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Thread: C5 Idling issue

  1. #1
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    C5 Idling issue

    have a 2003 C5 corvette with a 6 speed manual. Car has a TSP 228r cam and tsp headers. I am having issues with it stalling on decel, as soon I let off the throttle the rpms dip way down past idle which sometimes results in the car stalling. I am looking for some assistance as I am interested in learning how to tune using hp tuners as it would be cheaper than having the car tuned again. The first tune was done by mail order tuner. I would rather buy a MPVi3 than pay for another tune. Any advice would be greatly appreciated. Do i need a wideband to tune effectively? If I post a data log could someone assist?

  2. #2
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    You absolutely need a wideband, I use zeitronix, AEM is popular also.

    People who come in here posting tunes and logs get a lot of free help. If you don't have tunes and logs, and you can't clearly describe what is going on, your questions will go unanswered.

    I account for my time; spending time on here reading random threads has gained me a lot of useful knowledge - watching YT videos on tuning (goat rope garage channel,) is one thing, but seeing people work through their issues is better, also some great how to's here so you know where to start, ie:

    https://forum.hptuners.com/showthrea...e-(w-pictures)

    Dyno time is prohibitively expensive, so I download/reference a lot of tunes done on similar engines as the one I have. Why? I can do instrumented testing to help with VE tables and MAF scaling (wideband and logs,) but not very much with timing. I'm building a set of knock ears:
    https://www.miataturbo.net/ecus-tuni...example-61616/ - and will use these on the street and probably later on on the dyno to help get things better optimized.

    So, grab the tuning device and start, make small, individual adjustments that you can track (IE: I plan on using a spreadsheet to paste values in/keep track of all versions/changes to my tune,) and when you're stuck, post in here.

  3. #3
    Tuning Addict blindsquirrel's Avatar
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    The knock threshold is not really a good indicator of best timing. It'll start falling off a good ways before any knock is detected. Use only as much timing as it needs, not the most it will tolerate without knocking.

  4. #4
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    Well, what it needs is what makes the best torque (as far as I know,) but since I can't really measure that, I just want to avoid going off into no man's knock land. I haven't found any great information as to how to set up timing, only that my vehicle will need more of it as I'm using an aftermarket camshaft. I'll also be making power/torque at a higher rpm. I have read Banish's book - he uses a dyno, of course, and measures torque while adjusting timing on the fly.

  5. #5
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    Quote Originally Posted by chevyguy1991 View Post
    have a 2003 C5 corvette with a 6 speed manual. Car has a TSP 228r cam and tsp headers. I am having issues with it stalling on decel, as soon I let off the throttle the rpms dip way down past idle which sometimes results in the car stalling. I am looking for some assistance as I am interested in learning how to tune using hp tuners as it would be cheaper than having the car tuned again. The first tune was done by mail order tuner. I would rather buy a MPVi3 than pay for another tune. Any advice would be greatly appreciated. Do i need a wideband to tune effectively? If I post a data log could someone assist?
    Most of the time idle issues are fueling issues first. A car that is chugging on fuel especially during decel will never have a stable idle.

    I'd make sure the VE tables are tuned with MAF disabled at least initially. Log LTIT and STIT which should be added to the base idle airflow tables.
    Tuner at PCMofnc.com
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  6. #6
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    Quote Originally Posted by Alvin View Post
    Most of the time idle issues are fueling issues first. A car that is chugging on fuel especially during decel will never have a stable idle.

    I'd make sure the VE tables are tuned with MAF disabled at least initially. Log LTIT and STIT which should be added to the base idle airflow tables.



    The car runs perfectly 90 percent of the time, it usually happens when it the motor is between 90-140 degrees.

  7. #7
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    Ok log LTIT and STIT specifically in those temperatures but heed my other warning that this is usually a fueling problem first.
    Tuner at PCMofnc.com
    Email tuning!!!, Mail order, Dyno tuning, Performance Parts, Electric Fan Kits, 4l80e swap harnesses, 6l80 -> 4l80e conversion harnesses, Installs

  8. #8
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    Tune and logs

    Tune and logs
    Attached Files Attached Files

  9. #9
    Senior Tuner eficalibrator's Avatar
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    With any significant cam change, the FIRST thing you need to fix (after the injector data is confirmed, of course) is the OPEN LOOP airflow models. This means both MAF and VE should be recalibrated separately.

    After you fix the changes from stock in the VE surface, you will see that lots of other background functions (like temperature compensation, DFCO, coastdown, and idle) either fall into place or are much easier to fix.

    You probably won't have to move timing too much with that cam, a blanket addition of a few degrees might get you really close. Fix the air/fuel issue first since calculated air/cyl is actually an input to timing anyway.

    One hour of steady state VE mapping (in open loop, with a good wideband) is worth more than two weeks of driving around on the road. You'll waste more in gas $$ than you'd spend on dyno time and still have issues. Get the fundamentals right first before chasing some minor detail or "boogeyman issue."