Ignition timing?

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Pquiz, Jan 6, 2009.

  1. Pquiz

    Pquiz New Member

    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. GaryL

    GaryL Epic Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    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.
  3. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    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?
  4. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    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
  5. Pquiz

    Pquiz New Member

    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. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    It shouldn't. If it does, then something is wrong with fuel delivery.

    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. Pquiz

    Pquiz New Member

    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. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    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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