GM Truck Club
THE PREMIER CHEVY TRUCK & SUV FORUM
Founded in 2004 ~ We're the #1 Chevy Truck & SUV Forum.
Silverado & Sierra | Tahoe & Yukon | Suburban & Yukon XL | SUV & CROSSOVER
Page 1 of 2 12 Last Post byLast Post by
Results 1 to 10 of 33

Hybrid View

  1. #1

    Default What does "detonation" sound like? Engine "knock"?

    So I'm afraid I either have some detonation or "knock" in my new engine in my 89 2500 burb 350 TBI.

    Sometimes...usually shortly after I start the truck when I'm accelerating up an incline (where more torque is on the engine) I get a sound that sounds like my radiator fan is whacking into my fan shroud. I thought the extra torque was "tilting" the engine and the fan was running into something.

    But when I had my finace sit in the truck with and hit the gas and the brakes at the same to time to make the noise...the noise happened, but the fan wasn't hitting anything! It sounded more like it was coming from the engine. Only happens under load, starting from a stop un a hill etc.

    The other thing I noticed was it seems to go away once the truck warmed up.

    This makes me nervous. I'm not sure why my engine would be detonating unless the distributor is shot or was slipping??? But what is "engine" or "rod" knock....I've heard it used all the time but I guess I've never stopped to know for sure what it is?

    Am I experiencing detonation? Or rod knock? What should I do about it?

  2. #2

    Default

    Can you elaborate on the "new engine" I'm not sure I can describe pinging.
    When you hear hoofbeats, look for horses not zebras.

  3. #3

    Default

    If you have heard a Mercedes diesel engine at a stop light or a big truck diesel engine, that is the sound of knocking. Or a United Parcel Service Truck. I know when they are here from the sound of the truck!

    This can be caused by the timing being too advanced. The timing is all done by the engine computer. In general, sensors which input information to the computer which can change the timing are for the following...

    Crankshaft position
    Engine speed (RPM)
    Engine load (manifold pressure or vacuum)
    Atmospheric (barometric) pressure
    Engine coolant temperature
    Intake air temperature (retards timing when hot)

    (Your specific vehicle may not have sensors for all the above)

    Then also there should be a knock sensor. When the engine computer detects knocking via this sensor, it should retard the timing, then slowly advance it to the best setting without knocking. So possible problem with knock sensor not working too.

    Then there can be other problems which cause knocking. Older vehicles have this problem...
    http://www.lemonlaw.com/gm-engine-problem.html

    A GM Factory Service Manual Set would give instructions for checking each of the above sensors. (Order from helminc.com or a GM dealer.)

    Or take it to a GM dealer and they could put it on their fancy electronic testing gizmo's and tell what is going on.
    Last edited by bill190; 07-20-2009 at 05:19 PM.
    92 GMC Sierra 2500

  4. #4

    Default

    You have to set the timing on the 89 TBI. I would start there first. Get a Chiltons or Haynes to get the procedure. He has a knock sensor, but if the distributor is way off, it may not be able to correct.

  5. #5

    Default

    Thanks guys,

    I did set the timing the proper way (disconnect the timing computer wire etc) when I installed the engine (just a rebuilt stock TBI 350 motor) so it was at least o.k. to begin with. So if this is pinging from too advanced ignition timing then either the distributor was not tightened down enough and has moved, or something is malfuncitoning.

    Also, if mytiming was too advanced wouldn't this happend all the time? Not just when the engine was cold?

    Thanks for the description of engine knock...like a diesel...definitly not that sound, this sounded excactly like the very tip of my metal cooling fan was just barely tapping against something, about that speed and exactly that sound.

    Any other ideas?

  6. #6

    Default

    You could remove the fan belt. Start it up cold and drive it around the block. That would prove it one way or the other. Usually an engine will ping more when hot rather than cold. Another quick check is to loosen up the distributor and back it off about 1". That will retard the timing and it should remove the ping if in fact it is pinging.
    Jim

    2004 SILVERADO 2500HD LS
    Pro Comp Leveling Kit
    285-75-16 Cooper ST All Terrains
    Pro Comp Programmer
    Bilstein Shocks
    Linux Bed Liner
    Tinted Windows



    Other rides:

    1967 Landcruiser <350 Chevy>
    1970 Camaro
    1990 Geo Metro Convertible
    2007 FJ Cruiser

  7. #7
    Legend tlperry68's Avatar
    Join Date
    Oct 2008
    Location
    Huntington Beach, CA
    Posts
    1,504

    Default

    The only detontions I've done sounded like KAAABOOOOOOOOOOM. They weren't on motors.

    Rod knock is virtually alway pesent. If you only hear it s the RPM increases you might want to check the motor mounts. Sounds like something is moving and causing an impact into another moving part.

    How new is the motor?
    Trevor - Huntington Beach, CA
    2007 GMC 2500 4X4

  8. #8
    Legend unplugged's Avatar
    Join Date
    Sep 2006
    Location
    High Deserts of SoCal
    Posts
    2,554

    Default

    Quote Originally Posted by Big6ft6 View Post
    So I'm afraid I either have some detonation or "knock" in my new engine in my 89 2500 burb 350 TBI.

    Sometimes...usually shortly after I start the truck when I'm accelerating up an incline (where more torque is on the engine) I get a sound that sounds like my radiator fan is whacking into my fan shroud. I thought the extra torque was "tilting" the engine and the fan was running into something.

    The other thing I noticed was it seems to go away once the truck warmed up.

    Am I experiencing detonation? Or rod knock? What should I do about it?
    I'd bet my money on piston slap. The clue pointing me in that direction is that it seems to go away when the engine warmed up. Piston slap is nothing to worry about. Let the engine warm up and then drive it if it bothers you that much. Search these forums for more info on piston slap.

    Piston slap sounds something like this:

    [ame="http://www.youtube.com/watch?v=RuiJffXOJTY&feature=related"]YouTube - CA18det piston slap?????[/ame]
    There is no way to happiness....happiness is the way.:yipi:
    http://kx6ijq.blu.livefilestore.com/y1pcOFVNH4ix1hjyGUVyXK5LRfef7qSeWzlZDorpQhIEfkZ2ZA  _vXMYypuKMJFw671uF2ZPhjez_j-atRmcjM2zQKpQi1JSsB75/burb1.JPG
    High Desert SoCal
    93 K1500 burb (personal) 350 AT 3" Lift 250K+
    02 Honda Civic LX
    Looking for a 1990's Miata for an engine swap

  9. #9

    Default

    Quote Originally Posted by unplugged View Post
    I'd bet my money on piston slap. The clue pointing me in that direction is that it seems to go away when the engine warmed up. Piston slap is nothing to worry about.

    Yeah, that make sense.

  10. #10

    Default

    U-joints maybe? I just diagnosed my cousin's 2000 Silverado and turns out the front u-joint was GONE. He would have a weird ticking starting off the line and when he'd slow down to a stop. Judging from the fact that you have an 89, I'd bet it's not a u-joint for the front axle, since it was a real transfer case back then, but it could be the front u-joint on the rear driveshaft.
    Christopher

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 277K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half



    There are 10 kinds of people, those who understand binary, and those who dont...

    Remember kids, the only difference between screwing around and science is writing it down- Adam Savage

Page 1 of 2 12 Last Post byLast Post by

Similar Threads

  1. Stock "P" rims safe with "LT" tire pressure?
    By xycarp in forum Wheels & Tires
    Replies: 2
    Last: 05-31-2010, 09:38 AM
  2. 19__ Chevy Silverado"" PARTS ONLY"" No Box? 1/25-1/24?
    By ChevyFan in forum Chevy Parts eBay
    Replies: 0
    Last: 05-26-2010, 09:00 AM
  3. Replies: 0
    Last: 06-21-2008, 12:30 PM
  4. Replies: 0
    Last: 07-24-2007, 12:30 PM
  5. "Monster Mash" Singer Bobby "Boris" Pickett Dies At 69
    By Cableguy in forum The Coffee Shop ~ Chit Chat
    Replies: 0
    Last: 04-27-2007, 10:47 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •