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Thread: need help with really bad startup of new motor

  1. #1
    Tuner 1970ss8.1's Avatar
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    need help with really bad startup of new motor

    I have tried to get this motor running but all it does is surge and die. I have three logs. The last one has the wideband hooked up.
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    1970 Chevelle SS 8.1 Vortec T56 9" 3.00
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  2. #2
    Tuning Addict 5FDP's Avatar
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    What some of the parts used?

    Stock MAP sensor?
    What injectors?
    What is your fuel pressure?

    The wideband is correct, showed lean for the small amount of run time.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Tuner 1970ss8.1's Avatar
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    Stock MAP and MAF
    102mm DBC Tb conversion.
    42lb marine injectors
    Cam, ported heads, ported intake,
    PLX wideband

  4. #4
    Tuning Addict 5FDP's Avatar
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    See if it just wants fuel. Whack both the MAF/VE with 15% as a test.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  5. #5
    Tuner 1970ss8.1's Avatar
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    Does the data look ok from the injectors? I used data I found on the internet.
    I tried to copy and paste the VE it ended up over 110 so I undid it. Should I get new injectors with real data.

  6. #6
    Tuner 1970ss8.1's Avatar
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    The surging in the log was not me. There is no petal installed. I think it is the IAC.

  7. #7
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    Quote Originally Posted by 1970ss8.1 View Post
    The surging in the log was not me. There is no petal installed. I think it is the IAC.
    Thats doubtful your IAC never moves its stuck at 0 being fully closed.
    But if you look at yout log the TPS is constantly fluctuating. Which it should not. Also most logs read 4% or so and never below .8%. Your never truly in the "idle" state.

    Whats your tps voltage reading? Reset your throttle reading so it reads 0% so you can truly idle and try from there.
    1997 30th SS. Torqhead 24x, TFS heads, 223/235 cam, 4l80e, S60 D1SC 14psi

  8. #8
    Tuner 1970ss8.1's Avatar
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    I don?t understand how if the IAC is stuck at 0 and the throttle is closed how would I get a rev over 2000rpm

  9. #9
    Tuner 1970ss8.1's Avatar
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    Could this be caused by the VSS wires not hooked up yet. I just realized I haven?t hooked them up yet.

  10. #10
    Tuner 1970ss8.1's Avatar
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    So here?s where I?m at.
    I called fuel injector connection and was given the IFR table for the 42lb marine injectors. Also the Short pulse limit. I tried to add 5% to the short pulse adder table, per what they said to do, but the table won?t take it and returns to stock when I save it. The just e mailed me and said to leave it alone. They said they are the same injector as the stock ones just a different plate and the rest of the stock data is fine.

    Now the throttle body is a Chinese e bay piece of crap, took forever to get here from China. With the IAC and TPS attached, from China. Also I took a sanding roll to it not knowing it was important to not do that.

    So now I have a Nick Willams 102mm DBC TB on its way along with Delphi IAC and TPS sensors.
    The first time I started the motor it idled pretty nice but the TB was whistling really bad. I had no TPS or IAC readings and had found out that the Chinese e bay plug ends I had for TPS and IAC pushed the wires out when I plugged it in.
    This latest go at starting it up was with new Delphi plug ends. Now that I have the IAC and TPS plugged in it is doing this high rpm and low rpm ideling.
    So I feel like a good quality TB and sensors will help figure this out.

    Does anyone have an explanation why the engine would even be able to see 3000rpm with the throttle blade closed?

    Also how much of the 5.3 DBC data do I need to copy over? All the Idle tables under the Idle tab?

  11. #11
    Tuner 1970ss8.1's Avatar
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    Got it running ok but,

    I installed the new nick willams throttle body and the new IAC and TPS. Now it will start and hold and idle, but it is sucking really loud from the IAC hole. I pulled out the RCU and opened it up and it does have the IAC drivers, and the wiring is correct, but still have no IAC action. I even tested the IAC which was fine and the plug from the harness which had no readings. I even tried to move the IAC out of the TB with the scanner and pulled and pushed the plunger on the old IAC and the scanner read nothing. If I place my finger over some of the IAC hole in the TB it will get quiet and start to idle lower where I want it to be. Am I missing something in the tune, or can the IAC circuit be bad in the ECU? Ill post a log and tune file. Ive been working on the ve, bu the idle is still a no go until the IAC will work.
    Attached Files Attached Files
    My Avatar is my Wife and Proud of it!!
    1970 Chevelle SS 8.1 Vortec T56 9" 3.00
    2006 3500HD 8.1 vortec Allison 6sp 4.10 4X4
    2013 Audi A5 Cab 2.0tfsi Quatro
    www.mcmnapa.com

  12. #12
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    That PCM may not support IAC. Read this, http://lt1swap.com/cable_conversion.htm

  13. #13
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    That PCM may not support IAC. Read this, http://lt1swap.com/cable_conversion.htm

    The iac is a stepper motor with no feedback to say where it's at. That's why you have to get the IAC setup correctly at the get go.

  14. #14
    Tuner 1970ss8.1's Avatar
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    I just picked up a 2004 GTO PCM DBC. I?m going to give that a try.

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    Just make sure that the PCM has a service number and hardware number he references and you should be good to go with the TB you are using.

  16. #16
    Tuner 1970ss8.1's Avatar
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    Got the IAC Moving.

    The new PCM is in and working, the IAC is finally moving. It is running better but the AFR is all over the place and it is idle hunting up and down really bad. I went through the whole PCM and copied everything I could from the 8.1 PCM. It just so happened that the one set of tables I missed were the idle tab. I am also throwing a code for Crank Relearn, so I have to figure out how to do that. Here is a log of it idling and the tune files. This is my first time tuning a DBC so I hope I can get it soon. I also don't want to have to drill a hole in the throttle blade.
    Attached Files Attached Files
    My Avatar is my Wife and Proud of it!!
    1970 Chevelle SS 8.1 Vortec T56 9" 3.00
    2006 3500HD 8.1 vortec Allison 6sp 4.10 4X4
    2013 Audi A5 Cab 2.0tfsi Quatro
    www.mcmnapa.com

  17. #17
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    Here are a few things that will stabilize your idle.
    1. Open the TB min air screw until you get the IAC in the 40-60 range at a warm idle.
    2. Reduce the fuel at idle to achieve stoich. It appears to be 8-10% too rich.
    3. Reduce your spark overspeed table by at least 50%. That is a very aggressive table setting that you have now.

  18. #18
    Tuner 1970ss8.1's Avatar
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    If I open the TB to get the counts down I get out of the idle fuel cell and the rpms jump quite a bit. But I?ll try the rest of that.

  19. #19
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    Whats your setup for the motor? Where is the TPS voltage?

  20. #20
    Tuner 1970ss8.1's Avatar
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    The motor is a 8.1 bored .030, ported heads, cam, custom intake, 102mm TB, P59. My tps voltage is at .55