Thedunzelmon

My 2004 Mustang GT has been a victim of a very strange misfire problem since late July. It began when the car was 80 percent of the way during my travels to Mustang week from New Jersey. It only happened once on the way down (670 miles) and once on the way home. Weeks after I got home it started to happen every time I drove the car. Which then and now is once a week the most. I changed out spark plugs and Coils on plugs and thought I had the issue under control.. for about 2 and a half months and it began to happen again. Not as frequent but the problem was still there. To this point everytime it has happened it isn't at idle, or under load. I find it popping up while cruising at highway speeds or just cruising in general. No specific speed either just anywhere from 50-90 mph. The service light will begin to flash, there is a noticeable change in the tone of the motor and anywhere from 10-30 seconds later it stops and it'll running fine. I recently scanned the codes and I had a random misfire code, as well as misfire codes for cylinders 1, 3, 4, 5, and 6. The car is pretty much full bolt ons with comp 262 camshafts full exhaust cold air intake bigger throttle body and throttle plenum. Car has had an MPT tune on it for the last half year. Just changed back to my brenspeed tune (never had an issue with misfires with the car tuned by brenspeed) just to see if it's a tune related issue but I don't think this is the case. If anyone has any pointers or have had a similar problem please help a brother out. I think I'm going to start by testing o2 sensors and fuel injectors. Thanks in advance!

Derf00

What brand of coils did you buy? Ford or some off brand from e-bay/amazon? Off brands tend to have really poor quality so they are a gamble at best and can fail pretty quickly. Even some of the name brand coils have issues (accel, demon coils, etc). In the end Ford made their coils and throttle bodies pretty bullet proof. Best to stick with OEM for those components when possible.

Thedunzelmon

I had MSD blasters on the car when the car first started misfiring. Then I ordered motorcraft oem coil on plugs. Still have the issue. I haven't had a chance to take the car for a ride with the brenspeed tune back on the car I'll be able to tomorrow. I've read horror stories saying o2 extensions (since I have long tubes) can throw the readings off from the o2 sensors.. but I don't think it would be so bad as to provoke a very random misfire. It doesn't have a vacuum leak the car idles normally. The misfire seems too random jumping from one cylinder to the next to be a fuel injectors issue. Maybe a fuel pump issue?