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Offline robinson1509

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P0300 random misfire all cylinders
« on: June 26, 2016, 06:33:24 pm »
I just got around to resolving my misfire code. The engine was running as smooth as glass but my cel came on during the winter. I ran a scan and found p0300, and p03xx for all cylinders. After running the vag scan and staring at the blocks looking for the slightest clue to get me going in the right direction I decided to go for the kill and put my spare coil in. A bad coil will usally fail in pair 1-6  3-4  2-5 on the secondary windings but I had to change it to get things rolling. When I got no result with the coil I went to the plugs and wires. I curse the german engineers every time I think about the plugs on the vr. Still misfiring so I get desperate and throw in a maf and a cps. I do a fuel filter and test the fuel pressure, and I pressure test all vac lines. As I eliminate the most likely possibilities my ideas start getting more improbable. I checked my logged scans to find the exact date the cel came on and I noticed it was shortly after I replaced my serpentine belt and tensioner. (I washed my van when it was below zero and water got on the alternator froze it up and popped the belt.) I dropped the pan took off the belt and checked group 110 on the vag and no misfires. Tring to understand what was going on I put the belt back on to do another scan and notice the belt clears the tensioner by a hair. It seems the tensioner was at its limit and allowed belt slippage. I did check the voltage on the vag and with a meter on the alternator and at the battery but the problem occured at high rpm under load.So i replaced the belt with a slightly shorter one and the misfire codes were resolved. This is one of those things you occasionally read about in forums and in the back of your mind you think that does not happen, but when you eliminate the obvious and have tried everything what seems to be improbable becomes less impossible.
« Last Edit: December 19, 2016, 10:42:21 pm by robinson1509 »