Help! Strange Noise From Engine...Need to help brother move this weekend!

Discussion in 'GM Powertrain' started by Big6ft6, Jul 23, 2009.

  1. Big6ft6

    Big6ft6 Rockstar 100 Posts

    I have a engine/tranny (TBI 350.th400) is making a wierd noise, but the problem is it only happens under load so it almost impossible for me to crawl around the truck to try and pin-point the where the noise is coming from!

    The only way I can duplicate the noise without the truck moving is to put her in gear, stand on the brakes and give the engine a little gas to simulate a load...and I don't really want to be crawling under the truck with someone else doing that!:gasp:

    Here is my best description. When I'm pulling away from a stop sign, going up a hill or even just up my driveway...doesn't need much load....I get a rapid light metalic "ticking" noise....that increases/decreases with rpm and only happens under load.

    It sounds almost exactly like my metal cooling fan is tapping the edge of my fan shroud, but I took the fan off last night and sound still happened. I've never heard engine knock or pinging before or detonation but this noise almost sounds to "light" to be something that bad....but??

    I'm starting to think transmission maybe the torque converter? What else in the transmission would make a loud ticking noise under load?

    I had my fiance' get in the driver's seat so I could at least walk around the engine bay....I couldn't tell where it was coming from!! It is so frustrating...

    Please help, I have a rare chance to really show off my truck this weekend and help my brother move..but now I'm worried about my truck:neutral:
  2. EvilNetwork

    EvilNetwork Rockstar

    Sounds more like a rod knocking to me. You sometimes can't hear them at idle.
  3. Big6ft6

    Big6ft6 Rockstar 100 Posts

    Thanks for you vote Evil...that would make me very this engine has less than 1000k miles on on it...and becuase I don't drive the truck much..the 1-year warranty on the rebuild is expired. :(

    What is rod knocking exactly? Does that mean the rod is loose and is knocking against wrist pin in the piston or what?

    Rod knocking vs. engine knock vs pinging vs detonation....are they one in the same?
  4. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    To me pinging/knocking sounds like pebbles rattling in a tin can-a bit like you describe.It happens under load, and is usually more common in hot weather. It probably is something else, but it is worth a try to use 93 octane.

    The under load might indicate pinging.
    Try some 93 octane and see if it is less Fill up with 92 with a nearly empty tank , so you actually get 93 octane.

    If the pinging is gone or nearly gone, it is pinging/knocking.

    A build up of carbon can cause hot spots-preignition- or even increase the compression enough to cause detonation.

  5. Big6ft6

    Big6ft6 Rockstar 100 Posts

    Pebbles in a tin can? That sounds too random to be what I'm hearing.

    My noise sounds exactly like sticking a pencil into a house-hold box fan. A very sharp and precise tick-tick-tick-tick-tick...louder than a lifter, but a very sharp tick sound that increases/decreases with rpm but only under acceleration or load.

    An exhaust leak? Maybe?

    To add to the mystery, I hooked up a trailer with a bunch of yard waste the other day and had no problem all the way to the dump and back, didn't make the noise. Seems to happen most right after I start the truck when she's cold, but have had it happen once even after she's warm...

    I'm definitly going to do the high-octane thing to rule out detonation/pinging etc. The noise sounds very something metal rubbing aginst something else that is rotating.
    Last edited: Jul 23, 2009
  6. EvilNetwork

    EvilNetwork Rockstar

    Now that you de3scribe it that way... No I wouldn't suspect a rod. "Rod Knocking" is the pushrod for the piston. What usually happens are that the bearing between the piston rod and the crankshaft get spun or burn up, causing the rod to wiggle waggle around on the crankshaft, throwing it into the cylinder block.

    I wouldn't waste the money on high octane fuel at this point.

    If in a year's time you only drove it 1000 miles, I would say it is probably related somewhere in the valvetrain, especially when you say it now happens most when you start it cold. Try running a little Marvel Mystery oil thru it, then immediately change the oil. You probably have a lifter or somethign that didn't get lubricated properly on the rebuild and the problem has been exasperated by the truck sitting for most of a year.

    Good luck!

  7. Big6ft6

    Big6ft6 Rockstar 100 Posts

    Thanks Joe,

    I really apreciate you putting your head in on this one. I'm at such a loss and none of my immediate friends are car people so they're no help!:money:

    I'll listen again tonight, but last time I tried my best to listen is sounded almost like it was coming from the bottom of th engine or even the back of the engine/tranny connection.

    It idles perfectly quiet with no noise it only makes the noise under load, would a lifter make noise only under load? It only has 1000 miles, but I've driven probably at least every two weeks since the engine install, they're just mostly little trips haulin' and stuff.
  8. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    You are right- if your noise speeds up and slows down with RPMS it isn't pinging. Pinging isn't as regular,and has an almost muted rattlin/crackling sound to it.

    The fact that it doesn't always do it-even when towing something-is probably a good thing.If there was something wrong inside the motor you would expect it to make noise all the time. If it is something outside the motor-maybe the fan clutch.

    I wonder if worn motor mounts could moves "something" around enough to get it to regularly hit something.

    Sometimes a bit of electrical tape getting pulled toward the fan can make a little snapping sound.

    I don't suppose you could talk someone else into laying under the truck while you hold the brake.

    If you are feeling brave, you can put it up against a wall, and have someone brake while loading it up.This way, if the person on the brake slips, he can't run over the listener.

    My guesses
    Fan/fan clutch/alternator/waterpump/ No chance your belt tensioner is goofed up?

  9. Big6ft6

    Big6ft6 Rockstar 100 Posts

    More additional information.

    I took the truck fishing this morning.

    The noise ONLY happens when I'm pulling away from a deadstop and only for about the first 15 ft until I get moving..then it fades away quick.

    I can floor it going up a hill after the truck is moving without a problem. It seems to be related to the initial high torque required to get the truck rolling initially. Now I'm zeroing in on the location being near the tranny bell-housing or the back of the engine.

    In installed this engine myself so I bolted the bellhousing to the bloc, bolted the toque converter to the flexplate, bolted the flexplate to the crank flange etc. I'm starting to worry that something wasn't torqued properly and someting is flexing under the load of the initial start from a dead stop to a toque converter bolt...or flext plate bolt...or something. It is louder if I"m starting on a hill...

    But once I"m moving no problem...even if I give quite a bit of gas...but starting from a stop almost everytime..quieter on level surface, louder on hills.

    Any more really sounds like something rotating running into something. Flexplate, torque coverter?? Am I missing inside the tranny? It almost sounds like the clicking you hear when you slam your car into park too soon before the car has stopped moving....(not that I know what that sounds like:glasses:
  10. cw120568

    cw120568 New Member

    engine knock

    did you find an answer yet ? I have the same noise in a 1989 350 engine i just installed, sounds kinda like a lifter but not quite, coming from the back like the distributor. my engine has new cam and lifters, new distributor, i was wondering about the oil pump rod between the dist. and the pump it was kind of wobbly when i put the dist. in i had a hard time.

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