My wifes 2000 MGM has 100,000 miles and idles like a dream. It runs great until you get to about 55 or 60 mph then SOMETIMES it will miss for about 2 or 3 seconds, then it runs fine. It is very inconsistant. Sometimes it will go for a week without doing it. I wish the thing would throw a code in the computer but that has not happened. Could this be a coil pack going out? If so does anyone know how to "bench test" one?
Thanks,
Chuck

 

check that the wires are all secure on the plugs and coils. If the plugs have never been changed, it may be time to change them.

 

Chances are you have a coil on it's way out... Since it is something so intermittent it may be a bear to track down which one it is for sure.

Ford didn;t really specify any bench tests for these.. AS a rough guide the primary side (where the two wires plug on at the top) should be between .5 and 1.5 ohms.. THe seconday side should be 5,000 to 10,000 ohms.. Check this between one of the primary pins and the electrode to the spark plug.. You want to chack that one on both of the smaller pins to the elctrode separatly.... The hotter the coil is the higher the resistance will be..

The other way to check these which is a bit more exacting would be with an oscilloscope, unfortunatley very few have a scope that have the proper inductive pickup for coil over plug ignitions... Someday I will have one of these..

A good starting place, though, would be spark plugs.. 100K is about the life of them.. (Sadly that seems to be when these coils start going too) At the saem time you can inspect the boots of the coils. Look for signs of moisture or oil down in the spark plug holes...

Once again unfortunatly there isn;t really any great diagnosis for this problem. At this point I've had the best luck either waiting for the coil to completely quit or get worse, or else buying one new coil and switching it around till the culprit is found...

Just by chance though some other things that can cause a similar feeling problem are an egr valve that is opening too far, a shuddering torque converter, and bad gas (seems to be alot of that lately)... You may need to do some mroe investigating into this problem as far as weather conditions, temperature, driving conditions, and where you buy gas..

I must say this particular ailment has been on of the absolute biggest hair pullers I get in the shop.. They eitehr never act up for me, or do it so beifely that one can;t catch what is going on on a scan tool...