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Thread: HELP Request [REP] - Reduced Engine Power - Twin Turbo 427 Corvette

  1. #1
    Tuner in Training Turbo-Geist's Avatar
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    HELP Request [REP] - Reduced Engine Power - Twin Turbo 427 Corvette

    I have a 1999 C5 Corvette FRC with a 427 cubic inch engine and twin Precision 6265 turbos. Yesterday at the track, it went into REP mode on 3 out of 10 passes. It happens during launch when trying to get more aggressive than a 1.5x 60 foot. The car has the potential to go low 9s with the 6 speed transmission if I could launch it more aggressively, but getting aggressive with the boost controller and trying to apply the throttle quickly results in an aborted pass and spending your time going down the track at 25 mph. It's not very fun when the event is being broadcast online and it looks like the car can't get out of its own way. I told people I was trying to tune around it with HPTuners and they just scratched their head.

    I have attached the tune file. I'll upload all (3) log files later this afternoon from when it went into REP mode. The tune is scaled 50% and I've maxed out all of the tables that I know of to change. The combo spools very quickly. There is no 2-step, but it is at 19.2 psi by 18 mph and 44 lb/min at 24 mph.

    Please take a look at the tune and let me know if there is anything I have overlooked.

    current tune used on 4th pass with rep and ve changes.hpt

    *Important Info*
    This is the code I am getting:

    DTC P1515 Control Module Throttle Actuator Position Performance

    Circuit Description
    The commanded throttle position (based on accelerator pedal position and possibly other limiting factors) is compared to the Actual throttle position. The 2 values should be within a calibrated range of each other. Both the PCM and the TAC module redundantly monitor the Commanded and Actual throttle position. This DTC sets if the PCM detects the problem.

    So:
    DTC sets if the "PCM detects the problem". The PCM and TAC module monitor Commanded and Actual Throttle Position, but the PCM sets the DTC. These two values need to be within a calibrated range.

    Would the calibration parameters be in the PCM?
    Last edited by Turbo-Geist; 03-23-2017 at 11:15 AM. Reason: added DTC code

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    Bill@HPTuners's Avatar
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    Any dtc's?
    It doesn't have to be perfect, it just needs to be done in two weeks...

    A wise man once said "google it"

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    Tuner in Training Turbo-Geist's Avatar
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    Quote Originally Posted by Bill@HPTuners View Post
    Any dtc's?
    I think I've had most of them in the past. P1514, P1515, P1516. I had them all set to not report for this trip and no SES light for this track outing but it still trips the check engine light and goes into REP.

  5. #5
    Tuner in Training Turbo-Geist's Avatar
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    Here is another thread that I have checked and no real answers.

    http://www.hptuners.com/forum/showth...W-102-throttle

  6. #6
    Tuner in Training Turbo-Geist's Avatar
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    Here's a picture from a log this summer. I maxed out the P0101 values after this and thought it was fixed, but apparently not.


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    Tuner in Training Turbo-Geist's Avatar
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    Here's a picture from the 1st of 3 times that it happened yesterday.


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    Advanced Tuner Montecarlodrag's Avatar
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    Without knowing the codes it's tripping, I'd say you have an electrical problem (grounding very likely) that is making bad contact when the force of the launch moves the wires.
    There are sanity checks in the tune. Can't open your file here
    9 sec Montecarlo SS

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    Tuner in Training Turbo-Geist's Avatar
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    I listed the codes above. It's tripped 1514, 1515, P0101, P0103. I've made passes where I don't go full throttle at the launch and cut a 1.58 60 foot and it will make a clean pass all the way down the track. The car isn't even to the 60 foot mark when it goes into REP mode. Going easy on the launch is not the quickest way down the track. The traction is there, but the computer won't allow it. An electrical issue would show up as another dtc.

    I've also had it go into REP mode when pedaling the throttle in 2nd gear with lots of tire spin on the street so there weren't many g-forces during that event.
    Last edited by Turbo-Geist; 02-27-2017 at 04:25 PM.

  10. #10
    Tuner in Training Turbo-Geist's Avatar
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    Here are the three REP logs.

    REP occurs around 1:37 and cleared at the 2:09 mark
    rep.hpl


    REP occurs at 0:38.59 and cleared at the 1:06 mark
    rep 3.hpl


    REP occurs at 0:14.52 and cleared at 0:45.09
    rep 2.hpl

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  12. #12
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    Add ETC position to your PID's and check the difference between it and Throttle Position (SAE).

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    Quote Originally Posted by Turbo-Geist View Post
    I think I've had most of them in the past. P1514, P1515, P1516. I had them all set to not report for this trip and no SES light for this track outing but it still trips the check engine light and goes into REP.
    It doesn't help to remove them from reported. It will still kick REP.

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    Quote Originally Posted by Pekka_Perkeles View Post
    Add ETC position to your PID's and check the difference between it and Throttle Position (SAE).
    Thanks. I'll have to wait till the next trip to the track. It only does it during the launch and I have to be on slicks on a prepped surface to hook the power.

    Quote Originally Posted by Pekka_Perkeles View Post
    It doesn't help to remove them from reported. It will still kick REP.
    Yes, I've learned after doing some reading. It's unfortunate that HPTuners doesn't provide the functionality to turn off these annoying items that cause the car to go into Reduced Engine Power mode. The HPTuners interface is really beginning to show its limitations.

  15. #15
    Advanced Tuner Montecarlodrag's Avatar
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    Your tune seems to be scaled and you aren't near tripping the airflow limit set in your tune P1514 diagnostics. It's maxed to 4.1 g/cyl as it should. All other limits are also maxed out. It shouldn't be going REP as it is.
    The only things I would change in your tune are:

    Engine-Airflow-Electronic Throttle- Max rotation vs Pedal - Max it to 100%
    Engine-Torque Management-General- ETC TPS Max - Max it to 100%
    Engine-Torque Management-General- ETC Injector Disable - Set it all to 255

    Those tables are still limiting the performance of the engine and may be related to your problem.

    The stock PCM and DBW are very capable of hard launches. I have been able to get 1.39 60ft in a Fbody at 12 psi. We then tried launching the car at 20 psi of boost on the transbrake however 60ft didn't improve (tires spun). However the capability is there, I have never got REP

    The only other possibility is that your OS may have a few tables missing to disable those checks.
    9 sec Montecarlo SS

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    Tuner in Training Turbo-Geist's Avatar
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    Quote Originally Posted by Montecarlodrag View Post
    Your tune seems to be scaled and you aren't near tripping the airflow limit set in your tune P1514 diagnostics. It's maxed to 4.1 g/cyl as it should. All other limits are also maxed out. It shouldn't be going REP as it is.
    The only things I would change in your tune are:

    Engine-Airflow-Electronic Throttle- Max rotation vs Pedal - Max it to 100%
    Engine-Torque Management-General- ETC TPS Max - Max it to 100%
    Engine-Torque Management-General- ETC Injector Disable - Set it all to 255

    Those tables are still limiting the performance of the engine and may be related to your problem.

    The stock PCM and DBW are very capable of hard launches. I have been able to get 1.39 60ft in a Fbody at 12 psi. We then tried launching the car at 20 psi of boost on the transbrake however 60ft didn't improve (tires spun). However the capability is there, I have never got REP

    The only other possibility is that your OS may have a few tables missing to disable those checks.
    Thanks. A friend of mine pointed out the "Max rotation vs pedal" change to me last night. I'll check the other things that you mentioned above. Another thing he mentioned is the drivetrain abuse limit is set to 6600 rpm. I will be maxing any of these values to 8000 rpm. I don't care to have any of the safeties turned on and would prefer a way to disable them all. There needs to be a way to turn REP off permanently. I don't need a computer making decisions to limit how the car gets down the track. If you know of any other things that need to be set to where they are not a factor, I would appreciate it.

  17. #17
    Tuning Addict 5FDP's Avatar
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    To me it's not HPT fault that you can't get around some REP issues, it's the controller itself just can not handle it and make accurate calculations.

    HPT is an awesome tool but in some cases you still limited by the hardware that was built over 15 years ago.
    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.

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    Quote Originally Posted by 5FDP View Post
    To me it's not HPT fault that you can't get around some REP issues, it's the controller itself just can not handle it and make accurate calculations.

    HPT is an awesome tool but in some cases you still limited by the hardware that was built over 15 years ago.
    I disagree. If the coding is there to make it all work and enable REP mode, there is a way to also disable it.

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    Quote Originally Posted by Turbo-Geist View Post
    A friend of mine pointed out the "Max rotation vs pedal" change to me last night.
    I've tried to lower this to 88% and it did nothing.

    Furthermore, the REP happened also in dyno which had giant dyno wheels (45" or so). So no traction problems at all.

    I doubt you can fix this with tuning. What we did was switching to a stock 90 mm LS2 TB and without any tuning changes (apart from idle/idle airflow setting), no more REP.

    Another option is to discuss with your TB vendor.

    Anyway, check first what's happening with the blade as I already mentioned.

  20. #20
    Tuner in Training Turbo-Geist's Avatar
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    Quote Originally Posted by Pekka_Perkeles View Post
    I've tried to lower this to 88% and it did nothing.

    Furthermore, the REP happened also in dyno which had giant dyno wheels (45" or so). So no traction problems at all.

    I doubt you can fix this with tuning. What we did was switching to a stock 90 mm LS2 TB and without any tuning changes (apart from idle/idle airflow setting), no more REP.

    Another option is to discuss with your TB vendor.

    Anyway, check first what's happening with the blade as I already mentioned.
    I appreciate you relaying your experience. I am using a stock 90mm LS2 TB with the correct harness. As mentioned, it doesn't happen on the street or dyno because I can't generate the type of load and airflow that it sees when launching on a prepped surface with slicks.

    I'm hoping to get to the track again this weekend and try it with these changes and log what the blade is doing vs the pedal.

    This isn't something I am willing to accept. The car needs to launch harder. The traction is there and the parts can take it. I've got a computer blocking me out with REP and HPTuners won't give us the keys to turn it off.