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#759 - 02/07/06 11:04 AM Power enrichment and other fuel related questions  

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Here a couple of things I’d like to understand:

During PE (and assuming COT is disabled) the PCM will inject a certain amount of fuel ON TOP of what it would need if it was in closed loop.
Example: 1.2 PE means 20% more fuel than stoichiometric = 14.7/1.2 = 12.25
This should be the AFR I see on my wideband.
Correct?

IFR: I have installed a new set of flow matched Bosch injectors. They are built same as the stockers: they are rated at the same pressure and just flow a little more.
I also installed an additional fuel pump in line with original one.
Old injectors: 28.4 lbs/h
New injectors: 36 lbs/h
Old pressure: 55 PSI
New pressure: 64 PSI
The factor to calculate the new IFR is SQR(64/55)x36/28.4 = 1.3674
So I should multiply the old IFR values by this factor.
Correct?

VE: I drove around for a while in SD (MAF fail freq = 0, low octane table = high octane table). Result: all cells between 0 and 15 were +/-2% LTFT.
Can I assume that the stock VE table is correct? In this case I think the new IFR table is fine.
Don’t look at my signature: right now the engine is NA; it only has a K&N FIPK filter and has stock internals. That’s why I assume the stock VE is correct.

MAF table: after putting back the program to work with the MAF I logged Raw Frequency and LTFT. This allows me to make a pivot table in Excel and I can see for what frequency I need to change the G/sec value of the MAF table.
The result is fine, the method works: in closed loop all LTFT are pretty close to zero.
I had to change the stock MAF curve just a little (2-3%) and smooth it down so that it still looks like a curve.

Now the problem: In PE and commanding an AFR of 12.8:1 (see above how) I can measure values in the region of 13.5!
12.8 is about 14.8% more fuel, but 13.5 are only 8.9%!

Where is the mistake?

Is the stock VE table wrong and makes me believe the IFR table is correct?

Should I change the MAF curve in the high frequency range?

This of the commanded AFR is a BS? Should I just add/reduce fuel until is fine and don’t bother about the theoretical numbers?


OK, this was a long post, but how tell those things in a simpler way? wink

Thanks - Stefano

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#760 - 02/08/06 12:54 AM Re: Power enrichment and other fuel related questions  
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Your post is quite confusing since you state the engine is stock but are tuning MAF and VE tables, why I do not know.

There is zero reason with stock engine to be doing so.

I'd suggest go back to stock setting for those functions.
Set IFR to vales that would be close which is about 25% higher values then stock values are and set PE/RPM values across the table at 1.145

Do the flashing. clear any error codes, do idle relearn, drive about 30 miles for PCM to relearn and then do a testrun with a scanner recording.
From that data tweak the IFR to get LTFTs +/- 5% and only then tweak PE/RPM values.

From what I see in your post is your jumping all over the place and making one area better but then hosing that with changes that are not needed for the PCM will readjust and once LTFTs are close PCM will adjust properly and tune will be fine.
I suspect what you read on other forums has you chasing your tail.

MAF sensors measure airMASS, even if so called porting is done that does NOT change the sensors measuring ablity one bit.

VE as I have shown are for startup and decel under 4,000 RPMs and as a backup if MAF was to fail, THAT IS IT, so screwing with those tables only forces PCM to calculate functions like torque, engine load, airmass, etc incorrectly and thus adjust incorrectly.


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#761 - 02/08/06 02:36 AM Re: Power enrichment and other fuel related questions  

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Thank you for the answer,
Actually I haven't changed the VE table: I made a run in SD only to see if the IFR table was correct. Maybe not the best idea confused

The MAF is also stock and I was thinking it was an option to tune fuel by changing the MAF table (like before with the MAF-translator...)

But I understand what you say, It's probably so that I'm making too many changes in places that I shouldn't touch shocked


Another question: is the IFR table supposed to be a straight line? Or can it be curved so to have more/less fues at certain MAP values?

Thank you - Stefano

#762 - 02/08/06 11:09 AM Re: Power enrichment and other fuel related questions  
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The PCM could care less what the "line" looks like so yes the values needed for your IFR can be different

The pretty looking straight line comes from the cyberspace tuners who care more aobut what a line in a graph looks like then what the PCM really does, looks at a value and simply uses it.


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#763 - 02/09/06 03:30 AM Re: Power enrichment and other fuel related questions  

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Is it a good idea to log for MAP and LTFT and change the IFR table accordingly?

This only for cells 0-19.

I see LTFT values around 0% for cells #10 and 15 and about -8% at idle and cells like #0 and 1, that's why I was thinkin the IFR table could be something different than a straight line.

The other possibility is to change the MAF curve logging for raw frequency and LTFT.

I know both systems work(IFR and MAF), I just should choose a strategy and not change both as you wrote before:

Quote
From what I see in your post is your jumping all over the place and making one area better but then hosing that with changes that are not needed for the PCM

#764 - 03/02/06 11:50 AM Re: Power enrichment and other fuel related questions  

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OK, I left the MAF and VE table stock and played only with the IFR (logged LTFT's vs. MAP).

The IFR table is now a curve with a little higher values at low MAP.
The LTFT average is around zero +/- 2%).
The car itself drives as usual but the LTFT are more consistent. Tuning the MAF curve they changed depending on the driving time and on the wheater. Now they remain pretty constant.

The STFT's used to bounce up and down a lot (+/- 7-8%). Now they are about +/- 3%.

The big surprise is the fuel consumption: On the highway at constant speed it used to be much better than on country roads. Now it's about the same. I mean: on countrie roads it needs as "low" as on the highway! This in winter and during short trips.

#765 - 03/02/06 01:00 PM Re: Power enrichment and other fuel related questions  
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Keep in mind that as long as the STFTs are within its operating window then LTFTs values are ignored.
Being +/- 2% is just fine so you did a good job on tweaking IFR and as you mentioned its more constant which is good because that puts less work onto the PCM's slow 17 Mhz CPU and gives it more clock time to do other functions.

Its hard to look at gas mileage on cold winter weather but I'd suspect the MPG will increase a bit in summmer for keep in mind winter gas makeup does not give good MPG.

You might try a test of setting IFR a bit leaner across the board, as long as you do not have ping then engine will perform better and MPG will also increase.

Being you have water injection I would not expect a linear IFR table since when WI is on makes AFR about 8% richer thus IFR needs to be commanded with shorter injector pulse width when WI is on.


Lastly keep in mind if you tuned it correctly for better performance then MPG would take a hit but thats the purpose of performance tune right ?

But you can tune it leaner and still get performance by tuning the timing corretly to prevent the ping yet using a bit more fuel to prevent ping and using higher timing makes the power but in any case your on a better tuning path then you were before and the STFT is saying just that.


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#766 - 03/02/06 04:22 PM Re: Power enrichment and other fuel related questions  

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Quote
Originally posted by teamzr1:
Its hard to look at gas mileage on cold winter weather but I'd suspect the MPG will increase a bit in summer for keep in mind winter gas makeup does not give good MPG
What is the difference in the USA? Over here I think it's the same confused

Quote
Originally posted by teamzr1:
You might try a test of setting IFR a bit leaner across the board, as long as you do not have ping then engine will perform better and MPG will also increase
Does it mean that with positive LTFT's the engine is running light lean to stoichoimetric? And with negetive LTFT's it's light rich to stoichoiometric?

Quote
Originally posted by teamzr1:
Being you have water injection I would not expect a linear IFR table since when WI is on makes AFR about 8% richer thus IFR needs to be commanded with shorter injector pulse width when WI is on
WI turns on at 2 PSI and off at 0.5 PSI. For my particular (low boost) setup this additional enrichment happens in open loop only.
I was able to tune the IFR only in the closed loop range (20 - 90 kPa), over 90 kPa I just set it as a linear continuation of the curve.

I now have to check what happens in PE...
How does the PCM calculate the IFR under boost?
My MAP only sees 105 kPa max, the IFR goes only up to 100 kPa. Does it keep the last value @ 100 kPa? Does it extrapolate up to 105 kPa then it's linear?

I ask because there's something I don't understand:
After 105 kPa I think the PCM keeps a constant value. In reality there's less fuel flowing because of the backpressure in the intake manifold. But the PCM doesn’t notice that.
At the same time the MAF is checking for the amount of air and commands the injectors accordingly.
With constant PE vs. RPM values I should see the AFR rising proportional to the RPM (and to the boost).
In reality the AFR remains constant (that was with water alone. So the AFR wasn’t affected by the alcohol).
Why?

Something similar happens when the supercharger is disconnected: with constant PE vs. RPM values the AFR at WOT decreases at high RPM. Linearly.
Can I assume that my MAF is seeing more air than what really flows?
In NA and at WOT I see a constant MAP of about 90 kPa, so this is not something I can adjust with the IFR.
Is there some other factor that influences the AFR at WOT?
COT is disabled and the temperature is 190 – 200F. What else could it be?


Stefano

#767 - 03/02/06 10:46 PM Re: Power enrichment and other fuel related questions  
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In USA due to smog rules during the winter the gas makeup is different then in the summer since engines run richer in colder weather so more O2 is in winter gas and make have more Ethanol ( corn)which produces less MPG then summer grade which has more gas then corn.

With Boost and if over 1.2 grms/cyl as example which is the max for timing table then PCM just uses what the highest value its table supports.

Being engine is at 100 or 105 KPA still means engine is in WOT and O2s are ignored and so are the fuel trims so its simply functioning on what PE tables values are

With boost that means both PE tables of RPM and temp have to be adjusted.
Not sure what you mean but IFR functions up to 100 KPA ( as per LS1edit) but other tuning tools only show table to 80 KPA which I think really for them is vaccum values

Again as to fue trims, STFTs are what PCM adjusts IFR and not LTFTs and if STFTs are close to zero then its a mute point as to effects to overall AFR.

I think you may be looking too much into this for as long as NON WOT has fuel trims close and during WOT you have good timing and little or no ping then fine tweaking tune buys you nothing.

Consider EPA (smog) they feel no problem as long as fuel trims do not exceed -13 and +22 so in your case with +/-2 of fuel trims your pretty well tuned in.


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#768 - 03/03/06 02:52 AM Re: Power enrichment and other fuel related questions  

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This is what happens at WOT (non supercharged): the blue line is the commanded AFR (1.145), the red line is the result (smoothed).
Why is it a curve? I was expecting a parallel to the commanded AFR, but not a curve.

[Linked Image]

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