2003 Grand Marquis problems

[MadMan]

Originally Posted by Adam

I miss having older cars that I understand better.

You hit the nail on the head. You don't understand it, that's all. The crown vics are actually about the most-traditional modern computerized cars. They have their issues like any car, but there's a good reason why they were favored by police and livery for decades, and actually forced Ford to continue making them for 10 or so years past when Ford intended to discontinue them.

Get yourself a cheesy obdII scanner from ebay or amazon for ~$20. Even the cheapest one that won't describe what a code means is fine - just google the code number it gives you. Chances are good that if you have a misfire, which you do, you'll have a code (check engine light is on). The code will either indicate a particular cylinder (then you can focus your efforts on that one only [don't forget that fords are numbered 1234 on one side and 5678 on the other]) -OR- it'll say random/multiple misfire, then it'll be less likely to be one cylinder problem, and more likely a vacuum leak or something like that.

Like Eric said, these coils go bad all the time. And even if you pull a coil out and put a plug in the end of it, hold the plug to ground, and watch it spark while the engine runs, isn't necessarily a good indicator, as coils can stop intermittently, especially once they get hot. Also like he said, oil and antifreeze leaking into the spark plug wells is very common, and typically once the rubber boot is soaked in either, it won't insulate the spark very well, and will cause a misfire. So if you were ignoring that one coil boot that was wet with antifreeze, that's the culprit. If you get a code that indicates a single cylinder misfire, you can switch that coil with another, clear the codes, and try again. When the code comes back, if it's for a different cylinder, the coil is at fault.

Beyond that, vacuum leaks are fairly common. Ford liked to make some of the vacuum hoses out of thin rubber that expires easily and collapses, or thin plastic tubes that crumble or crack. Check all vacuum connections to the intake, especially in the back where it's less obvious, and just look at the integrity of the hoses and tubes. Most commonly, it's the rubber hose that goes to the evap purge valve, it collapses and the vacuum sucks a hole open in it. Though less common, the big rubber intake hose coming from the air filter can also crack, and create a small leak that will be worse under varying conditions. Remove it completely and take a good close look.

Another common issue is that the electrical connectors for the coils AND the injectors have a tendency to have their clasps break, making them able to come loose under the vibration of the engine. Ensure they're all tight. A loose one with a broken clasp can be easily remedied with a pencil-eraser size dab of silicone right into the space where the clasp of the plug broke off. Plug it back in, and when it dries, it will stay in place, but still be easy enough to pull back off for service.

Another thing to note - although it won't cause a misfire - is that this type of air flow meter tends to get dirty and needs to be cleaned once in a while to maintain performance. A can of air flow meter cleaner will help you with that.

Happy hunting!