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Old 07-21-11, 01:19 PM   #1
twigass
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Default merc 175 overheating

hey guys got a question for you about a 03-04 merc 175hp, 2 weeks ago was fishing a tourn and wouldn't let me get up on plane then started to over heat also had some unburnt fuel coming out of the exhaust ports, when taken to dealer they said nothing wrong maybe a bad plug. fished another tourn sun day did the same thing and missed weigh in took back to the dealer and this time they said it was a map sensor but i am not finding anything with the over heating being related to the map sensor has anyone had this happen to them or know of it happening on anyone else s looking to hear from u nofear and anyone else
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Old 07-21-11, 06:35 PM   #2
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it is used to monitor the vacuum, or lack of vacuum, in the intake manifold area. in the use of forced induction, it is also used to monitor the pressure of air inside the intake manifold. it assists the computer in determining the amount of fuel to add to the air fuel mixture based on engine load and throttle position. if the sensor is bad, it can cause the engine to run too lean,

I stole this from another article online

hope it helps
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Old 07-21-11, 07:08 PM   #3
nobass
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could ba as simple as cloged water port. bad impller on water pump. did they do a compression test. when mind did that head was cracked. i would look at wtaer issues as thats how engine is cooled. hope it something simple.
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Old 07-21-11, 07:52 PM   #4
twigass
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Yes they did a comp. test 125 to 130 on all cylinders the water psi was running at 10 to 11 so maybe they do have It figure with that map sensor I guess I will find out on friday when the part comes in thanks for the input.
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Old 07-21-11, 09:40 PM   #5
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Unless at idle water pressure is low,runs around 8 at idle at speed should be way above 15 psi,mercs can run with as lil as 12 but any turns make it go lower.Set on transom say 4 in deep should be over 20 running.
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Old 07-21-11, 11:20 PM   #6
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id go in the water pump first, especially if its been more than 2 yrs since its been done.
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Old 07-21-11, 11:52 PM   #7
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A bad water pump wouldn't cause the raw fuel coming out of the exhaust. A map sensor would make sense. lean engines run hot.

Last edited by mrmuskie5; 07-22-11 at 11:23 PM.
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Old 07-22-11, 08:33 AM   #8
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Quote:
Originally Posted by Embrey View Post
id go in the water pump first, especially if its been more than 2 yrs since its been done.
At the same time I would also replace the T-Stats.
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Old 07-30-11, 08:56 AM   #9
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Hey Twigass, Not going on plane shouldn't have an effect on over heating unless your motor is laboring too hard trying to do so. From what you discribed it sounds like one or more cylinder isn't firing. I had a similar problem that turned out to be a bad switch box. Number 3 wasn't firing and had a very hard time getting on plane. That would also explane the unburned fuel. It took a dyno test to find the bad box as it tested " ok " with the meter. Hope this helps. Bill
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