Rough Running

[Bear1949]

3 weeks ago the truck started running rough. I changed spark plugs & fuel filter...no improvement. The truck has 300K on it and has had regular servicing. It comes up with an engine code of PO300, random misfire. Any suggestions of where to go from here? Thanks.

[jro909]

check the coils, wires...clean throttle body, check MAF sensor..air filter...it could be so many things man with that many miles lol...congrats 300 is awsome...any issues otherwise on that long stretch to that mileage?

[Bear1949]

check the coils, wires...clean throttle body, check MAF sensor..air filter...it could be so many things man with that many miles lol...congrats 300 is awsome...any issues otherwise on that long stretch to that mileage?

thanks for the info, actually it is 300 kilometres (Canada) which is about 136,000 miles. no other problems except fuel pump.

[98 Z71 SLT]

Check your fuel pressure regulator....

 

if ok, replace your intake manifold gaskets

[Bear1949]

check the coils, wires...clean throttle body, check MAF sensor..air filter...it could be so many things man with that many miles lol...congrats 300 is awsome...any issues otherwise on that long stretch to that mileage?

[Bear1949]

Check your fuel pressure regulator....

 

if ok, replace your intake manifold gaskets

 

 

thanks - will give that a try

[VVT]

Buy some stuff called "intake cleaner" and remove your intake at the throttlw body. Spray in and all around the opening of the throttlw body. These things often get gummed up and the sensors in there dont work properly. The intake cleaner works and its cheap. My 01 4.8L used to get so bad it would die when you took your foot off the gas. I had to do the intake cleaner trick about once every couple of years.

[Bear1949]

Buy some stuff called "intake cleaner" and remove your intake at the throttlw body. Spray in and all around the opening of the throttlw body. These things often get gummed up and the sensors in there dont work properly. The intake cleaner works and its cheap. My 01 4.8L used to get so bad it would die when you took your foot off the gas. I had to do the intake cleaner trick about once every couple of years.

 

 

thanks...it's running smoother now

[VVT]

No problem glad it worked out for you. Dont by shy with that stuff let er rip again in a few days I had to drown mine to get in running smooth again. The root cause is the PCV oil consumption issues these newer LS engines have. It gets everything in the intake track all gummed up with oil film. If it happens too frequently you can add a PCV catch can to eliminate most of the oil vapor.