12HT blowing alot of black smoke if boost is over 15psi?

Discussion in 'Diesel Tech and 24 volts Systems' started by dousty, Dec 26, 2011.

  1. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    Gday,
    I have just fitted my EGT (pre) and Boost gauges to my 88 Sahara after I pulled them off my 5spd wagon. My 5spd also has a 12ht and has been tweeked to 13psi and fuel adjusted to peak at 700* max eg sand or towing. All adjusting screws on the Sahara's FP still have anti tamper tags in place.

    Straight up the first hill with nothing adjusted I got to 750* pre turbo in 3rd OD (Wholesale tranny/valve body) before I relented. That was at 7.5psi boost. It didn't surprise me as I found the 5spd wagon making the same temps when it was stock. I then put my boost adjuster in and guessed at the setting.

    Once I got going again I found that at any boost level over 15psi I got clouds of dark black smoke...a hell of lot of smoke behind the wagon visable in the rear view mirror through tinted windows! Once I adjusted it down to 13psi, where I wanted it, there were no more clouds.

    What was causing this? Also my EGT is still as high as 690* with no adjustments made to fuel. I expected the temp to drop alot once the boost was increased. My 5spd wagon dropped to 600* once I wound the boost up.

    Maybe there is an issue with the Sahara's fuel pump?
  2. ForealBoreal

    ForealBoreal 1HZ Boostin SILVER Star

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    5,480
    Location:
    North Coast British Columbia
    egts shouldn't go over 650 max.
    I would say your over fueling. Turn it down

    If you have an intercooler you could try increasing the boost if you want to push it.
  3. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    hmmmm yeah but I have two 12ht's and both were going over 700*C stock as a rock?
  4. blis

    blis

    Messages:
    729
    Location:
    in cold north
    I get my 12ht up to 680c when pulling a trailer uphill with 33"s... On the subject, your turbo could be leaking oil at that boost therefore causing overfueling symptons... Also, 12ht has boost compensator so as you increase boost it increases fuel too under boost (up to certain limit set by rack position and other things inside governor)...

    How about your exhaust? still running std exhaust, if yes, then try going for bigger and straighter exhaust...
  5. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    Thanks Blis. Both vehicles have 3" mandrel exhausts.
  6. Thats hot dousty,i'd be worried up around 700,mine sits alot lower running @ 13psi max,500 odd on long hills
  7. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    It that pre turbo goldy? How is your new Chinturbo going, by the way?
  8. Tapage

    Tapage Club 4X4 Panamá SILVER Star

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    was your boost compensator ( aneroid ) adjusted in the process .. coz that will be the reason to have more fuel when you are overboost ..
  9. Tim-HJ61

    Tim-HJ61 SILVER Star

    Messages:
    430
    Location:
    Perth Western Australia
    Dousty

    I'm really surprised you're getting 750* with a standard set up. I assume we are talking Celsius.
    The other issue that doesn't seem right is the sudden cloud of smoke at 15psi and nothing below that

    The boost compensator works on a bellows aneroid and gives graduated extra fuel as boost goes higher

    If I recall. GBentink told me it is at max opening at 15psi, but I may be wrong on that

    If you're getting a sudden rush of extra fuel, I'm wondering if it is not working properly, perhaps sticking. Can you check the hoses going to it to make sure they are not bulging and absorbing the pressure like a balloon.

    Or it could be that your turbo just cannot supply the amount of air needed to manage the volume of fuel. Actually, that really is what is happening, but again a sudden big cloud of smoke and such high EGT on a standard pump setup isn't right. Could be a weak turbo.

    The theory is that as long as your EGT are not too high, 650*C, then you increase air then fuel until you're happy or blowing smoke. If you've got smoke then increase air ie boost . A standard CT26 will push 15psi happily and 19psi up to 22psi okay but it does to lose efficiency at the higher end. If your turbo can't keep the black smoke under control, then an upgrade such as a Gturbo will help keep the smoke and EGT under control.

    I can't recall if I was able to provide maximum fuel volume with the standard CT26 or whether I could only do that once I installed the GTurbo. I rarely see 500*C per turbo now with the 600mm FMIC, 3" exhaust, full fuel and GTurbo

    Tim
  10. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    Thanks for the response. Both wagons were over 700C with no fuel or boost adjustment at all.

    When I load the engine to hold 2300rpm with full throttle (3rd with lockup) it will stay at 590C regardless of time. Once it starts climbing to around 3000rpm it will be just under 700C and still climbing as revs go over 3000rpm This is With 13psi boost at both 2300 and 3000 and fuel settings as standard (anti tamper tags in place).
  11. Yeah pre turbo,ching chong lurbo wery good!:D

  12. Tim-HJ61

    Tim-HJ61 SILVER Star

    Messages:
    430
    Location:
    Perth Western Australia
    What happens if you take it back to standard boost?

    Tim
  13. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    haha very good
  14. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    I'll let ya know tomorrow.
  15. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    ok back at standard boost, ie no boost controll installed

    2300rpm
    full throttle
    3rd gear and convertor locked
    7.5psi
    680-690*C pre turbo


    Again once the revs start climbing(as hill is crested) the egt will go over 700 and continue climbing until the next gear is selected.

    Bear in mind that fuel pump is untouched and these readings as inline with the readings I took from my other 12ht when it was stock.

    So, has anyone else measured 12HT EGT's before modification? I have done two of them now and both giving similar figures. My EGT and Boost gauges are Autometer Cobalt and were bought new for the purpose and are the same gauges used on both wagons with egt probe fitted to the same location in the manifold.
    Last edited: Dec 28, 2011
  16. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    There is where the egt is mounted.
    IMG_0308.jpg
  17. :eek::eek::eek: Wow

    How long does it take to get to those temps dousty,girlfriend has my truck up up at mudgee for a few days,back tomorrow,ill take it for a similar run when she's back and see what i get to compare,hows your water temps when its got egts that high?
  18. :eek::eek::eek: wow

    Girl has my truck up at mudgee for a few days,back tomorrow,ill take it for a similar run and compare what i get.

    Hows your water temps when egts are up that high?

    What psi is your overboost light coming on at?
  19. dousty

    dousty

    Messages:
    209
    Location:
    NSW, Australia
    Cooling system has no problems with those EGT's. I have my silver wagon tuned for 700*C max and run it in the sand regularly with family and enough camping gear for all of us. I also have a third Autometer Cobalt gauge for coolant temp with probe fitted to thermostat housing. The highest that silver wagon got was 195F which was enoguh for the fan to kick in and hold it.

    And overboost comes on at 14-15psi.
  20. Reason i ask is since i put new turbo on and new piston and rings my water temps are up,it will climb up to about 97-98c on long climbs etc.

    I haven't checked it but my boost gauge may not be right,those water temps and overboost light kicks in at 8-9psi on boost gauge on mine.

    So if i have boost well above what i think ive got i never see egts like you have. I might have a crappy boost gauge,you could have a crappy egt gauge you know,your temps don't make sense.

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