BOTTLE ROCKET

iTrader: (4)

I am running a SD tune on my 98 (02 PCM) H/C FI vette, and have run into a strange issue
My VE table has very low #s in the 400-4000rpm to about 80 KPA compared to every table Ive seen or tuned (stock, modded, etc)
I have 19s-20s through around 400rpm-2000rpm and 35KPA. When I set up and scan STFTs, It just keeps me pulling and pulling until they are that low. I know they #s are not correct because once they are low, I get tip in, and when I start the car warm, it will go to flat line (18 afr) on my onboard wideband.
I really want to tune it with the STFTs because of the ease, but something is obviously not right. I am not a veteran tuner, but have tuned the MAF and VE tables on several cars with great success, and never seen this before.
NOTE: For what its worth, the car was DEAD ON when I had the 98 PCM in, but although the car is strong and runs good, I have never gotten all of the bugs out of it since the swap.

gametech

iTrader: (1)

Are you SD tuning with the MAF still wired in? Do you still have a MAF PID in your scanner? With the MAF wired in, it is possible to fail it without the computer ignoring it. This causes your VE changes to be mostly ignored. If you are tuning SD with a MAF PID logging in your scanner, it may be interpolating your airflow error between the real SD error and the zeroed out MAF false error.

BOTTLE ROCKET

iTrader: (4)

Thanks Gametech
I do not have the MAF in the car, have placed the settings to cause it to fail, but have it on "no MIL light". I know it cant be "eliminated" (no error reported) because the computer has to see it to fail)
The MAF PID is still "listed" on my scanner but I don't think it is reading. (Haven't noticed it because I'm not looking at the data and my wifes car still uses it so I didn't remove it) I can remove it if it is causing an issue of course

MontecarloDrag

iTrader: (3)

Delete the MAF reading from the scanner, it can skew airflow readings.
Set the P103 to fail on first error and enable the DTC. You will see the SES light but it doesn't matter, you will now the PCM is running full SD. You can disable the SES light after you finish the tune.
Set the MAF Fail high to 0 Hz

Use the wideband to tune VE, add fuel to the low rpm cells until you have no stumble nor hesitation on tip ins.
If you are tining idle cells at idle, make sure you have the car outdoors with a lot of ambient air flowing. Tuning in the garage or into the shop walls will have you chasing your tail.

BOTTLE ROCKET

iTrader: (4)

Bumped the VE table up a bit and set 101,102,103 to MIL on 1st. Started the car and it didn't want to run. Pig rich by gauge and no MIL light. I checked DTC and had codes for them. (They are UNCHECKED so NOT enabled)
As a note, 106 is "unchecked, and a "2", no MIL light. It I a MAP sensor so it seemed odd it was not activated. (I didn't uncheck)
Is it possible my "H/C, intake, full exhaust car is really that "inefficient" out of boost? The cam is a decent size blower cam but on a 117LSA
What should my clylinder airmass be at low and cruise rpms?

rpturbo

iTrader: (47)

I am new to tuning, and in a similar situation. I pulled ~`10% out of ve and was able to get mine to start and run, but still pulled more once I got it logging. I got iinterupted on my vacation, but will be back at it next week.

Brando5641

iTrader: (3)

Depending on the cam you usually have to pull a decent amount of fuel at idle from my experience. After I can get the vehicle to idle on its own I use the stock O2 sensors to get the idle fueling close. I will copy the long term fuel trims and paste special on the VE table and multiply by %. Lots of folks will disagree but it works good for me.

MontecarloDrag

iTrader: (3)

Be aware that you can't trust a wideband blindly at idle on a cammed engine, much less on headers. A narrowband O2 is completely useless in this situation.

When I Tune idle I look for what the engine wants, I don't care if the wideband says 13:1 or 16, if the motor is happy I give it the gas and timing it wants.
For cruise you can tune like usual but use a wideband, stock O2 tend to run cold and not read properly.

Many cams need fuel pulled on the lower RPM range, the lope means it is misfiring and having reversion. It is less efficient in a way.
They usually need more idle air, more timing and less fuel. Not all cams are the same so you need to listen what the engine wants.

For some cams you need to go full time open loop, some of them run better in SD.

Exidous

iTrader: (11)

What size cam and did you reset fuel trims after you upped the VE a little but before you started it? Smallish cams like mine 225/227-114 tune just fine with the NB/WB at idle. It has -2* overlap.

Make sure that you are always tuning with the engine fully warmed up. Except for the RAF of course.