Getting a P0300 random misfire for my 2001 Silverado Z71 5.3

jjcominito · February 7, 2014

as i was driving my truck i got a flashing service engine soon on my dash, went to have it checked and got a P0300. the mechanic said it was misfire on multiple cylinders with a lean on 1357 side. he checked all the spark plugs and wires, coils even went and had the injectors cleaned. this was done to both sides. the code was erased and next day same thing happened. what can it be?

txab · February 7, 2014

Intake leak possibly

1997SierraSLT · February 7, 2014

A GM truck?......

after 16 years of owning my 97' GMC, I have totally given up trying to find out what triggers this misfire condition. After about 3 years of owning it, I bought a cheapy code reader so I could plug into OBD-II port and simply clear the codes and get that check engine light to go off.

keyboardcommando · February 8, 2014

check compression?

farago2r · February 8, 2014

I had a P0300 and P0171 code pop up last week and it was my O2 sensor on bank 2 sensor 1. I've also had to replace an O2 sensor when truck read P0300, but it was bank 1 sensor 2.

I have a 2005 silverado Z71

Doug_Scott · February 8, 2014

Why did the mechanic only look at ignition system for misfire? Did he ignore the other message about lean condition?

The lean condition will also cause misfires. Look for vacuum leak now. Intake to cylinder head is pretty common. Vacuum line condition should be checked as well. Brake booster can also be a vacuum leak. Point is, always do basic checks first, before changing parts.

Springer Tom · February 8, 2014

as i was driving my truck i got a flashing service engine soon on my dash, went to have it checked and got a P0300. the mechanic said it was misfire on multiple cylinders with a lean on 1357 side. he checked all the spark plugs and wires, coils even went and had the injectors cleaned. this was done to both sides. the code was erased and next day same thing happened. what can it be?

Had the same problem, was told to replace wires, plugs, intake gaskets. Did all that didn't fix it. Found this forum and Wrencher said bad upstream O2 sensor on driver side. Low voltage to sensor sends lean code, which in turn sends more fuel to bank 1, resulting in multiple missfires. Replaced $40 O2 sensor and truck runs great. Wish I did that first. Good luck

Pjwolcott34 · February 10, 2014

Had o2 sensor code go on then while driving it started to drive terrible so brought it to check codes again and now I have p 0101 code also I changed pass anger side after converter sensor and the spark plugs but still runs terrible I don't know what else to do