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Strange KNOCK.....help me figure it out

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by twenty_below0, Dec 15, 2001.

  1. twenty_below0

    twenty_below0 1/2 ton status

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    OK, the story goes like this, the other night I was going home and noticed the truck felt as if it was pushing something, so I stopped and listened to hear it RATTLING like crazy and my oil pressure was at 0 at an idle, at 40 mph it was at about 20 lbs. on the guage and the temp. was a little higher than usual, 210, also now had a miss at idle so I lempt it home and put another pump in it the next day,(last knight) Pressure went back to normal but still rattling, just not as bad......and the really rough idle is still there, like it's only firing on 7 cylinders, checked distributor and it was pretty burnt changed everything but the wieghts and springs and the wieghts are worn out )bushing) but cant get them here, so put some others in that weren't quite as bad, still the same symtoms, rough idle etc. and if you slowly give it gas up to about 3800 it sounds fine smooths out but if you throttle it then it KNOCKS, like a valve slapping a piston, or firing on 2 cylinders at the same time, sharp pop, pop, almost like a sharp back fire, and if you try to start 1 out of every 4 will be hard to turn over like a timing problem or when one get's HOT, but the motor has about 10,000 on it and didn't jump time so did the lifters FAIL because of the low oil on the top end or is it in the distributor, an ignitiom timing problem, firing at the wrong time....I'm am really puzzled and dont want to tear the top end apart if it's in the distributor or something........any suggestions THX Mike
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I think the first step would be a compression test. Confirm that all 8 make good compression. If the compression checks OK I'd fire it up and start pulling plug wires off one at a time. If it's missing at idle you'll find out which cylinder is missing cuz the idle speed won't change. Use insulated spark plug pliers...

    You say you swapped the oil pump? Any chunks in the pan? I doubt it has anything to do with the distributor or timing if all this started with a '0 oil pressure' situation. What pressure does it have at idle with the new pump? If the motor was oil starved long enough there are many things that could have happened...flattened cam lobes, ruined bearings, scored cylinder walls etc etc etc.

    Good luck

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
    <a target="_blank" href=http://coloradok5.com/gallery/project_T2> tRusty pics...</a>
     
  3. twenty_below0

    twenty_below0 1/2 ton status

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    Yeah a compresion check is a good Idea, I will do that, NO on the chunks or shaving etc. looked good and pressure is 15 at idle and 40 at 2,200 rpm's after it's good and warm 195 degrees, a littlen bit of fine smooth grey graphite type stuff in the bottom of the pan, since this only the 3rd oil change I believe it's from braking in.....maybe not??he pump was a high volume pump and the reason it quit PUMPING was the tube slipped out about 1/2", the new pump is also a high volume....how probable is the cam going out?it was ran at 20lbs. of pressure for about 30 miles at 2,200 rpm's so not bad but you could here the top end rattling a bit. THX mike
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I would just eliminate any major problems first. If the compression checks out then go from there. It just seems odd that it started to run like crap as you lost oil pressure. I hope it's not related...

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
    <a target="_blank" href=http://coloradok5.com/gallery/project_T2> tRusty pics...</a>
     

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