Few months ago, had a miss in cylinder #3 (Bank 1), replaced coil on that cylinder, and it was banished forever.

Soon after, I started to get an intermittent code for P0430 Catalyst System Efficiency Below Threshold Bank 2. Then, all hell broke loose, and I started to get p0305 and p0306, along with misfire so bad that it completely stops acceleration. When at its worst, I get misfire codes for all 4 cylinders in Bank 2.

The misfire is now bad enough that this truck struggles to accelerate at all sometimes, and getting onto the highway is a battle. I've found that taking it out of overdrive seems to help. When the engine is already spinning at 2500 rpm, it's easier to accelerate further, but she always starts popping off anyway, and completely hits a wall at 3500 rpm.

The misfire itself sounds like a Carbureted engine backfiring. I can hear pre ignition events going at the same time. When accelerating from a dead stop, she's usually fine, but other times will immediately start her whole dramatic act, and then run like complete garbage upon returning to idle, and continue to do so until I Rev her in neutral.

Using the live data function on my scanner reveals the Bank 2 cat is definitely not doing anything, but reads the exact same temp as the other cat, which I verified using my laser thermometer. When suffering from the worst of the misfire, both 02 sensors for Bank 2 will read a constant 0.000 while the CEL flashes continuously, and will stay this way until the CEL stops flashing. Then I can resume acceleration until it hits a wall of misfire again.

I'm having a hard time believing that all 4 coils, injectors, or any other components could suddenly fail in quadruplicate, all on the same side of the engine. I was ready to believe a clogged cat, but I've been told again and again that a clogged cat cannot cause misfire. Fuel pressure is a constant 65 psi.

Any ideas? TIA.

 

This sounds like an issue with the electrical feeds to that side of the engine. The top side engine wiring harness leads into another connector which then leads back to the ECM. I would carefully pull that connector apart and inspect it for corroded terminals, perhaps a broken wire or wires somewhere along that path.

If you're still driving the vehicle with this condition I'm sure its possibly damaging other parts too.

 

@ Viceroy454:


I would say your assessment is correct in discounting the possibility of multiple failures (COP's, Injectors) all on one bank. Also the ECU will give very meaningful codes for faults in coil and injector circuits - such as "Primary fault in Coil Circuit 'X'" where 'X' is A thru H for Cyl's 1-8 (Beats me!) And on injectors it will report exactly which one Cyl (1-8) is at fault.


But, given your initial code concerning CAT System Efficiency, and a "FLASHING CEL" (which indicates a condition exists sever enough to cause catalytic converter damage), I disagree with the assessment that it 'cannot cause a misfire'.

Based on your description of the misfire condition sounding like a 'Carbureted backfire', that is exactly what it could be if exhaust back pressure (from a plugged cat) got so severe that the expanded combustion gases can't exit the cylinders - they would try to exit the intake valves during the next intake stroke back into the IM.

Your O2 sensors reading 0.000 during while CEL is flashing makes sense too --- The ECU has removed the positive bias to the O2's because it is going OUT OF CLOSED LOOP on that bank, (and is probably killing the injectors on that bank also) trying to eliminate the cat damaging condition.

I saw a video on YouTube once showing a clever and simple diagnostic procedure to eliminate a "clogged cat" that might applicable for you here.

At the expense of a high level of "strange noise' for a short time, REMOVE the upstream O2 sensor and drive the vehicle around the block. If the exhaust is restricted, you will notice a marked difference in performance. Don't make any judgments based on the noise because you're going to get lots of that either way.


Hope this helps.