2.4 liter coil, plugs and wires help for all
Hello all, I just wanted to post a story on how things finally came together for my 1998 dodge caravan. Brief history, starting summer 2010, developed an intermittant miss, worse when warm, didn't happen often but very annoying without any active or pending codes for months. finally got a code p302 (misfire cyl 2). changed spark plugs and same thing happened. checked resistance of ignition coil, was very close to spec. checked the ohms of all 4 spark plug wires which were all spec (4.2ohms cyl 1 and 4 and 3.2ohms cyl 2 and 3). I figured wires were ok but decided to test anyway by swapping wires of cylinders 2 and 3 and seeing if the code will shift to misfire cyl 3. I cleared the codes and waited several months for the code to finally come up again, came back again as misfire cyl 2. I moved to injector testing, resistance of injectors were identical to each other. shoved fuel injector cleaner with almost every tank for months and got no improvement. past month vehicle was sputtering and popping under acceleration or going uphill. code again misfire #2. sprayed water on the wires at night and looked for arcing, nada. then I had an idea to use an inductive timing light to test rates of firing of sparkplugs. this way I can leave the vehicle running and move from cylinder to cylinder. cyl 1 was for the most part consistant, occasionally missing, cyl 2 was shooting light consistantly machine-gun-like fast, cyl 3 was consistant and cyl 4 was missing quite badly. Ok, swapped wires 1 and 4 and wires 2 and 3 and retested with timing light and got the EXACT same result, cyl 1 was occasionally missing, cyl 2 was shooting consistantly fast, cyl 3 was consistant and cyl 4 was missing quite badly. this then seemed obvious that the coil must be bad if I'm getting the same results with swapping wires. I knew that cyl 1 and 4 fire at the same time and so does cyl 2 and 3 with this waste spark system. I figured I should see the same sparking rate with all cylinders. I bit the bullet and bought a new coil for 80 bucks. put new coil and tried timing light again. no dice. this time I got missing cyl 1, consistant cyl 2, machine gun 3 and machine gun 4. road test immediately got a code for cyl 3 misfire. swapped wires 2 and 3 again and road test got cyl 2 misfire....FINALLY VERIFIED. got new wires and the thing runs like a watch. Moral of the story, don't only go by resistance testing of the wires to determine if they are good, unless it is obvious that one wire is way off. my bad wires tested perfectly with resistance, but that was OFF the vehicle. they were no good when running in the vehicle. I even put my old coil back on with the new wires and it works great. what I can't figure out is why some cylinders have what seems to be double the sparking rate of others. I believe all cyl should be sparking quickly. my original coil has no misses by watching the timing flashes, but cylinder 2 and 4 fire at what seems to be double the rate of cylinders 1 and 3. contrast that to the new coil which has rapid firing cylinders 3 and 4. I don't know why I got the same results during diagnosis when swapping around my old wires, I'm thinking that maybe since the wires of 1 and 4 have to bend the other way when swapping them, maybe I opened up new cracks to short out, but what are the odds of getting consistant bad results like that which point to a coil? (I'm just glad I have a valid reason to return my new coil, it is missing in cyl 1) P.S. check the resistance of new wires in the store before you buy them, you'd be surprised at just how off spec and inconsistant they are with each other.
Last edited by mirageman; 06-08-2011 at 01:57 PM.