knocking and pinging under load.

[pies]

2001 chev silverado with a 5.3 litre. the truck has 160,000 kilometers. my truck has recently started knock and ping when the engine is under any type of load. the truck will throw code p0300. the problem is particularly bad when the engine get up to 3000 rpm. i have replaced plugs, fuel filter ,air filter. i have check maf and it seeems to be fine . the fuel pressure is around 58 psi when idling. any suggestions on how to repair this problem would be appreciated. thanks pies.

[2000CAYukon]

With that many kms, why not replace the plug wires as well? P0300 says random miss fire so a bad wire or two could be the problem.

//2000CAYukon

[pies]

before changing the plugs, i soaked everything under the hood with water at night, just to see if there was any sparks or leaks from the wires or coil. didnot see any arcing.

[2000CAYukon]

Originally Posted by pies

before changing the plugs, i soaked everything under the hood with water at night, just to see if there was any sparks or leaks from the wires or coil. didnot see any arcing.

Did you check the resistance of each wire?

//2000CAYukon

[J-Ri]

Carbon buildup can cause that. The carbon in the cylinders basically raises the compression ratio (and creates "hot spots"), creating the need for a higher octane fuel. Go to a higher octane fuel and see if it goes away. Don't just switch to the higher octane, or soon it will start pining again, this time much worse. If it does go away, get an induction flush done. BG makes an excellent kit that we have had 100% success with.

[j cAT]

If you installed the wrong plugs this will occur. did you have pinging and then replaced all the parts listed?then your engine probably is carboned up. how did the plugs look? also re-torque plugs to 15ftlbs pinging will loosen them.

[pies]

ping and knock was there before everything was replace and still is. not quite as bad , but still there. before it would start at about 3000 rpm's and the trip the miss fire code. now it seems that if you try to work the engine at all it will trip the misfire code. took the truck to the stealership and had a complete diagnosis done. they are telling me that the catalytic converters are plugged. if this possible to cause the misfire codes, and shouldn't it have trip more codes than just the po300 code. thanks pies. .

[J-Ri]

Originally Posted by J-Ri

Carbon buildup can cause that. The carbon in the cylinders basically raises the compression ratio (and creates "hot spots"), creating the need for a higher octane fuel. Go to a higher octane fuel and see if it goes away. Don't just switch to the higher octane, or soon it will start pining again, this time much worse. If it does go away, get an induction flush done. BG makes an excellent kit that we have had 100% success with.

Start with that, lots cheaper than two cats

[j cAT]

I believe that it is very possible that your exhaust is restricted.If engine at idle runs normal and only pings under load. I would first remove all plugs and compare color and gap and condition make sure platinum did not fall off tip on plug. if color is lt gray to white this is normal. if some or one is fouled black wet etc.. check compression and spark, replace plug, maybe cracked, sometimes you cant see cracks. this will give missfire.coil could have a bad connection. if all plugs look the same then exhaust restriction is likely. Especially if you did not keep on top of your maintenance, and allowed this to continue for a long period of time. excessive carbon on the pistons/combustion chamber will also be there. I forgot! it is possible the knock sensor is bad this is under the intake manifold.I hope not.

[maxwedge]

I'd follow up on the cat issue which can cause misfire codes and egr problems which can aggravate pinging under load, how did they determine the cats were restricted?

[pies]

the mechanic at the dealership scanned the truck and could not find anything wrong with the truck, except the misfire code. he then took out the left o2 sensor and the truck did run a little better, i took the truck back to my shop and removed the whole cat assembly and found that the left hand side was plugged. replaced the cats and the truck runs like new again. thanks for the help pies.