Cat Converters, O2 Sensors, Weak Acceleration?

[jddrock]

Hello!

I have a 2002 Ford Explorer Eddie Bauer 4x4 with a V8. A few weeks ago I noticed that the acceleration was getting weak and it was running slow. After a couple more weeks it got the place where I couldn't get it to run above 25 mph. The rpms won't go above 3,000 and after a minute normally start capping out at 2,500 even when hitting the accelerator while in park. The engine seemed to run fine while idling but would struggle and then sound like something was limiting it when driving. To get it to shift gears I would have to let off the gas a lot when it reached around 2,000 rpms or it would stay stuck in that gear. The cat converters were all replaced at the start of this year. For the last couple months until just recently I had a P0420 code which I kept erasing because I was pretty sure I was just needing to replace one of my O2 sensors. Both downstream O2 sensors got replaced in the last 6 months or so at different times. The cat converters were knocked on and shaken while cold and I don't hear any crud knocking around in there. Today I took off both downstream O2 sensors and took it for a quick drive. Most of the power was restored to the vehicle when I did that. It seemed to be idling normal, the rpms were freely moving, the engine didn't feel limited, and shifting felt back to normal for the most part. I know that's usually a sign of clogged cats but my cats were clogged before so I had them replaced in January. They're brand new! Is there something more I should be looking into?

Jeremy

 

[shane10]

I had similar symptoms as you're describing on my 02 4.0 on a couple different occasions. On the first occasion the flange nut located right behind the upstream o2 sensor had a leak, causing a very inaccurate reading as air would put in and out rapidly. The second were simply my upstream o2 sensors going bad, unplugging them, and eventually changing them fixed this problem.
Not sure if it's the same on the v8, but downstream sensors on my truck only measure outtake gases, and have no function on air/fuel mixtures, only upstreams do. Try unplugging both upstream o2 sensors and see if that fixes the problem.
Highly doubt it's clogged cats unless some unbelievably cheap ones were used, I still have my factory cats @ 200k no problems.
Good luck
EDIT: CEL on? Any codes?

 

[jddrock]

Thanks for your suggestions! I’ll look into those things. No CEL or codes.

 

[shane10]

Thanks for your suggestions! I’ll look into those things. No CEL or codes.

Strange with your symptoms I'd except a code or 2. Not questioning your knowledge but just to confirm, downstream sensor is behind cat, upstream is before cat, right behind exhaust manifold.
I've also heard a lot of people have problems with any aftermarket o2 sensor besides occasionally Bosch, although a bit more spendy maybe go with motorcraft for these

 

[jddrock]

Strange with your symptoms I'd except a code or 2. Not questioning your knowledge but just to confirm, downstream sensor is behind cat, upstream is before cat, right behind exhaust manifold.
I've also heard a lot of people have problems with any aftermarket o2 sensor besides occasionally Bosch, although a bit more spendy maybe go with motorcraft for these

No worries! Yes sir, downstream is after the cat and upstream is before the cat. I agree! The only code I had for a while was P0420 but even that has yet to reappear.

 

[jddrock]

Also, when you suggested unplugging the upstream sensors are you saying unplug them electrically or actually unscrewing them?

 

[donalds]

Electrically

 

[jddrock]

Electrically

Thanks!

So I put the downstream sensors back on and unplugged the upstream ones and my vehicle seems to be back to normal! The only thing that seems a little off is when the vehicle is shifting. Especially when it gets toward 65 mph and upward I had to back off the gas a good bit to help it shift and continue to speed up. Other than that it feels pretty much back to normal. Could the problem really be as simple as needing to replace my upstream O2 sensors?

 

[donalds]

Yes it's a strong possibility

 

[donalds]

I would replace them just my .2¢

 

[shane10]

I would replace them just my .2¢

2nd that, the first time I experienced o2 symptoms I thought I had a totalled engine on my hands, can really messmess things up. Again I'd suggest motor craft if possible. Good luck