Intermittent misfire problem

I have a Mustang GT 2003. I just took it to a shop to get a series of things done for standard maintenance, 66,000 miles: new brake pads, brake fluid, coolant refill.

I asked them to check out an intermittent sluggishness or rough running while going uphill and during acceleration. Its not terrible and doesn't happen all the time but its annoying.

Previously, I replaced the fuel filter to try to fix the problem. It didn't help at all. The problem has not gotten worse and I've driven this car little over about 1 1/2 years since it started having the problem.

I was told it is likely an ignition coil problem, but because the check engine light is not on it is not going to tell them the cylinder with the problem. Are there other ways to tell which cylinder is the problem? Is it work checking the fuel pressure, replacing the spark plugs or troubleshooting or replacing the MAF?

Any suggestions would be appreciated because I don't know where to continue looking for the intermittent issue.

- Andy

Spark plugs replaced; works fine now

I had the spark plugs replaced. The problem doesn't appear to be there anymore. Because it was intermittent, I'll watch it closely. I did some tests and couldn't recreate the problem under load going up hills.

Thanks for all your advice.

Spark plugs / ignition coil testing

Looks like the spark plug change did it for me. The car runs very smooth now.

By the way, I read the Chilton Repair Manual for 1996-2003 Ford Mustangs. They claim that an ohmmeter or multimeter can be used to check the primary and secondary circuits of an ignition coil. They have resistance figures published in that book and they claim that if the resistance is off by even a little it indicates a problem.

By the way, the procedure for removing and testing coils is different depending on the year of the car and wether its DOHC or SOHC and if it's 6 vs 8 cylinders. They describe the different ways in the book.

I didn't bother trying because it looked a little difficult to actually remove the coils to check the secondary circuit for each one. On the Ford 2003 GT the air intake is in the way of the left 4 and there's also a bracket over each group of 4. Looks like you don't have to remove the coil to test the primary circuit, just unplug the power cable.

Maybe some day in the future I'll get to have fun playing with the ignition coils.