rebuilt 8.1gxi-a in a 2002 265ssi chaparral with only spark in cylinders 1 and 6


New member
DIYer here, with lots of help from a few freinds with good mechanical skills, i know enough to be dangerous and that's about it. Please advise if you have any ideas. I Blew a piston, bored cylinders out .002, turned cam bearings, crank bearings, and 3 angle valve grind, i believe resrfaced heads. this was 2 years ago at the start of the pandemic, machine shop subbed out crank work to another shop in another city and then covid hit. Crank was stuck there a few months. Put it back together, installed in boat, We were getting good fuel to all cylinders but only spark in two cylinders and partial spark in two cylinders swapped coils and wires and ecm, and determinded they were good, suspected bad base timing so we pulled the engine determined timing was 180 out, swapped it, put engine back in the boat now we have spark in cylinders 1 and 6. We suspect now either the reluctor wheel was removed and put on wrong although the shop said they never removed it, or it was misaglined in shipping/handling. we put a cheap oscilliscope on the crankshaft position sensor, here is a link to a short video of what that looked like so someone hopefully could tell me if the reluctor wheel is sending a good signal. The scale is off and the video is upside down but that's what i have now, Thanks for your help


Active member
I am good with electronics, but your problem is over my head. Point being and maybe I am wrong. If you look at the timing between square waves, they are off. As in some cylinders are firing and some are not. Which you already know! But you may not from looking at the wave form.


New member
Well it's the 8.1 GXi-A which has individual coil packs and all the ignition and timing is from the ECM that compares the crank's and the cam's position via the sensors

Bt Doctur

Super Moderator
Staff member
is the crank RELUCTOR gear installed NOT THE ONE FOR THE TIMING CHAIN
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