[cclay6482]

Have a 99 Tahoe 2wd, approximately 140,000 miles. Bought it at around 80,000 miles. Since I've had it, had intermittant problems where it would not start in the morning. The issue seemed random, the only potential common thread was it seemed to happen most often on rainy/humid days. After it sat for 20-30 minutes, it would start up like nothing ever happened. Over time, I've replaced the mass air flow sensor, ignition module, distributor cap/rotor, plugs, and wires. Recently, I discovered that during these no-start periods, if I removed the fuel pump relay and cranked it for a bit, it would start up immediately. By the way, I've also experienced the #5 cylinder misfire issue that I've seen in several forums.

About a week ago, we had a pretty significant ice storm, and the Tahoe sat in the driveway while we drove the 4wd truck. Yesterday, I went to start it, and had zero luck. Turns over, but will not start. In addition, it's wanting to ignite cylinders out of sequence - it will crank ok for a bit, then hesitate or stop due to what seems like ignition occurring before TDC. I pulled the distributor cap off and dried it out, but it didn't help. Fuel pump hits 60 psi immediately after the key is turned on, but it does drop down to almost zero shortly thereafter (with the key still on; not sure if this is what it's supposed to do). By the way, I also have replaced the fuel pressure regulator.

I'm thinking at this point it may be the crankshaft or cam position sensor. I would like to pinpoint the problem so I don't waste any more time or money on problem. Any ideas would be greatly appreciated.