Viper Drive-by-wire Throttle Response Tuning Issues

[MeentSS02]

Gen 4 Vipers have a pair of drive-by-wire throttle bodies - these were a new addition for the 2008-2010 cars. Up until that point, they had been cable operated. One of the major gripes about the Gen 4 cars is the utterly craptastic throttle response, and I'm trying to fix that.

We have these two tables available to deal with the throttle:



I've been adjusting the Pedal Percent Torque Request table with good results, but it is pretty tempermental if you adjust it too much...one step too far, and the car goes into limp mode, and that's no fun (it won't listen to any input at that point, spits and sputters everywhere...you have to pull over right then and there and shut it down). Any ideas what this table references to put it into limp mode? I'm getting to the point where I can tell if it is going to happen (the car bogs a bit usually), but I can't figure out why exactly it does it.

Any thoughts?

[Keith@HPTuners]

See if its setting a DTC and try disabling that.

I've found on my car I can avoid limp mode by disabling the DTC's that were being thrown.

[MeentSS02]

Well son of a biscuit eater...didn't even think of trying that. It definitely sets two DTCs (although I can't for the life of me remember which two...something about internal torque and the other is a forced idle). Thankfully, I'm getting very good at setting them, so I can make it reappear in a few minutes. It drives like a big wet turd with the table set back to stock, so I'm hoping I can get around this.

[SultanHassanMasTuning]

^were you able to get the throttle to open fully at lower RPM's?

[Keith@HPTuners]

There's no power to be gained by fully opening the throttle at lower RPM's, on any naturally aspirated viper.

The twin throttle bodies flow an insane amount of air.

[MeentSS02]

Quick update on this...disabling the codes didn't exactly fix this issue. The car still went into limp mode, only when it did it, the dash lights didn't do a thing. It just started idling erratically as it always does, and wouldn't stop until I fixed the issue.

That said, the issue was really my own fault. At first glance, it didn't look like I had changed some of the values all that much, but when I did a quick percentage change calculation in Excel, it showed that I was asking 70-100% more in some areas of that table, so I can't blame the PCM for being a bit mad at me. Can't fix stupid I suppose...

[MeentSS02]

Keith,

One more quick question regarding throttle response...back in the day when the Gen 5 was getting ready to hit the streets, I remembered seeing this thread:

http://forums.viperclub.org/threads/...=1#post3116780

...where they mention reducing the throttle lag from 450ms to 250ms. Is there a pedal gain rate or some other time related table available in the code? You can affect the delay somewhat with the pedal percent torque request table, but I feel like there's something I might be missing...

[MeentSS02]

Dan Lesser also mentions it here:

http://forums.viperclub.org/threads/...=1#post3105286

Although that makes me wonder if it is just a hard-coded value that can't be changed.

[MeentSS02]

Bump!

[Revolution]

And sugestions on this topic!

[MeentSS02]

So here's a bit more of my thought process as to why I think there's something missing to tune the throttle response.

As mentioned above (and alluded to in the links), the 2013 throttle response was supposed to be made better than the Gen 4 (2008-2010) since it was a common complaint of Gen 4 owners (and incidentally, I've not heard any complaints from Gen 5 guys about crappy throttle response). When I first looked at a 2013 base file, I noticed that the pedal percent torque request table was definitely different than the same table in the base Gen 4 file. After looking more closely, the y-axis is scaled differently, which accounts for the majority of that difference. I went ahead and did some linear interpolation to change the 2013 y-axis scale to match the 2008 y-axis, and then compared the base Gen 4 values to the base Gen 5 values. Here's what that looks like:



As you can hopefully see, the base Gen 5 calibration pedal percent torque request table has significantly smaller values (to the tune of 40% to nearly 60% less in some areas), yet the throttle response from when you step on the pedal to when the engine does something has been improved. I know the Gen 5 cars have a lighter clutch assembly, but I just get the feeling that there's something else driving the throttle response to be better.

I'm probably pissing in the wind here, but stuff like this (and my 6 month old daughter) keeps me up at night.

[MeentSS02]

Bumpity bumptiy...curious if there was any progress made, but I'm sure with SEMA, Ford stuff and the rest of the Mopar line-up, this is probably on a back burner in a land far, far away. Not that I can drive my car with this weather and all

[Keith@HPTuners]

According to what I was told, the reason the newer engines have better throttle response is due to physical differences in the engine themselves, not a result of tuning.

[MeentSS02]

Interesting...my findings showing the differences between the 2013 and 2008-2010 calibration seems to corroborate that as well. I also read recently that the perception of better throttle response from the Mopar PCM was as a result of timing/fueling changes alone, and that Mopar didn't actually mess with any throttle tables.

As per usual, I was hoping it was a pretty cut and dry, easy thing, but nothing appears to be easy with this PCM. I'm guessing since laggy drive-by-wire throttle response seems to be due to tightening EPA regulations, they wouldn't make it easy to get around. I'm sure there's also a fair amount of liability involved given the potential safety issues of making the throttle response instantaneous...

Anything else in the Viper pipeline at the moment?

[MeentSS02]

This thread:

http://driveviper.com/forums/threads...uch-horsepower

...I think is further proof that these tables are best left alone.

[Keith@HPTuners]

Yup.

I tracked my high HP race car as hard as possible and was able to work out all the track bugs with the public available software. No need to modify the throttle/torque tables.

Also, there is another mechanical issue that can occur on Gen4/5 vehicles and happened in the early days of the ACR-X series. The connections to the throttle themselves can become loose or wiggle on bumps and curbs throwing the car into limp mode. Many racers have special pigtail modified TB's from Arrow, myself included.

Also, in my case, the only way to clear the limp mode was to kill the master power switch. Fortunately on my race car, that toggle switch is right on the door. Easy to kill it on the track, just not good during a race!

[Jack B]

Keith:

I have a Gen V and have been using HPT. I think my 10.85 is the best ET to date fore a Gen V. I was hoping you could answer a few questions

1. Does the latest version have the compare function working?

2. The fuel tables seem to lose resolution in the mid 12's, should the maf table be modified.

3. I have logged the pcm pulling throttle at launch. If the 60's stay above 1.7 sec there seems to be no intervention. If the 60's drop into the 1.60's, the throttle does not want to close on the pedal. Will the torque table help rectify this issue?

Yup.

I tracked my high HP race car as hard as possible and was able to work out all the track bugs with the public available software. No need to modify the throttle/torque tables.

Also, there is another mechanical issue that can occur on Gen4/5 vehicles and happened in the early days of the ACR-X series. The connections to the throttle themselves can become loose or wiggle on bumps and curbs throwing the car into limp mode. Many racers have special pigtail modified TB's from Arrow, myself included.

Also, in my case, the only way to clear the limp mode was to kill the master power switch. Fortunately on my race car, that toggle switch is right on the door. Easy to kill it on the track, just not good during a race!

[Nine Ball]

Regarding throttle response, I have an observation about this.

I had an early 2013 Viper (#00039) and it had a laggy throttle response when you hit the pedal, before it would react. I never got the ECM re-flashed by the dealership, but when I traded that car in the tech at Tomball Dodge told me there had been two later factory reflashes since the one in my car.

My 2014 Viper isn't as laggy. I've noticed right away that 2nd gear at 60 mph hits are pretty quick. So, this tells me that Dodge already made some adjustments in throttle response.

Might be good to see an early 2013 Viper stock settings vs a later 2014 Viper stock settings, to see if anything changed. Then you could mimic the changes, perhaps.

Tony

[MeentSS02]

As an update to this thread/issue - on Sunday I was able to go out and mess with a few things since the new beta released that had some additional parameters for the Viper.

The first thing I did was try to readdress the throttle response tuning issue - I uploaded a tune I knew would throw it into limp mode, and sure enough, it did. I then disabled this little guy:



And tried again - still ended up going into limp mode. It looks like it still throws a P061A (internal torque something blah blah blah). I did not have a chance to really dig into it, so I didn't get to try disabling this code or messing with anything other than the Pedal Percent Torque Request table. For now, I set everything back to stock (throttle-wise), and it runs fine.

On a brighter note, it does appear that the cam control works:



It does not respond to anything commanded on decel however...works just fine at WOT though. I was trying to emulate the Arrow PCM exhaust burble everyone seems so excited about (hence why I was trying to advance the cam under decel), but no dice there either.

[Cali]

I just tuned one today ( 2014 ) and didn't get into the throttle side of things. Just basic stuff.... timing , etc. But I had no issues about the " throttle relearn " that needed to be done at the dealership.
Because I drove 2 hours to do the tune, my heart sank ... but the owner said everything was fine.. no issues..
Was this relearn something that only applied to earlier years? or was fixed in a newer release of 2.25 ?