I have a 2003 GT Mustang.Bought it from a family member and he pressure washed the engine a while back.It now runs like a V7 but no engine lights come on to indicate a bad coil pack or maybe it has a defective fuel injector.Any ideas would be greatly appreciated.The car has at least 140,000 miles on it.

 

Since the problem coincided with pressure washing the engine, pull each coil and look fown in the plugwells for any water that's pooled up. If dry, before reinstalling the coils inspect the rubber boots for any cracks, deterioration or signs of current arcing through (usually a browin-ish dust like substance).

It's possible that one of the coils was damaged due to being run while wet but without a CEL to tell you which one(s) all you can really do is replace all 8, which isn't cheap. If you decide to go that route and don't want to spend $300+ on a new set of oem units (which are the best you can buy), I have had good luck with a set I got off Ebay a few years ago. Seller's name is AIP Electronics, and all 8 were sitting on my doorstep for about $70.

If the engine is washed in the future, invest $40 in an electric leaf blower so that you can dry it all up good before starting it. I wash the engines in all of my vehicles periodically and having that leaf blower around helps a lot.

 

^^^^ this