2000 GM 5.3 P0300 again..

[Tzu]

I briefly looked through the forum questions, but I am very tired so forgive me if this was covered recently. My '00 Silverado 1500 had the code pop up when I was leaving for work doing about 35mph after a cold start and 2 min warmup. I replaced the intake manifold gasket last year and she fired right up afterwards with no problems and no CEL. The truck has 242,000 miles and does not start hard or stumble when hot/cold. Runs fine, but seems to go through more fuel than normal. New OEM spark plugs 40,000 miles ago, original wires, fuel filter 10,000 miles ago, cleaned MAF sensor at time of intake R&R, truck runs fine with no loss of power. I know its a hard one to nail down, but would O2 sensors do this? A dealer is $70 diagnostic fee minimum, maybe it's worth it to replace 1 part or skip it and do 2 sensors at home in the driveway? Anyone with similar code and how did you fix it? Thanks..

 

[turtlevette]

My 02 Suburban 5.3 sets this code every fall. I'm starting to think the switchover to winter gas does it. I merely reset the code with my reader and I'm good for another year. Cheap way to do this is just disconnect the battery.

 

[KB2008X]

Your best bet is to clear out the code and see if it comes back soon. One occurrence of a code is not cause for alarm. Two times and now you have something to work with.

If it still has the original spark plug wires then that's the obvious starting point. I'd probably replace them regardless of whether the code comes back or not. Be sure to choose the brand of wires carefully, they are not all created equal.

 

[NMBurb02]

Originally Posted By: KB2008X
If it still has the original spark plug wires then that's the obvious starting point. I'd probably replace them regardless of whether the code comes back or not. Be sure to choose the brand of wires carefully, they are not all created equal.

This. They should probably be done every $100k or so. Go with ACDelco or Delphi as either of those are probably the OE.

 

[Doog]

I would do a heavy fuel system clean up in your gas followed by a complete tune up and see if it throws again. You may have a lazy 02 sensor or leaky injector. My guess is you have a leaky injector. But for 242k not bad.