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1994 Mercury 175 HP EFI Dropping 3 Cylinders

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berrymr

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I have a 1994 Mercury 175 HP EFI outboard that has an intermittent problem where it seems to be dropping 3 cylinders. It is not reliably repeatable. I have taken it to a dealer 3 different times and they cannot get it to act up long enough to find any problem. The symptoms are that it happens when being started, it will accelerate slowly to a plane and run that way for a couple of minutes then it will suddenly kick in on all 6 cylinders and take off. While it is running on 3 cylinders it runs hotter than when it is running on all 6. It does not happen everytime it is started. It does not happen repeatably after sitting for several days of after being run and shut off. It has never dropped to 3 cylinders after running on all 6. Needless to say it idles poorly when it is on 3 cylinders. Compression on all 6 cylinders is good. The fuel system has been replaced. I feel like it has to be an electrical parts issue. Any ideas?
 
berrymr said:
I have a 1994 Mercury 175 HP EFI outboard that has an intermittent problem where it seems to be dropping 3 cylinders. It is not reliably repeatable. I have taken it to a dealer 3 different times and they cannot get it to act up long enough to find any problem. The symptoms are that it happens when being started, it will accelerate slowly to a plane and run that way for a couple of minutes then it will suddenly kick in on all 6 cylinders and take off. While it is running on 3 cylinders it runs hotter than when it is running on all 6. It does not happen everytime it is started. It does not happen repeatably after sitting for several days of after being run and shut off. It has never dropped to 3 cylinders after running on all 6. Needless to say it idles poorly when it is on 3 cylinders. Compression on all 6 cylinders is good. The fuel system has been replaced. I feel like it has to be an electrical parts issue. Any ideas?
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I have the identical problem but it’s not dropping an entire bank. Last time it was doing it it was 2 cylinders on one bank and one on the other. I pulled the plug wires and have spark to all cylinders. Plugs are new this year. Any suggestions?
 
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faztbullet said:
What year? What HP and how did you find it was 2 on one side and one on other?
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1996 175 EFI

I know that it was two and one because I pulled the plug wires while it was running on 3. Could hear which ones dropped and which ones didn’t. But could hear spark jumping to the plug on all 6.

Last night I ran it for about 10 mins and it never ran on 6. It’s usually only a 30 second to 1 min problem. Clears up randomly on its own.
 
Ran it tonight, seemed fine for about a mile and then it dropped cylinders at WOT. It’s never done that before. Issue seems to be getting worse by the day.
 
Stop running it!!! If you have clogged injector those not firing are also not getting oiled! Need to check fuel pressure the send injectors and ECU to Brucato to have cleaned and tested.
 
faztbullet said:
Stop running it!!! If you have clogged injector those not firing are also not getting oiled! Need to check fuel pressure the send injectors and ECU to Brucato to have cleaned and tested.
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The oiling point is such an obvious point that I completely ignored. Thank you for the blunt reminder. :eek: Guess it’s time to take it out of the water and get to pulling parts. Any rough idea of cost for the Brucato services you noted?
 
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