6nz"d BXS Acert thumping noise

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by w9l, Jun 29, 2020.

  1. w9l

    w9l Medium Load Member

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    In an 05 379 build date May 04. Bxs 550. When it was still a Bxs with an other than original ecm (I don't know what ecm just that it was a totally different pin count than oe) it made a thumping noise in a pull like someone trying to kick a hole in the front floorboard/firewall area. Converted to single per shop recommendation. BW 1496988 Disabled iva and use 6nz ecm. Did great for about 5k miles before it blew head gasket and hydrolocked overnight. Inframed with Cat industrial low comp cyl packs. 6nz head. Reman Cat cam. Reman Cat injectors. Did great for about 14k miles. Power and mileage decent. Then started that thumping again. Took it back and complained. Shop ran overhead and took fuel away from it. No noticeable change. Complained again, same thing. Truck has Scangauge on it. Shows 585hp tops. Disgusted with shop so took it to another with dyno cause that is what I figure it will require to find. They remove fuel temp mod (I didnt know it had) ran overhead and did something to calibrate???timing. Did cut out test, blah, blah. All good, no dyno. Guess what? Still thumps, but now water and egt are higher and fuel mileage down .5 into mid 3's. Thump is much worse when engine is heat soaked and pulled below 1500. Makes good power but I keep it wound up like a B/C model all the time. I think it is a mechanical issue with injectors that a laptop doesn't show. Is that possible? All anyone wants to do is cut fuel or put a different tune in it. So far, cutting fuel has been poor bandaid for problem. Guy wants to put his "enhanced 550 1850" file in it for around a grand.....
     
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  3. w9l

    w9l Medium Load Member

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    Forgot to mention.. Broke shaft on s410sx 1496988 at 120k miles. Cold side disintegrated. Tops out at about 41psi on new gauge but needle bounces about 2 or 3 psi when thumping.
     
  4. Dodsonf855

    Dodsonf855 Bobtail Member

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    Check for broken valve spring. May possibly be valves trying to gall in guides. Just ran thru this with a tuned up emodel. Head was built at machine shop and guides were teamed too tight. Not trying to scare but some thing to think about.
     
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  5. Shawn2130

    Shawn2130 Heavy Load Member

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    My company truck with over 1 million miles on the 3406 E (almost 40,000 hours) is in the shop now getting new wiring harness installed and several sensors.

    Truck sounded like it was running with a dead cylinder but runs on all 6.

    Shop did injector cut out etc. Can’t find the problem. All 6 injectors pass.

    Under load the truck would shake like the crank will break.

    Cat ET couldn’t pull up any codes. Everything is good. Likely mechanical.

    They said just change the injectors. All 6 done, top set done.

    Truck also smoked pure black At times, also felt like it’s pulling harder than normal with a full load.

    A few weeks later, I got the truck to pull hard coming up to the mechanic shop, got the flashing light and half power.

    Told the mechanic to check quickly before the computer clears it like it was doing previously. The light goes out but the mechanic caught the code.

    Found the problem, 5 volt reference, low voltage. Bad wiring harness.
     
  6. w9l

    w9l Medium Load Member

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    Supposedly, all sensors and injector harnesses have been changed since this condition started. After getting the inframe done it seemed to really clean up and act right for about 10-15k miles. I have never had it smoke pure black. Your description under load is near spot on. Engine is extremely noisy to me at all levels. Sitting idled up included. Truck has a straight thru 42" muffler underneath and 7" straights with drive in inserts in them, also straight thru but only about 2 ft long. My W990l 425 mechanical has an 18 inch sort of a muffler behind turbo, under floor with 6" straights and is alot quieter and smoother idling or wot. 5 decibels cruising. And it is far from stock.
     
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  7. Shawn2130

    Shawn2130 Heavy Load Member

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    W9L: Just got my truck back today.

    so far the missing has disappeared.

    hopefully it stays that way.

    The mechanic showed the wiring harness to me, it was in terrible shape. Old.

    This truck is completely straight piped.

    No muffler anywhere other than the turbo.

    It’s horrible to hear the engine sputtering, popping and missing when it’s loud.
     
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  8. w9l

    w9l Medium Load Member

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    I hope your ills are cured. The guy working on this one claims it is in the "tune" and while I am skeptical of that it seems that needed eliminated as a variable to proceed. He cleared and flashed what he claims is a known proven 600 file with no guaranty it would cure the problem but with the agreement if the driveability- mileage and temps - didn't improve he would either tweak it or reflash it. Who knows? I am thinking maybe better off to invest in an amp and some subs....
     
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  9. Shawn2130

    Shawn2130 Heavy Load Member

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    This morning is the first time the truck fired up and ran smoothly.

    Hauled a 200 Deere excavator 1 hour one way and so far, no missing.

    Just smooth Cat power.

    While the injectors were not at fault, the ones in the engine now does produce a bit more power.

    They’re smokier than the previous ones but clean up nicer.

    Overall, I’m happy.

    The last truck I had, a 2001 Sterling with the M11 Cummins, went through a lot of injectors. 2 shops worked on it, replacing ones they thought were bad and I did some too.

    One rebuilt injector lasted 900 miles. Another lasted 3,500 miles.

    Then my boss gets a set of 6 used ones. They went trouble free for 31,000 miles.

    Then 2 more failed.

    They caused a lot of shaking and then gets stuck open keeping the engine up at 1,500 rpms making it a pain to shift gears since the top rpms are about 1,700.

    I’ve learned since then that New injectors are the way to go, not just for big trucks but diesel pickups as well.

    But my boss still doesn’t want to pay the price of new so gets them rebuilt.
     
  10. Shawn2130

    Shawn2130 Heavy Load Member

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    Also, I have a company 2005 Freightliner Classic with the BXS ACERT.

    I’m in the process of overhauling that engine.

    While I have read and seen a lot of people convert to the single turbo, (my boss wants to too.) I have chosen to keep the 18 to 1 compression pistons, and the 2 turbos.

    The computer is flashed with a 575 hp, 2,050 tq file which worked well.

    The inframe is being done due to a cracked head from the previous driver running it without coolant (more than once). He had the 550 Cat file. Not the file I have now. Big difference between the 2 files.
     
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  11. Brettj3876

    Brettj3876 Road Train Member

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    Deleted IVA's, 18 to 1 packs and way way too much timing did the head in. Lucky that's all that happened and the pan wasn't laying on the ground.

    You wanna retard the timing when dumping more fuel in. As the engine gets heat soaked, hotter intake temps + hotter fuel will actually ignite it sooner (meaning even more timing) so much that it's trying to force the crank to spin opposite way.

    Read this article. The guy goes way in-depth

    maxxTORQUE: Diesel Timing
     
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