so I’ve been waiting to get out on the boat again to be 100% certain but now I’m thinking about it, key on engine off is the 1/3rd throttle movement with no change in percent/voltage like you described but then, key on, and engine running, there’s an immediate change in engine rpm/tps percent/voltage just like there is supposed to be… The only thing is, I have not checked to see if the tps reads all the way to 100% while running. I will do that tomorrow and report back with the results.


^ if there is a difference between the two, do you know what could cause that?

What state are you in? a large portion of your sensors get a 5 volt reference signal sent to them, since you've virtually changed every sensor and the return output changes on tps, it leads me to believe you have a green connection in your harness or a problem with your ecm/ Whats part number on the ecm? these engines also have a est switching signal to distributor that's also 5 volts, after 300 rpms this signal switches it from 8 degrees timing to run on the timing table (Yes CFM, again, your 100% right on this est thing). Had a engine on my dyno with saltwater intrusion in harness/rotted connections and it would randomly go from being froze at 8 degrees to normal timing and power would reflect it . Was a mefi 3 and threw a code though. Since you have a mefi1, Im not sure if the 5 volts was say wavering to these sensors including the timing est switching if/what code it would throw or if knock module was acting up. I do know when the one I was dynoing did it, it lost 150 ft lbs tq and hp and ran rich as hell. Since the efi is blind speed density, it would still get the same amount of fuel based strictly on may and rpm and run super rich.

im in Mass. it’s been raining every day I’ve had off so I haven’t been able to make it down. I’ll find out the ecu serial number.

that is a good thought, I literally just read about that in another merc book last week and was wondering if it was not switching like it should. Especially because it’s all cylinders that are misfiring and not one individual one. I will look into that next

where are you in Mass?

Western Mass. Were on the Ct river mainly in Northampton, Hatfield, South Hadley area but if someones willing to help Ill tow the boat even up to a few hours if I need to for a hand. I REALLY want to get this figured out before I put it away for the season. I feel like its literally RIGHT there and with everything fresh, it should run damn good once this last piece is figured out.

IF something in harness randomly lets est switching power work/not work you would also see it on a timing gun. Would go from whatever you have base timing set at (usually 8 degrees) to having whatever table shows , a drastic difference.

One alarming thing I just read is that the tone/idle is supposed change when it’s put into service mode, which it did not do. I’m going down tomorrow and going to check the power to the bypass wire and all the reference wires at each sensor. I’ll also take a video from start to finish from idle to plane so you guys have a better idea of what’s going on. I apologize for not explaining it well but I’ve never encountered something like this before

It may very well be already stuck in service mode, the one I dynoed that had a bad connection that was green in the loose butt connector I found in harness made no diffference whether i put a jumper wire in fwiw until I fixed it. It would work normal randomnly if i wiggled harness near distributor until I found that. it was down 20% in power and afrs plunged to rich side when the est wire didnt tell it to go on normal timing table at 300 rpms like it was supposed to if i pulled it on dyno.

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What rpm is the engine idling at that might tell you if its in service mode