I noticed an engine miss unload last Friday, so Sunday I changed the plugs and checked resistence (primary and secondary) on the coils. All the coils checked out ok, but the #4 plug didn't look as good as the rest of them. Anyway, I didn't find anything to be an obvious problem, which bothered me, so I decided to put some more miles on it and see what happened. The next day, I left the house and the engine felt fine. In fact, it felt fine and didn't miss for nearly 30 miles of driving before the miss (under load) returned. The check engine light flashed for 3 cycles then I drove to Autozone to pull the codes. The codes where P0300 (multiple misfire) and P0304 (misfire on #4). That evening I swapped the #1 and #4 COPs. I figured that I would put some more miles on it and when the check engine light returned, I'd have the codes pulled again. If the misfire was still on #4 then the problem was the injector. If the misfire was on #1, then the problem was the COP. The next day, I left the house again and the engine ran fine...like normal. After about 20-30 miles, it started missing again and the check engine light flashed again,but only 1 cycle this time. I pull into Autozone to have the codes pulled but the same code reader used before now said there were no codes. I explained to the autozone guy that the light just flashed but again he told me there are no codes to be found so I went home and did nothing. I figured that I needed to drive it more and get the check engine light to flash again. The next day, I left the house and like before the engine ran great, then after about 20-30 miles it started acting up and the check engine light flashed again. Again, I went to Autozone to pull the codes but again there was nothing found. I called a service/mechanic shop about this and they told me they could do a level 6 scan which would run about $119.00, but I figured that if the problem could only be the plug, injector, or COP and boot, I could replace the injector andCOP and boot cheaper. However, I realize this is a gamble. I was wondering though if the computer would detect a bad injector causing a misfire and that is why the Autozone scanner says there are no codes to be found.

Any thoughts and/or help is very appreciated. This is my wifes vehicle and she on my ars to get it fixed...as cheap as possible. My current plan is to roll the dice and replace the injector first.

thanks.

Rob

 

Do a search for several recent threads, all dealing with 98 expedition misfire conditions. It sounds like you have one additional bad coil pack and the cheapest way out might be to replace one coil pack with a new one, drive the vehicle and if it is not any better, take the coil pack you just removed and swap it with the next xoil pack. Eventually you will find the problem. I recently explained how I got the codes with a scanner on one of those threads.

 

Ford's OBD II will not pick up a COP that has not failed "hard"....I mean it needs a almost if not complete failure to give a code. You may have had one totally failed COP on #4 and #1 and a slow dying one somewhere else that has not "hard" signalled.
You may have to change the plugs on these also, plug fouling is not uncommon on a failed COP.
Also, don't be surprised if its a O2 sensor either or a clogging IAC valve. Check your connections to be sure they are locked down and don't forget the vacuum lines, one could be cracked.