Misfires and catalytic converter

[valley_man0505]

The vehicle in question here is a 96 Explorer 4.0 and it is being driven by my ex-wife, so I am working on limited information here. After first buying the vehicle used a year and a half ago, CEL came on after 2 weeks. Dealership replaced O2 sensors and 1 catalytic converter and problem went away...briefly. After that, they were unwilling to help since it bad more than 30 days. Since that time, the CEL has periodically come on due to a cylinder misfire--nearly always cylinder 3, but one occasion of a different cylinder (don't remember which one). Also, CEL codes periodically came up that say the catalytic converter needs to be replaced. That is what she tells me they told her at Autozone but I have yet to get a hold of the actual code (maybe Autozone is interpreting a code as being caused by the cat and it could actually be a O2 sensor or something like that).

Yesterday, it got to the point where the truck barely runs and is ready to die. It idles very rough immediately after starting and sometimes dies. I don't think that is related to the cat since it happens so soon after start. It used to go away after warming up, but now it does all the time--even going 70 down the highway (could speed up past 70 yesterday, though). She had the code checked again and it is something with the cat again (damn, i just wish she'd give me the actual code!). How do I attack this? It appears that maybe a lean condition (did get a lean code once with one of the misfires) caused one of the cats to go bad. Which is the more immediate problem since she can only do one at a time for financial reasons (and not even sure if she can do one). Do I go after the lean condition first or the cat. If the lean condition is causing the cat to go bad, I know it will just happen again if I replace that without fixes the lean condition, but I need to get it running now and then work on the rest over the next few weeks. Any suggestions?

 

[valley_man0505]

oh, more info: the problem started last summer, then went away over the winter--now, it got really bad again that it started getting warm outside. Not sure it this is a coincidence or not--I would find it hard to believe that the outside temp could affect much since the engine temps do not change.

 

[yogi_pahl]

First you need to have the cylinder misfire looked and fixed or you will just keep messing up the cat and o2 also. What happens is the raw unbent gas goes throw the exhaust and will burn up the cat. Maybe unplug both o2 and see if that helps, Check to see if you are getting spark to all the plug wires and they are in the right order. Not to sure about the 96 4.0 but on my 99 4.0 the plug wires snake there way around and looks ez to mess up the order. Im new to the exploder but hope this in some way helped.

edit... I know on some cars if the cat goes out the car will run leaner to help with the emmisons but if ur car is misfireing the cat will not effect that need to have that checked

 

[valley_man0505]

thanks for the response yogi. the first thing I did last summer when the misfire condition first showed up was a complete tune up which included replacing all plugs and wires, but that didn't help. I also seafoamed things just in case (hoping some of it would find its way to the egr valve just in case). now, i am leaning towards something around the fuel injector causing the misfires (maybe the one instance where a different cylinder misfired was a fluke).

 

[yogi_pahl]

When it come to engines there could be a lot of thing wrong. Just start from the basics spark air and gas. Since you said you did a tune up with plugs and wires and it didn't help. Did you try the coil pack pull the wire from each plug and see how good of a spark you get. Since it is the EZ thing to do then move on to the gas and the injectors. Im Not by no means a tech in any way so if im wrong some one point it out i hat to give bad info.

 

[ThePhoenix]

did you try the fuel filter?

 

[99sportisme]

my truck did the same thing right after i bought it cuz the dealer washed the engine and got water or whatever into the spark plug wire boots. changed the plugs and wires and made sure i had lots of that electrode gel stuff in between the plugs and wires and everything works pretty good.

 

[RedEB]

I feel your pain, I just went through a nasty misfire incident myself. What type of wires are you using? Also, MAKE SURE that all of the spark plugs are not defective, one my plugs came defective from the factory...and the one I replaced it with was likewise defective (same box...doh!). So double check that. Also, check the fuel pressure, though it is odd that the misfire is only cylinder #3. I know that #3 wire is near the exhaust, it is possible that it is in such close proximity that it is being burned right through...
Other than that, (and besides all of the good ideas above) I'm not sure what it could be.
Best of luck,
Greg