REP during a loss of traction?

I've seen REP now with two Vette's, both very powerful and having problems with Reduced Engine Power when the traction is suddenly lost. No problems in dyno at WOT though.

This particular car is a C5 Vette with forged 427, ported LS3 heads, YSi, around 17 lbs boost, 22x/24x cam, early LS3 TB and so on.

I've tried to get rid of all items that would lead to a REP. Tune is 50% scaled and (I hope) usual suspects have been maxed or eliminated.

Attached is a log where the traction is suddenly lost between frames 443-453. Based on the feedback from the driver of the car, roughly at the same time, P1515 is activated (Electronic Throttle System Throttle Position).

In the log at frame 448 you can see how the injector duty and apperently also injector opening time suddenly go very low, AFR goes up but still at the same time, EQ ratio stays at 1.27 (and commanded AFR does not change either), which I think indicates that the PCM goes into some kind of error mode - probably because of P1515.

Any opinions?

This morning I realized that I should compare rev limit situations in dyno and when the traction is lost in the street.

I'm not sure how the rev limit works; if it is just a fuel cut. At least the timing doesn't seem to change. I begin to wonder if the cut has two stages, first cutting spark from cylinder by cylinder and if that does not help, then cutting fuel. That would explain why in dyno logs I don't see injector opening time go low, because revs "behave nicely" and do not go as high over the RPM limit as they go in the street when traction is lost.

Anyway, I still wonder why P1515 activates. Furthermore, there seems to be also this "C1278 - TCS Temporarily Inhibited By PCM" when the traction is lost. But not in dyno..

I also realized that I need to reduce the cutoff resume a bit. Now both cutoff and resume are at 6900 rpm, which does not make sense.

Quote:

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Originally Posted by Pekka_Perkeles

This morning I realized that I should compare rev limit situations in dyno and when the traction is lost in the street.

I'm not sure how the rev limit works; if it is just a fuel cut. At least the timing doesn't seem to change. I begin to wonder if the cut has two stages, first cutting spark from cylinder by cylinder and if that does not help, then cutting fuel. That would explain why in dyno logs I don't see injector opening time go low, because revs "behave nicely" and do not go as high over the RPM limit as they go in the street when traction is lost.

Anyway, I still wonder why P1515 activates. Furthermore, there seems to be also this "C1278 - TCS Temporarily Inhibited By PCM" when the traction is lost. But not in dyno..

I also realized that I need to reduce the cutoff resume a bit. Now both cutoff and resume are at 6900 rpm, which does not make sense.

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C1278 is part of the REP routine. They go together. Get rid of the REP and the C1278 goes with it.
While I don't care to argue with anyone in here about this I'll go ahead and tell you something that may very well fix the problem. Put a value of .3 (yes! .3 and not .03) in your ETC scalar and redial in all of your airflow tables and tell me if it doesn't go away. You might just be in for a pleasant surprise.
:usa:

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Originally Posted by blownbluez06

While I don't care to argue with anyone in here about this I'll go ahead and tell you something that may very well fix the problem. Put a value of .3 (yes! .3 and not .03) in your ETC scalar and redial in all of your airflow tables and tell me if it doesn't go away. You might just be in for a pleasant surprise.
:usa:

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You know, I might actually try that. Thanks for the tip.

This particular combination (C5 PCM, 427, LS3 TB, 22x/24x cam) has been very difficult to tune at idle. RAF has now huge values, otherwise it just doesn't run. If I use Desired Idle Airflow value(s), it won't work at all...and so on. I always thought that the "calculated" ETC Scalar might have something to do with that, but as they say: when tuning, try to minimize unknown factors and stay for example with mathematical equations, which as such of course makes sense. As far as scaling for 2.23 limit, all idle-related values had to stay unmodified (which I think is something not that uncommon, by the way, but I wonder why..).

Quote:

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Originally Posted by Pekka_Perkeles

You know, I might actually try that. Thanks for the tip.

This particular combination (C5 PCM, 427, LS3 TB, 22x/24x cam) has been very difficult to tune at idle. RAF has now huge values, otherwise it just doesn't run. If I use Desired Idle Airflow value(s), it won't work at all...and so on. I always thought that the "calculated" ETC Scalar might have something to do with that, but as they say: when tuning, try to minimize unknown factors and stay for example with mathematical equations, which as such of course makes sense. As far as scaling for 2.23 limit, all idle-related values had to stay unmodified (which I think is something not that uncommon, by the way, but I wonder why..).

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Ok, I see that you used a LS3 throttle body. Does it have a gold or silver blade in it? If you have a gold blade, it's truly an LS3/7 TB. Silver is LS2. I have yet to take the time to sit down and study the LS3 TB issue myself, but I can tell you I don't know one person that's had success running that TB on a C5 PCM. Every one of them gets the REP issue that you're dealing with. There are obviously tables that we don't have access to and I'm thinking one of them is the culprit.
The answer may also lie in the throttle maps. The way I understand it, TAC module sends out a signal and expects an in-range response from the TPS to validate its position. I've noticed some significant differences in pedal position vs. throttle position values in the throttle maps between the C5 and C6 LS3 tune files. The answer may also lie in there.

The TB is GM 12570790, which I think is an "older" LS3 TB with silver blade.

I haven't yet logged TPS voltage (and other ETC-related stuff), but I will definitely do that next time. I'm not sure what to diagnose based on that info, though..

LS2 TB seems to have cured a bit similar problem:

http://www.hptuners.com/forum/showth...light=12570790

Quote:

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Originally Posted by blownbluez06

C1278 is part of the REP routine. They go together. Get rid of the REP and the C1278 goes with it.
While I don't care to argue with anyone in here about this I'll go ahead and tell you something that may very well fix the problem. Put a value of .3 (yes! .3 and not .03) in your ETC scalar and redial in all of your airflow tables and tell me if it doesn't go away. You might just be in for a pleasant surprise.
:usa:

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Quote:

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Originally Posted by Pekka_Perkeles

You know, I might actually try that. Thanks for the tip.

This particular combination (C5 PCM, 427, LS3 TB, 22x/24x cam) has been very difficult to tune at idle. RAF has now huge values, otherwise it just doesn't run. If I use Desired Idle Airflow value(s), it won't work at all...and so on. I always thought that the "calculated" ETC Scalar might have something to do with that.

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I don't like at all when OP doesn't respond what happened with the problem.

This time I was the OP and now it's time to respond.

The problem was engine being weak at or around idle and some stalling problems. REP was not that big problem, as the customer can handle that easily.

Now, yesterday I did what Bret suggested, i.e. changed the ETC Scalar to a 0.3 and boy, what a difference it made! Obviously I had to redo RAF table, but the end-result was unbilievable. The owner of the car just loves it. It may bee too much for the average person, but whoever likes a rapid throttle response with a feeling of engine having plenty of power, it's worth to try. Thanks again Bret!

Quote:

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Originally Posted by blownbluez06

C1278 is part of the REP routine. They go together. Get rid of the REP and the C1278 goes with it.
While I don't care to argue with anyone in here about this I'll go ahead and tell you something that may very well fix the problem. Put a value of .3 (yes! .3 and not .03) in your ETC scalar and redial in all of your airflow tables and tell me if it doesn't go away. You might just be in for a pleasant surprise.
:usa:

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is this just for stock size LS3 TBs or would you put .3 in the ETC scaller when using a NW 102 LS3 silver bladed TB on a 01 c5 vette?

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Originally Posted by dallasvette

is this just for stock size LS3 TBs or would you put .3 in the ETC scaller when using a NW 102 LS3 silver bladed TB on a 01 c5 vette?

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You may try it, but it will probably make the throttle response very aggressive. At least that's my experience.

Hi , OP what solved the REP problem? I'm boosted with LS2 TB and getting REP at WOT. If I break traction it usually happens instantly. If I maintain traction it only does it sometimes at high RPM. P1515. I can't figure it out. I had this same TB on my car when it was NA and it never did this.

Quote:

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Originally Posted by nkautz

Hi , OP what solved the REP problem? I'm boosted with LS2 TB and getting REP at WOT. If I break traction it usually happens instantly. If I maintain traction it only does it sometimes at high RPM. P1515. I can't figure it out. I had this same TB on my car when it was NA and it never did this.

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It is kind of complicated.

We used NW 102 next year and had problems with that as well and there were other changes as well, such as scaling. Then when again switching back to 90 mm LS2 unit, there wasn't any problems anymore.

I did tune some of the TB settings, though (those ones having warning with permanent PCM failure risk and related to TAC module). I don't recall the specifics anymore, but I think I changed values with pretty small percentage, step by step.

Do you have the older style LS2 TB?

My throttle body is GM 12570790. I have not touched ETC scalar or the "risky" TB settings, yet. I have maxxed out the airflow error tables and scaled my IFR/VE by 1/2.

This will solve your problem https://www.tpis.com/parts/view/53 did the same with me. TPis 90MM Throttle Body.