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Code P0300

Tiny
DANIEL SANCHEZ
  • MEMBER
  • 2001 CHEVROLET SUBURBAN
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
I cannot find what the problem is.
I got new:
Intake and throttle body gasket
New plugs and wires
New Hoses and EGR gasket
New Map sensor
New MAF sensor
Knock sensors and harness

Freeze frame reads:
P0300
Fuel system 1. OL
Fuel system 2. OL
Load_pct. %7.5
ETC. 99
SHRTFT1. % 0.0
LONGFT1. % -0.8
SHRTFT2. % 0.0
LONGFT2. % -0.8
MAP (inHg) 18.3
RPM (/min) 1557
VSS (MPH) 0
MAF (lbs/min) 2.447
TP. % 10.2
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Tuesday, March 5th, 2019 AT 2:33 PM

9 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening,

The first thing I would do is check the fuel pressure. that is the most common reason for the 300 code.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Roy
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Tuesday, March 5th, 2019 AT 4:12 PM
Tiny
DANIEL SANCHEZ
  • MEMBER
  • 5 POSTS
So my fuel pressure is fine when the key is clicked forward roughly 55 to 57. But when I try to start the car the fuel pressure drops down to 20 and the car won't start. I did replace my fuel pressure regulator but same issue.
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Thursday, March 7th, 2019 AT 9:00 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Got it.

You need a fuel pump.

It is in the fuel tank. The tank must be dropped to gain access.

Roy
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Thursday, March 7th, 2019 AT 9:21 AM
Tiny
DANIEL SANCHEZ
  • MEMBER
  • 5 POSTS
Changed the fuel pump. Same issue!
I did a vacuum test on the intake manifold and it is swinging wildly from 0 to 15 inHg. It will only stay steady is I give it gas at around 20 inHg. So do you know what that may indicate?
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Thursday, March 7th, 2019 AT 2:29 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Did you verify the fuel pressure test?

If the vacuum gauge is like that, do a compression test.

Roy
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Thursday, March 7th, 2019 AT 2:31 PM
Tiny
DANIEL SANCHEZ
  • MEMBER
  • 5 POSTS
I did re-verify the fuel pressure it was right on at 59psi. Okay, so a compression test is next. If there is no or low compression where do I go from there?
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Thursday, March 7th, 2019 AT 2:33 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Lets see what the results are before we discuss a course of action.

Roy
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Thursday, March 7th, 2019 AT 2:40 PM
Tiny
DANIEL SANCHEZ
  • MEMBER
  • 5 POSTS
Results
Cylinders
1 - 160
2 - 160
3 - 0
4 - 170
5 - 170
6 - 170
7 - 170
8 - 155
I checked cylinder three on three different occasions and all read 0 compression. Would this be the cause of the P0300 code? If so what do I do from here?
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Friday, March 8th, 2019 AT 8:20 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Air up number 3 cylinder and see where it is leaking from. It could be a valve, piston or something else.

The head will have to come off.

That is also the reason for the misfire code.

Roy
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Friday, March 8th, 2019 AT 8:25 AM

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