ntc350 bc cummins no power in high gears?

Discussion in 'Trucks [ Eighteen Wheelers ]' started by flc120, Dec 18, 2014.

  1. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
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    well just bought me a lil 90' t800 with a big cam 350 cummins hadnt hauled anything with it yet and i noted that the truck lacked a little power once shifted into hi range. has all filters changed, fuel tanks look clear and clean. now this morning i thru a 80k load of groceries and couldnt get truck to 45mph in the low gears truck feels as if it has power but once you shift to hi range it feels as if it falls on its face completly. turbo whistles and you can hear it spool up no black smoke. you can stand on her wide open throttle and truck doesnt boost in hi range. it has only one filter system for fuel which appears to be original as iits the camister type with filter mounted upside down and coolant hoses going to canister?im not fond of this setup,lines look old and have some sharp turns to pump. i was thinking of bypassing the crap it has now and making new fuel lines from tank to pump direct to see if its a fuel issue.


    anyone else with input would be surely appreciated. hopefully iits something small, i dont have anyone else to ask. ive never had a mechanical cummins do this????

    help please going to haul my second local trip now
     
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  3. little cat 500

    little cat 500 Road Train Member

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    id start with the fuel lines on a truck of that age there prolly swelled shut inside
     
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  4. flc120

    flc120 Heavy Load Member

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    im hoping it is fuel ive never had a problem like this with mechanical cummins engines
     
  5. flc120

    flc120 Heavy Load Member

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    Miami,FL (yeah i know :( )
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    drove to.my second trip of the day, this load felt alot lighter but truck is still not giving me the power???feels like a f250 witha whole lotta weight on it. truck seems to be geared low like a 4:10 or larger has a direct 9spd on 11r24.5 does 55 at like 1600-1700rpms i know shes not a fast truck but it should at least get up to max speed
     
  6. Longhood379

    Longhood379 Medium Load Member

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    Put a pressure guage in the check port where the line to the head comes out of the pump, and see what the pressure is like under load, is the pedal pressure popping the break over spring ?? put a vacuum guage before and after the filter.
     
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  7. baha

    baha Road Train Member

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    Or you can look at pump and put a fuel press. gauge on it to see how its doing?
     
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  8. pup

    pup Light Load Member

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    Dec 3, 2011
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    If the fuel supply & throttle linkage check out ok, i'd look at the fuel pump afc diaphram. A failed afc diaphram would behave the same way. The engine will not get max fuel pressure. Remove the steel line that runs from the intake manifold to the back side of the pt pump. Fuel in the line indicates a failed diaphram. I adapt a radiator pressure tester hand pump to the line to check if the afc chamber holds air pressure.
     
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  9. Mr.X

    Mr.X Heavy Load Member

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    Yup,and make sure that turbo whistling aint an air to air leak, If it sat for a few years without full tanks there could be quite a lot of water in the bottoms of those tanks, maybe somebody turned the pump down? Maybe play with the button and see if you can get better throttle response. I have run a 350 just recently in a log truck and nobody knows the difference, of coarse log trucks go up the hill empty and down the hills loaded. 2400 rpm on the flats, few trucks can catch me, lol.
     
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  10. flc120

    flc120 Heavy Load Member

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    Miami,FL (yeah i know :( )
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    well thanks for the input guys, i dont have access to guage, if i did were do i connect it to. i have a gas fuel pressure guage will it work?
     
  11. flc120

    flc120 Heavy Load Member

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    Jul 11, 2012
    Miami,FL (yeah i know :( )
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    also let me add that im figuring the pump to be open cause when you rev it from idle truck goes over 2k rpms no issues and revs well. last night i deleted fuel filter setup it had and ran a bypass with the same lines, just did my first trip of morning on highway it felt somewhat better but not much, still no power goin up hill. let me add truck doesnt miss or smoke whatsoever anything. i plan on running new lines with a universal filter base and mount a 1000 type filter.
     
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