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Mercury 40 ELPT EFI Motor Problem

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mjjm

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I just purchased a 2007 pontoon boat equipped with a 40 hp Mercury outboard. The dealer says it has about 130 hours on it. Starts fine but after running between 10 and 30 minutes the RPM's (and speed) drop off, then resume, then drop, etc! Took it to my local Merc dealer and he tried a bunch of stuff including checking fuel, fuel reservoir, fuel pump, changing coils, replacing oil and filter, spark plugs, computer analysis. Also checked for grounds and temp sensor and oil pressure. Couldn't find anything really wrong other than it goes into "guardian" mode occasionally. Took the boat back this past week (dealer did a lake test and it was okay) but it's doing the SAME THING! He thinks it might be worth replacing the wire harness. I'm wondering if anyone has seen a problem like this (intermittent)? If so, any ideas on how to correct it?
 
He thinks it might be worth replacing the wire harness.
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Find a better dealer...he wants to throw parts at it to fatten his wallet. Apparently this engine is a 4 stroke..."cked oil pressure". The next time it starts acting up use an insulted pliers to pull the spark plug wires off one at a time. When you pull a wire and it gets worse that cylinder is working. When a pulled wire causes no change that is the problem cylinder. I would start bt inspecting the electrical plug to each injector for corrosion and any thing else out of place.
 
guyjg said:
Find a better dealer...he wants to throw parts at it to fatten his wallet. Apparently this engine is a 4 stroke..."cked oil pressure". The next time it starts acting up use an insulted pliers to pull the spark plug wires off one at a time. When you pull a wire and it gets worse that cylinder is working. When a pulled wire causes no change that is the problem cylinder. I would start bt inspecting the electrical plug to each injector for corrosion and any thing else out of place.
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Thanks for the feedback! I will try your suggestion this weekend. You are correct that this motor is a 4 stroke, 3 cylinders. Any idea whether the "computer" on these things can be screwed up? Or, since this engine meets California emission standards, whether something related to emission controls MIGHT be affecting the performance? When she runs at "normal" RPM (around 5500 RPM), it's nice and smooth. Seems a bit "rougher" when it drops to 4800 RPM.
 
find anything really wrong other than it goes into "guardian" mode occasionally.
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That sounds like an intermittent electrical connection or a dirty or failing sensor.
Seems a bit "rougher" when it drops to 4800 RPM.
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Focus on the EFI portion of the engine. Keep us informed.
 
I will call the Merc dealer and ask if he found any "faults" other than guardian mode. I know he removed and tested the temperature sensor. It tested out fine. He couldn't easily get to the oil pressure sensor but he said he hadn't heard of those failing and disconnected the wires to it for some type of test, which it passed. As you can see, I have very little knowledge of these motors (my first outboard). Any other sensors come to mind that should be checked, particularly relative to the EFI portion of the engine as you have recommended? He did find that the oil had been overfilled (which fouled the spark plugs). Changed oil and filter and plugs. Didn't seem to affect this problem at all.

Forgot to mention--the dealer's tech was wriggling each wire while the engine ran to see if anything happened. Supposedly when he did that to the spark plug wire on middle cylinder the engine cut out. He wasn't sure it that was just a coincidence but he put electrical tape on the wire. Makes me think maybe replacing the wire harness does make sense? Can you just replace spark plug wires?
 
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Can you just replace spark plug wires?
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Yes you can.
He did find that the oil had been overfilled...
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If you run the engine on short trips the engine can make the oil level increase thru contamination from combustion by-products. A thermostat that opens too soon will also contribute to the oil contamination process. Since you are not the mechanic it's cheaper to change the one HT plug wire vs.. the engine wire harness. Your call.
 
Hi! I have a pontoon with an 40HP Mercury Efi too.

Since last year I'm having the samo problem as you have. As I run some time (10, maybe 20 min) when I go down with the power, the engine start to cough and do not follow if I wont to increase the power. In that moment I shut down the engine and start it again immediately, with no problems with the power. It runs OK. Since yesterday the engine stasts to show me, that the temperature is too high (163 f), with beeping loudly. I do not understand why, as the cooling water jet is running out of the engine without problems and strong.

It seems that your and mine problem are preety the same. Did you solve the problem? How? Tnx, Alex
 
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