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Sun Sep 12, 2010 9:14 am

91 Automatic

Scenario:
Drove to work at 1:30 PM and she ran just fine. No indications that anything was wrong. Weather is cool and dry. Take her out for dinner break at 4:00, again runs fine.

FYI It does rain later while at work, but not a heavy rain nor very long.

Leave work at 9:00 PM and she seems to start up Ok. Let it idle for a minute or two before driving off. Pull out onto the main road (35 mph) and it seems way down on power and the tach just falls off at 2000 rpm. Totally caught by surprise, so I start working the throttle thinking it's going to die. Nurse it into a parking lot and I can now tell it is misfiring badly. It does remain running at idle, so I figure I can nurse it home on the back residential roads and I have less that a mile to go. A few time I can get the RPM up by being heavy on the gas, but it always falls off flat and feels like it's dying. Coasting I can hear it backfiring. Make it home and I can smell raw fuel in the exhaust (no Cat to worry about). Go inside shaking my head wondering if it's just moisture related.

Went out this morning to dig into diagnostic time. Thing is, she starts up normally and now runs fine. This again makes me wonder about moisture, but it wasn't a hard rain and I never even drove in it. The Van just sat there.

Any ideas if this was a fluke event, or is this a sign of a new issue cropping up? Could the ECU just of been confused? I wish I had thought to try shutting it down last night when it was missing and then restarting it, but I was afraid it wouldn't make it home.

Sun Sep 12, 2010 9:42 am

Your symptoms me think to check the temp II and oxygen sensors, or OXS wiring. Of course if your problem is intermittent that makes it harder to diagnose!

Sun Sep 12, 2010 9:49 am

O2 sensor is brand new and the wires are perfect.

I don't think a bad O2 or Temp sensor would produce such a bad misfire. Just make it run very rich.

The cap and distributor also looked bone dry this morning.

What happens if the flapper in the airbox/meter hangs up? I drove the van one time last year after forgetting to reconnect the airbox electric plug, and it exhibited a similar loss of power, but not a misfire.