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  1. #1

    Default Ignition timing?

    I have a 1999 Chev. Suburban 5.7 litre sfi. After the engine warms up,
    the ignition timing doesn't seem to be responding under a load. If you
    accelerate slowly, it runs fine. If you accelerate quickly, it spits
    and sputters and backfires. I have replaced the tps. The ignition
    module and pick-up coil tests fine. An Autozone scan indicated PO452
    code (which was showing up a good while prior to symptoms). The
    symptoms first showed up during a long trip then not again for several
    weeks. It has now gotten to the point that it does it every time it
    warms up. Cooling down the engine and restarting it runs fine again
    until it heats up. Any ideas or suggestions?

  2. #2

    Default

    Check your fuel pressure, it sounds like it might be a little low, it should be at or above 60 psi to run correctlyl. Mine was doing something similar to that a few months back. If I did full throttle acceleration, it would only go to about 4,000 rpm's. It had enough fuel pressure to run normally (it was showing around 55 psi), just not under load.
    Gary

    99 K 1500 Suburban
    78 Silverado Big 10 w/factory 454
    00 S-10 Blazer
    1976 Trans Am
    1980 Honda CB900 Custom

  3. #3

    Default

    I once had a similar thing happen that was due to a loose battery cable.

    I would probably test fuel pressure as suggested.

    Any sign of spark leak or similar from the wires/plugs/distributor?
    '98 K1500 Suburban LS 5.7 L 4L60E NV246 ARB
    '92 Ford Explorer XLT 4x4 4.0 L A4LD BW13-54 Trac-loc rear
    "My toys were the greasy cogs and springs and pistons that lay around all over the place, and these, I can promise you, were far more fun to play with than most of the plastic rubbish children are given nowadays." Danny in Roald Dahl's Danny The Champion of the World

  4. #4
    Legend

    Join Date
    Feb 2008
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    Default

    Distributer could have a slight crack causing this, and the battery would have nothing to do with this, if your car is running well you should be able to disconnect the battery while its running without it killing, that would be an alternator issue
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual
    285/75/16
    ___________________________
    Jason

  5. #5

    Default

    Would the fuel pressure change due to engine temperature? It only takes one minute with engine off--when you crank it back up it runs fine again until engine heats up again.

  6. #6

    Default

    Would the fuel pressure change due to engine temperature?
    It shouldn't. If it does, then something is wrong with fuel delivery.

    the battery would have nothing to do with this, if your car is running well you should be able to disconnect the battery while its running without it killing, that would be an alternator issue
    I know on older cars, that aren't as "electrically intensive", you can disconnect the battery and it will still run. On my '98 (and I'm assuming his '99 is the same), the PCM gets power directly from the battery through it's own cable. If the battery cable is loose or disconnected, the PCM and the rest of the engine management system (including fuel delivery, fuel injectors, ignition system) have no power and the engine won't run.

  7. #7

    Default

    There is a direct correlation between the engine reaching normal operating temperature and the spitting and sputtering. It runs perfectly before it reaches normal operating temperature and after it cools down a minute or so.

  8. #8

    Default

    With that, I would probably also put a scanner on it in addition to the other suggestions. See if there are any trouble codes/pending trouble codes. Watch engine parameters to see if there was anything that seemed to go haywire when the engine warmed up.

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