p300 ! thanks for narrowing down gm

[pottss55]

2002 silverado 4,8 poped the 300 code . I have good fuel press 58, 59 lbs every cycle.Truck has no power and spark knocks like crazy when you step down on it , and doesn't pull at all, has sound under hood like when you turned the breather cover over on dads 72 la mans [a big intake roar] . to me it feels like exhaust is plugged but no 02 or cat codes . yes it is an airtex fuel pump from autozone but pressure lbs are right and i have replace fuel filter.

[j cAT]

Originally Posted by pottss55

2002 silverado 4,8 poped the 300 code . I have good fuel press 58, 59 lbs every cycle.Truck has no power and spark knocks like crazy when you step down on it , and doesn't pull at all, has sound under hood like when you turned the breather cover over on dads 72 la mans [a big intake roar] . to me it feels like exhaust is plugged but no 02 or cat codes . yes it is an airtex fuel pump from autozone but pressure lbs are right and i have replace fuel filter.

intake manifold gaskets ...

ever use carb cleaner on this engine?????

[pottss55]

no never cleaned with any cleaning agents , replaced knock sensors in feb . wiped out intake when i had it off . have check for leaks around intake with propane nothing detected

[j cAT]

Originally Posted by pottss55

no never cleaned with any cleaning agents , replaced knock sensors in feb . wiped out intake when i had it off . have check for leaks around intake with propane nothing detected

drive around with the fuel pressure guage on and see if it can keep up the pressure...

the reason I mentioned the cleaning of engine/use of carb cleaner is because you replaced the knock sensors...these usually go because of engine cleaning/degreasers/carb cleaner solvents...these usually damage rubber/plastic wiring insultion etc.....

how long has this been your vehicle ?

[pottss55]

I have owned truck 3 yrs , replaced back knock sensor hole was full of crap clean out and built dam with rtv. When ya hold down on gas with the air roar under hood the cel will start flashing but give up no other code than p300 , tomorrow i will remove up steam 02s and test drive.

[pottss55]

not sure i can view gauge will driving ,gauge has a 16" hose , may be able to make extension on it, have reved up and viewed gauge with no drop , pump is 18 months old .Have friends @autozone and they will replace it because i bitched and told them it was junk, but they only have airtex pumps but gauge has not proved pump bad yet

[j cAT]

Originally Posted by pottss55

not sure i can view gauge will driving ,gauge has a 16" hose , may be able to make extension on it, have reved up and viewed gauge with no drop , pump is 18 months old .Have friends @autozone and they will replace it because i bitched and told them it was junk, but they only have airtex pumps but gauge has not proved pump bad yet

also check the air ducting from the maf to the throttle body..if air is bypassing the maf it will run lean ..

[pottss55]

tomorrow I'll take intake off and check gaskets maybe something happen there , I put new felpros when i replaced knock sensor , loud air noise is coming from somewhere . air intake from air cleaner to front of engine all look good . Places fuel gauge on windshield so i could read it gauge was always between 55 and 60 psi .do intakes every crack or strange things happen to them?

[j cAT]

Originally Posted by pottss55

tomorrow I'll take intake off and check gaskets maybe something happen there , I put new felpros when i replaced knock sensor , loud air noise is coming from somewhere . air intake from air cleaner to front of engine all look good . Places fuel gauge on windshield so i could read it gauge was always between 55 and 60 psi .do intakes every crack or strange things happen to them?

many a GM intake manifold has cracked ...

with this engine it is usually just gaskets....make sure you follow the torque and sequence

need torque wrench

[pottss55]

set down with all my notes decided to check back press ,removed both up stream 02's made up a pressure gauge 0-10 psi gauge left side had almost .5 psi right side had 3.5 to 4 psi . replaced head pipe , its like i have new truck ,no more p0300 code

[j cAT]

Originally Posted by pottss55

set down with all my notes decided to check back press ,removed both up stream 02's made up a pressure gauge 0-10 psi gauge left side had almost .5 psi right side had 3.5 to 4 psi . replaced head pipe , its like i have new truck ,no more p0300 code

with the one side restricted it was a little harder to troubleshoot ..

they usually plug up when something goes wrong. make sure the O2 sensors are good...

good luck ..

[pottss55]

j cAT is there a good method to bench check 02s ? they aren't tripping any codes , is good good when no code tripped or can they be lazy ?

[j cAT]

Originally Posted by pottss55

j cAT is there a good method to bench check 02s ? they aren't tripping any codes , is good good when no code tripped or can they be lazy ?

you have to check these with a scanner that can read the sensor output when the engine is running ...they all work the same basicly an alternating voltage output...

when the sensors get old [100,ooomi] or damaged by contaminates [silicone,antifreeze] they then get out of range and can cause poor performance or damage the cat converters...


as a saftey proceedure when replacing a cat converter , you should replace the upstream sensor...

[pottss55]

will replace both up sream 02s this week . My only qustion now is how does my truck now when i have a little money saved up?