Hi gang, my 97 caravan ES 3.8, 207k miles, is having a little issue. It feels like the engine is mis-firing but no MIL light and no pending codes. I put my Davis CarChip on it and drove to work. The CarChip tells me the fuel system is in "open loop with a system fault. This means the fuel system sees a system fault, so it will not make any adjustments. The fuel system will run as if it was not getting any reports from the other sensors". When I got home I connected my Acton Super Scanner (still no codes) but it did show two RPM fields fluctuating between 747 and 770 at idle. O2 sensor S11 was fluctuating between .08 and .825, O2 sensor S12 was more steady fluctuating between .430 and .510.
I know it's due for new spark plugs and wires, and the fuel pump and fuel filter have never been changed. Any ideas about the engine bucking like it's misfiring?
Thanks,
Party On

 

If you know the plugs need changing, I would start with that. Maybe one fouled out. I'd suggest a full tune up while your at it.

 

You were right dsolorio. I pulled No.1 spark plug and found the electrode completely burned away. I've never had a spark plug this bad before. Went ahead and changed the plugs and wires, fuel pump and fuel filter. It's running great again.

 

That's great to hear, its always best to start with the easy stuff first so you don't end up spending a ton of money and time on something you didn't need to.