02' hawk

iTrader: (6)

Like the titile says my D-1 is surging at idle so the tuner said that he could not put a tune on it. I called up Procharger and they said that the blow-by valve was not working properly. He instructed me to take it off and manually test the valve. Step one was to open the valve by hand and put your finger over the vaccum port and watch the valve to see if it closes. Mine did not. (Diaphram still good) The next thing i did was checked the vaccum line connections. What i did was hooked up the line again and started the car with the valve in my hand. (It stayed open) The reason i know this is happening is because when i disconnected the 2 hoses coming from the intercoolers the mass air flow sensor was reading fine!! I even put my hand over the 2 hoses and could feel the air surging!! Does anyone have any other ideas what is making it surge at idle and i think he said it was even doing this at part throttle.

02' hawk

iTrader: (6)

Anyone?

andereck

Maybe there is towel stuck in your tubing somewhere.

kp

iTrader: (34)

If you are using the stock ATI airbox/twin intercooler and MAF you have to go in and adjust the MAF tables quite a bit on the low end. Find a tuner that has done them before and thats a simple problem to fix..

02' hawk

iTrader: (6)

How will this fix the surging? This tuner has done alot of these and he said that he has never seen one that needed this much added at idle.

02' hawk

iTrader: (6)

I'm tuning a '02 T/A with a built longblock (not stroked) w/ heads, decent size cam, full exhaust, fuel system upgrade, and an ATI Procharger setup. The car is still MAF based for the time being. The customer put a GM 85mm MAF on it, and left the screen in place.

In SD, idle and part throttle tunes out perfectly. The moment I re-enable the MAF the fuel trims peg out to +25%. Via RTT, I've added in approx. 256% more to the stock values to the MAF transfer (for this particular MAF) just to get the fuel trims to come down. That's insane! Just to give you an example, at 1500 hz the value is 3.64 g/sec, whereas the stock transfer value for that MAF is around 1.42 g/sec. We either have a fairly large vacuum leak, which I tend to believe is the issue, or either this car is just going to have to be tuned in SD period.

As a side note, the Idle Desired Airflow is reading quite low (around 4.xx to 5.xx g/sec), which is much lower than I would expect, even when the STIT isn't really indicating any adapting to keep the car idling (which idles absolutely great in SD mode).

This is what he posted a while back if this helps.

02' hawk

iTrader: (6)

We had came to a conclusion that if we put the MAF sensor on the inlet side of the supercharger that would cure the erratic readings. This workes out very well because it wont max out the sensor as fast.

kp

iTrader: (34)

Putting the MAF on inlet will cost you boost.

Just start upping the MAF numbers from 2000-6250hz until you ltrims fall in line at idle/part throttle. Problem is the where the MAF is located the air pretty much just 'stalls' there and the MAF barely sees any airflow at idle and lower rpm part throttle. Its nothing new really, I have tuned a few dozen ATI f-bodies and they are all the same..

andereck

The only thing that would cause the blower to "surge" its airflow delivery is change of engine speed. If you remove the outlet tubing from the blower and start the engine as long as the engine speed remains constant the delivered airflow will as well. I'm not kidding about looking for a shop towel or obstruction.

kp

iTrader: (34)

Trust me thay all do it to a point, its just something with the plenum and the placement of the stock MAF. The idle/part throttle lb/min drop quite a bit for some reason, I have tuned quite a few of these so its not isolated. The more stock the car is the less it does it but if you pull the screen and have a cam it will do it. I have logged cars with the stock intake and then did the ATI setup and the difference is obvious.

Its also easily fixed..

andereck

Maybe I misunderstood the original post. I was thinking he meant that the supercharger itself was surging in airflow, not the engine surging, rolling. FWIW the last LS1 F on the dyno used the supplied Predator to tune and had no idle or part throttle drivability problems and a fairly low maf fluctuation at idle according to OBDII data. I wish I had the numbers, but it was single digits.

kp

iTrader: (34)

Its not really a fluctuation in the MAF output, what happens is the reported airflow drops, the fuel trims go way positive and it just runs out of fuel and starts surging (like a carbed roots blown car when cold), it mailnly happens below 6250hz and if the screen it out of the maf it gets worst. Dont really know exactly why it does it, my gues is there is a little bit of pressure (bypass cant get it all) in front of the throttle blade when its closed most of the way and the amount of air going across the MAF element is reduced.

But like I said its very common, used to be more of an issue before LS1edit and whatnot but these days a lot of guys SD tune or most know how to deal with it by changinf the MAF calibration down low a bit..

02' hawk

iTrader: (6)

I'm not really that fluent in the tunning software but i will forward this info to him and see what he thinks.

How much boost will i loose moving the MAF?

02' hawk

iTrader: (6)

Yes the supercharger is surging a little bit of air causing the #'s to go back and forth (my understanding why we can't tune it "correctly" with the engine running at the same rpm's.

02' hawk

iTrader: (6)

So from what you guys are saying; this is normal? Is my tuner stupid?

Frost

iTrader: (45)

Haha... didn't you say you forwarded him this thread? Ask him how many SCs he's tuned.... He can swing the bias away from the MAF down low and more towards the VE besides just chopping the bottom of the MAF table. If you are running 9psi or higher though you really should think about 2bar tuning.

02' hawk

iTrader: (6)

Well i haven't forwarded this info to him yet. Well he should know this stuff if you are in the business of custom tuning in my opinion. Should i take my car somewhere else? Not to name any names.

02' hawk

iTrader: (6)

He said that he has tuned alot of forced induction cars and trucks. I have seen them.

kp

iTrader: (34)

You can tune 1000 forced induction cars and trucks but if one of them wasnt an F-Body with a Procharger its kind of moot. No one is saying he is stupid, just do what I said and it will work. Or you take the MAF out of the picture ad idle but temp changes will drive you crazy when its cold..

I ran the stock MAF for years with no issues other then changing a few numbers, most guys end up going SD/2Bar but since I had a 98 I kept the MAF and lied to the PCM - it never know any better

Brent@LPE

ORLY? On the PRO MOD it only surges when its FAT!
Kevin is spot on ..Really it comes down to how big that baby cam really is .We run a pretty agressive cam in our ATI stuff,for one reason the customer wants the THUMP plain and simple. with that being said centrifugal superchargers are some of the most easiest things to calibrate as far as power adders go. They are with out a shadow of a doubt the most repeatable,constant "power adder " on the market.And they make for some of the most repeatable calibrations on the market today. As long as you have the basic criteria of injector slope you should easily be able to start and idle a procharged car.Once a constant Idle speed is obtained attack the the throttle blade set screw to get the IAC count in a reosonble realm and start your logs from there. There are plenty of threads about IDLE tuning and you should really have no problems.Honestly with the added airflow @ idle it makes them a peice of cake