ok so ive been doing alot of work on my blazer lately. has over 200k miles, but recently. when i it gets to a certain point of running(warmed up). if i step on the gas it will kinda act like a random missfire, power drops off and feels like im pulling a trailer all the sudden. also will give me a random knock sound when trying to accelereate. only in drive. also oil pressure guage will bounce a little ive noticed. looking for ideas. alot of the motor sensors have been replaced, also have rebuild throttle body, and top end. when i first start her up tho. she sounds amazing. sounds like a good running motor. I do have a exhaust leak at drive side flange. i broke a bolt and have been working on getting screw piece out of exhaust mainfold. not sure if that could be cause these issues or not. also egr valve control solenoid feedback tube broke, repaired and broke again, the egr valve control solenoid is also 1 of the few remaining things that hasnt been replaced but is about to be. just waiting for it to be delievered. as for codes that it shows,. 42, 43, 54. code 43 has been an ongoing issue since right before top end rebuild.sensor has been replaced twice, connector for sensor has been replaced. code 42 is more recent, and 54 is real recent, egr valve is new, like i said the control solenoid is on its way. hopefully that will get ride of code 54. So my question mostly is what is the likelyhood that the loss of power and werid drive caracterist are related to either exhaust leak or egr valve control solenoid being the cause? or is there somewhere else i should be looking for an answer to why my truck is barely driveable at this point in time.? hopefully someone has the answer to my problems or knows enough to point me to the right direction. thanks

 

Mine was doing pretty much the same thing when my cat was clogged up.

 

I replaced the distributor cap and rotor, replaced cat converter, and now runs like brand new.