help troubleshooting - 250ci becomes slow when hot

Discussion in 'Technical' started by dmboshkov, Jun 13, 2017.

  1. dmboshkov

    dmboshkov Member

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    hello, forum I need some help to understand what could be the problem with my maverick, is a 1976 ford maverick OZ 2v 250, cam 264/264, with a holley 350 pv 8.5 and jets 56, timing is 14, vacuum at intake was 16Hg. She ran great for about 4 years, but since last month she lost power, I had to lower power valve to 7.5 and then 6.5, also the jets I lowered from 56 to 54 then 52, 50, 48,46. Now she runs fine a couple of minutes and then when it is hot at normal operation temperature (180F) she doesnt whant to run, is very slow, the vacuum at the intake is 4hg.
    I thought that could be the coil or the module since the spark plugs are very black, I changed the coil and module without luck same issue, also I thought that could be the carb, I borrowed another holley 350 and it has the same behavior. Please can you give me some advice what else could be the problem with my maverick. Thank you.
     
  2. Krazy Comet

    Krazy Comet Tom Supporting Member

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    You've covered your bases fairly well...

    Assuming no leaks, low vac means the engine isn't pumping very efficiently... If you haven't checked compression I believe I'd verify that was OK...

    Are you sure the balancer hasn't slipped?? That would retard timing but I'd think it wouldn't run very well when cold...
     
  3. Doug

    Doug Member

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    Sounds like either a fuel line is collapsing or a bad fuel pump . Had a car that ran great cold . When it warmed up it would back fire and no power
     
  4. Mavman72

    Mavman72 Gone backwards but lookin' forward

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    Considering the mods made to this engine...Do you still have a catalytic converter on it??? If so...It may be plugged up...Also as stated above...ignition timing/lack of sufficient fuel delivery/ low compression...Will the engine still rev freely after the problem starts??? Possible vacuum leak that only rears its head after engine/components are warmed up...
     
  5. dmboshkov

    dmboshkov Member

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    Hello, thank you for your help, it doesnt has a catalytic converter, just a cherry bomb. I did check the fuel pump and it seems to works fine but I will check again, still I need to perform a vacuum leak test on the intake and the compression test, once I do those tests I will let you know what we found.
     
  6. dmboshkov

    dmboshkov Member

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    Hello again, the compression test showed that all cylinders have 80psi, i think we have to take out the head and check gasket, rings, pistons, it seems like i have to repair it :(
     
  7. Krazy Comet

    Krazy Comet Tom Supporting Member

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    Exactly 80 psi on all cylinders seems odd but if correct you're found the problem...
     
  8. dmboshkov

    dmboshkov Member

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    well, not exactly 80 in each cylinder, but around, the values are 81, 83, 80, 75, 80, 78, the compression is very low, i believe should be around 120, in any case we have to take out the head and see whats going on
     
  9. Mavman72

    Mavman72 Gone backwards but lookin' forward

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    Sounds like bad rings...BUT...You should do a few more things before you tear it down...Re-do compression test but . Squirt some oil in each cyl, (make certain the throttle is wide open for test) crank engine through a few revolutions. Then test compression. (Oil each cyl as you test em) not all at once. If numbers come up...Its bad rings. If not, its bad valves. Probably not valves in your case. (Engine would run rough all the time) Good luck.
     
  10. dmboshkov

    dmboshkov Member

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    thank you for the advise, i will do the compression test again with the oil in the cylinders
     

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