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p0300, ruh roh!

This is a discussion on p0300, ruh roh! within the External Engine forums, part of the LSx Technical Help Section category; Motor went out locked up we installed this used motor and have been having this trouble ever since. Used motor ...

  1. #41
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    Motor went out locked up we installed this used motor and have been having this trouble ever since. Used motor has 110000 I believe 145 compression don't have the sheet in front of me we ran bg injector cleaner in it hoping it was a couple injectors a little dirty Then swapped out the entire injector rail

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    Checking my manuals, the diagnostic for a P0300 starts with performing a CKP System Variation Learn Procedure. It appears that this has to be completed utilizing a Tech II. The procedure involves plugging in the scan tool, enabling the learn procedure, warming up the engine, and slowly raising the rpm to 4,000 and then immediately releasing the throttle. The engine is then turned off for no less than 15 seconds to complete the learn procedure.

    The remaining diagnostics all focus on O2 sensor output, vacuum leaks, engine grounds, injector wiring harness, fuel pressure, fuel contamination, and restricted exhaust (ie. a bad catalytic converter). Have you checked fuel pressure with the revs up?

  3. #43
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    We had the Chevy dealer do the relearn made no difference also checked for updates checked fuel pressure it is good

  4. #44
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    Back of the intake where the MAP sensor plugs in is leak free? The vacuum "T" back there and associated lines all good? Have you done a spray test around things?

  5. #45
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    Yes checked that oring sprayed test a few times

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    So, if you unplug the MAF the problem completely goes away?

  7. #47
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    Correct with a mass airflow unhooked the scanner will not pick up a single misfire with it unhooked he had a rough idle but that's pretty normal for not being hooked up but no misfires

  8. #48
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    Just changed cam sensor no difference took off both belts just for the heck of it no diffrence

  9. #49
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    What year was the engine you took out and what year was the one you installed?

  10. #50
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    2001 is the one we took out not sure right now of the one we put in don't have the sheet with me of the 1 check sometime supposed to be the same same engine code is there a difference

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    Yes - depending upon the year they can have different cams, injectors, intakes and heads. Could be as simple as a tuning issue.

  12. #52
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    Same here what is the Sahara and one is a Silverado only difference

  13. #53
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    Sorry dang autocorrect it's a same year only difference is one is A Sahara in one is a Silverado

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    Ok -- chances are that they are in fact the same engine then.

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    Yeah where lost pull valve covers next week

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    I was never able to figure mine out. Haven't done quite the level of troubleshooting you have Tbocambridge. I moved away and mine's sitting in storage for the last year, no chance to work on it. But it sounds exactly the same. I recall disconnecting the MAF and not seeing any misfires. Put a new MAF on and they came right back. Please keep posting though. I will be getting back into mine over the holidays and your posts will be helpful. Hopefully one of us gets it figured out!
    Last edited by cheezus; 10-25-2015 at 01:14 PM.

  17. #57
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    Thanks and yes we will be sure to post what ever when ever we find it out

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    What wires and plugs are you guys running? Plug gap?

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    Factory wires first then Napa premium I don't remember the gap but if that was the case shouldn't it be on other cylinders as well

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    Haven't pulled the valve covers yet either going to do a leak down test first and also looking for a local ecm to swap out

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