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Discussion Starter #1
I have an Siliverado with a 5.3 v-8 that has a constant check engine light on. I had the codes checked a year ago and it had a P0449 code. It was suggested to replace the Evaporator Emission valve as it usually is the culprit. I replaced it and that didn't fix it. So I just kept driving it.
I noticed the engine definitely has a miss fire especially noticable at low rpm. So Since the truck tank of gas might last 6 months I figured it could probably use a fuel cleaner to clean the injectors. I added a can of SeaFoam to the tank and that did seem to help the miss a lot. I had ran that tank of gass out and I decided to run a full tank of ethanol free gas because the tank lasts for a long time. Shortly after maybe 50 miles I noticed the check engine light was now flashing. The flashing would be replaced with the solid light then and then it might start flashing again. I had Autozone check the codes and codes po300, 332, 449, and 455. All codes came up again except the 332 which is the knock sensor 2 circuit low input bank 2 didn't come up twice.
I am wondering if using the injector cleaner sea foam might have caused the injector misfire code 300? I am also wondering could bad spark plugs or wires be causing the miss fire code 300?
Code definitions.
PO300-random misfire detected. PO332-knock sensor 2 circuit low input{bank 2}. PO449-evaporative emission system vent control circuit intermittent. PO455-evaporative system leak detected {gross leak/no flow}
For plugs and wires parts alone cost around $160 with a bit of a discount given to me.
I would appreciate any input from those experienced in cause of problem codes.
 

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Discussion Starter #2
I had the engine idling while I pulled coil wires at the coil one by one to see if any cylinder didn't effect the idle. All cylinders showed a rough run when disconnected. I was getting a little zap when pulling one coil wire so I am guessing that wire possibly has a defect in it.
 

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I’ve had all these codes on my 5.3 in the past. But not all at the same time.
For me the problems were:
random misfire was leaky intake gaskets
Knock sensors were bad, there’s a TSB on replacing them and how to prevent water corrosion. Replace the harness too as it’ll shatter when you go to take it off
Evap system was my purge canister. On the suburban / xl you can’t relocate it but the pickups have a tsb for relocating it
Sounds like you possibly have a bad ground or wire too on the evap circuit
 

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Discussion Starter #4
What can I spray around the hoses and intake to find iar leaks in hoses or gaskets? Can I use starter fluid or is that to explosive?
Also what spark plug is best to use? I read some say don't use a double platinum plug and use a tridium instead but then I read those made by Bosch are known for throwing codes and misfires real quick after installing. I heard the the Delco 41-962 from Amazon could be rejects being sold through one of their suppliers.
Since the knock sensor has low input could maybe replacing the wire connector to it could solve that problem?
 

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The Flex fuel intake gaskets were known to go out more rapidly than the non-FFI motors. I tested mine with carb cleaner, but my leak was bad enough to cause "loaping" and stalls in the engine when the engine was cold and ambient air temps were high.
 

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Discussion Starter #6
I ordered a code reader that does more than just reading the codes. I bought two cans of carb cleaner to test for leaks. I should get the code reader this Friday. I did replace the gas cap which had seen better days. I also cleaned the fill neck surfaces for a better seal to the new cap. When I get the reader I will clear the code and see if the code comes back with the new cap. I am hoping that ends the code.
I am holding off getting plugs and wires till I see what the reader says.
 
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