Engine issue

salmonkiller01

salmonkiller01

Well-Known Member
2020 mercury 200 four stroke
Idle rpm fluctuates 540-640 randomly
At cruise speed 10-40 fluctuation. Not normal
New plugs, gapped checked multiple times
New filters twice
Fuel Pressure running 45psi. Steady and bled rails
What the heck! Waiting to get into shop!
 
Throttle position sensor bad? You could likely do a resistance sweep test on it with a multimeter. Sounds like a sensor skippin a beat
 
I had the same problem with one of my mains. I found and fixed a small leak in the fuel line at the filter housing and I figure it was somehow sucking air, I also ran injector cleaner through the engine at high concentration at the same time. Not sure which fix fixed the problem, but hasn't been a problem since.
 
ryanb said:
I had the same problem with one of my mains. I found and fixed a small leak in the fuel line at the filter housing and I figure it was somehow sucking air, I also ran injector cleaner through the engine at high concentration at the same time. Not sure which fix fixed the problem, but hasn't been a problem since.
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I have went thru my fuel system, bled my fuel rails and no air. I ordered a set of plug wires and another set of plugs. The gauge fluctuates fast so it is electrical I think. No audible miss but engine shakes
Fuel
Pressure 45 psi no fluctuation
Went thru every power ground go engine
Re gapped plugs
Tried a new coil and swapped around thru the originals.
 
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I haven’t used the boat as low tides won’t let me launch however o2 senor had failed and the ECM got remapped with an update
 
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So what happened here? They scanned it, found a fault on an o2 sensor, replaced it and did an update? Though they nailed it? Still having the same symtoms?
 
salmonkiller01 said:
Going to have to get it to a shop. Fly by wire so I can’t even find a TPS.
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All fuel injected engines have a TPS. You cannot check the voltage without diagnostics.

Won't be a map sensor


Fyi those spark plugs are iridium and you cannot gap them or else you will scrape off the surface material ( iridium). Also this might sound a bit dumb, however those plugs are pieces of albsolute ****. Only plug in my 25 year career that I've seen just not work whatsoever or work intermittently. Like I'm talking not work at all. Most plugs get weak over time or get arched out but these plugs are absolutely bizarre.


Unplug the shift switch. Just rule it out

Also just assuming that your battery connections are proper and bolted down tight with a nut?

Ohh and one more tip. The last verado I fixed had 2 bad CDM modules ( ignition coil ). Sometimes those cdm modules can be wierd. The engine should run with one dead hole. Meaning it will stay running. Won't run nice but it will die with 2 dead holes. So unplug a CDM module one at a time and see the outcome.
 
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