need some help tuning my 408

[Silverado420]

So im not really sure where to even begin, but ive got a throttle by cable 102mm tb on my 408 with alot of mods, and sometimes ill get a weird response from the tb when i give it gas, it actually causes the engine to die, but if i let up on the throttle, it responds like i gave it gas,
i could really use some help with my tune if anyone wants to help out thatd be fantastic.

[Silverado420]

and now if it goes into closed loop, it runs like crap and dies, but runs great in open loop, and the idle seems to surge when i shift gears

[5FDP]

How much MAF and VE tuning have you done?

I'd start there, then idle corrections and closed loop will function way better once the airflow model is corrected.

[ryan_axberg]

I would disable your short and long term fuel trims and adjust your maf curve since I see that you are running rtt maf. Once you get that dialed in then you could enable them again if you want to. I have found that once it gets dialed in though I just let it run in open loop all the time and it works really good. I would also cut way back on the start up airflow amount and add in some start up airflow delay. hope this helps

[ryan_axberg]

and put the adaptive idle to zero so you are only getting short term idle trims

[Silverado420]

Actually, I've never done any MAF or VE tuning before.

[Silverado420]

Thanks for the advice, now when you say put the adaptive idle to zero, which table are you talking about? I have a couple choices to choose from.
Also any idea on warm starting issues?
I drove the truck last night but when I went to leave the gas station I was stuck there for about an hour waiting for the engine to cool down before I could start it again. Other then that It runs great

Thanks again

[ryan_axberg]

the adaptive idle is under idle, airflow, then adaptive idle airflow. Since your tuning in MAF, the maf sensor reads the amount of air coming in and your maf calibration tells how much fuel to give it for how much air is coming in. I would say get a aem wideband, set your power enrichment tables to like 1.18 which would command like a 12.5 afr when your flooring it and adjust the maf curve so that you get that afr. You should set up a MAF error chart on the scanner, that makes it a lot easier. If you are running lean then you add to the curve if your running rich than you lower the numbers. The numbers are just how much fuel you give it. Smaller numbers are less fuel and bigger numbers are more fuel. Im sure there are videos on youtube to set that up in the scanner. If you don't have a wide band you can still tune the maf when you are idling and cruising, but the o2 sensors can only read around 14.7 afr

[Silverado420]

what do you think so far? haven't had time to log any data yet though.

[DougO]

you need to max the temp on your ltft its at 131, right now it will come on, max the desired torque per gear as well, are you going to tune the ve in open or closed loop? Are you using a wideband? with my limited tuning knowledge your going to need more braf as well

[ryan_axberg]

I see your log says ve tune, but your running 1 bar maf in you operating system. You can tune your ve but your maf calibration is what you air fuel ratio is going to come from. Also I would set the PE MAP table enable to like 85 kpa and your throttle to like 40 to 45 percent. So when ever your under 45 percent throttle and 85 kpa you will be commanding a 14.7 afr. Wideband o2 sensor would be the first thing I would get.

[5FDP]

You do understand that just because it has a 1 BAR MAF enhanced tune does not mean it completely disregards the VE table right?

The VE will always be active, it's no different than if the OS was left stock. In a blended calibration it's using both.

He needs to calibrate both the MAF and VE if it ever wants this engine to run and perform smoothly.


This is taken directly from HP Tuners for what the enhanced OS offers.

1 Bar MAF - Enhanced: This enhancement is for vehicles using a MAF. It has been added to allow vehicles to use RTT while not in speed density mode.

Ideally the OP should have never use the 1 bar enhanced because it still leaves him with both VE tables and it only use the secondary VE table while in speed density. It makes an extra step of calibrating the secondary VE, then copy paste each row into the primary VE and interpolating to create and smooth the rest of the table. The 1 bar speed density enhanced OS would have removed the secondary VE and left him with only the primary VE.

The MAF sensor still functions as normal even in speed density upgraded OS calibrations.

[ryan_axberg]

Yea, I think during throttle transitions or something it uses the ve tables. I have changed the ve table on different maf trucks and I couldn't tell any change in afr.

[5FDP]

If changes are made to the VE while the MAF is still active and fuel trims are still active, yeah you won't see much of a change because things are working against it. Disabling the MAF like he has now is the way to calibrate the VE side, then enable the MAF to calibrate that with the VE "disabled". Tuning WOT for minor changes past that would be mostly MAF after both are dialed in because it would exceed the dynamic airflow switchover point.

[ryan_axberg]

yea, i didn't see that he disabled the maf. When I have tuned different things I just turned off stft and ltft and made a ve afr error and maf afr error and got those to within around a percent and that seemed to work fine for me.

[Silverado420]

Well I have my wideband hooked up finally, and running super rich ( 9.5-11) but also found out that someone miss wired the IAC valve at the pcm so I swapped those around and now can't get it to idle to save my life. lol So I guess I will start all over and go from there.

So do I switch the OS to NOT be the 1Bar MAF?

Thanks again for the infomation and help guys, it's a huge help

[ryan_axberg]

if your maf is enabled then you are running off of that and if its not than you using your ve table for fuel calculations. I know people seem to like disabling the maf to get the ve table dialed in first then doing the maf, but personally I dont think that is necessary. I just log in my scanner a maf error and ve error chart and change them both at the same time. You don't need to switch the operating system. I think that you can only do a operating system change once anyways, not positive though.

[5FDP]

To calibrate both MAF and VE without any cross data or skewing, they have to be done independent of each other. Take for instants you want to calibrate the VE far past 4,000rpm where the stock dynamic airflow setting is, that setting would have to be raised up to redline and if the MAF was still working it would be skewing your data the whole time because your are getting fueling calculation from the MAF and VE when you only want the VE.

Disabling the MAF gets you only VE data and setting it to MAF only would get you just the MAF. This stuff is critical when you get into heavily modded engines or engines that support boost. Each half the airflow model needs to be dialed in so they jive together.


You can revert back to the stock OS with a write entire, then change the OS and write entire that back in. If you don't want to change the operating system you just need to know how that OS uses speed density. All changes will be done to the secondary VE table. So it's a small game of logging the data, copy/paste the changes and flip flopping between your two VE tables to make them the same.

[ryan_axberg]

good to know, how do you know if it is only using the maf and not a mix of maf and ve together. I have been tuning a little bit of my boosted truck and I have a 3 bar speed density tune so there isn't a maf on there anymore. I have heard that you can't properly tune a turbo car with a maf sensor even if it can read high enough.

[Hoosier Tuner]

how do you know if it is only using the maf and not a mix of maf and ve together.

I log MAF Airflow as well as Dynamic Airflow. When these are pretty equivalent you know that VE isn't involved. When there is a divergence you know the computer is taking VE into account. I used to also plot in the chart versus time one of these two divided by the other and when it got suitably away from 1 would know that VE was being taken into account, but lately just plot MAF and Dynamic Airflow together in the chart vs time and get a pretty good handle on when the VE is being used by the computer.

Edit - I also do these two with two different scales in the same section of the chart vs time, one scale so I can see differences at low airflows and another at high airflows.