Expert: Robert Summers - 5/16/2008

Question
has a miss fire code randoom po300 and then has a code for miss fire on  cylinders 1 3 5 7 i did compression check all where 125 the truck still runs but poor has power to coil and ground there is a triger wire but dont understand how to check it , i sent it to a dealer and they told me to replace engine so i have it back at my shop now , and the injectors have a pule to them , iam lost thanks

Answer
Hi Chris.... do you have a scan tool with a lab scope... if you can get one try using lab scope on the ign system and see if you have any shorts to ground in the system. they could be very small but if you look at the patterns on the scope and compare them with ones you can get on the internet that show good patterns. replace anything that shows a pattern that doesn't match a good pattern. i know that this sounds complicated but anyone that knows how to use lab scope will understand what i mean...the most common cause of that misfire is the cap and rotor as they are a known problem providing this is not a distributorless engine.... hope this helps