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New engine runs Worse on 92 octane? HELP!

Discussion in 'The Garage' started by Topdown, Dec 5, 2003.

  1. Topdown

    Topdown 1/2 ton status

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    The title says most of it but the symptoms are:

    stumbles and tries to die when coming off a corner on 92 octane (a little stumble on 89) but no stumble at all on 87.

    it also stumbles on the 1st to 2nd shift when driving slowly (25mph or less) on 92 octane but not on 87.

    WTF?

    Oh, did I mention that with 87 octane, under load it seems to ping quite loudly but not ping under load with 92?

    ??

    Help /forums/images/graemlins/1zhelp.gif
     
  2. shane74

    shane74 1/2 ton status

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    That sounds like you might have a couple issues going on.
    [ QUOTE ]
    stumbles and tries to die when coming off a corner on 92 octane (a little stumble on 89) but no stumble at all on 87

    [/ QUOTE ]

    I take this is "mild" acceleration? Not ripping up pavement to get going? Ok, stupid question first..how's your fuel filter? Are you running 1 or 2? I took the one out of my carb and run an inline filter right after the pump. Easier to change and much better than the little paper p.o.s. that comes in 'em. I'll be installing a primary one in-line back by the gas tank soon along with replacing/relocating my fuel shut off.

    [ QUOTE ]
    also stumbles on the 1st to 2nd shift when driving slowly (25mph or less) on 92 octane but not on 87.


    [/ QUOTE ]

    This sounds like a mix of carb and timing. Has this been a problem that has gotten progressively worse? Or did it come on all the sudden? On my last high perf. motor, I was constantly having to adjust my timing and fuel mixture. I finally sold it and built a good solid strong engine that ran well off the cheap pump gas /forums/images/graemlins/tongue.gif


    [ QUOTE ]
    with 87 octane, under load it seems to ping quite loudly but not ping under load with 92?

    [/ QUOTE ]

    Well, after reading this, you may need an expensive fix. Like I said, on my last high perf. engine, I had to tweak it consantly. Part of the problem was that I over built it for the street. It would ping like a futher mucker unless I ran a blend of av-gas and super.

    Anyway, I know this is a DUH statement, but it all sounds like fuel delivery (too much or not enough) and timing (are you running too far advanced/retarded?)to me. Since I don't really know what you have under the hood, I won't be much help. If you're going to be at Troy's on Saturday, we can take a look at it if you want. Do you know Pete at AA carb.? If not, go see/meet him. He's kind of by Woody's off of St. Johns. If he can't tell you whats wrong with it...then you've got a BIG problem.
     
  3. Topdown

    Topdown 1/2 ton status

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    its a 9.1:1 compression GM crate motor. running 10* at 800rpm timing (just like the spec says I should run).

    Its so strange. No issues show up at all when I run 87 octane fuel. I will check the fuel filers and probably put in an inline also. I dont know if 1st gens had a filter inside the tank but I dont think they did.

    like I said, its a GM crate motor, 330hp, 350Ho Deluxe... not much more than a stock crate motor and definitely not a real high performance engine. I might try retarding the timing a little and running 87 octane fuel... its cheaper /forums/images/graemlins/thumb.gif
     
  4. shane74

    shane74 1/2 ton status

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    [ QUOTE ]
    I dont know if 1st gens had a filter inside the tank but I dont think they did.


    [/ QUOTE ]
    Nope. They only had a filter either in line or inside the carb housing.

    You probably just need to have your carb and timing adjusted. Prolly nothing too major. /forums/images/graemlins/thumb.gif
     
  5. mudjunkie 82

    mudjunkie 82 1 ton status GMOTM Winner

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    Sounds like a Timing issue................
     
  6. 99firehawk

    99firehawk 1/2 ton status

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    What do you have for a distrubtor? Did you check to see how much total advance you are seeing. What size jets are you using, is your fuel level set properly, hows your air cleaner, what vacum port are you using for advance?
     
  7. 88Silverado

    88Silverado 1/2 ton status

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    Hesitation on initial acceleration (pulling away from a light) or light acceleration sounds like a lean condition. I would suggest you check the accelerator pump first to make sure its giving a shot of fuel when the throttle blades are moved. You might need to make some changes to the air/fuel with that new motor.

    Initial timing at 10 should be no problem. Im running 14 initial and 36 total @ 2800 and no pinging with 87 on my cars 350 with 9.2:1 and 63cc cast iron head setup.

    BTW, I had a 84 Camaro V6 that had the opposit problem. Would only run and not hesitate on Chevron 92, ran like sh!t on anything else. Your lucky /forums/images/graemlins/wink.gif

    Higher octaine basically just adds more anti knock compounds to the fuel. You should get less pinging on 92 than 87 However, 87 has more energy than 92 octane. You can actually generate more power on 87 than 92. Heck, I drove my old 68 VW 85 miles on Coleman white fuel when I ran out on the way home from a camping trip. That has little octane ran the car at 70mph to the gas station /forums/images/graemlins/thumb.gif (it did ping abit under load /forums/images/graemlins/blush.gif)

    If you have a vac adv on your distributor make sure thats working too. Shouldnt make a difference which port its on, they basically do the same thing.
     

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