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.
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Last edited by mirageman; 06-08-2011 at 12:57 PM..
Just an FYI and you may have figured this out, but the resisitance can check out OK but it was probably the insulation of the wire that developed tiny cracks in them and thus some "leakage" of the spark. While the "night and spray water" test may have failed or you just could not see the glow, bad insulation on wires can cause problems that can cause you to chase your tale.
My two cents is start with the simple stuff first(as you found out, this is for others), ignition problems start with the plugs and wires, probably the cheapest thing that could cause problems.
yeah, I was running around in circles on this one and was glad to post to help anyone else who may come across a similar issue. anyone else perplexed as to why the coil seems to fire at double the rate on only two cylinders? both old and new coil did this but with different cylinders new coil was BWD brand made in china, not oem...but the question remains. As I understand it, one coil in this pack fires both cylinders 1 and 4 simultaneously (cyl 1 on power stroke and cyl 4 on exhaust wasted spark) and the other coil of the pack likewise fires on cylinders 2 and 3 simultaneously. If this is true, I would imagine that every wire would fire twice as fast as any vehicle with a regular distributor but that doesn't seem to be the case. maybe an electrical pro here can chime in on this one
Last edited by mirageman; 06-09-2011 at 09:32 AM..
Mirageman, Thanks for posting this. You may have saved me God only knows how much mney and headache. I'm having a misfire on #2 that only happens after driving til warm/hot and parking (with closed hood) and then restarting. Already replaced plugs, cap and button, but wires tested ok, so I was about to start replacing sensors and EGR. Think I'll take another look at the wires. Which seemed like the most likely culprit to begin with, but I trusted my meter and skipped over them. Wish me luck! I'll let yall know what happens.
Decided to swap 2 and 4 for the trip to buy wires to see if misfire would move with wire# 2. It went away. But it came back to #2 later after it got hotter. Skipped wires again. (got a set in van just in case, just hate to waste that $30. Cleaned contacts on Distributor,CTS, injector 2, and then the wiring harness connector to injectors. It was BAD! Also replaced PCV and cleaned hose, extremely clogged. Then cleaned Throttle Body just for good measure. Still don't think I got it. Only tomorrow's heat will tell. Starting to look like rad fan relay...