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A25c won't accelerate

Discussion in 'Shop Talk' started by Dakotab19, Jun 10, 2019.

  1. tctractors

    tctractors Senior Member

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    The A25C has a wing mounted fuel tank plus a rear of cab high mounted boost tank, if the tanks are filled up you will not have any Sucking air issues, it is common to find faulty lift pumps on these engines but they still manage to run well enough, the Alpha drive can be something to check plus the torque stall speed will give you good information on the engine condition, a few air bubbles in the filter bowl would not be your running problem, your looking in the wrong place if it starts, revs and sounds good. tctractors
     
  2. Dakotab19

    Dakotab19 Active Member

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    So I did some testing with a fuel can today, and feeding the pump with another can didn't do anything to help the air bubbles, but what I did notice was that the pump consumes a lot of fuel. I ran the truck for maybe 2-3 minutes and it sucked a lot of fuel out of the can.

    This caused so much return fuel to be sent into the bottom tank (which was practically full) to finish filling it all the way and caused fuel to shoot out the feed line.

    Is this normal for the pumps on these to have such a large amount of return fuel.
     
  3. Dakotab19

    Dakotab19 Active Member

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    So if the valve is good will the pressure at the bleed port on the filters, where my book says to take fuel pressure readings, be somewhat consistant?
     
  4. Dakotab19

    Dakotab19 Active Member

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    What is the Alpha drive, and what do you mean by torque stall speed?

    The truck starts good and sound good but it revs up real slowly, and when you try to drive it it just acts like it has no power.
     
  5. Se.la

    Se.la Well-Known Member

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    Can you do a stall test and give us the max RPM you've got.
    should be between 1850-1950 rpm
     
  6. tctractors

    tctractors Senior Member

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    Dakotab, its not intended to sound bad but you are somewhat flogging a dead horse worrying about a few bubbles in you jar, the rear fuel tank is 2 feet higher than your engine, the alpha drive is the bit in front of the injector pump that drives your pump, its an advance - retard injection control oil pressure fed, to stall test your torque you need to stuff it in gear 2nd or 3rd and stall the drive via the foot brake or up against resistance then stuff your boot into the throttle and note the rev speed, then under no load note the high idle speed, then post here but no half baked crap like " Around or Nearly" but the correct data. tctractors. p.s. How many up-shifts will the G/Box make on a clear flat road? does the Torque lock in the low gears? is the drop box in high or low?
     
  7. Dakotab19

    Dakotab19 Active Member

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    Will just putting the gear selector in to 2nd or 3rd gear positions from a stop be ok to stall test the truck?
    I cannot get the truck to accerate past 5 mph even on a level surface, when you try to accelerate the truck just barely moves along and has no power. It has so little power that on slightly muddy ground, where it sunk in a bit, the truck had to be pulled out by a tractor.
     
  8. Nige

    Nige Senior Member

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    G..G..G..Granville.........!! Fetch your cloth.
    Yes. You need to do 2 tests: -
    1. With the transmission in neutral and park brake on, accelerate the engine to full throttle - note the maximum RPM.
    2. Release the park brake, put your left foot on the service brake, and put the transmission into 2nd or 3rd gear. Floor the throttle with your right foot - note the maximum RPM.

    Post those two numbers back here.
     
  9. Dakotab19

    Dakotab19 Active Member

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    Does anyone know what pressure the overflow valve should open at, I decided before I did the stall test I would check it, also will the valve always leak some?
    I tested it with air and a regulator and it opened around 12-15 psi. ( Sorry for the gap but the regulator I have isn't the most precise)
     
  10. thepumpguysc

    thepumpguysc Senior Member

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    1.5 bar..== 21 psi..
     
  11. Se.la

    Se.la Well-Known Member

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  12. Jam

    Jam Well-Known Member

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    Hi all. I am really late to this party but I had this problem a few years back with an A25c. Looking in from the front of the engine there are two air solenoids under the right hand side of the windscreen. One of mine stuck in an open position sending an air supply down to the trans retarder. These trucks don’t need to be in gear for the trans retarder to work. The truck would hardly shift out of first. Disconnect the air supply temporarily to these valve and let us know. I have a thread here somewhere about rebuilding that truck that goes through it all?
     
    Se.la likes this.
  13. Dakotab19

    Dakotab19 Active Member

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    Do both solenoids work the trans retarder?
     
  14. Jam

    Jam Well-Known Member

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    Ya one for each power level (one does 1st gear & overheat and the second full power retardation). Take away the feeding air supply and let us know?
     
  15. tctractors

    tctractors Senior Member

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    I did bring up the retarder question in post 57 but air bubbles sort of blocked any interest, tctractors
     
    DB2 likes this.
  16. Dakotab19

    Dakotab19 Active Member

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    Ok so a bunch of info on the situation so here goes.

    I put on the new overflow valve I talked about earlier, this made a little difference, the truck now accelerates ok in park from idle to about 1000 rpm, and decent from 2000-2400 rpm.

    I did a stall test on the truck and the highest it would rev is 900 rpm.

    The trucks max rpm is 2400. (Is this high enough it doesn't go into the red until 2800).

    I unhooked the air line going to the retarder, this didn't seem to make any difference in neutral.

    I found out the transfer case sensor is unhooked.

    That all said I did try driving the truck around, and the truck actually drove better, it would actually rev up to about 2200 rpm and I was able to get it to shift into 2nd.

    Any ideas on the best course of action?
     
  17. Dakotab19

    Dakotab19 Active Member

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    Also I did notice the Aneroid covers have been off, and I'm wondering if someone messed with the adjuster. Does anybody know how to get the, what look like, headless screws out of the covers?
    IMG_20190911_203015820.jpg IMG_20190911_202957332.jpg
     
  18. Se.la

    Se.la Well-Known Member

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    High idle speed should be 2600-2720rpm.
    2400 is to low
     
  19. Dakotab19

    Dakotab19 Active Member

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    Should the governor be adjusted higher then, or would adjusting the Aneroid be better first.
     
  20. thepumpguysc

    thepumpguysc Senior Member

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    EVERY ONE I've ever done, the aneroid HAD to be adjusted for faster {lower} boost..
    IF u can somehow get a boost guage inline, that would tell u which one first..
    OR u can TRY to adjust the speed at the throttle stopper bolt..
    JUST REMEMBER, THAT stopper bolt will only get u "so far" & THEN CUT THE SPEED BACK if u went TO FAR..