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Chris (aka- Moose)
Chris (aka- Moose), Mercury Technician
Category: Mercury
Satisfied Customers: 1913
Experience:  16 years experience with Mercury
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My 1994 Mercury Grand Marquis missfires A LOT!!!!!. The CHECK

Customer Question

My 1994 Mercury Grand Marquis missfires A LOT!!!!!. The CHECK ENGINE light comes on after driving it about 1-2 miles and stays on. This repeats each time the car is started and driven. This has been going on for last 20,000 miles. The spark plugs show NO issues and are clean (white in color).Just replaced the fuel filter (along the frame) and NO improvement. The car has several "issues" none of which are severe enough to cease driving it safely but with its age and number of miles on it etc. it likely is NOT worth putting a lot of money into it and since I am retired and on a LOW fixed income I just don't have the funds to "throw at it" and not get it solved. I added TWO cans of Sea Foam injector/engine treatment in 1/2 tank of gas to no avail. It seems to missfire less and have more power when I "soft pedal" the accelerator slightly If I have it checked with those hand held diagnostic testers will it detect exactly what the problem(s) is/are? Help!!
Submitted: 1 year ago via CarComplaints.com.
Category: Mercury
Expert:  Vladgmru replied 1 year ago.
Hello and welcome to JustAnswer.My name is ***** ***** years 4.6L engine are known for ignition wires problems. Ford has changed design several times.If you never replaced ignition wires, it is worth to do it. What usually happens is an ignition wire could allow spark occurring within spark plug well before it reaches the spark plug. It usually happens under load, like when you accelerate etc. It would be really handy to know what trouble code it sets as you mentioned about the check engine light.I can guess it could be related to EGR system or O2 sensor ( very common issues for this model). Anyway, these problems would not likely cause engine misfiring.Another thing I would like to mention is a vacuum leak, inspect PCV and other vacuum hoses for any leaks.
Expert:  Vladgmru replied 1 year ago.
Hello and welcome to JustAnswer.My name is ***** ***** years 4.6L engine are known for ignition wires problems. Ford has changed design several times.If you never replaced ignition wires, it is worth to do it. What usually happens is an ignition wire could allow spark occurring within spark plug well before it reaches the spark plug. It usually happens under load, like when you accelerate etc. It would be really handy to know what trouble code it sets as you mentioned about the check engine light.I can guess it could be related to EGR system or O2 sensor ( very common issues for this model). Anyway, these problems would not likely cause engine misfiring.Another thing I would like to mention is a vacuum leak, inspect PCV and other vacuum hoses for any leaks.

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