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Rod Knock?

Discussion in 'GM 6.5 Diesel Engines' started by GMC 6.5TD Guy, Jun 2, 2009.

  1. GMC 6.5TD Guy

    GMC 6.5TD Guy New Member

    Jun 2, 2009
    Guys, first post on this site and wanted some more opinions on my knock

    I'm not exactly sure what the cause of the sound coming from my engine is but I'm sure its not good.

    The truck was just normal and then the next day started to make this loud tick sound that really gets loud with engine rpm increase. Oil pressure is albout half scale on the gauge and steady warm.

    I've gotten in around the engine with a broom stick but I couldn't isolate where its coming from, I'm listened to the vac pump and its pretty quiet. Top pans have some ping but not quite like I'm hearing.

    I've checked the balancer/pulley, couldn't move the balancer with both hands and the pulley moved a little when I wiggled it but the rubber looks pretty good but has a rough surface.

    I had the belt off and ran the truck, no difference.

    New injectors last year and no smoke black or white.

    Hopefully its nothing serious. Thanks in advance.

    Vid, hopefully will work, still not sure how to do links


  2. GMC 6.5TD Guy

    GMC 6.5TD Guy New Member

    Jun 2, 2009
    Sorry bout the checklist, gotta get used to the site.

    0. Describe in detail the problem you are having. Please be as descriptive as possible.
    Strange tick/knock in engine. Changes frequency with engine rpm.
    1. Does the engine crank, or 'turn over'? Yes
    1a. Does the engine start and run? Yes
    1a1. If the engine does not start - Crack injector line: do you have fuel? Yes
    1b. Do you have a Wait To Start Light & the amount of time (seconds) lit. Yes - Normal
    1c. Ambient Condition (temperature outside indicate F or C) 15 C °
    1d. Engine Cranking speed (if you have an accurate tachometer). Normal
    1e. Are you experiencing stalling? No
    1f. If Stalling, describe (upon startup only, down the road, hit a bump etc) N/A1g. If Stalling, do you notice loss of dash or instruments? N/A
    -note if experiencing stalling,you must indicate PMD location in #24.
    1h. Check turbo inlet and air filter for obstructions. Cone filters have lost disk and stopped air to turbo. None
    1i. In a no-hot start, pour a bottle of room-temp water on the injection pump. Does it start now? N/A
    1.1 Lift pump test - describe results - Fuel flow with no stall
    2. Service Engine Light while running?- On
    2a. Service Engine light does glow during start/cranking/bulb check: Yes
    3. Model year - 1996
    3a. Odometer reading (indicate if in miles or km) 280 000km
    3b. Miles on major engine components if been replaced (example Injection pump) - Turbo, crossover, CDR, injectors - Last Summer New.
    3c. Indicate the model number on the Injection pump (starts DS4 or DB2......) - DS4
    4. Have you scanned for engine codes? (varies by pre/post 96) - Yes
    5. List exact results on engine codes: P0712 and P0406 Always been there
    6. Air Filter condition (visual check) - Good condition
    7. Fuel filter condition (freshly changed/condition unknown/mileage since changed) - 6 mon old
    8. Condition of Battery terminal connections (removed, cleaned and tightened) - All Complete
    8a. Known condition and age of the batteries. - <1Yr Good condition
    8b. Are batteries of differing age or are they a matched set? - Same age and matched8c. Condition of Major Grounds. (same drill as batt - removed, cleaned, retightened) - All Done
    9. Upon cold start, does the radiator hose get hard quickly? - No
    10. Upon cold start, do you have excessive white smoke? - No11. Do you have excessive cranking time before the engine starts? - No
    12. Have you used the block heater, and does this effect engine starting?(only try for starting problems) - N/A
    13. During hard acceleration, do you have excessive black smoke? - No
    14. Do you have any unusual exhaust smoke issues? - No - A little white on startup
    15. Turbo check out - pass
    16. Do you have an EGR on the engine? (An F or an S engine code 8th VIN digit) - S
    17. Indicate if you know if it’s a 1500, 2500, 2500HD, 3500, 3500HD. - 1500
    18. Indicate fuel that you are using: Bio-diesel, #2 Diesel, #1Diesel, SVO/WVO, other - #2
    18a. If running a VO (Veggie Oil fuel) setup, indicate details of your conversion (homemade, or packaged system)
    19. Are you using any fuel additives? If so, please list. - TC-w3
    20. Please indicate geographic region you are in: (example: Texas or Canada) - Canada
    21. Do you have any service history available that might pertain to the problem you are having? - No - New oil a month ago
    22. Please indicate any modifications to the vehicle that might help us diagnose better. - EGR delete recent
    23. Upon unscrewing the fuel cap, do you have a large vacuum formed in the tank? - No
    24. Location of PMD/FSD? On the pump/remoted over intake/remoted out of engine bay (please specify placement specifically) - Skid Plate
    24a. If remote mounted, describe wiring harness (homemade or purchased from a vendor?) - Homemade
    24b. Indicate the location and condition of the FSD/IP grounding wire. - on IP
    25. Are ALL glow plugs in proper working order as per this thread? - yes
  3. ak diesel driver

    ak diesel driver 6.5 driver

    Feb 7, 2009
    IIRC a rod knock will get quieter as you rev engine and get really loud when you back off. A main will stay pretty consistent. Having said that I have had injectors that sounded like a bearing going out.
  4. GMC 6.5TD Guy

    GMC 6.5TD Guy New Member

    Jun 2, 2009
    My knock is consistant, increases with rpm. Did the vid load? I can't see it.
  5. GMC 6.5TD Guy

    GMC 6.5TD Guy New Member

    Jun 2, 2009
    I did do some listening again and it appears that the pulse in the injector lines is in time with the knock.
  6. CtChevy427

    CtChevy427 Still Kicking.... Staff Member Lead Moderator

    Apr 14, 2008
    North Haven, CT
    Could it be valve train related?
  7. mitchedo

    mitchedo New Member

    Aug 9, 2008
    Bountiful, UT
    I vote rod knock, or bad lifter. It's not the chuff-chuff sound of a stuck valve. It's not the typical tic tic sound of a bad lifter (though the sound quality of Youtube isn't that great); What I hear is the definite heavy metallic sound of a rod knock. The rod knocks I've heard are pretty consistent with rpm changes, though sometimes putting a load on will change the sound up a bit. I had a far more subtle noise than that in my engine before the rebuild. It is gone now.

    Of course, there is the ever-present possibility of a wasted vacuum pump or crank pulley or harmonic balancer, or even a busted flex plate, but the sound is definitely metal on metal to my ears through my Klipsch ProMedia speakers.

    I have never heard an injector knock, but I have heard rod knocks and valve train noise, so my opinion is worth exactly what you paid for it.
    Last edited: Jun 3, 2009
  8. Missy Good Wench

    Missy Good Wench Wild Blonde from Cloud Mt

    Nov 19, 2008
    Newberg Oregon
    The noise I am hearing sounds like Crank speed rather than cam speed.

    Gert a helper and try loosening each injector line one at a time and see if you can isolate it.

    This does not sound like a rod or any bearing for that matter.
    Bottom end issues are usually very hard sounding.

    Very well may be an injector taking a leave.

    How many miles on the engine??

    Possibly a wrist pin bushing that going or gone.

    These engines have a habit of wearing out wrist pin bushings.

    Keep the faith Bro.

    Last edited: Jun 3, 2009
  9. GMC 6.5TD Guy

    GMC 6.5TD Guy New Member

    Jun 2, 2009
    280 000km on engine

    I have checked the pulley and balancer, tried to wiggle them with both hands. Couldn't get any movement of the balancer a little from the pulley. Ran it with the belt of still there so I'm thinking its not related to those componets.

    I hope its not bottom end related:nonod:

    I do know that when I first start the truck cold there is no noise, then after a few minutes it starts and it start very quickly. Like flipping a switch.

    I took it for a short ride the other day, from a cold start I left the driveway and there was nothing but by the time I got 50ft from my drive, bam started to knock.

    How can I identify a bad wrist pin without having the engine apart?

    Thanks for the help guys, hoping for the best.

  10. GMC 6.5TD Guy

    GMC 6.5TD Guy New Member

    Jun 2, 2009
    Can I do a wrist pin with the engine still in the truck?
  11. Slim Shady


    May 28, 2008
    Check the easy stuff first, I am betting injector stuck open or leaking. Been there and done that, crack each injector until you find the one that is causing the noise.

    Injectors sound just like a rod knock and vary with engine speed they get louder as the speed increases.
  12. Matt Bachand

    Matt Bachand Depends on the 6.5

    Jun 10, 2008
    Worcester, MA
    Each circumstance varies, but wouldn't an injector open enough to cause a knock (predetonation) also show white smoke out the pipe?

    My injector knock was only under acceleration, and the white smoke what clear as day. It wasn't 100% tied to engine speed always for sure.
  13. Matt Bachand

    Matt Bachand Depends on the 6.5

    Jun 10, 2008
    Worcester, MA
    Cracking the injector lines may also help indicate which cylinder you are having trouble with, even if its not an injector issue.

    If you notice big change from cracking injector, swap it with another injector and see if it follows.

    The sound may go away when that cylinder looses the fuel and starts missing. Even if its not the injector, you can verify bank/cylinder before ripping into it, hopefully.

    Someone with a proper scanner can even shut down cylinders without busting out a wrench if you know anyone.
  14. Slim Shady


    May 28, 2008

    Brand new injectors in my new rebuild a few years back and ran fine then started to knock :eek: loud knock to. Sounded like a rod and finally cracked injectors and the knock went away when I hit the right injector. WHEW :D

    Actualy there never was any smoke at all burned clean
  15. 96TD

    96TD Recruit

    May 6, 2008
    Wilmington, MA
    I have the same problem as GMC, and I'm trying to look at it this weekend. How much do you have to open the injector line to find out if this is the problem? I cracked a few just a little, just until I got a small amount of fuel out of it. Do you have to open the line alot?
  16. Matt Bachand

    Matt Bachand Depends on the 6.5

    Jun 10, 2008
    Worcester, MA
    just enough for the engine to stutter/stumble/miss, usually happens at same time a little fuel comes out, enough to stop the pressure buildup so the injector doesn't pop. keep in mind that little dribble of liquid fuel you see, is all the injector gets and with the pressure and nozzle it 'atomizes' it into gas form.

    So, no, not a alot.
  17. 3500GMC

    3500GMC What T F, over

    Jun 7, 2009
    Nashport, Ohio
    GMC 6.5 TD Guy, did you find the problem? The sound your engine is making resembles what I am dealing with right now.

    As soon as this front passes by and quits raining I'm going to get out some wrenches .
  18. bison

    bison Well-Known Member

    on a stuck closed injector releasing the press is enough,on a stuck open one you may need to back off the nut a couple of turns and pull the line off its seat.
  19. 96TD

    96TD Recruit

    May 6, 2008
    Wilmington, MA
    Well, I didn't want to hijack, so I started my own thread since I have two motors with similar sypmtoms. It is titled My rapping motors. If I find anything out, I will definately post here though.
    I'll start now. I ordered a set of injectors from Heath Diesel/ I figure even if the motor is gone, I'll use them in whatever goes under the hood. Anyway, I talked with Bill, and he said if it was overheated, which it was, then it may have a damaged piston. He suggested that I remove the oil cap, start it and let it idle. If the oil chimney chugged like a choo choo, then I have a bad piston/cylinder. Well, I have a locomotive under the hood. So, you might want to try that. I tried it on my second motor, and it had blow by, but it wasn't chugging. So this may actually be a viable motor. I'll try the injectors in this motor first.
    Good luck with your diagnosis. If I have any updates, I'll let you know.
    On a side note, has anyone noticed that alot of people have been major motor problems?
  20. GMC 6.5TD Guy

    GMC 6.5TD Guy New Member

    Jun 2, 2009
    Sorry for the delay but I was tied up pretty good with non 6.5 issues over the last couple of weeks but I'm back at it again now.

    I bought a scope and I did some listening, here is the results:
    -Oil pan, hardly any noise other than a whirring
    -Injectors, all sounded similar. They were all "ticking" but none stood out to me
    -Block, usual diesel banging
    -exhaust manifolds, normal on drivers side, knocking on pass side
    -valve covers, drivers side pretty quiet, pass side knocking, in tune with the overall knock

    So I've got the upper intake, lower intake, turbo, inner fender and injector lines to get off now so I can take a look inside that valve cover. I'll keep posted with pics when the time comes.

    96TD or 3500GMC any luck on your ends?

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