2010 Mercury Other engine shaking for some time

2010 MERCURY
113,000 MILES • 4.6L • V8 • RWD • AUTOMATIC
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ABUIBRAHIM
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I have mercury grand marquise 4.6L 2010, the car start flashing the check engine for some time with some shaking in the engine and if I go to the back side there a sound with this shaking like BF BF BF BF , the car looks like sucking the air from the exhaust and push in same time fast in idle while the car stop only,
this issue goes and back to normal if I let the fuel level in the middle 1/2 but if I refill a full tank its back again, I want to know what is the causes for this issue?
I changed the sparks and some coils and I clean and check fuel injectors and I changed also the fuel filter
Dec 16, 2015 at 9:39 AM
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HMAC300
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scan for codes and check fuel pressure with a gauge auto parts rent it.
Dec 16, 2015 at 10:43 AM
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ABUIBRAHIM
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i checked the code and its says coil7 i change it and no change shows up in the engine ,about fuel pressure i dont know whats the way to do that iwill ask about it
thanks
Dec 16, 2015 at 10:49 AM
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HMAC300
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check compression and have coolant system pressure checked for a blown head gasket.
Dec 16, 2015 at 10:51 AM
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ABUIBRAHIM
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i checked the compression its shows 90 psi about coolant system i did not change the coolent fluid since 5 years
Dec 16, 2015 at 10:54 AM
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HMAC300
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compression is to low so it's either a blown head gasket or a valve problem most likely. it should not be lower than 20% of other cylinders.
Dec 16, 2015 at 12:31 PM
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ABUIBRAHIM
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I will do wash and remove sludge from engine might be help, thanks for your help
Dec 16, 2015 at 5:27 PM
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HMAC300
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that won't help if compression is low.
Dec 17, 2015 at 5:22 AM
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ABUIBRAHIM
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So what I should do if the compression is low?

Do you think if the fuel system semi-plug some where is will cause the low compression?
Dec 17, 2015 at 5:26 AM
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HMAC300
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have it properly diagnosed to see if compression is low it may be a burnt valve or head gasket problem. fuel pressure has nothing to do with compression . I have no further comments or suggestions.
Dec 17, 2015 at 6:07 AM