P0300 And P0420 Codes - No Spark Drivers Side

mattpopovich · July 6, 2011

I have a 2000 silverado LS, 5.3, 2WD, 103,000 miles and it recently started running very poorly. It had not had a tune up so I started by changing plugs, wires, fuel filter, cleaned air filter, etc... None of that made any difference and it had thrown a code so I checked and the two that came up were P0300 - Random Multiple Misfire Detected and P0420 - Catalyst Performance Below Threshold (Bank 2). It starts and idles just fine (a little rough, but not bad), but when you accelerate it has no power and above 1500 rpm it really struggles and cannot go above 3500 rpm while driving. I hooked an inductive timing light to each of the plug wires and found that at idle there were slight misses that got worse up to about 1500 rpm at which point every cylinder on the left (drivers) side quits firing. I started checking on the right side because the P0420 code says bank 2 and I thought, correct me if I am wrong, that the odds were on the drivers side and the evens were on the passenger side. When I found no problems on the right I was a little confused and went to the left and bingo - no spark. Has anyone had this happen or know where to look? I have seen various things like swap the O2 sensors and see if the problem follows, replace the cats, check the main engine wiring harness ground wire, clean the MAF, etc... Can anyone narrow it down for me? There is a bullitin that says to perform a fuel injector balance test on all 8 cylinders, because it is possible that if one injector is bad it can throw off the whole bank, but would that make it quit firing? Any help would be greatly appreciated.

ChevyTech77 · July 6, 2011

Replace the convertors. Known issue. Test the back pressure in the exhaust to confirm.

mattpopovich · July 7, 2011

Replace the convertors. Known issue. Test the back pressure in the exhaust to confirm.

I will check the backpressure tonight or tomorrow and let you know what I find. Thanks.

mattpopovich · July 9, 2011

Replace the convertors. Known issue. Test the back pressure in the exhaust to confirm.

I will check the backpressure tonight or tomorrow and let you know what I find. Thanks.

I checked the backpressure and the driver side held at about 1 psi regardless of rpm. The passenger side read 5 psi at idle and pegged my 15 psi gauge at 2500 rpm. Very clearly a bad cat - Thanks ChevyTech77 for the suggestion. Now when I replace the cat what will keep this from happening again? I will check all the O2 sensors before installing them. Anyone have any other suggestions? What else would cause the cat to fail?

mattpopovich · July 11, 2011

Replace the convertors. Known issue. Test the back pressure in the exhaust to confirm.

I will check the backpressure tonight or tomorrow and let you know what I find. Thanks.

I checked the backpressure and the driver side held at about 1 psi regardless of rpm. The passenger side read 5 psi at idle and pegged my 15 psi gauge at 2500 rpm. Very clearly a bad cat - Thanks ChevyTech77 for the suggestion. Now when I replace the cat what will keep this from happening again? I will check all the O2 sensors before installing them. Anyone have any other suggestions? What else would cause the cat to fail?

I replaced the Y-pipe/cat assembly and the problem is resolved. Does anyone see an underlying cause to the cat failure or do you think it was just time for it to go? I have no codes showing up now and it is running great. Thanks.

ChevyTech77 · July 11, 2011

Depends. I've seen a lot of cats replaced on GM trucks in the past 10 or so years that don't seem to have any mechanical engine issues. I also hear how E10 is killing them along with the lack of zinc in engine oils anymore not to mention the usual oil and coolant burning/using issues. I wouldn't sweat it at this point. Probably just a faulty cat, to be honest, unless your engine is burning coolant or oil and then in that case, get those issues fixed before the new cat gets hurt.