3406B hopping/starving for fuel

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by PSM379, Nov 27, 2021.

  1. PSM379

    PSM379 Medium Load Member

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    I will try to explain this to the best of my ability. I am running a 3406B cat it is a 7FB 400 HP water jacket engine. I had a similar issue with 1 of my other mechanical engines I had and what fixed that isn’t fixing this. Engine pulls strong, starts strong, runs good for the most part. Now under a load let’s say I’m rolling into slow traffic, down shift still rolling 1400ish rpms, I get back into the throttle easy I get what feels like a hopping/sputtering, now if I try to roll into the throttle gently it will continue this, if I back out and then get into it hard it some what smooths out. After bouncing it back and forth with good friends that now there stuff and my experience with these engines also I thought for sure collapsing fuel line under suction. 2 weeks ago replaced every fuel line, new fuel filters, removed primer pump and installed block off plate, and it still did it to me. Transfer pump? Something in injection pump? It was rebuilt 1/2021 when engine was done. This has been doing this since the rebuild, sometimes it can go a few days without doing it. Since the truck sat a while and the fuel lines all looked dry rotted and old I figured it had to be it, and with freight finally slowing down and bit and doing some other engine work I finally got around to doing all the fuel lines. With no luck. I know there is some great knowledge here so figured I’d look for advice. I’m sorry if I come across like a idiot and not explaining my issue well. Thanks in advance for any input and help!
     
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  3. Oxbow

    Oxbow Road Train Member

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    I'm not going to be able to help as all I can think of is the transfer pump. Everything else that I can think of would likely be consistent and not sporadic. Things that come to mind are air to fuel ratio, timing advance sticking, or maybe the governor flyweights, but if that was rebuilt recently it shouldn't be the governor.

    @wore out , will be able to help if anyone can.
     
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  4. PSM379

    PSM379 Medium Load Member

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    Thanks for reply. Wonder if they transfer pump would be sporadic like this. It does it often under a load, even if I’m cruising down the road 65 mph 1500 rmps if I just lift a bit to let a truck merge or traffic flow slows up, just as I get back into it, it does it. Wish I could get a video of it. It would be hard though.
     
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  5. Oxbow

    Oxbow Road Train Member

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    I wouldn't think so. Do you have a fuel pressure gauge? That would probably answer that question. I suppose a bad nozzle might be a place to look as well, but then again I would think it would be consistent.

    I'm just spitballing here as I am no mechanic, just happen to own a couple of B models.
     
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  6. Oxbow

    Oxbow Road Train Member

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    This is going to sound funny, but do you run Cat fuel filters?

    The reason I ask is we needed to change filters on our excavator recently and didn't have the Cat replacements with us. We did however have a Napa filter.

    The hoe ran good for a few hours, no fuel filter restriction warnings via the ecm, but then started to cut out periodically. I figured we had another problem, but thought to change to the correct filters before calling a tech out. Sure enough that was the problem.

    I try the cheap fixes first. Lol
     
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  7. PSM379

    PSM379 Medium Load Member

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    Thanks, yes I only run cat filters.
     
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  8. AModelCat

    AModelCat Road Train Member

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    Did it since overhaul? They get the fuel pump timing off or timing advance is sticking?

    Get any smoke out of the pipes when it acts up?
     
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  9. wore out

    wore out Numbered Classic

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    What water separator are you running? If it’s the canister style with the screen you can clean they will sometimes suck air around the center bolt on top, the o ring around the can itself and around the bottom if over tightened. Check the finnting on bottom of transfer pump they are bad to be a little loose and suck air. I have also seen the check valves in the transfer pump get hard from sitting and cause a low fuel pressure issue.
     
  10. PSM379

    PSM379 Medium Load Member

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    No smoke actually.
     
  11. PSM379

    PSM379 Medium Load Member

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    thank you. Will check it out, running a spin on water separator right now.
     
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