ok i have a 2000 silverado with the 5.3 in it. has roughly 120,xxx miles on it. now my problem is that it detonates under even the slightest load. i have a PCV catch can, new wires, new plugs, clean MAS, and i run premium ( which is bankrupting me by the way ). burns a quart and a half every 5000 miles which is normal for the miles. i have ran two cans of sea foam through it and have checked all vacuum hoses and EGR valve. I have noticed a decrease in mileage as well. now what the **** is wrong with my truck? I race motorcross and pretty much spend every dollar i have on my bike, not my truck, so i cant just start throwing money at the problem. i am also a student so time is a limitation as well. so please, PLEASE help with!

 

Have you changed the plugs / wires
Are you sure its knock?

Clean the injectors?

Derek

 

fuel pump could be going out

 

yes i have changed the wires and the plugs and could a fuel pump do that? my backflow valve is broken so i have to get a new fuel pump anyways but an old pump wouldnt really cause knocking would it?

 

If the pump wasn't flowing enough and was running lean it would...I'd replace the fuel fiter also if it hasn't been done already. If this helps, when tdrumm's Grand Prix had a problem with the cat converters it started pinging horribly, as well as misfiring as indicated by a blinking ses light.

 

Pump going out definitely causes knock because of lean conditions. Your pulsewidth will go way up along with your injector duty cycle if the pump is going out. Can't go wrong with a walbro 255 and fuel filter replacement.

 

I don't know if anyone thinks this but under high load at low rpms. Like when the TC is locked going up a hill I always hear knock on just about any vehichle and stock vehicle. The manual says you might hear knock slight knock when going up a hill but as long as it is a low throttle low rpms and its not real loud its ok.

 

yeah i have replaced the fuel filter already and the fuel pump does have 120k on it and the backflow valve is broken so i do need a new one anyways. what is a good pump? i build custom off-road suspension, not motors ,so any info you guys can give me is sincerely appreciated.

 

There is only one "R" in motocross.

 

The walbro 255 is a cheap and easy upgrade that is much better than a stock pump. You can typically get the correct walbro pump with the right pigtails and such for 100'ish or cheaper.

who cares, typo's happen