97 GMC Sierra v6


Asked by Mar 29, 2016 at 01:46 PM about the 1997 GMC Sierra 1500 C1500 SL Standard Cab Stepside SB

Question type: Maintenance & Repair

Recently put in a new engine in my 97 GMC Sierra
and now its throwing a P0300 code random
misfire. I've changed everything from the spark
plugs, spark plug cables, ignition coil, distributer
cap, distributer wheel, and ensured the timing is
lined up. Just not sure what else to do?

11 Answers


When was the injectors last cleaned? You could try dumping in a bottle of Techron in the tank now then when you fill up put in either Chevron or Texaco fuel and drive it as you normally would, see if that has an effect on the code in about a week or so. Or you could have them professionally cleaned. You have done everything else that normally causes this code.


Watched a video and a guy said something to do with the cats being blocked up, could this happen?


It can but you normally notice a big loss in power and the engine just won't rev up, and you will also hear a loud hissing sound out the exhaust.


It does have a large amout of power loss but the engine does rev up and I've noticed the is a small amount of fluid that sprays out of the exhaust?


Today I loosened up the exhaust manifold from the exhaust pipe to check if the code would go away and see if any power was returned and there was not


That was the next thing I was going to suggest. Did you have the distributor re-synced with the crank sensor after you did the work? Some shops can do this but your best bet is the dealer. You can't actually set the timing on this engine, but you have to be close for it to run.


I was able to sync it yes. I lined up the crank with the line and tick mark on the block the lined my distributor up according to the manual.


I went and got some chevron injector cleaner and a full tank of gas now im going to just drive until the fuel runs low?


That's mechanically, how about electronically?


What about the fuel injection system?


Electronically syncing the cam sensor with the crank sensor. If there ws something wrong with the fuel injection and this being a vortec engine you will have the check engine light on and all kinds of running problems.

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