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Lou P.
Lou P., ASE Certified Technician
Category: Chevy
Satisfied Customers: 4499
Experience:  building and driving chevy's since i was in the womb!!!! camaro and corvette enthusiest, access to factory diagrams and tsb's
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Chevy 350 poping through TBI carb and making a knocking noise

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Chevy 350 poping through TBI carb and making a knocking noise when warm. Please give ideas after you read what I've aready investigated.
when did the problem start happening?????? was it before or after parts were replaced??????
Customer: replied 7 years ago.
It did it before any thing was replaced. I would also like to say that it has a lack of power.
how does the plug look when you take it out????? oil??? carbon??????
Customer: replied 7 years ago.
yes some carbon even though the plugs are fairly new
ok its a long shot but heres whats probably happening.... bear with me,,,,,,, Theres probably excess carbon built up on valves,and piston. when the injector fires some of the gas sticks to the carbon and whats left makes its way into the cylinder however becasue of the carbon on the piston it's probably hot and ignites the fuel before the spark plug can causing a "knock or ping" because after the fuel ignites the spark plug ignites and the flames both hit each other causing the noise. i come to this result of lots and lots of experiance with the very same problem. so you might be able to clear up this problem by buying some throttle body cleaner and carb cleaner. run the engine at 2500 rpm and shoot short bursts in to the throttle body to see if it wil burn up some of the carbon. i'm willing to bet thats whats happening. many of my past and present camaros with 305's and 350's and a ton of miles DON"T like cheap gas due to the carbon built up on the pistons. other than doing what i suggest you can also fill up with 92 octane and use a bottle of techron fuel injector cleaner and'or seafoam (autozone) and i am almost 100% positive you will be happier than i don't even know!!!!!!!
Customer: replied 7 years ago.
So I understand that explains the knock noise. But what about the poping back? With the air cleaner off you can visually see the fuel being spayed up when it pops. Also have you ever heard of trickling water into theTBI to clean carb off the piston and valves much like a blown head gasket does to the leaking cylinder. When it does pop it seems to do it two quick one.
The popping back could also be due to the firing of the cylinder happens so fast it ignites before the vavle can close. also i have heard of water in the intake and it is vary effective. however some people dont under stand you can't just pour water in and hope it cleans but since you brought it up i think you obviously can handle it so yea you can do the same as i suggested with the carb cleaner. rev engine to 2500 rpm and you can slowly trickle water into throttle body the only problem with that is it will only clean the piston and not the valve. so you can try that first and if it doesnt help go ahead and get that techron and also use the carb cleaner.
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