occasional flickering check engine light

Posting follow up to issues. Back on the water for a day, skiing and cruising. So far no flickering light and all seems normal on gauges.

Not to start into the oil debate questions for this vintage engine but the first couple of years I used Pennzoil 40W and switched to Rotella t 15W40 after reading posts regarding zttp content to minimize lifter wear.


Thanks o all for your input and info

Thanks for the information. Since I posted the question, I was looking at what I think are the switches in question based on reading other posts.
It appeared the switch on the top of the engine water pump was maybe just a touch loose and could be sending incorrect or intermittent info.

I will be taking the boat back out on the coming weekend and will try disconnecting these leads if and when the light comes on again. I don't think I can recreate the trouble in the driveway but may try it anyway.

I do know the oi pressure is typically at 40lbs when running at speed and it does decrease somewhat when you slow to idle. This combined with a defective switch could be the cause of the troubles. Time will tell.
I will also try to download the engine manual and read through it. I do have a quality VOM I can use.

Here's some info from the service manual courtesy of Lewy 2001 showing the SLOW circuit.

lewy2001 wrote: The other brown/black wire should go to the oil pressure switch. The SLOW mode can be invoked by either low oil pressure or high engine temperature. From the GT40 Service manual in Reference section.

I did a quick search and found a couple of posts but will start a new on more specific to my issue.
2001 GT40 in a 196
Engine has about 550 hours on it and has been flawless since I bough tit in 2006. Late last summer check engine light cam on after taking 3 or 4 skiers for runs. As soon as we brought it down to idle speed it flickered.
Shut the boat off and go back out later. All good until after it was run for a while. All gauges normal except the volt meter was reading high.

Put a new battery in this year and replaced the starter solenoid since the studs broke while I was removing cables to clean. Headed out to the lake. All good until end of 2nd day. After a cruise around the lake, maybe 40 - 50 mins when I pulled back the throttle the light flickered on again .

If you get rpm up over 1000 it would go out but eventually it was on pretty solid. I have looked at posts about this and they referenced temp switch and oil pressure switch but in those cases someone had re and re'd the wiring or did not have a functioning temp gauge.

Since there is not OBD port to use a code reader does anyone have any experience and or troubleshooting information they could share to narrow down what is causing the issue. boat seems to run fine and pulls strong until the light comes on. It did go in limo mode once last year when this issue started.

Looking forward to hearing from the experts out there.