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PCM's & Tuning Discussions regarding PCM's and tuning

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Old 09-24-2004, 10:16 PM
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HP Tuners Injector Flow Rate table

I just want to inform people about something I recently learned, regarding one of the fueling tables. The confusion is not really caused by HP Tuners, but rather by the way GM defined this one particular table.

Most tables that look at manifold pressure in KPA, are referenced to absolute pressure in KPA. That's all well and good, but the Injector Flow Rate vs. KPA VAC table is referenced to vacuum from ambient pressure instead. Along the top of the table are values of 0 VAC on the left ranging to 100 VAC on the right. People should be aware that 0 VAC (KPA) refers to zero vacuum, or in other word WOT. 100 VAC (KPA) refers to maximum vacuum, or in other words closed throttle.

It's worth noting that the injector flow rate is not a constant as many would assume, but instead a curve where the flow rate depends on manifold vacuum.

John
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Last edited by johnt; 09-24-2004 at 10:20 PM.
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Old 09-24-2004, 10:25 PM
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also, in the upcoming version i have put the flow rate in lb/min for imperial units
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Old 09-25-2004, 07:19 AM
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Quote:
in the upcoming version i have put the flow rate in lb/min for imperial units
And for those of us who can't wait...just divide grams per second by 0.126 to calculate pounds per hour.



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Old 09-25-2004, 07:48 AM
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Here's what I ended up scaling my IFR table for 42.5 injectors. It still needs a little more tweaking, but its close for my car. The top table is stock, the lower is what I'm running now. Anyone else have a table to share


Last edited by John F; 09-25-2004 at 08:41 AM.
 
Old 09-26-2004, 10:11 AM
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Quote:
It's worth noting that the injector flow rate is not a constant as many would assume, but instead a curve where the flow rate depends on manifold vacuum.
Is this true for the 04+ pcms as well?
 
Old 09-26-2004, 12:00 PM
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Quote:
Originally Posted by seriesIIIChump
Is this true for the 04+ pcms as well?
yes......... (apparently 3 characters for yes is not an acceptable post length)
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Old 10-02-2004, 12:54 AM
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was this the only change you made for 42.5lb injectors to work properly? I know for everycar its gonna be a little different, but just wondering if this is the only thing really needed to change to make 42lbs work..

I just switched to them, and using a mini-afc, which i dont like using really...
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Old 10-02-2004, 09:26 AM
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Steve,

You may not need the AFC. In the past, we have used devices like the AFC, ICCU, etc for two reasons. First, as a means of spoofing the MAFF in order to trick the PCM to shorten the IPW on larger injectors and second, to scale down the MAFF on big cars that would normally overrun the MAF table's 11,500 Hz limit. Philosophically, I don't like making changes in more than one place, since it takes more work to keep everything in sync and working right. I'd rather confine all my changes in the PCM. Unfortunately in my case, I'm still using the ICCU to scale down my MAFF to a flat 95% to keep from running off the end of the table. One of these days I'll get around to putting in bigger MAF like one from an '04 GTO along with a new table so I won't need to scale.

Steve, as long as your MAF frequency never exceeds the 11,500 Hz limit, then you should only need to change your IFR table in your PCM to make the 42.5 injectors work right. From the looks of it, it looks like John F multiplied his table by 1.25 and based on his recent PB it looks like it worked well for him. Since every car and every set of injectors is different, I would start by multiplying the entire table by 1.15 (to be safe). This will probably still be a little too rich, but it's safer, and you can tune from there. The idea is to change the multiplier until your average LTFT across all driving conditions is close to zero. Just be sure to give the car plenty of driving time to allow those LTFTs to settle out, before making another change to the IFR.

Once you do that, you may notice that even though the average LTFTs average close to zero, that they may vary quite a bit across the entire range. If that happens that will because the new injectors have a different linearity than the stock ones that you replaced that the table was tuned for. I can help you with that if/when the time comes. That's corrected by changing the slope of the table.

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Last edited by johnt; 10-02-2004 at 09:40 AM.
 
Old 10-02-2004, 09:44 AM
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well i know i wont need the afc once i do the code in the PCM...

so all i should change is the ifr vs kpa... then once i change that, make the slight adjustments needed to make it perfect..

so if i go by 1.15 my table should be like

stock ifr 4.55, 4.60, 4.67, 4.76, 4.78, 4.79, 4.80, 4.81, 4.82, 4.84
new ifr 5.23, 5.29, 5.37, 5.47, 5.50, 5.51, 5.52, 5.53, 5.54, 5.56
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