Check engine light flashing and engine shake only when the car stop(Idle)

ABUIBRAHIM

MEMBER
2010 MERCURY MARQUIS
4.6L
V8
RWD
AUTOMATIC
100,000 MILES

My previous problem it was misfired on coil 7, as per the code, I changed the coil and about 2 years the check engine light start flashing again, I went to workshop and he said the computer read a code of misfired coil 7
Now, I change the coil 7 again with new one and I inspect and clean all injector's also I change all the 8 spark plug with new one, still the engine light flashing when I am in stop position (idle) and while the light is flashing and engine start shaking for about 3-5 min, then its become stable and engine light remain on the board but not shaking. I did every thing related to coil 7, what I did in period of the last two years it was I change the oil from 20/50 to 20w5 I don't know is that related for my problem? Any advice? This things happen after I leave the car in home for about 10 days without using. Thanks

6 Replies

WRENCHTECH

MECHANIC
20,761 POSTS

It's totally unrelated to your misfire problem but using 20W50 oil in that engine is about the fastest way to destroy it. That engine call for 5W20 and nothing else.

What is the exact code number being set?

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Sunday, November 8th, 2015 AT 5:02 AM

ABUIBRAHIM

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13 POSTS

Thanks for reply the code is P0307

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Sunday, November 8th, 2015 AT 5:06 AM

WRENCHTECH

MECHANIC
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That tells you the computer has sensed a misfire but doesn't tell you what caused it. The first thing you have to determine is whether the misfire is due to lack of spark or lack of fuel, or even something else.

You said you inspected and cleaned all injectors but I don't know how that is even possible.

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Sunday, November 8th, 2015 AT 5:10 AM

ABUIBRAHIM

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Thanks, so what I have to do? The sparks is new and the fuel is octane 95 and I changed also the fuel filter, for your information when the engine start shaking a increase the rpm for 2-3 time and the shake is gone. What I should do more or change, the cylinder 7 compression I checked its was 90 psi

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Sunday, November 8th, 2015 AT 5:15 AM

WRENCHTECH

MECHANIC
20,761 POSTS

Unless you have some electronic test equipment I don't see how you can do any of this testing yourself.
You could remove the coil and put a spark tester on the end of it to test for spark but that's about the extent of what you can try yourself.

By the way, 90 PSI is not very good. You probably should test compression to all cylinders to compare.