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Thread: cant get engine to start and idle

  1. #1
    Tuner in Training
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    cant get engine to start and idle

    I have a 2003 5.3 with a LS2 intake and Vrx3 cam(226/228-.585/.588-114). The engine also has a POWER throttle body. It has been in another shop as VATS was already taken out. Im not sure what else may have been changed also, so I have no original baseline. Just what I pulled first go. Sitting key on eng off the scanner numbers look good and seem to be correct during cranking. I tried to start with original tune that was in ecm and also followed the idle tune guide I found on here. Neither will run. The car starts to fire then dies. Occasionally it will run for a few sec then die. I have also played with the advance and airflow trying to get lucky enough to get a baseline log. Any help is greatly appreciated. Attached is the tune it came in shop with and also the tune after following the idle how tos. Hopefully I'm missing something simple as I am still learning, as always.
    Attached Files Attached Files

  2. #2
    Tuner in Training
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    Please help. I did get this to start and have a log now. I have researched and researched and learned a ton but still missing something. What I have is a 5.3 from a 03Silverado with a LS2 intake and VRX3 cam. 226/228 .585/.588 114+4. As far as I or the owner know thats all that was done. I pulled original tune (also as far as I know) and added to for cam. I should also state VATS was out already so someone had been in there.

    It starts up with very low choppy idle 3-400, then spikes upward around 2000, then seems to level at around 1200 which is down from 1600rpm last try. I also noted the IAC counts are 150 always which is the iac reset setting. I'm not sure why or if I should see them move. I checked all wiring and also swapped for another to no avail. Is there something in program keeping this locked at 150?

    So far I have done the following.

    Changed injector data. I pulled info from a stock ls2 file. Flow vs KPA, offset, short pulse adder, and min injector.

    Raised the temps in closed loop enable to lock into open loop. Also checked for lambda 1 in eq ratio at operating temps. This file has no gains so that's all I did there.

    Set target idle to 900 across the board. Add 1g/sec base air in park and gear. Added 2 deg advance to idle from 0-1200rpm and .08-.28 g/cyl. Multiplied main VE table by 60% at 400rpms, 80% at 800rpms, 90% at 1200rpms, and smoothed selection from 1200-2000 rpms. Also added 50 cam revs before decay.

    I do not have the wide band hooked up yet as just trying to get something steady to start from.

    I did go to school for all this but was twenty years ago, OBD1 era, so I understand theory but not always exactly what I'm looking at on the tables. This is a whole new ball game. We have done a ton of LT and LS swaps through the years but most have been just that "swaps" and no tuning besides paying someone to remove VATS and fix tire size and fans.

    I appreciate any and all help/advice.
    Attached Files Attached Files

  3. #3
    First thing I come to....your file says 5.3...but your cylinder volume says 4.8l.
    1968 Bel Air Wagon
    L92/6L80E

  4. #4
    The "V" in the 8th digit of your VIN also indicates a 4.8L. Do you indeed have a 4.8L? When i do a comparison log, less difference between your file and a 4.8(79) then a 5.3(124).
    1968 Bel Air Wagon
    L92/6L80E

  5. #5
    You said power throttle body. Do you mean Drive by Wire(DBW)? If DBW, you shouldn't have an IAC. If its DBW, is it the GTO throttle body that came with the intake? If DBW, is it working, key on with intake off and see if it respond to pedal input. I ask because the log file does not show any TPS.
    1968 Bel Air Wagon
    L92/6L80E

  6. #6
    Tuner in Training
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    Wicked thank you for the reply. It may very well be a 4.8. I have heard of peeps getting burned thinking they are getting a 5.3 As far as I know there is no good way to tell visually. It is drive by cable. Power is the brand name and like everything else w this project, I have no good info whats been done or where it came from. This may be dumb question, but where are you reading the VIN?

    As of late, I did get it to crank and will idle erratic at around 12-1300rpm. I have not cracked the throttle and still not figured out the iac froze at 150.

    Was out last week so hard on it this week. Makes me wonder if I actually have a 4.8 or 5.3 and what compt?? compt serv 12576106, hardware 12570558. According to the research this compt will work with drive by cable. If the iac driver isn't in the computer, it would explain why I don't see the counts move. Will pull cover and check in morning. Thanks again

  7. #7
    Tuner in Training
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    I do have a 5.3 with 4.8 compt. Dished pistons told the tale. And my lack of training didn't see to take the 1 out of ect system options. So all is well and learned a lesson. Got the tps and iac dialed in and idles at 900 but really rich. Wide band was pegged. I have a 5.3 compt in stock. Is it worth trying to use the 4.8 or just start over? Its the same compt and hardware no. but looks to be a lot to try to change to correct numbers.

  8. #8
    Tuner in Training
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    Changed to the 5.3 compt this morning. Re did all my flow rates, TB scaler(thx LS tuning guide), & system options. Fired and tps and iac out of whack so re did. Then started idle tuning by Rinkrat and Krambo. Awesome write-up. Thank you. That really helped a lot. Tons smoother but still very rich. Found we had a wrong temp sender, that may have caused a problem.

  9. #9
    Carolina,
    Glad to see you you made some progress.
    VIN is seen in the "Edit"->"Calibration Details" section. Full VIN is 2GCEC19V031291397.
    1968 Bel Air Wagon
    L92/6L80E