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Discussion Starter · #1 · (Edited)
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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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 :confused:

 

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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?
 

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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.. :p

I just switched to them, and using a mini-afc, which i dont like using really...
 

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Discussion Starter · #8 · (Edited)
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.

John
 

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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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Discussion Starter · #10 ·
Baddabing ;)

If you need help from there, just let me know.

BTW, save your old table. Once you start making changes, it will help us know how just much you drifted from the original values. Then we can take John's table and your's and start a database to help others.

John
 

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deffinatly save your old tables. we went through about a dozen different tries today to get the injectors tuned right. At one point (about our 10th try) we went back to our 7th try. Always write down what you changed so you can go back.
Chris
 

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well first try at using 1.15* method helped some... car felt strong, running .970 02's, but its getting better..

3rd WOT run, blew the downpipe off the race pipe... sigh, crappy SLP clamp system.. must order flanges soon..

after it blew off, WOT runs were showing .955 o2's.. :rolleyes:

It felt nice tho..

Also i love my new idle settings.. last night got in a 5min talk with some guy in a new caddy, about how badass the car sounded. while i was in subway getting my food, i noticed he was out there checknig the car out while it was still running. he was waiting for me to come out and talk :D

I dropped the idle between 50-75, it idles well too, it doesnt drop and jump up alot..
 

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Discussion Starter · #13 ·
Guys, just one more thing. Make sure to give the PCM a chance to learn before deciding you want to try another change your fueling. Give it at least a day of driving at various TPS.

Steve, if your WOT O2's settle at .970 or so, then I would take the stock table, multiply it by 1.17 and drop that one in there. In general, I prefer to work off the original tables until I baseline a file.

John
 

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uummm guys, like JohnT mentioned, the table is supposed to be a linear progression. for some reason my car didn't like it. so I tweaked it. dont use my table as a baseline. the table I posted is what my car seems to like for idle and cruising only. it still isn't right for WOT though :mad:
I was hoping there would be a few people who posted what they're running for a table with larger injectors
 

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using the 1.15 seems to work for idle and normal driving.. but WOT still isnt to happy... WOT seems to still jump over 1.000 and i get 3* KR... just keep playing with it i guess...

at least nothing has changed since i removed the miniafc.. now its just time to start figuring out what to plug in..
 

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Discussion Starter · #18 ·
A few more comments.

First of all, the IFR should only be used to tell your car what injectors you're running so that you can get your LTFT's close to zero. It should NOT be used to set your A/F (O2s) at WOT. There are other tables and much better ways to do that. First things first. We first get the LTFTs right for cruising, idling, and heavy acceleration, and THEN worry about WOT performance.

Having said that, if you guys are finding that your car runs a little rich with more throttle (more negative LTFT's), that means that the IFR needs to be "flattened" a little more. John, I noticed that your stock IFR table varied by 6.4% across the entire range, and that your modified one varied by 5.9% across its range. You may want to bring up the left side of your table a little bit while reducing the right side of the table.

Just as another data point, the variance on my table from one end to the other is only 2.4%. I'm running bigger injectors than you guys and my car is set up differently, but it highlights what I'm talking about. In your cases, I'd try maybe 4% and see which way things move.

And stay off the WOT for a little while until the fueling gets a little closer.

John
 
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