Code P0300

Tiny
LOUD_8.1VORTEC
  • MEMBER
  • 2003 GMC SIERRA
  • 6.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 111,000 MILES
Hello,

After a week of diagnosis, the problem gets worse. At first, I had a p0171 that was related to a vacuum loss, so I replaced it so the idle was going a lot better I even changed the MAF sensor the throttle body. I started it and all the DTC codes were erased so I did a road test. The problem I wanted to solve was poor acceleration and bad mileage. Nothing to fix it was the same and even after 50 km the check engine light it is again to flash on my return p0300 appeared and more before or after the repairs p0300 has appeared and more before or after repairs I can move the MAF sensor without change and question catalyst or 02 sensor would surprise me and even impossible because I have another lq4 of 350,000 km o2 sensors have never been changed and catalysts are not plug. To get back to the problem after 1 week of diagnosis I noticed a silement to injector 8 and 6 by removing them I realized that the o ring was damaged. I want to point out that before doing this the truck idle fine answer to the Park compared to before the replacement of the intake gasket. New part and ok before continuing new: spark plug, wire, intake gasket Fel-Pro, gasket manifold Fel-Pro ok: coil was changed 1 year ago and are tested and fine "injector too" I have 55lbs fuel pressure at wot and 49-50lbs at idle. In addition, I have 175 lbs of compression and have all cylinders so no mechanical misfire. To continue I changed the o ring of injector 8 and 6. So more psst sound but as soon as I did this my engine is run rough and I really felt the said misfire compare to before replacing the o ring injector and the check engine light flash all time compare to before I understand more I am not looking for scanner and an Innova 3320 it can read freeze frame data. After changing the o ring injector I did another road test and it’s catastrophic I feel like riding on 4-5 cylinders when I remove the spark plug to take compression and oddly (all this happens after the replacement of the o ring injector which has all spoil by the same fact the progress made) the spark plus 2468 (rich) and the 1357 o (poor roll) yet before I replace these darn o ring apart the poor acceleration the idle was perfect help. In addition, after o ring replaced and the road trip the ltft b2 16% ltftb1 0%. But before this replacement at my first road trip the ltftb1 was -1.6% ltftb2 -1.6% seem good. I want to repair it without spending all my money and I didn't do the crank relearn because I don’t have a proper scanner.
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Sunday, October 2nd, 2022 AT 7:48 AM

3 Replies

Tiny
KEN L
  • ADMIN
When the check engine light flashes continuously it means the PCM is bad. I would change it out with a rebuilt unit, you can get by searching Google or eBay, have your VIN number ready. Here are the location and instructions on how to change it out. Check out the images (below). Please let us know what you find.
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Monday, October 3rd, 2022 AT 10:59 AM
Tiny
LOUD_8.1VORTEC
  • MEMBER
Are you sure because your response is short next to my question? Because I want to be sure before dropping $400 to $500 into a new PCM.
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Wednesday, October 5th, 2022 AT 10:48 AM
Tiny
KEN L
  • ADMIN
I think we should do the crankshaft relearn procedure before replacing the PCM, so if you run the codes does anything else come up?

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

We can check the PCM wiring as well here is a guide and he PCM wiring diagrams to help you with the test.

https://www.2carpros.com/articles/how-to-check-wiring

Make sure there isn't a short to ground or high resistance. Check out the images (below). Please let us know what happens.
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Saturday, October 8th, 2022 AT 10:26 AM

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