QuestionI HAVE A 1997 GMC SUBURBAN 4WD 5.7 1/2 TON K1500. "OBDII SAY'S RANDOM MISFIRE P0300. JUST DID A TUNE UP CHECK MY WIRES THEN TOOK IT TO A SHOP THEY COULD NOT FIND THE PROBLEM.I HAVE 200,000 MILE ON IT AND THIS IS THE ONLY THING THAT I HAVE HAD HAPPEN TO ME, I ALWAYS HAVE IT SERVICE. WHAT MAY IT BE??"
Answer
fuel inj
Was this problem there before you did the tune up ? Did you change the cap and rotor ?
The distributor cap is the first place i look on this one. Next , if all the ignition
parts are good (and i have had a bad cap out of the box) i look at injector problems
and lower intake manifold leaks. when is the last time you changed the fuel filter ?
Check fuel pressure , it should be 56 to 62 psi. Then turn the key and see if the fuel
pressure holds. If it bleeds off I'm betting of fuel injectors , open the throttle plate
and see if there is a strong gas smell , look in with a flash light and see if it
looks wet. I bring this up because there was a lot of problems with the CSFI injectors
on these engines , so much so that there was a recall , that recall is out of date for
you , 10 years or 200,000 whichever came first. there is also a conversion from csfi
injection to mfi as a correction. the problem with these were the injectors not opening
properly , staying part way opening or the fuel pressure regulator leaking (fuel pressure
regulator is part of the injection system) I have commonly seen fuel on one side of the
intake and the other side dry when i run across this.
hope this helps
