Adjusting timing

Discussion in 'GM Powertrain' started by Crawdaddy, Nov 17, 2008.

  1. Crawdaddy

    Crawdaddy Moderator Staff Member

    As some of ya'll may know, I've been trying to get the motor in my Suburban tuned up and working at peak efficiency. Over the weekend I replaced the coolant temp sensor that wasn't working and replaced all the spark plugs with Autolite Platinums. Now after I buy and drop the hotter Accel or MSD coil in, I should be good to go. So, now to adjust the timing...

    Referring to this thread: http://www.gmtruckclub.com/forum/showthread.php?t=14855 I have been trying to do a tuneup/performance mod that should yield better mpg and power. The spec for the plug gapping was .035", however, the plugs came from the store gapped at .045" and I thought that would be a good starting point to widen the gap. At idle it seems to run well so far, no missing or anything, most likely due to replacing the plug that had chipped porcelin on the insulator (one of the previously dead cylinders). So, I'm going to drop a MSD or Accel high-volt coil in to make sure the spark can easily jump the gap and then I want to bump the timing. Well, I'm not quite sure how I can do it and find the butter zone easily. I know with older carb'd motors you hooked a vacuum gauge up to the intake vacuum and adjusted the timing and carb until you got the highest readings. However, this is a Throttle-body injection intake system, so it's half-carb half fuel injected.... I don't know where to start. So, how can I evaulate how close I am to getting it right while it's idleing in the driveway. I'd like to avoid having detonation when I'm trying to accelerate on the interstate :lol:


    PS: What does pinging/spark knock/ detonation sound like? I've never heard it before as far as I know, and I would hope it's not loud enough to hear while driving...
  2. GaryL

    GaryL New Member

    Im not sure exactly how to adjust the timing on the TBI motors, but I know you need to unplug a certain wire or you will be fighting the computer. As far as what detonation sounds like, it will make your Suburban sound like it is diesel powered.
  3. Crawdaddy

    Crawdaddy Moderator Staff Member

    I read the sticker on the core support for the radiator and found the plug to disconnect to drop back to base timing. I'm just trying to figure out how to know in the shop when I've got it set right. I've been told that just by sound you should be able to tell. However, I've never tried and I don't want to screw it up too much.
  4. retired

    retired New Member

    Use a timing light and just add 2 more degrees to the factory setting.
  5. Crawdaddy

    Crawdaddy Moderator Staff Member

    only 2 degrees? for the broncos they're knocking them back 5-7 usually...:gasp:
  6. retired

    retired New Member

    GM you advance the timing for more power. Without getting into all types of performance issues adding just 2 degrees is enough.
  7. Crawdaddy

    Crawdaddy Moderator Staff Member

    so I should advance it to 2 degrees BTDC. OK, we'll see what happens. I definitley want to achieve max mpg and if power comes along with it, so much the better :)

Share This Page