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p0300 2000 chevy 5.3

1171 Views 25 Replies 9 Participants Last post by  popsg
have a 2000 Silverado with a 5.3 and have a p0300. cylinders 1 & 8 are dead misfires at idle but when you get the rpms up the misfire moves and starts jumping around to all cylinders. have new plug wires and plugs have also had the injectors test and cleaned. tested wires from ecm to each injectors wire and they are good. have swap coils from cylinders. 1&8 are still dead till you get high in rpms then it moves to multiple cylinders. did a crankshaft and camshaft sensors and timing gear and chain. and i still have the dead cylinders on 1&8 till i get high in rpms then it moves to other cylinders and did a compression test on the motor have 150psi across all cylinders. pretty stumped any info or recommendations would be extremely helpful tired of throwing parts at it and nothing working.
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What's your fuel pressure?
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You need to solve the fuel pressure problem, first. Should be better than 57psi. I had this P0300 on mine with poor fuel pressure.
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did fuel pump and fuel filter and fuel pressure regulator. have 50 psi at rail. it bleeds off to 0psi when motor is shut off. what else could be the reason for low fuel pressure. injectors leaking by?
Still too low on the fuel pressure. Upper 50's (57+) at idle or it will not operate properly. These engines verge on prima donna status with fuel pressure, in my experience. I have a 2000 5.3L and a 2004 5.3L, both of which despise low fuel pressure.

I'm going to number these for easy reference.

  1. Fuel Pump
    1. When did you do the fuel pump, regulator, and filter?
    2. Was the pump new? New doesn't mean "good"...
    3. What brand?
    4. Did you update the fuel pump electrical connector when you swapped pumps?
  2. Fuel Lines
    1. Have you checked for leaks in the lines?
      1. Highly, highly recommend checking the connections at the filter very closely. Flare fittings are very sensitive to improper alignment and torque. Common leak point and would result in low pressures if the leak was significant enough.
    2. Do you smell raw fuel?
  3. Fuel Injectors
    1. How quickly does the pressure drain occur?
    2. Were the injectors pressure tested?
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someone mention it could be injectors leaking down after truck is shut off
Yes, it could very easily be leaky injectors causing all your problems. But before continuing the parts cannon w/ new injectors, I wanted to have you check all the free fix failure modes I could think of.

Move ONLY Injector 1 to another cylinder while leaving everything else alone (including Cyl 8 components). Does the Cyl 1 misfire move with Injector 1 to another cylinder? Did the Cyl 8 misfire change?

Question: Do you have any other codes? I just noticed this was not specified.
DO NOT use a test light to check injectors. Use what is called Noid light . And will tell you if the is firing an injector .
ARES 71500 - Noid Light & IAC Test Kit - Easily Eliminate EFI and IAC Systems as Causes for Non-Starting Vehicles

This is the one I bought to work on the same vehicle type. Worked well.
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