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Backfire thru Plenuim on TPI

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by jmpd, Sep 1, 2000.

  1. jmpd

    jmpd 1/2 ton status

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    I'm having trouble dialing in the adjustable fuel reg and timing on new motor with new cam.. I have the timing at about 10-12 degree advanced. it ran like sh*t with it at stock 6 degrees. the fuel pressure reg is set about 8 pounds above stock. The motor runs great, but every once in awile it will backfire thru intake. No codes come up. It seems to do it the most after a i drive for a awhile, then stop at a light and then take off. It also did it today a freeway speeds

    Need info

    Thanks
    Michael
     
  2. realsquash

    realsquash 1/2 ton status

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  3. jmpd

    jmpd 1/2 ton status

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    350 TPI stock ECU, cam is compucam 2030 for factory roller cam replacement. intake lift 301 @ 452, exhaust lift 310 @ 465rocjer arm 1.50..... advertised duration270 intake 276 exhaust,on stock rebuilt motor, motor 10 over, new springs on valves(the ones that crane recommended for cam) They also said I needed a new adjustable fuel pressure reg for cam. This is supposed to be a replacement for 87-89 roller TPI

    Fuel pressure set at 55 psi, 7-8psi over stock

    Thanks in advance
    Michael
     
  4. realsquash

    realsquash 1/2 ton status

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    What size injectors are you using, and is your system still mass-air? It sounds like yer gonna need to get a new chip made or your going to have to learn to do it yourself. Have you changed compression? The cam you have is much larger than stock, therefore changing the signature of the engine. You can guess-n-check forever, but to do it right you need to hook up a PC and read out what's really going on. With the initial timing advanced you are prolly helping the low-end, but your are prolly creating knock higher up.



    Squash
    http://www.trailrunners4x4.org/users/realsquash
     
  5. jmpd

    jmpd 1/2 ton status

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    Valves where the problem, I called Crane and they told me that it sounded like 1 or 2 valves where a little to tight. i re-adjusted all the valves and it is running great.

    Thanks for the help

    Michael
     
  6. 88Jimmy

    88Jimmy 1/2 ton status

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    Hey jmpd
    How do you like your cam Im thinking about getting the same cam. What is your setup tire size rear end gears.
    Where does you cam come in at (rpm)are you happy with it?
    Robert

    350 Vortec TPI D60 14Bolt 4.56 4"lift 35 BFG A/T
     
  7. jmpd

    jmpd 1/2 ton status

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    88jimmy,
    I only have a bout 60 miles on motor, but the cam rpm range is from 2000 rpm to 5500. It pulls stong all the way from dead stop to 60-70 miles an hour. I have not taken the motor over 4000 rpm yet/ still breaking it in. But I can tell a huge difference.

    Truck is 84 w/88IROC TPI, 700r4, 3" lift with 33's and 3:73 front 10bolt open, rear 12 bolt lock-right
    Michael
     

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