Hi, I've seen many advice on issues and I was hoping that maybe y'all could help me in my dilemma. Thanks

Dodge Ram 96'
V8 5.9 360
167k miles

I've always had the check engine light on with no obvious problems and never bothered me till my inspection test came up due. I went to an autozone and got my CEL checked and it was an o2 sensor so I bought it and replaced it.

After I had replaced the sensor, CEL was still on and I figured it would disappear as the PCM reads the new sensor over time. Right after the replacement my truck started to run too rich. The scent of gas was always present and I had noticed that it was eating up too gas. It would take 3 gallons of gas ($13) a day to get to work and back home which was only 10 miles back and forth. I replaced the cat with a magnaflow cat because it had a crack in it. The only problem at this time was the fuel issue.

A week later, I went and took off the o2 sensor and it was covered in black gunk. I got a clean dry rag and just wiped the gunk off. I put it back in and turned on the truck and reved it hard to see if the fuel smell was still present and it wasn't. It wasn't running rich/lean anymore. While I was reving the truck a lot of black smoke came out the exhaust and probably cleared the unburnt fuel leftover in the exhaust.

The current problem now is this... while driving high speeds (40mph) the truck will make a "popping" sound and it sounds like its coming from either the cat or intake gasket I have to let go of the gas pedl and floor it real hard to make it go away and it will try to stall. So I get out of the freeway and take the small streets... the truck will buck and jerk while accelerating and once I get to a stop or slow down... the truck's rpm goes below 500 and sometimes it was just die or rev up on its own but turn back up easily if it dies. As long as I drive the speed limit the truck won't act up, it only acts up if its going at high speeds.

I've been to several mechanic many times and they don't know what the issue is. Before I went to a mechanic, I though I could fix it on my own... I have done a full tuneup... replaced IAC valve, TPS, new timing belt and cleaned the throttle body... one mechanic said it was the fuel filter I went and did the whole fuel pump and fuel filter swap and made no difference... I've noticed a performance gain like faster respond to acceleration, flooring, etc... but I still have the same stalling, jerking issue and its really annoying driving super slow!!!

Sometimes I hear a hissing noise under the hood and I've gone through several cans of carb. Cleaner trying to find a vacuum leak and I just can't...

As of right now I have the CEL on for a high voltage on the upstream o2 sensor.

All this happened after I cleaned the gunk off the o2 sensor... maybe its contaminated? But how could an o2 sensor really cause all these issues :/ I don't get it...

Maybe its the crankshaft sensor? But I had that replaced back in Jan. Although it does have that issues where it sometimes dies when changing the gear to reverse...

Thanks for your time, and id really like some help... I really love this truck and don't want to lose it.... maybe for a new Challenger ......NAH!.... not yet. Lol

 

Have you read the end-all-plenum thread yet? Sounds like you might need to read up on the plenum gasket repair.

 

O2 sensor was covered in oil for a reason as well as the probs you had with the old cat. Def need to read this as this is most likely your problem. https://dodgeforum.com/forum/2nd-gen...um-thread.html

 

So everything leading to the plenum :/ ill probably go tomorrow and get a full diagnostic test done and see everything that is wrong with my truck... would the test show issues with the plenum?

Or should I just go ahead and replace the plenum right away?

 

look down into the tb and see if oil is in the botom of the tb

 

I just looked inside the tb and there is sign of moisture from oil... its not flooded... just moist all around

 

Plenum blown, cat and o2 is no good. And for future reference, like while you replace the plenum or ANY electrical component for that matter, disconnect the negative battery cable before doing any such work.