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Thread: Help me understand spark timing

  1. #1
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    Default Help me understand spark timing

    I am trying to tune a 5.3L 2002 pickup. I logged it for the first time last night. For some reason it is getting KR once in a while at part throttle while cruising down the road. I'm not sure if it is false knock or not. Anyway i high light the part in the log where the KR is occurring and going into the tune tool to see where it is in the spark table. The cells selected show a value of -.5 and -.7 however the actual spark timing is much higher. It is showing an average of 28 degree's advanced. How is the high octane spark table showing such a low number yet the actual timing that is being scanned so much higher?

    I understand that other influences such as coolant temp, IAT etc.. affect the spark but under normal operating conditions shouldn't the spark timing follow the spark table pretty close? Also I believe there is a PID that shows which table it is pulling spark off of, what is that PID for the LS1 pcm?

  2. #2
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    Oh i have one more random question. On this pickup the tow/haul button does not work anymore. I don't use it for a lot of towing but when driving in the mountains in regular mode it does a lot of searching for gears and the constant shifting is annoying. Is there a way to get the tow/haul transmission tables to see how they are setup, so i can make it search for gears less in regular mode?

  3. #3
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    If you could post a log file and your tune file, that would help!

    thanks, bc

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    Okay here is my log. The tune is basically stock, and i haven't messed with any spark timing values. I know i need a wb to see what the actual a/f is, but i haven't had the time to install it. plus at part throttle it should be in the 14.7 range anyway.

    I have since installed the stock tune and the knock retard has almost completely gone away at part throttle, but I'm still unsure how the ecm is getting the value for spark advanced as it seems it is all over the place.

    thanks for any help you can give to straighten me out a bit.

    I was wondering if i was getting KR at part throttle because i was shutting off the EGR and air pump to hopefully increases mpg.
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  5. #5
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    your only doign 1500 rpm the map is high 80+ and afr commanded is 14.7?? it would probbaly be real not ideal conditions i dont think. thats my opinion but i dont know much still new to this.

  6. #6
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
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    GPR:

    I am not sure you are logging the corresponding GM.DYNCLAIR.DMA PID to match up what spark value you are 'commanding' in the High-Octane Spark (or did I just miss it?)

    I am curious what gear are you in with that 'part-throttle'. I would imagine some overdrive gear, as you have a really high MAP for such a low throttle opening.

    If you are punching it in an overdrive gear you are more likely to experience a lot of stress on those pistons..probably is real knock. Especially at such a low Rpm..it is evident you are not in PE Mode, so you are not getting the benefit of additional fueling.

    Seems like lot of spark for that low of an Rpm and high MAP.
    Last edited by WeathermanShawn; February 9th, 2010 at 11:34 PM. Reason: Grammer
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  7. #7
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    If it were me I would richen it up some at the MAP values and the commanded AFR just to see if it goes away. I took your tun file and made some changes, I'm not saying it's correct or even the correct way to fix the problem but if the knock goes away it will give you a direction to fix it.

    Lee
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    230" Dragster - 2000 LS1, 02020003 Speed Density, PRC 2.5 Heads,
    MS3 Cam 237/242 .603/.609, Vic Jr. intake, Holley 1000CFM TB,
    PowerGlide, 5000 stall converter. 8.70@154 MPH

    My Projects Homepage: http://www.horsepowerracing.com

  8. #8
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    Thank everyone for the help. I'm a newbie at this as well and still learning how everything is working. That was a log file of my drive into work and i was cruising down the interstate, then i get off the interstate and pull on a highway cruising at ~55 mph. I was very surprised to see that much KR just cruising along, and that is why the a/f is at 14.7 as i was not in PE mode yet.

    I was thinking the same that, as sometimes it hits very high spark timings. However I haven't messed with the stock spark tables at all. I will try another log and add in the commanded spark PID. I think my main problem was i took the stock tune and changed a bunch of stuff then went and logged it, so i have no idea what is causing the excessive KR. Put the stock tune in and a lot goes away. I'll have to start changing one thing at a time from now on. It was weird cause with that tune i also got really poor gas mileage, when i was taking things off like cat protect mode, air pump, and egr to hopefully get better mpg's.

    Do you guys have any other suggestions on PID's to log?

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    I don't believe it's spark, I thinks it's too lean. With a WB and autoVE you would quickly find the problem.

    BTW, keep the EGR. By disabling that it would definitely induce knock and reduce mileage. A lot of people love to disable it and I'm not sure why!

    I would go back to stock and start over and richen it up a little in the areas it knocks.

    230" Dragster - 2000 LS1, 02020003 Speed Density, PRC 2.5 Heads,
    MS3 Cam 237/242 .603/.609, Vic Jr. intake, Holley 1000CFM TB,
    PowerGlide, 5000 stall converter. 8.70@154 MPH

    My Projects Homepage: http://www.horsepowerracing.com

  10. #10
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    I agree, I think my biggest problem is that it is lean from a few mods i made and i need to get my WB hooked up to see what is really going on.

    I like disabling EGR because it will costs you power at WOT, but at part throttle i will leave it alone.

    The more i think about it, how would I be lean at these part throttle cruising conditions? The engine should be in close looped mode and the a/f should be around 14.7:1, unless my o2's are going bad, correct?

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