jclayc

iTrader: (8)

I recently got my rebuilt LS6 tuned (TFS 220 heads, Comp Cam 229/239 .627"/.621" 111.5+3, 63lb injectors, Fast 92, LS2 90mm TB, LS7 clutch and 19lb lightened flywheel among other things). After the tune, aside from producing somewhat disappointing dyno numbers (390hp/383tq), the issue is that the car idles and runs fine but, when coming off the throttle, the engine dips down to around 260-300RPM and sometime dies (?particularly if I'm turning the wheel sharply?). If it doesn't die, it'll dip and rev, dip and rev like 5 times and eventually find idle around 950RPM.

I believe the culprit is the light flywheel, requiring the Throttle Follower Decay be adjusted ?DOWN?. Is that correct? Does anyone with heads/cam and a light flywheel have their HP Tuners file they can post for me to look at?

FuzzyLog1c

iTrader: (4)

I wish I had HPT, because I originally had this problem following my tune at Janetty Racing and Slowhawk Performance fixed it. I have a 13 lb flywheel and a clutch that has about half of the rotating inertia of your clutch, so this is definitely a solvable problem. This may help:

https://ls1tech.com/forums/pcm-diagn...-question.html

NIKDSC5

iTrader: (10)

I doubt it is the flywheel although a heavy one would help the situation. But an ls7 clutch with a 19lbs FW is not very light. If you had the 13lbs fidanza FW then it maybe worse. But with a larger cam I would think it is going to take a change in driving style. Is it just during slow maneuvers? The added strain coming from the ps pump would just make it worse.

jclayc

iTrader: (8)

thanks Fuzzy - that short post was one I found earlier and was helpful in turning me on to reducing the decay. I have a feeling a really good tuner is the best solution.

NIKDSC5 - it drops and hunts coming off of pretty well any speed but only drops and dies at very low speed (and when turning). And it doesn't drop and hunt only while the clutch is depressed - if I'm going like 40 in 4th, quick clutch and pop it out of gear and get off the clutch/coast, it still dips to like 300RPM and hunts 4-5x.

by changing driving style - the only way to avoid the big drop is to blip the throttle or, moreover, heel to toe the throttle a bit when decelerating. I can live with it but I'd like to think it's tune-able.

don't know if it's related but I've also noticed some bucking when accelerating at low speed.

NIKDSC5

iTrader: (10)

Yeah, my driving style change was in relation if it was only at slow speeds. What you got going there I have no idea, and cannot help. Good luck!

jclayc

iTrader: (8)

although I think it's the flywheel, could it be a vacuum leak? I checked by spraying carb cleaner around all the typical areas when it was at idle and didn't get a RPM change but if it was a leak "exposed" when the engine shifts (like coming off speed or turning a corner) maybe that could be introducing extra air? (I'm not getting any codes.)

FuzzyLog1c

iTrader: (4)

It would have to be a really big vacuum leak to do that. If something is loose enough to occur when you're cornering, I'd be surprised if it didn't already fall off the car.

kyle242gt

Maybe it's the load from the PS pump causing it to die, which suggests a weak idle, low load/rpm setup.

Could a vac leak do that?

07CTS-V

iTrader: (6)

It's most likely from the flywheel. Idle proportional, idle adaptive, and coastdown calibrations.

I don't have my laptop with me to send a tune file or look at yours.

Darkman

iTrader: (2)

When I installed a lightweight flywheel in my LS6 V I had no problems. Later, however, after the addition of a mild cam and Trickflow 215 heads, I had the same symptoms even with a good tune. I could drive around just fine but if I approached a stop sign in 4th gear and suddenly lifted the throttle and pushed in the clutch it would die. Other times the idle would hunt under similar circumstances. In working through this, my tuner reported that under those circumstances, i.e. lifting the throttle and pushing in the clutch, that the stock tune was pulling ALL of the timing advance - presumably in anticipation of dual-mass flywheel, which would have maintained the requisite idle. (I know this is in layman's terms, since I am not a tuner).

jclayc

iTrader: (8)

Darkman - did your tuner get it resolved?

punishmentcycle

iTrader: (6)

I know guys are going to be against this but I had the same problem. My fix was drilling a small hole in the tb blade.

Darkman

iTrader: (2)

For the most part yes. It is perfectly behaved when stone cold, or thoroughly warmed up. It does exhibit the problem occasionally when "lukewarm." Specifically, if the car is parked for a few minutes (after bring driven to normal operating temperature) and then restarted before the engine is completely cool. I have not gotten beck to the tuner yet to investigate that condition.

bmylez

iTrader: (3)

I've heard this both ways. A couple people told me to absolutely get the LS7 flywheel (~27 lbs, I believe), as opposed to the 20 lbs flywheels they have on eBay. You're saying that 19 lbs isn't very light. Just trying to make up my mind on that one since it would be for a DD, with the wife possibly driving it (rarely).

NIKDSC5

iTrader: (10)

I ran the ls7 in my corvette with the 13lbs FW with no problems. I realize the weight difference in vehicles but when you compare a spec or monster single disk with the ls7, the 7 is heavy. Now running an aftermarket single disc with the 13lbs FW I would only advice for a track car. But IMO the ls7 with a 19lbs FW is not light by any means. Unless you're comparing it with the stock dual mass, then wow, yup it's light.

FuzzyLog1c

iTrader: (4)

Yeah, the 20.4 lb steel flywheel included with the F1 Racing LS7 clutch kit is by no means light. Having put over 10,000 miles into it and a 13 lb Fidanza flywheel on the same clutch, I'd say that when my car had the steel flywheel, the car was the easiest overall to drive.

Once you drop below that point, you improve your ability to rev match, but you have to slip the clutch more carefully. The latter happens more often, so it wins out in the competition for "overall" driveability. Nowadays, I'm loving my McLeod RXT, which has less than half the rotating inertia of the LS7 + 13 lb Fidanza, so this CTS-V is definitely in the realm of "not an easy car to pick up and just drive."

bmylez

iTrader: (3)

I'm used to having light flywheels in all my cars, but I've never owned a 3900 lbs car. Just don't want to make it undriveable for everyone else (although I hate other people driving my car, but who doesn't) and/or difficult for myself since I honestly don't plan on hitting a track, just maybe a drag strip here and there. But at the same time, I do want to maximize power, and I know the stock flywheel robs some power for sure, although LS7 flywheel is already a healthy loss in rotating mass.

DMM

A couple things you can check and do here. First, your throttle body scaler value is incorrect for the increased a 90mm throttle body surface area. Here's where I would start:
- change the scaler value (Idle-->Airflow-->ETC area scaler) to 0.0192. You will likely have to tweak your base idle airflow again.
- Your Idle spark and main spark maps do not match. I would copy from the main spark map and interpolate the missing cells. There is a 4*+ jump when the PCM goes between maps.
- Your cranking VE does not match your main VE map. Do the same as above (if your VE map is correct).
- Zero out your adaptive spark when trying to diagnose this problem. I've had timing jump all around and cause a hunting idle from this swinging as much as 25*. With the size cam you have I would tighten up the amount of retard quite a bit and leave more advance than retard to control underspeed, if that makes sense. At the very least you're not "trying to hit a moving target" during diagnoses of this problem.

I'd be willing to believe that most of your problems are associated with the incorrect scaler value (since this represents the throttle blade area, every multiplier is based from this value) and having too much adaptive idle timing retard.

Your tune looks pretty good otherwise (without seeing a datalog that is). I would go into torque management and max out "max torque vs. RPM" instead of leaving it zeroed out.

Also, if it's bucking at low speeds pull some timing in those area's to see if it gets better. If you have stock heads the timing you have may be too much using fast burn chambers. You may benefit from pulling some timing throughout the tune, honestly. Was your timing done from the dyno or just a guess? It's pretty much 25* across the board and not all cam/head selections do well with that.

Edit: One last thing...your injector data is incorrect for your stated injector size. This may be trivial since you seem to have tuned your MAF and VE, but thought I'd let you know your data was off.

And to answer your throttle decay question, you would be looking to make positive adjustments. You can start by zeroing them out and go from there once you've gotten everything else taken care of.

UnsafeAtAnySpd

^Twin disk should work well. I don't have as much experience with different setups as some of these guys, but I do really like the Katech LS9 setup I have in my car.

jclayc

iTrader: (8)

Wow, thanks for the detailed feedback DMM. I tried putting the ETC Area Scalar to 0.0192 a day or two ago and didn't note a difference but will try the other things. (My heads aren't stock, they're trick flow 220s.) Unless I have specific values to try, I doubt I'll try to adjust the injector sizing... Maybe I'll read more on that. Thanks again.