Misfire after coil and plug and injector replacement

Asked by Jfaff86 Aug 11, 2018 at 08:18 AM about the 2003 Mercury Grand Marquis GS

Question type: Maintenance & Repair

I have a 2003 mercury grand marquis with a 4.6l
engine. It threw a misfire 1 code and misfire 5
code. I replaced the coils and plugs and it's still
misfiring on cylinder. It had perfect compression
and I changed the injector. If you run it for 15 min it
clears up and runs fine then 20 min later it misfired
again. I'm truly stumped.. any suggestions??

4 Answers
30

Tloc answered 5 years ago

I'm having same issue with my 99....6&7 misfire

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20

Guru3VLXL answered 4 years ago

switched to non alcoholic gas 89 octane may need a new coil; but my misfires occur after it rains...seems to cure the problem every time.

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20

Len answered 2 years ago

I have a 2003 Grand Marquis. Got P305, 306, 316. Changed Plugs, coils and Injectors (18 yrs old w/60K ) still miss fires. Reset Check engine light, plugged in scanner, turned Key on and got EGR issues which never came up when light was on. Changed EGR Valve= Problem solved !

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