2004 Express 3500 with a 6.0 liter.The engine misfires on cylinders 2, 4, 6 and 8
2004 Express 3500 with a 6.0 liter 100,000 miles. The engine misfires on cylinders 2, 4, 6 and 8 when it gets warm after driving it for a little while and of course the check engine light comes on. If you let the van sit overnight, the problem goes away and it drives fine for a short while until the engine is hot. Our GM mechanic says the engine in running lean, (computer code shows this), but he has no idea why and he has no idea why it is misfiring after the engine is hot. He let the van idle for almost 4 hours plus he drove it several times but could not duplicate the problem, (even though this has happened to us several times and we had to be towed 80 miles home). He also says we have good fuel pressure, at lease while he is observing it.
So far, we have had to replace the cat and the muffler. We believe the cause for the cat failure was due to the engine running lean.
This is so frustrating because we really love this van and use it for towing. We would hate to get rid of it. Any ideas would be grateful.