose all odd # cylinders and the 3 coils for the even bank sparks fine. I switched around the upper and lower switch boxes and the problem persists. I ohm tested the trigger as per my Merc manual, while moving the timing lever and the #'s all stayed in spec. Should I pursue the trigger more, or should I look to the stator?

 

[WillyBWright]

Re: 1990 3.4L 250hp no-spark on 3 cylinders...

Trigger works in pairs. Three failed cylinders eliminates that. You swapped switchboxes and nothing changed, so they Shouldn't be the problem (never say "never" with those things). I believe your stator has two separate circuits, one to electrify each switchbox. Each of those have separate high speed and low speed windings. One of the low speed windings must've failed. I'd say it's the stator. But put an ohmmeter to it first to confirm the diagnosis.

 

[Capt Randy]

Re: 1990 3.4L 250hp no-spark on 3 cylinders...

Just removed and ohm'ed the stator. You are correct. The low speed windings for the 1,3 and 5 cylinder banks are open The others are fine. Now to find a 40amp stator for a 3.4L!!! The saga continues....