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1996 GMC Sierra P0300

Tiny
DABAKER
  • MEMBER
  • 1996 GMC SIERRA
  • 4.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 154,000 MILES
The truck starts fine and runs well. If I drive it 20 plus miles and let it cool of just a little (time to shop at Lowes 20 min) it starts and you can feel a misfire. The check engine light comes on and throws a P0300 code. I have replaced cap, rotor, plug wires, plugs, upper / lower intake gaskets, thermostat.
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Wednesday, March 19th, 2014 AT 1:53 PM

2 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
If you have the spider fuel system, I always check that first. That system is noted for problems. Check for proper fuel pressure, key on engine off, 60--66 psi. Engine idling around 55 psi. That key on engine off spec can be critical, once the vehicle starts it will run with less pressure.

Check that the pressure doesn't drop like a rock with key off, if it does, you have a pressure leak.

A hot restart issue could be caused by leaking injectors/poppets.
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Wednesday, March 19th, 2014 AT 2:55 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Just to add, you could use a vacuum gage on your crankcase dipstick tube. Idle, 1--3 inches is fairly normal. A little more could be a pcv system issue. A lot more and it sounds like vacuum leak?
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Wednesday, March 19th, 2014 AT 3:00 PM

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