Need help with understanding MAF adjustments.

[hymey]

MAFhz is not an output, it's about as much of an independent variable as we got.

as per SD vs MAF tuning, read this: http://redhardsupra.blogspot.com/200...ss-models.html

I stand corrected. Hertz isnt and ouput but data from the MAF sensor. With the air/flow being the output function in grams per sec.

Very interesting write up.

[dfe1]

Does anyone see my point?

I definitely see your point. I believe GM abandoned the MAF-only system because of issues with response time during rapid throttle transitions. The older MAF-only systems (1986-89) had excellent drivability characteristics, but I'm sure the LS-style MAF/MAP systems offer improved fuel efficiency and lower emissions.

[hymey]

I tuned a VE Maloo HSV today with LS2 and e38, M6. Apart from spending 6 hours diagnosing why the motor ran of 4 cylinders.(A broken wire from the heavy handed exhaust fitter) I finally got it running on 8 and started to tune it mafless, we ran into some other minor tuning issues which were quickly sorted but once the sd tune was complete. The MAF was plugged back in. To my surprise the car now idled at 16.3:1 compared to the mafless tune of 14.7:1. Topend mixtures were spot on at 12.9:1 but I had to scale the bottom end of the MAF to get fuel mixtures spot on. And just to prove that this is the correct way of MAF tuning I tried to alter the VVE table(with the proper one saved) to alter afrs at idle and light loads, but It didnt help. Scaling the MAF sore immediate results. So when your MAF is out like this adjusting the VE tables won't help. It required significant adjustment. So I am all in favor for the mafless tune first then maf calibration last! Not fudging figures to get required results

[joecar]

Joel, good job...

[jfpilla]

Joel, good job...

I'm with Joe. My favorite method.

[swingtan]

So I am all in favor for the mafless tune first then maf calibration last! Not fudging figures to get required results

I'm with Joel here as well. Over the past couple of weeks Joel and I have been talking about the 90mm MAF and how it works with the E38 ECM. I know there are a lot of guys out there that swear by the "SD Rules" philosophy, but things are changing with the E38 ( at least for the moment ). Here's a few points that I've come up with on this....

1. The 90mm MAF is large enough to not be a significant restriction is most applications. Sure if you are chasing every last kW / HP for a full race car, it may be an issue, but for most street cars it's not too bad.
2. The E38 ECM is much faster than the LS1 PCM. It seems to suffer much less from the old "MAF Delay" issues seen in the earlier cars. From what I've read and heard, the biggest advantage of SD is the responsiveness that comes with it. Both Joel and I have tested E38's and found that there is not much between a correctly set up SD tune and a correctly set up MAF tune.
3. The new Transient Fueling tables for the E38 seem to rely heavily on MAF data. Turn off the MAF in the tune and you turn off Transient fueling as well.
4. In std. form, the 90MM MAF is calibrated to just over 500g/S of air. Again, this should be OK for most street applications. If you need to measure more than 512g/S of air, then it may not work for you.

There is one big issue that the MAF suffers from. With a SD tune, you can place the IAT sensor in an optimal place to get accurate air temps while reducing the effects of heat soak. The 90mm MAF has the IAT sensor built into it and it can suffer from heat soak. You can cut the IAT sensor wires and splice in a remote mount unit, or you can modify the stock unit to reduce the effects of heat soak. I had a play on the weekend and came up with a mod that may help. Rather than clutter this thread, I'll post up some pics in a new thread.

Simon.

[dfe1]

For what it's worth, I think the only significant advantage of SD over Mass Air is more consistent fuel control at idle on engines with long duration camshafts. Tuning LS1/E40/E38/E67 systems can be a bit confusing because the processor may be using speed/density calculations, MAF readings or some combination thereof to determine fuel flow. That being the case, the tuning sequence noted in previous posts is the only one that really makes sense. Since injector flow rate is a known constant, it's best to start by making sure IFR reflects actual injector flow. With that done, the next logical step is to disable the MAF and optimize the VE table. Following that, the MAF table can be optimized. When that's done, switching between Mass Air and speed/density should have a minimal effect on fuel trims-- until atmospheric conditions change.

[Chuck CoW]

I know you guys thought this thread was long gone...

Sorry to open this back up, but..........I've got an interesting question that I've always thought about and could never resolve a solid answer for myself.


Let's take a stock corvette and note the fuel trims after a drive.

After adding a CAI and Headers, the fuel trims rise by about 8% or so clearly reflecting that we've added airflow and the compensation trend is for the pcm to need to add about 8% fuel to bring it back in line.

This seems to hold true for LS1 and E40 pcms using a conventional VE table and a MAF.

Back when the E38 first appeared in Vettes, I noticed that I'd add the same CAI and Headers and would take her for a drive and the fuel trims would be the opposite....The LTFTs I was tracking would go negative indicating that the pcm had subtracted fuel as if it was too rich...

But Why? In the LS1 example we've ADDED AIRFLOW and fuel trims went up indicating the need for more fuel.....

Why is it that in the E38/E67 controllers ADDING airflow caused the trims to dive negative? Doesn't adding airflow dictate adding more fuel?

While I've got plenty of these vehicles under my belt now and I've got it working to my liking....I often wonder if I've missed something simple here....

At times I've assumed that the new generation of MAFs gets overstimulated by an increase in airflow and/or over reacts at low airflow....or maybe that a vortex of air is responsible for the overstimulation?

Maybe it's just because the math and the lack of a conventional VE table has changed?

In principal, they should be the same....and it threw me for a loop for the first bunch I tuned.....But, then it just became the same old "just make em' happy" procedure....

Anyone ever thought about/notice this besides me?

I welcome your thoughts.
Chuck CoW

[johnsZ06]

Anyone ever thought about/notice this besides me?

I welcome your thoughts.
Chuck CoW

I've experienced the same thing with my 07 Z06. It had a CAI and headers plus a ported TB. Monitoring the trims showed -10% on average. I was like, WTF? It was completely opposite on my 02 just as one would hypothesize.

What does it mean? Hell if I know but, like you, would like to hear from the pros!

[Redline Motorsports]

Chuck,

One thing to consider is that when making changes like a CAI to a "factory" calibrated air system, its not just the increase of air that effects the MAF's but also the change in airflow through the MAF has changed. Maybe more so with the new style MAF....

I think the other issue is the coefficients that are used for fuel computation in the E38/E67 process. More factors are used in the final calculation that we forget have an impact.

I agree with the "make it work" method sometimes!

HT