Cam'd LS3 help
 

I bought a 2008 C6 with a mild cam (228/232/598/600/113), CAI, LT's and tune.

I have had a really bad surging problem since I have had the car, really bad. Bucking and surging under light load. I replaced the original Callaway Honker (known to cause some LS3 maf turbulence) and replaced it with an LS3 C6 Airaid. That took care of about 85% of the surging.

I installed a set of TSP 1 7/8 LT's w/o cats and I ported the intake knowing I was going to get a retune.

Yesterday at Diablosport, Johan retuned the car and it made 475rwhp (untouched as I got there) and the fuel was way off everywhere. After adjustments it ended up @ 485rwhp on a stingy load bearing dyno, on a Dynojet it would have been even better. Seeing the fuel off so much we didn't bother "street" tuning the surging out since a small test drive in 1st and 2nd it seemed to resolve it.

After jumping on the interstate on the way home I noticed the surging is still there and it is mainly noticable in 3rd and really noticeable in 4th @ 2K. It almost feels like a plug missing though that's not the case. Plugs are new and gapped @ .40 (FYI).

I am (not so) sure it's MAF related since just changing the CAI made such a huge difference.

Can anyone offer advice for us to try on the next tune? Any help would be appreciated. Any adjustments to the maf table or something? I am trying to do some homework so we don't waste too much time.

Complete mod list

2008 M6 1LT
TSP Off road 1 7/8's 3x3
228/232/598/600/113 cam
Dual Valve springs
Airaid CAI
Ported TB
Ported LS3 intake
UD pulley
New GM LS3 maf (installed it before the dyno, same exact symtoms)


Thanks,

Jason

http://i48.photobucket.com/albums/f2...3_m6_jason.jpg

Hmmm, little help over here. :nod:

There is your problem. Get a full tune, not just a dyno tune. You need the VE and MAF tuned at all of the normal driving conditons, not just WOT. You paid for a tune, get a tune. Your cam isn't big enough to do it.

Agreed, I am only looking for advice for what direction to look into when we do look at it again. LS3 maf's are VERY sensitive. Thanks :nod:

PM sent.

A 228/232 cam should be fine. A common cause of bucking and surging is too much timing. Data log while the car is in the "bucking surging zone". Via the data logs determine at what RPM and at what cylinder airmass (g/sec) cylinder the bucking/surging occurs. Then find the corresponding area in your Main Spark / High Octane table and try lowering the timing. As a test try lowering it by 5-10 degrees to see if it makes a difference.

Exactly what I was looking for! Thank you.

Question-

If there was too much timing, would plug gap affect it at all? They are at .40 now so would opening them or closing them affect that? Just curious.

In other words, if I went out and gapped them at .50 today, would it affect it at all if it is timing? Tough call probably.?

Which spark plug are you running?

For your setup I would recommend the TR5 gapped @ 0.040".

Regarding my earlier suggestion, it may be a good idea to switch the car to pure MAF mode. I realize this may seem a bit counter intuitive (because you are wondering if your MAF is possibly to blame) but if your car has been modded (which is has) your VE table will no longer be correct and will not be correct until the car is properly tuned. If you switch to pure MAF mode, (and assuming your MAF transfer function is correct) your fuel trims should then be pretty good, versus the VE fuel trims which (because of your mods) would be incorrect.

I'm running a TR6 gapped right at .40. I only have the TR6 since I plan on a 100 shot later. FWIW, the car came with TR55's gapped at .50 and the surging was terrible. The first thing I did was swap a new set of plugs thinking the bucking/surge was plug related. With a new set of TR6's @ .40 I got the exact same result.

I am going to forward all your advice, thank you.

I would bin the maf for a start and get a good SD tune and your problems are just a combination of timing and airflow. Get the VE table right then start to creep up on it. I tune my own and can afford to make small adjustments and log to get their if your tuner doesn't have the answers get another one.

cheers

The 08s are not like the 411 box cars, they do not have a VE.... They have coefficients. Coefficients are tough to grasp, but the PCMs are VERY fast.

SD is not needed with this setup.


I can get that cam to run well to 12-1300 with no issues. You can call me if you would like to discuss it over the phone.

Bucking is most commonly (before timing that is, though all variables play a role) excessive airflow.

Here is your hint; airflow final minimum ;)

^^^Yeah, but with the E38s, even if the base airflow is dialed in, there's aggressive interaction between the timing tables that causes harsh bucking. It's evidenced by a saw tooth pattern in the timing in the data logs. There's some "trickery" to getting this out.

There's some other tricks to making the E38s drive smooth, but that's all the secrets I'm willing to share today. Check with me tomorrow LOL.

It's pretty easy to tell if it's the MAF causing the bucking. Just open the MAF histogram, and at steady state, see if it's jumping from cell to cell. Don't worry about it jumping from cells next to each other, that can be the EFFECT, not the CAUSE. What you're looking for is the MAF to be jumping more than a couple cells over.

Also, as I stated before, make sure there's no harsh timing adjustments being made by the PCM. Make sure your timing line in your scanner looks steady.

Thank you Loius. Next week would be the earliest we can try anything. I sent you a PM anyway.

Thank you Frost. I will be bringing my laptop to go through all the advice if needed.

Thanks Ed, you know, since this opportunity only lasts until today, you could PM me your thoughts?? :D

You can get them out of whack pretty bad, and they will still drive OK. If You move it more than 5-7, thats when it might get a little upset, but its more than that.

You can neuter the timing table, and it will go away. The minute you add advance back in, it starts to buck.

How do you normally get it to iron out? Fuel. How do you add more fuel with out the trims taking it back away? Thats the question of the day :D

That's top secret chit right there. I could tell you, but I'd have to keel you! Texas is a long way to drive for dat!

Stop by Richmond on the way to TX and have a beer or so :)

If the items mentioned in the thread are logged and the event time is noted, you should be able to see where to attribute it in the log.

Its real simple, and the problem only gets worse the bigger the cam is :D

As mentioned by the masters above, timing is really a small part of the problem. The bigger problem is getting your running airflow correct (it never is right after a cam swap) and get the fueling right (this requires revising the VE coefficients and rescaling the MAF tables). First, you must get the airflow tables right because if you don't address these, you'll be chasing your tail with the fueling and timing tables. The ported TB is not doing you any favors here by the way. When in doubt, err on the side of being a little rich in your transitional fueling. This takes a lot of the stumble out of the system as you go from light to heavier load.