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new 383 spitter and sputering

Discussion in 'The Garage' started by S. Burnham, Mar 14, 2006.

  1. S. Burnham

    S. Burnham Registered Member

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    ok i have just built a brand new 383 for my 88 blazer. it is flat top kieth black pistons, 97 c1500 roller cam and lifters, stock heads, and tbi. when the motor is cold it idles up and down and if you ease on the gas it spitter and sputters. it will go it just has no power. after it warms up it idles fine and has a lot of low end torque, but when you get to about 2grand it starts doing the same thing. if you hit the gas hard it does not want to go at all. when we adjusted the valves the passenger side is getting good oil pressure but the drivers side is barely getting at all. I had a circle track racer that told me that the valves are out of adjustment. they seemed to be right on but i may be wrong i have been before. i stuck a timing light on it just a minute a go and it is set at 0. when gassed it jumps staight to 12 degrees. and when you let off it drops straight back it is not gradual at all. i have not timed a motor in 12 years until now so is this correct? I did have a miss hap when instaling the oil pressure switch on the back of the intake that was not good. the brass fitting broke into the blockl and we had to brake it out. soem brass pieces and filings got into the oil jacket. we pressured up the pump with a primer and blew out the hole before putting the sending unit back in. i did find some fine particals in the oil but nothing larger than a grain of sand. does any body have any ideas or suggestions on my problem? i would appreciate any help i can get. thanks in advance.
     
  2. ryan22re

    ryan22re 1/2 ton status

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    did you disconnect the timing connector when checking the timing?

    if thats not it, i would bet you are in need of a custom chip.
     
  3. S. Burnham

    S. Burnham Registered Member

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    i did but only to set the timing. i pluged it back up to when i reved the rpms
     
  4. beater_k20

    beater_k20 Banned

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    pull it back out, disassemble it, and clean EVERYTHING. metal particles in the engine, the size of particles from breaking up a brass fitting are not acceptable in any engine. you'll be VERY lucky if it didnt damage anything. i'd almost bet on replacing the cam bearings and lifters. you're very likely starving it for fuel with the stock TBI, stock ECM tuning and increased displacement.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Ignoring the whole metal pieces in my engine portion, even though you have a pretty mild cam in there, that 383 is probably running fairly lean now, and you don't want to end up like another member here did, melting a piston because of that. Same situation...stock TBI parts/programming, larger engine.
     
  6. yoshisv

    yoshisv 1/2 ton status

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    I dont think disassembly will be needed, But i would change the oil. That has nothing to do with it spitting and sputtering. I beleive there may be something wrong with the fuel system, And it may be as simple as a stoped up fuel filter or line.
     
  7. S. Burnham

    S. Burnham Registered Member

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    i ordered 2 454 injectors and they are identical in size except for the nozzel holes. i am thinking about trying those and see if that will solve the problem. any body tried that yet. it should give it more fuel volume. i checked and the pumps from a 454 and 350 are the same. the only thing that i think is different is the 454 hase a slightly bigger bore for the throte.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    If you get lucky and the 454 injectors are just right, then if the injectors/fueling truly are the problem, you certainly could eliminate the issue.

    Injectors are measured in lbs/hr, so as long as you can keep the fuel pressure the same between two differently rated injectors (say 350 vs. 454 although I have no idea what the stock rates are for them) then the amount of fuel injected will obviously go up. IF you are say, 10% lean across the board, and the 454 injectors flow 10% more, theoretically there should be no problem. I somewhat doubt you know exactly how much more fuel the 383 needs, although you may have calculated that, I'm sure there are fueling calcs online.

    The system can compensate for fuel demands up to a point, but a major issue is WOT, which means the O2 sensor is not being used to calculate the fuel mixture. Very important time to know that the engine isn't going lean, and preferably around 12-13:1AFR.

    Of course, we are now talking about a different motor, which may like different timing too.

    If you think the valves are not adjusted right, take care of that first obviously. Plenty of posts about how to do that.
     

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