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Posting a reply to: RE: 99 Mercury 175 EFI lost power

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[QUOTE]Mark H. - 8/18/2009  1:10 PM

Your compression is within Merc Spec.  They prefer no more than 10 PSI difference between all 6 holes but 15 is spec.  The one I have now is 105-118.  It's when they read 25 that you have a serious issue :(   (Been there once)

You can call Merc and they should be able to tell you what spec is for fuel pressure.  I do know that the high pressure fuel pump (Big silver thing on the front Port-side of the motor) suspect you know this being a mechanic, is something that can cause the issue you are having.

Most issues with the larger EFI's revolve around.

1. People not changing their water pump impellor like they should.
2. Not letting that motor warm up before putting the throttle down to bring the boat up on plane.  There are two thermostats in that motor, one at the top if each cylinder head,  when that motor is warmed up it will start to pee out the indicator hole.  Recommend not hammering down until then.   Yes, that means you have to wait an additional 2-3 minutes before heading off to the next spot.
2-B.   Not running a anti-carbon deposit additive in your fuel.  This is HUGE, I'll repeat HUGE with EFI's and today's fuels.  One ounce of Merc's Quick-Klean per 6 gallons of gas.   Every time you add fuel.  Sea foam is NOT the same thing, it's a great product, (I know I ran it through our old dirt-track race motors) but it is not the same as Quick-Klean or Yamaha's Ring-Free.  Keep the carbon deposits from building up behind the piston rings (i.e. no stuck/cracked rings) and the motor should not "blow" on you.
3. Some of them had charging system issues.  I had one unit that the stator went out in and the same unit had a faulty voltage regulator (there are two of these) that was letting too much through.  However this boat was tournament walleye boat before I bought it and I suspect the charging system was being over-taxed on a regular basis.  One needs to consider what they hook to the starting battery and then ask the stator to keep up with it!
3. I have found the EFI's to run superior on sythetic oil such as Amsoil or by using the semi-synthetics such as Merc's Optimax oil or one of the other premium brands.  Much less smoke, much smoother through the power-band, much cleaner.  Inside of my props were spotless when using synthetic oils, no carbon deposits building up at all.
4. There is an oil pump drive gear in EFI's.  It is a brass gear and my mechanic told me he has seen a few of those fail but not common.  I remove mine and inspect it annually just to make sure it's in good shape.

1. Fuel Additive
2. Let it warm up before putting it down.
3. Change impellor annually or bi-annually on the outside.
4. Regular maintenance to plugs, fuel filters.
5. Synthetic oil.
6. Enjoy years of trouble-free performance.

Good luck.   Will be interested to see what you find.[/QUOTE]

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Mark H.

Posted 8/18/2009 1:10 PM (#394701 - in reply to #394376)
Subject: RE: 99 Mercury 175 EFI lost power

Your compression is within Merc Spec. They prefer no more than 10 PSI difference between all 6 holes but 15 is spec. The one I have now is 105-118. It's when they read 25 that you have a serious issue

(Been there once)

You can call Merc and they should be able to tell you what spec is for fuel pressure. I do know that the high pressure fuel pump (Big silver thing on the front Port-side of the motor) suspect you know this being a mechanic, is something that can cause the issue you are having.

Most issues with the larger EFI's revolve around.

1. People not changing their water pump impellor like they should.
2. Not letting that motor warm up before putting the throttle down to bring the boat up on plane. There are two thermostats in that motor, one at the top if each cylinder head, when that motor is warmed up it will start to pee out the indicator hole. Recommend not hammering down until then. Yes, that means you have to wait an additional 2-3 minutes before heading off to the next spot.
2-B. Not running a anti-carbon deposit additive in your fuel. This is HUGE, I'll repeat HUGE with EFI's and today's fuels. One ounce of Merc's Quick-Klean per 6 gallons of gas. Every time you add fuel. Sea foam is NOT the same thing, it's a great product, (I know I ran it through our old dirt-track race motors) but it is not the same as Quick-Klean or Yamaha's Ring-Free. Keep the carbon deposits from building up behind the piston rings (i.e. no stuck/cracked rings) and the motor should not "blow" on you.
3. Some of them had charging system issues. I had one unit that the stator went out in and the same unit had a faulty voltage regulator (there are two of these) that was letting too much through. However this boat was tournament walleye boat before I bought it and I suspect the charging system was being over-taxed on a regular basis. One needs to consider what they hook to the starting battery and then ask the stator to keep up with it!
3. I have found the EFI's to run superior on sythetic oil such as Amsoil or by using the semi-synthetics such as Merc's Optimax oil or one of the other premium brands. Much less smoke, much smoother through the power-band, much cleaner. Inside of my props were spotless when using synthetic oils, no carbon deposits building up at all.
4. There is an oil pump drive gear in EFI's. It is a brass gear and my mechanic told me he has seen a few of those fail but not common. I remove mine and inspect it annually just to make sure it's in good shape.

1. Fuel Additive
2. Let it warm up before putting it down.
3. Change impellor annually or bi-annually on the outside.
4. Regular maintenance to plugs, fuel filters.
5. Synthetic oil.
6. Enjoy years of trouble-free performance.

Good luck. Will be interested to see what you find.