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Ron Z.
Ron Z., - Mercury Tech -
Category: Mercury
Satisfied Customers: 18863
Experience:  18+yrs experience. State Inspector and Mercury Diagnostics
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I have 2004 grand marquis ls 4.6l. I have changed its all

Customer Question

I have 2004 grand marquis ls 4.6l. I have changed its all coils, spark plugs and even cleaned the injectors. still its engine is misfiring
Submitted: 1 year ago.
Category: Mercury
Expert:  Ron Z. replied 1 year ago.

If you are sure the spark plugs are gapped correctly and the coils are all firing correctly, then the next thing to check for is intake air leaks. With the engine running, carefully and sparingly spray some throttle cleaner around the base of the intake. If the engine responds, this is a sign of a leak and the intake gasket will need to be replaced (make sure to visual inspect the manifold itself for any cracks at this time as well). If the intake leak test proves no leaks, then the injectors will need to be tested. With the engine running, remove the electrical connector to one injector at a time. The engine should respond with a worse idle. If not, inspect the electrical connector and wire harness to the injector for any loose, broken or damaged wires. If the visual inspection checks ok, injector pulse should be checked with the use of a noid light. If the inspections check ok, the injector will need to be replaced. If all of the injectors appear to be firing correctly, then a cylinder compression test will need to be done. If my answer has helped you, please help me by leaving a rating using the stars at the top of this page or accept the answer so I may be credited. If you cannot rate or do not see the rating stars, please let me know. You can ask follow-up questions after you rate.

Expert:  Ron Z. replied 1 year ago.


Expert:  Ron Z. replied 1 year ago.

Hi! I noticed this thread was still open, so I thought I'd check in with you and see how you were making out? Was there anything else I could do for you in reference to this issue? Did you have any other questions?