Merc 4-cycle stalling, shutting off, misfiring at WOT. It was the TPS.

[wrd1972]

Okay I have been chasing an super annoying issue on my Merc 90HP 4-cycle for years now, and I wanted to pass along the fix for me.

I saw the following symptoms:
-Randomly hard to start, cold or warm
-Randomly turning off when throttling down to neutral from WOT
-Random powerful and jarring misfires when at WOT

Its hard to diagnose things without the official Mercury scanner, and also when you dont have quick easy access to your boat. But all the pieces started to point to the position of the throttle lever, so I decide to take a chance and replace the throttle position sensor (TPS). So I have had two long days at the lake since replacing it, and there has not been the slightest single hiccup with the motor...Woohoo! I am feeling very good that this issue is now resolved. BTW, the TPS can be replaced in less than five minutes with a basic Torx driver and a can of beer.

Finally and for good luck, I gladly chucked that thing from the bow and sent it to the abyss of my local lake. Good riddance. LOL.

Keep on boating guys.
Bill

[curtiscapk]

Nice to know good find!

[Reiner]

Hello,
This maybe the problem I have on my 150 HP 4-stroke Mercury. Are you able to post a pic where the TPS is located?

Thanks Reiner

[wrd1972]

This is the best I could from on-line videos.

Again super easy to replace. Disconnect the sensor cables and remove two Torx screws. The old sensor will then pull off. You will see the metal throttle body shaft (where the TPS connects) will have a blade-like feature similar to a flat-tip screw driver. That feature needs to align with the plastic slot on the new TPS. Once its aligned and pressed onto the TB, simply rotate the TPS just a tad and bolt it on. Done.

[Reiner]

Thank you, my 150 HP looks a bit different but that will give me an idea.