stock 5.3 spark knock

[LS ROB]

silvy.hpl08 silverado-mine.hpt

Stock 5.3, modular intake tube, k&n filter through the stock box. I've been noticing lately that my fuel mileage seemed to be getting worse (15.3 avg.) and the truck drives ok some days and other days it feels lazy. I decided to take it out for a quick session and grab a log. Note: I normally run low grade gas and opted for 100% low grade (87 I think) this evening. After a few heavy footed throttles I noticed it starting to feel a little better just normal driving. Get home and look at the log and I see spark knock and the MAF trims seem a tad lean to me. **** I have never modified the tune, this is the stock tune pulled from the truck as is. Is this spark knock excessive for a stock tune?

[2xLS1]

Get rid of the junk K&N filter. Good chance it has oiled up everything downstream of it.

[Alvin]

I wouldn't say it's a K&N problem. The fuel trims aren't that lean to indicate the MAF has been oil fouled.

I think its a gas issue straight up. Some of the later GEN 4 5.3's are really sensitive to knock. Usually the ones with VVT.. Didn't check yours to see if that's what you got.

I would try a solid tank of 93 and see if ti changes drastically. If it doesn't maybe check on the knock sensors. When they age they sometimes get way too sensitive. If it does change and you still want to run 87 you'll just need to start pulling timing slowly to get rid of the knock.

[Fast4.7]

Probably carbon build up. GM Top engine clean or Mercury Quicksilver PowerTune.

I have put close to 400K miles on K&Ns without any MAF problems and this includes Nissans with dual MAFs.

[LS ROB]

Thanks guys. I'll look into all of those suggestions and see what i can come up with.

[mr.rogers]

I'm having the same issue stock 2008 tahoe 5.3, 8 deg of knock on a wot pull and 4 on light accel. Any ideas where to look first?

[RDF1]

Wait till low fuel light comes on and throw in 10 or 15 gallons of 93 octane and see what it does.

[village_idiot]

Try at least 89 fuel but 93 if you can. My 18 GMC 5.3/8L90 will ping on 87 low rpm/high load or anytime pulling a trailer. Stock truck/tune (still in warranty). If I run 89 or better in it, it goes away. Ive just continued to run 89 since I noticed it.

[LS ROB]

I haven't gotten a log on it yet, but I can confirm that running higher grade octane has helped. Overall drivability is better and feels stronger. I guess you really don't notice it as much while it's "learning" itself down.

[Fast4.7]

My old 350 spark knocked enough on 87 that it was always in the low octane timing maps. I put 91 in it and then later gave it a slight timing bump on 91. Power and fuel mileage both greatly improved. Never will understand the waste of time and effort to run 87.