So my cat was clogged up last weekend causing my truck to not run at all, I got it removed and a new peice of pipe installed but ever since then my milage has dropped dramatically, I was getting around 600-650 km per tank, now I'm lucky to get 300-350 km's


I changed my plugs last night to see if that would help any, the old plugs that came out looked relatively new but were completley black and covered in what looked like carbon build up-which I am assuming is from the clogged cat. My milage doesn't seem to have gotten any better with the new plugs, I figure my front O2 sensor is probably in just about as bad a shape as my plugs were, what else should I be trying to replace/clean to get my mialge back up to what it was?

 

Your plenum gasket is blown, period! Do a search on here and you will find all you need to know about it.

 

replace front 02.

 

I noticed that when I was searching on here, I thought that hot back pressure may have blown it out

Is there a quick way to check if its fooked without having to tear into it? I am still working out of town and I won't be able to fix it for a week or so (when I get home and have access to all my tools)


I also will change the o2 sensor next time I get a chance

 

i don't think clogged cats cause plenum leak.
other way around - plenum leak contributes to clogged cat.

 

As Zman17 said do a search for gasket info.... tips and troubleshooting info.
Before you replace that cat, are you showing any codes? Could help determine why cat failed...

 

Ya I just did a search on the plenum gasket replacement, seems like a bit of work to do....not too bad though

I have only had the truck for a couple of weeks, it had a check engine light that would come on every so often when I first got it.......obviously it is on all the time now as I don't have a catalitic converter. If the plenum gasket was blown before I removed my cat wouldn't I have had poor milage to begin with? Thats why I was wondering if the clogged cat could have caused it, or at least made the problem worse and caused my milage to drop so dramatically

 

Check the plenum. And do it by removing the TB and looking with a flashlight and mirror. I am in the middle of installing the Hughes plate I have had laying around, I thought mine was good going by the TSB, well, I was wrong! The TSB check is a worthless waste of time. I started about an hour and a half ago , and now I'm looking at an intake manifold full off oil that didn't show up by looking down the TB or the TSB check.

 

I will check it next time I am home, seems like that and bad o2 sensors are probably the cause of the poor milage. Is there anything else people know of that could cause me to have such a dramatic milage drop?

 

Well I pulled one of the spark plugs I installed yesterday for the hell of it, and its completly covered in black **** now too after only one day. Do you guys figure that is residue from the exhaust problem or a very leaky intake gasket?