Check Engine Light On


Asked by Jun 20, 2016 at 09:47 PM about the 1999 Mercury Grand Marquis 4 Dr GS Sedan

Question type: Maintenance & Repair

I have a 1999 Grand Marquis. My check engine light is on and it says it is a
cylinder 6 misfire according to autozone machine. I have replaced the
spark plug, and properly gapped the spark plug cause the one I pulled out
wasn't. I have replaced them all and properly gapped them. I put a new coil
on cylinder 5 because it was broken and not on all the way either. I have
replaced fuel filter as well. I have put fuel injector cleaner in it as well. What
else can it be?

6 Answers


P0306 MERCURY - Cylinder 6 Misfire Detected - Possible causes - Faulty spark plug 6 - Clogged or faulty fuel injector 6 - Faulty ignition coil 6 - Fuel injector 6 harness is open or shorted - Fuel injector 6 circuit poor electrical connection - Ignition coil 6 harness is open or shorted - Ignition coil 6 circuit poor electrical connection - Insufficient cylinder 6 compression - Incorrect fuel pressure - Intake air leak

2 people found this helpful.

well I think I found the problem when replacing the spark plugs there was oil in one cylinder and antifreeze came out of another. Is this a busted head?


Cracked head or head gasket. No easy solution. No matter what, it needs to be torn apart and checked, (magna fluxed) for a cracked head, and possible shaved for flatness. Sounds like this engine had gotten hot in order for this to do this, as it looks like the heads, and possibly the block are aluminum. Depending on what you want to do with the car your looking at around $3000 for a re-manufactured engine, plus labor. Depending on the condition of the cam shafts, and how many miles are on this thing, a re-manufactured head is around $500. These prices are from a warehouse I use in CA. so depending on where you live, this could be more.

1 people found this helpful.

Thanks that's what I was thinking as well. I did see where the intake hoses can leak into the cylinder and I did a leak on a hose. i have clamped that and since then and replacing all spark plugs and properly gapping them the check engine light has gone off. There is no more skipping and jumping and losing power going up hills. I hope it's not the heads but will a professional mechanic look at it. Thanks for your help.

1 people found this helpful.

I have a 2005 Mercury Grand Marquis check engine light on what does it mean

9 people found this helpful.

Check the plastic manifold it may be cracked due to high heat/ wrong coolant whatever. It will leak causing misfires not that hard to change.

1 people found this helpful.

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