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I own a 1996 Chevy Tahoe. It is a 5.7L Vortec with 4 door.

The engine is knocking and pinging and the power is sluggish after there were some servicing done and I can see that the CMP/CKP correlation is off in the scanner. Before I take the truck to the service to have it fixed, I would like to make sure about some things.

The servicing done was basically replacing the valve lifters. This procedure means the whole engine is disassembled and assembled again. I realized the distributor cap is not aligned correctly, thus there is some offset in CMP sensor readings.

Questions:

  1. Camshaft position sensor (this is the CMP/CKP correlation) gives -11 degrees at 1000 RPM. It should be 0 degrees, right?
  2. "Ignition timing advance" value though, is something around -26 degrees (could be +26 degrees as well, not 100% sure). What's the ideal value for this?
  3. Are these values related? I know #1 is fixed with distributor rotation but I don't know how #2 is fixed, or even if there is something to fix.
  • Why is it out of time in the first place? Did you have the distributor out? Something you might try in before you take it to shop (if you haven't been mucking with the distributor) is to disconnect the battery for 30 mins then reconnect. This my force the system to relearn and then run correctly. – Pᴀᴜʟsᴛᴇʀ2 Feb 20 at 11:53
  • Thanks for the suggestion. I updated the question. – Ali Ok Feb 20 at 11:58
  • Before you do the reset, it sounds like your distributor is out of time. Double check to ensure your timing is set correctly and that the alignment between the #1 spark plug wire (where the rotor points on the distributor cap) when the engine is at TDC on the #1 cylinder. It is really easy to get this out of time by one or two teeth during reassembly. Also double check to ensure you've got your wires going to the right cylinders. – Pᴀᴜʟsᴛᴇʀ2 Feb 20 at 12:06
  • Thanks @Pᴀᴜʟsᴛᴇʀ2 . Distributor timing is about CMP/CKP right? What about the questions #2 and #3? Any idea? – Ali Ok Feb 20 at 12:42
  • If you get distributor timing correct, it will most likely clear up the problems in #2&3. If your distributor is one tooth off, it could account for the 26° you are seeing (you'd need to advance it one tooth to compensate). There are 13 teeth on the distributor gear, which equates to ~27° per tooth. If you get the timing right and do the relearn, I think it will clean up all your issues. Just a hunch. – Pᴀᴜʟsᴛᴇʀ2 Feb 20 at 13:18
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The distributor may have been installed incorrectly or not adjusted after install.

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  • That would fix the CMP/CKP offset but what about the ignition timing advance? Any idea what the ideal value for ignition timing degree is? – Ali Ok Feb 21 at 6:38
  • Advance is controlled they the PCM, so there is no ideal value. – Moab Feb 21 at 14:22

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