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Thread: 8 degrees retard on stock timing table.

  1. #1
    Fuel Injected!
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    8 degrees retard on stock timing table.

    For my 1995 Burb, in my sig.

    So I noticed this awhile ago when I advanced the entire table 4 degrees. A lot of retard around 1600 RPM, especially at low vacuum, 70-75kpa. My current tune has the timing tables back to stock and I'm still getting the same 8 degrees retard in the same area. Base timing at the distributor is 0 degrees.

    The cap/rotor/wires/plugs are all about 4 months old. Havent pulled the plugs to see how they are doing yet, wanted someone to sneak a peak at what I got going on, maybe I missed something somewhere in the tune. Overall the Burb runs great and gets about 13mpg.

    I've attached needed files.

    Thanks
    Attached Files Attached Files
    1995 Chevy C2500 Suburban 5.7 4L80-E, 16197427, BNKM, $31

    Hooker Long Tubes headers, dual 2.25" exhuast, mufflers. TBI mods, Moates APU1, TunerProRT, CAI, 4 core radiator

  2. #2
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    forgot to add picture
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    1995 Chevy C2500 Suburban 5.7 4L80-E, 16197427, BNKM, $31

    Hooker Long Tubes headers, dual 2.25" exhuast, mufflers. TBI mods, Moates APU1, TunerProRT, CAI, 4 core radiator

  3. #3
    LT1 specialist steveo's Avatar
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    8 degrees of retard is a lot, that means the knock sensor is getting pegged. at low vacuum like that, it's a concern for sure.

    since the stock timing tables are always conservative in high MAP areas, i'd be inclined to try adding about 10% more fuel in the area of concern to determine if the knocking is due to insufficient fuel in that area. trying to cure knock with less timing is often the wrong answer.

    another thing is, though.... 1600rpm and 70+ kpa? it shouldn't be spending much time there. that's lugging territory.

    at the same time you're trying to resolve that problem, you should be trying to make your transmission shift earlier so it never spends much time there.

  4. #4
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    i find the right slight incline to get it to hold 1600 rpm at 70 kpa. I was thinking about a little more fuel as well. I've run the BLM tables through the Correction Tables a few times, but I wouldnt mind trying a little more fuel there.

    I'm assuming the knock is stock with 210,000 miles on it. Do they become more sensitive as they age? Never messed with them much.

    Interesting thing perhaps, or not, is that even when I bumped the entire spark table up 4 degrees, I was still getting the same 8 degrees of retard.
    1995 Chevy C2500 Suburban 5.7 4L80-E, 16197427, BNKM, $31

    Hooker Long Tubes headers, dual 2.25" exhuast, mufflers. TBI mods, Moates APU1, TunerProRT, CAI, 4 core radiator

  5. #5
    LT1 specialist steveo's Avatar
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    I was still getting the same 8 degrees of retard.
    may very well be false knock, then.

    if you can verify it's not real knock you can probably just disable knock retard entirely for that region and call it a day.

    again, not an automatic trans expert, but 70kpa @ 1600rpm should be shifting imo. i would never operate an engine with that load at that rpm. as a ballpark, could be 2300rpm @ less than 50kpa and take less fuel, being easier on the engine. not that it should be knocking, but i just dont like seeing logs with lots of running at that kind of load.

  6. #6
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    I'll tweak the fuel map around that area. I'm almost at 1/4 tank gas. I'll fill it up with 93 tomorrow, flash a tweaked tune, see if its still there.
    1995 Chevy C2500 Suburban 5.7 4L80-E, 16197427, BNKM, $31

    Hooker Long Tubes headers, dual 2.25" exhuast, mufflers. TBI mods, Moates APU1, TunerProRT, CAI, 4 core radiator

  7. #7
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    might run a bottle of that chevron fuel treatment you might have a carboned up issue that don't show up but at that rpm.1/4-1/2 qrt. marvell mystre oil in the engine oil seamed to help my worn out v6 it had a lot of knocks at hyway cruising speed [I don't know if it was carbon or mechanical but both to gather lowered my knock count to where I have not been trying any more tunes,last mpg 21.7 ].

  8. #8
    LT1 specialist steveo's Avatar
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    actually yeah could be carbon for sure, you should just run half a quart of seafoam through the intake. works faster than techron.

  9. #9
    RIP EagleMark's Avatar
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    Techtron is good stuff for maintenence, I use it in a tankful every month or so. But not fast acting...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  10. #10
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    I heart Seafoam for sure. Its like a carb rebuild in a bottle. I ran some through about 2 months ago. I also have some Amsoil Power Foam. I'll run that through when I get home, and get some Seafoam from work tomorrow. Depending on the weather I may have some time to check the spark plugs. I actually have a set of CR43TS plugs to replace the Autolite Platinums that are in there. Maybe do that today, before the power foam treatment. I'll monitor retard today after the fresh tank of high octane and the tweaked tune I did last night. Bumped up the VE tables around 1600@70kpa about 8 percent, then tweaked it by hand.

    I'll let ya know how it goes.

    Thanks
    1995 Chevy C2500 Suburban 5.7 4L80-E, 16197427, BNKM, $31

    Hooker Long Tubes headers, dual 2.25" exhuast, mufflers. TBI mods, Moates APU1, TunerProRT, CAI, 4 core radiator

  11. #11
    LT1 specialist steveo's Avatar
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    johnson/evinrude engine tuner is way better than seafoam too, if you live near the water and have an outboard dealer locally. as the stuff is specifically designed to decarbonize cold running, abused 2-stroke engines, it's very aggressive. i swear by it. but seafoam is way more available.

  12. #12
    RIP EagleMark's Avatar
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    Speaking of Evinrudes... I picked up an old one, about 5hp, that looks like new on a stand for $40 at a garage sale yesterday...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  13. #13
    LT1 specialist steveo's Avatar
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    what model?

    i am a specialst in vintage johnson/evinrude outboards, especially rare parts acquisition, if you ever need anything.... you know who to ask

  14. #14
    RIP EagleMark's Avatar
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    I'll take a picture and start a thread so we can give Scrufdog his thread back...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  15. #15
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    Filled up with 93 octane and most of the retard went away. I can still get 2 degrees of retard at exactly 1600rpm@70kpa, but no where else, and I have to work to get it to retard at that spot.

    I changed the spark plugs and foamed the intake and cylinders, that didnt hope. Going to change the cap/rotor/wires with some Accel stuffI have laying around. Coil is already Accel, few weeks old.

    7 of the spark plugs showed normal wear as expected for 600 miles usage. Half white/half tan, no deposits, no oil, no damage. Cyl #3 however, had hardly any tan on it, almost looked new still. I have the pics on my phone, I will try to get them here if you wanna take a look.
    1995 Chevy C2500 Suburban 5.7 4L80-E, 16197427, BNKM, $31

    Hooker Long Tubes headers, dual 2.25" exhuast, mufflers. TBI mods, Moates APU1, TunerProRT, CAI, 4 core radiator

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