Weird gt40 miss/stumbling - please help!

Kyle,
I wish I knew more about the GT's. All I can do is suggest going to the GT diagnostic thread in the FAQ's. Also, I know once more members come on, you will get some help.

kylem428 wrote: Gt40 miss

Kyle,
To me it sounds like the engine is surging rather than a miss??

So I have an intermittent issue I am experiencing. My 1995 gt40 will miss and stall when warm but when it happens the tach will bounce all over the place despite the engine running at 1k rpms or less. Of note is that I burned an alternator belt recently and replaced it. It has had a smoking belt issue since I’ve owned the boat. Seemingly my tired mando alternator was putting out a steady 13.5 volts after replacing the belt but only around 12 before.   In Thinking this through, my stalling problem began after the new belt was put on so on a whim I took it off and the boat ran flawlessly immediately thereafter off the battery. Didn’t skip a beat.

I guess I am going to order the 100amp alternator upgrade kit tomorrow with the hope that it was entirely the alternators fault sending a strange voltage or spike to the system causing the ecm to act oddly. Anyone have a similar issue or thoughts on what else I should be checking? I changed the relays just to be safe but Initially I was also thinking possible distributor issues, pip sensor, iac valve, tps, ignition module or ecm, but if removing the belt solved the issue, I think it’s the alternator. Given the wacky tach, I am certain it is electrical based. My hydrophase also registers odd tach readings when the issue presents itself, so it’s not the 6-8 cyl selector on the tach. Also both the Tach and digital rpm read outs function flawlessly when the issue isn’t happening. I’ll try to link to a video I took.

I appreciate any thoughts or insight!

Thank you,

Kyle
Kyle