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??Knocking Problem??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by mpascino, Mar 18, 2001.

  1. mpascino

    mpascino 1/2 ton status

    Jan 1, 2001
    Likes Received:
    Maybe someone has had a similar problem.....I recently installed a new motor in my K-5. 350 bored 30 over 10.5 compression mild cam and so on running off of a TBI fuel injection system. I built this motor a few years ago , ran it in my own car, pulled it and it sat for two years. Now there is a ?knock? in the motor. It always ran perfect before. I have changed all the rod bearings and the main bearings along with the oil pump and pick up. I still have a knock. When I pull the sparkplug wire out of the #2 cylinder the knocking stops, I honeslty think the sound is the cylinder firing into the exhaust header.... Has anyone else had this problem? Also after the motor warms up the oil pressure drops very low, is it possible it could be the sending unit for the guage? The guage is kind of jumpy so I think it is in acurate. I am in direr need of advice anyone got any suggestions?
    Thanx ,

    You call that dirty!?
  2. jimmyjack

    jimmyjack 1/2 ton status

    May 11, 2000
    Likes Received:
    Tucson Az
    When you pull the #2 wire and the knocking stops that would indicate a bad cam lobe I think. Make sense? Does it do it more under load or all the time. I had a cam that was burned up and it would back fire through the carb. Thats all I can offer. Good luck, keep us posted.

    creepin' and crawlin'

  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Feb 17, 2000
    Likes Received:
    Yeah I have seen your issue. Infact I'm fixing it on my Supra Right now. Burned the exhaust valves on #2 when the injector went lean in my case. I would start by doing a compression check and see what you get. In my case I was showing great on all cylinders except #2. I took the check valve out of the compression test hose and hooked it to my air line while on TDC of that cylinder. Sure enough I was getting major air out the tail pipe. Pulled the head and both exhaust vavles were burnt.
    My guess is that you went lean because of the TBI. Either your O2 sensor gave it up or the TBI is not adjusting for the Cam and compression. Probably a burnt valve....maybe a stuck lifter holding tha valve open. Possibly a stuck valve from sitting. Had decent luck with GM Topend engine cleaner. Ran some though the Supra motor trying to cure my issue. opened the engine right after and it really did clean and soften up the carbon. If it's a stuck intake valve I would say there is a good chance it could free it.

    Diging it in the dirt with my K5's
    <A target="_blank" HREF=http://grimsk5s.coloradok5.com/>http://grimsk5s.coloradok5.com/</A>

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