I have a 96 Explorer XLT w/ the 4.0, 2WD. In December, the MIL came on and I had code 420, catalyst system below efficiency. I checked for bad connections, changed the O2 sensor behind the cat, etc..., but the MIL kept coming on for a few trips. Then it just stopped coming back on. I didn't think anything of it until recently, when my X started to have a hard time starting after not being driven for a few days. On the first attempt to start, the engine would seem like it was going to start, but then cut out immediately. I'd restart it, and it would sputter to life. Very similar to the first start after changing the fuel filter (no gas). I checked the fuel pressure, and it was good. Scanned for codes, and found a pending code 420 again, but no MIL. Cleared that and figured I'd let the car rest for a few days and then check the fuel pressure in that condition. I was wondering if anyone has figured out what's going on with this code 420, and if it's related to my hard start condition. I thought it might be bad gas too, with the price wars and everything. My fuel economy seems to be linked to this code 420 as well. I was getting 20 MPG in the summer w/o codes, then I had codes and I was getting 18, then it went up briefly/recently to 20 again, and now it's down to 18. This is on a trip from LA to Santa Barbara (about 340 miles round trip, go on the same day/time every occasion), so I don't think the MPG can be explained by driving habits. Unless I was just getting incredible milage at first and 18MPG is more normal.

Thanks for any help!

 

how many miles are on it and when was the last time you put spark plugs in it ?

 

I'm up to 111,000 mi. When I got the truck in August, I did everything--new fuel filter, plugs, plug wires, air filter, trans filter/fluid, coolant flush, new radiator hoses, new thermostat. My policy is to assume that most people don't know what "regular maintainence" is, so I change everything when I get a vehicle. I did notice that one of the ears that holds one of my plug wires securely in the coil pack is stressed, so I'm going to take that in to Kragen's to get it replaced under warranty, but the plug wire seems to be in there pretty good, and I think I'd have bigger problems if it was really loose.

 

Have you ever cleaned the injectors, IAC, and the MAF? All three of them could make it hard for the X to hold an idle...

 

I have an idea, check your throttle plate, right behind it spray solvent on a rag (not in the intake) then wipe right behind it. sometimes oil sludge builds up there from the pcv valve and doesnt allow enough air through the IAC (idle air control). try giving it gas when starting this will increase the air intake of the engine. but wipe around there as a maintience proceedure. Possible that the cams are off, the tensioners are bad on that engine. Thats all I got.

 

maybe you got some bad gas

 

Thanks for the tips, guys! It must have been bad gas, because it hasn't failed to start since I refueled. I'm still going to clean the throttle plate and have my injectors serviced anyway, though. Can't be too careful!