Intermittent code P0300

Tiny
07BURBLTZ
  • MEMBER
  • 2007 CHEVROLET SUBURBAN
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 220,000 MILES
I am having intermittent p0300. Only really noticeable at idle and like I said it's intermittent. To the point the code will clear after enough ignition cycles. I have already replaced all the lifters, cam was in good condition, the VLOM, oil pressure sensor, MAP sensor, injector on 6, plugs, wires, cleaned throttle body, cleaned the MAF, had the heads gone over and milled.03, the wiring loom/harness is in decent shape. I will also get a p0306. (The reason I replaced injector) to no avail. The service stabilitrak, and service traction control will kick on at idle. If I raise the RPMs and hold it it will go away with no check engine some times. If I don't raise RPMs it will begin to miss harder to the point the check engine light flashes. Oil pressure is decent but could be a little better, never lower than 30, never higher than 58 or so. What should I load into the parts cannon next?
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Tuesday, February 2nd, 2021 AT 5:10 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

It sounds like you have done a lot of work already. I do have a question. Anytime I have a random misfire and a rough idle, I suspect an engine vacuum leak. Have you checked all over for leaks? Also, I realize you did a lot of work, but is compression within the manufacturer's specs? If you have a live data scan tool, can you tell me if the short term fuel trims?

Take a look through this link. It explains how to locate a vacuum leak.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know if you have already checked that or if you have other questions.

Take care and God Bless,

Joe

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Tuesday, February 2nd, 2021 AT 7:02 PM
Tiny
07BURBLTZ
  • MEMBER
I have not checked with a gauge, but I have sprayed the intake/head mating surfaces with brake cleaner. I will see if I can get it in tomorrow to check with a gauge. What is spec? It's an lc9 with vacuum assisted brake booster.
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Tuesday, February 2nd, 2021 AT 7:14 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

At idle, you should have between 17 hg and 21 hg. Let me know what you find. Also, if you have a live data scan tool, let's take a look at the short term fuel trims. That can tell us a lot. We can determine if the fuel mixture is lean or rich based on it.

Let me know if you have other questions.

Take care and God bless,

Joe
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Tuesday, February 2nd, 2021 AT 7:30 PM
Tiny
07BURBLTZ
  • MEMBER
Thanks! I will see if I can get a vacuum gauge and I'll scan it and let you know.
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Tuesday, February 2nd, 2021 AT 7:32 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Sounds like a plan. I'll watch for your reply.

Take care,
Joe
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Tuesday, February 2nd, 2021 AT 7:50 PM
Tiny
07BURBLTZ
  • MEMBER
Both Ltft and stft are negative. I was pouring over the scan tool and bank 2 was worse. But I noticed my ethanol content was reading 30% after I filled it from empty with premium. Thought it odd the percentage was so high. I also reset trims after resetting ethanol content. Also this issue has been going on for about a year. Gas type/ethanol content/octane hasn't made a difference.
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Friday, February 5th, 2021 AT 4:56 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
What were the actual fuel trims? I need to know how far in the negative they were.

Take care,
Joe
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Friday, February 5th, 2021 AT 8:13 PM
Tiny
07BURBLTZ
  • MEMBER
The Ltft was -15 on bank 1 -22 on bank 2, the stft -2 on bank 1 and 0 on bank 2.
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Saturday, February 6th, 2021 AT 4:36 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

Since the trims are negative, that indicates the computer is trying to reduce the fuel to the engine. Have you checked fuel pressure?

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

Let me know.

Joe
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Saturday, February 6th, 2021 AT 5:05 PM

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