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2000 5.3 1500 - P0300 Random Misfire

51K views 17 replies 9 participants last post by  DerekA 
#1 ·
Hey, I have a 2000 GMC Sierra 5.3l V8 with 161,000 miles (260,000kms) and It has a P0300 Random Misfire code. The truck runs perfect around town and on the highway but the misfire is relative to RPM. If i hold the revs at 1900rpm or more it misfires and the SES light flashes. So on the highway at about 70mph or over it will miss. around town it does not unless i put the shifter into 2nd and let the RPMS climb. The Truck has Had a FULL Tune up. The only thing done besides a Tune up was a new fuel pump installed last year. Has anyone encouterd this issue!!?? Maybe the Intake?
 
#4 ·
+1 on the intake gasket. i had the same problem. changed all my plugs and wires just for service and didnt help. i then tested all my coils and they were good. tested the injectors, all good. so since the intake gasket is a very common problem with these motors, that's what i will be changing next.
 
#10 ·
So I had this problem on thursday and spent the whole weekend figuring it out! Check both banks of you spark plugs and see if one bank is running richer or leaner than the other, ie blacker or whiter (my bank 1 was running VERY rich causing the P0300 code). Also you can swap your two upstream O2 sensors with eachother, and see if you start getting a bank 2 random misfire code if you are hesitant to blow $100 on diagnostics :p
 
#11 ·
Plugs were all in really good shape. Used the GM Tech II Scan tool to look at fuel trim and O2 sensor readings. All seem to be within spec. The misfire count is on ALL cylinders but 1 , 4 and 7 seem to have the highest misfire counts. cylinder 2 for example has a miss count of 16,000 where 7 has a miss count of 54,000 . Fuel pressure is also perfect. 60Lbs. Ill try and check my intake tomorrow, hopefully with some results.
 
#15 ·
I have this code (P0300), as well as P0171 and P0174. I've replaced the fuel filter and fuel pressure regulator and also cleaned the mass airflow sensor with the recommended cleaner. Also, I've tried to spray all around the intake manifold with carb cleaner and had no response to that. Since it's throwing both bank 1 and 2 I didn't think it would be one of the O2 sensors or any coils, wires or plugs... Any suggestions on where to go from here? Thanks.
 
#17 ·
sflynn006 said:
PR_Rado said:
I had the same problem along with two other codes, and it led to an O2 sensor. You've got it right by checking your intake gasket by spraying it down as I did that test as well. My intake is good....... For now.
What were the other codes? P0171 and P0174 by chance? And which O2 sensor did it lead to?
I believe those were the codes. If I remember correctly, it was the sensor on the passenger side before the cat.
 
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