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Merc 150 EFI not reaching WOT specs

N

notshy

New member
Hi Guys,

I have a 2006 150hp EFI on a 5.8mt fibre glass hull. I am only able to reach 4000rpm wound right out and trimmed up and should expect to get atleast over 5000. i expect it is over fueling some how. It has a black deposit inside the prop, and the mechanic says the plugs look washed (too clean). he is too busy to fit me in to hook up the diagnostic tester. I have tested 3 out of the 6 coil packs and are fine. Tested while cold head and air Temp senders. I have the manual for this engine fron online. Anyone else heard of this happening to this motor or know of a likely cause?
 
. I have tested 3 out of the 6 coil packs and are fine.
Click to expand...
Test the other 3 packs. Test each plug wire for spark that will jump a 7/16" gap...use a gap tester. You want to see a bright blue loud snapping spark. Make a gap tester to see all 6 sparks a one time to compare them.
 
A couple questions -

is this boat "new to you"?

did she ever make 5000 rpms?

5.8 metres is about a 19 footer, and fiberglass to boot - heavy boat - could have too much prop - hull could have sucked up some water adding a couple hundred extra pounds...

(have to guess until we get some history on the rig)

Give us a good description and a bit of history - no sense trying to fix the motor if the boat itself is the issue...
 
I have had the boat for a few years but swapped OB last year from a 1983 115 Johnson to the Merc. The Johnson used to do the same speed (50km/h) which is what I can only get out of this motor. No water in hull. The motor is second hand and as long as I have had it, it has never done 5k. Prop is a vengance SS 14.5 17p which I have been told should make the boat zing no worries at all and if the motor is running correctly I should be scared to go WOT. I installed the motor. First I tried running it in the second lowest position and it would not trim properly, so I have dropped it to the lowest pos. and it trims and runs quite well now. The temp gauge only moves off "C" until the poppit opens and then drops again so I thought it could be temp related......I have just replaced T-stats and inspected poppit to which had sea weed stuck in it. I have not been able to test it yet, but the mechanic says it probably won't be the case for the over fueling. I bought the motor from a boat dealer and know that it was serviced last august so the plugs should not be that old. All plugs look very similar so I am thinking the problem is isolated to one coil pack.
 
Tach setting is the same, so that's not the issue.

14.5D/17P actually does sound "under propped" for your rig - so agree, would expect you would need to keep it "backed off" to prevent an over-rev.

A timing light will quickly rule out a bad pack - however, I would expect that you would feel a hesitation etc if you had a cylinder not firing (of two or three - would be shaking like a wet dog on a cold day).

The "washed clean" plugs sounds like it's getting lots of fuel but somehow not "breathing" properly (assuming it's firing) - could be an air in or exhaust out issue (either would restrict rpms).

First off I would confirm that all the plugs are firing. If they are, I would then check 1) the throttle body - make sure the butterfly is not restricted (opening fully at full throttle) and 2) inspect the air plenum (I would pull it and have a look - a bees nest in there would certainly cut your air intake).

Also, less likely due to it's sheer size, the exhaust tube could be likewise plugged - bees/wasps/mice can crawl inside and set up house - if the motor has restricted exhaust it will burn rich and fail to make max rpms.

So a couple other things to look at IF the ignition is ok...
 
Not 100% sure yet but finally got it on the DDT and WOT voltage is 3.8 volts which is at low end of the scale. Idling voltage ok. Will ocean test by fiddling with the TPS while on the go.
 
A benchmark for you Notshy......my 5.8 metre fibreglass half cab does 5750 with a 17P MiragePlus and 5500 with a Solas Rubix 17P 4 blade. I mentioned the exhaust tuner as it is a common problem with the 2.5 mercs. Causes an overly rich condition and fouls plugs. If one cylinder drops you will lose 800rpm. Motor is the same as yours, 2006 Merc EFI 150hp. I went through everything when mine had the problem, even put in CC reeds. Dropped coils etc come up as faults on Smartcraft (if you have it installed). MAP sensor can get plugged with oil but doesn't really affect WOT. Make sue ALL the earths are good. Do yourself a favour and check the tuner before spending $$$$$
 
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Sorry, you have lost me. I can't remember reading about an exhaust tuner in the manual. I'll look into it. I have got the boat shop where I bought it from looking into finding a second hand TPS for me. He is a little embarrassed at the fact I told him the DDT says the motor has done more than double the hours he advertised it to me as doing as he went off the analoge gauge. Not real pleased myself but he seams genuine.
 
Sorry Notschy I thought I had already suggested the exhaust tuner but I hadn't! Check the tuner as they fall off on the 2.5 mercs and cause a rich condition, plug fouling and erratic midrange.
 
Thanks for the heads up. The motor isn't really coming up with those probs so will try the TPS with a sea trial and trying to drop the linkage off at WOT and push it to max and see if she'll get up and boogie, as it does reach higher voltages on the DDT (with linkages disconnected) pushed further over. Just need the time and a mate to help. I will go from there after it's not that.

Cheers all for helping!
 
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