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

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Old 12-29-2004, 12:23 PM
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Injector Flow Rate vs manifold kPa table

Ok, it seems that the 2 tuners available for the Grand Prix have different ways of editing the IFR vs. kPa tables.

HPT uses g/s vs manifold vac in kPa
DHP uses mSec/g vs manifold kPa

This caused me a lil confusion at first, and would like to share my findings w/ everyone.

1. Injectors are rated in lb/hr @ 43psi fuel pressure by most mfg's.
2. Stock injectors are rated at 36lb/hr @ 52psi fuel pressure (as spec'd by GM)
3. The conversion from lb/hr to g/s is 1 pound/hour = 0.1259978 gram/second
4. MAP kPa is kinda backwards. 0 = lots of vaccum, 100 = 0 vac (atmospheric pressure). The MAP sensor in the GTP is a 2 bar (200 kPa or 29psi) sensor. This is odd, in that the IFR table only goes from 0kPa to 100kPa. I would ASSume that once you get above 100kPa, it maintains the last known value.
5. If you take the rating of an injector, convert it to g/s, multiply by .001, take the inverse of that number, you will get your inj flow rate as recorded in the editor.

For example.

Lucas 009 injectors. Rated at 42.5 lb/hr @ 43psi.
At 52 psi, they become 46.47lb/hr.
Converted that is 5.85g/s.
Converted again it becomes .00585 g/ms.
The inverse of that (mSec/g) is 170.65.

If you were to use the rated flow of the injectors it would look like this.
42.5 pound/hour = 5.3549056 gram/second
5.35 x .001 = .00535 gram/mSec
1/.00535 = 186.92 mSec/gram

And stockers would look like this:
36 pound/hour = 4.53592 gram/second
4.54 x .001 = .00454 gram/mSec
1/.00454 = 220.26 mSec/gram

Now, I am not exactly sure how to tune the inj flow rate table w/ this information, but I would assume you would find your base MAP reading (for instance, in Jenays car, at 19in hg vac, her map reads right around 35-36kPa) and stick that number in there. To add fuel using that table, you would increase the g/s or decrease the mSec/g number. This would indicate to the PCM that you have changed injectors, to a smaller one, therefore holding them open slightly longer and adding fuel.

Anyone else have theories or hard facts on how the inj flow rate table works?

Jason
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Old 12-31-2004, 10:19 AM
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no one huh?

I guess yall just never touch that table?
 
Old 12-31-2004, 10:40 AM
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That sounds about right. I wonder why DHP did it differently? There must be a reason for it. Every other tuning package I have seen uses g/sec.

-Geoff
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Old 12-31-2004, 03:08 PM
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Quote:
Now, I am not exactly sure how to tune the inj flow rate table w/ this information, but I would assume you would find your base MAP reading (for instance, in Jenays car, at 19in hg vac, her map reads right around 35-36kPa) and stick that number in there. To add fuel using that table, you would increase the g/s or decrease the mSec/g number. This would indicate to the PCM that you have changed injectors, to a smaller one, therefore holding them open slightly longer and adding fuel.
Jason,

I'm not sure I'm following everything you wrote so I'll just give you my view of how it works and how I tell people to adjust their table.

When somebody moves up to bigger injectors (i.e. from 36# stockers to 42.5 lb Lucas), if you do nothing your car will run overly rich. Ok, we all know that. The bigger injectors flow more fuel so you end up rich. This can be corrected by something like an AFC but the right way to correct that would be by changing the IFR table so that the PCM knows that the car now has bigger injectors. When the PCM knows that the injectors are bigger it will modulate the IPW (down) so that proper amount of fuel is used.

The first questions most people ask are, in which direction do I change the IFR values, and how much do I change them by? The first order approximation is to change it by the same percentage that your injectors changed. In the example above, going from 36# to 42.5#, the injectors increased by (42.5-36)/36 = 18%. The first thing you now do is increase your entire IFR by 18%. If you're using HP Tuners you can do this by selecting all and multiply by 1.18. You raised a good point that not all injectors are rated at the same pressure. Some are rated at 43, some are rated at 52, and some are rated at 58. Now, you can go ahead and calculate how much you need to adjust your 18% by taking the rated pressures that the manufacturers specify (assuming you can find them) into consideration, but you'd still be off anyway. You'd be off because unless your injectors were flow tested, they seldom are exactly what their specs say they are. Not only that, but different brands of injectors always seem to have different linearity of flow versus the pressure of the manifold that they are injecting into. So what am I saying? I'm saying stick with the 18% as a starting point because you will have to fine tune anyway. Keep reading.

OK, so now you increased your IFR table by 18%, but things still don't look perfect. If that's the case you'll have to adjust the IFR table. That table has a bunch of entries ranging from 0 KPA VAC on the left to 100 KPA VAC on the right (for HP Tuners). ) 0 KPA VAC corresponds to no vacuum (heavy throttle) and 100 KPA VAC corresponds to maximum vacuum (no throttle). OK, now lets say that your LTFT's are consistently very positive. That means that as the table is set now, the car is not getting enough fuel to be at stoich, so the PCM has to add fuel. The way to fix that would be to lower the values in the table by some small amount. Doing that will cause the PCM to use longer IPWs because it now thinks that it has slightly smaller injectors. Conversely, if your LTFTs were consistently negative, you will want to raise the values in the table.

There's one more case and it is the more complicated of the three. What if your LTFT's are in one direction when you're off the throttle, and in the other direction when heavy on the throttle? This is when the fun starts. You will need to start changing the slope of the line defined in the IFR table. You may need to increase the values on the left and decrease those on the right, or vice versa depending on what you see. When you're done, your LTFT's should hover close to zero for various throttle settings. Just make sure that the line in the IFR is a nice smooth line with no steps in it.

I hope that helps.

John
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Old 12-31-2004, 05:19 PM
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Thanks John, I can always count on a detailed explanition when you reply.


What we are dealing with right at the moment is that when I start the car first thing in the am, if she trys to drive it before it goes into open loop, it will sputter and die. However, after it goes into open loop, the LTFT's are hovering between 7 to -5 (depending on tpa, accel or decel).

I guess I'm gonna have to do alot of logging, and find out which way to move each cell.


Now, It seems that you agree that adjusting the IFR table is the way to go versus adjusting the maf table.

Jason
 
Old 12-31-2004, 06:15 PM
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Jason,

Is this the same car you had PM'ed me about? IIRC, that car had an XP cam, S3 heads, small pulley, LS1 TB, an LS6 MAF, and an ICCU. Nice to see you're starting with an easy tune!

With that cam/heads/pulley/MAF I'm afraid that you may overrun the MAF table so you shouldn't ignore the ICCU (MAF adjustments) altogether. However, it would be easier if you plug in your LS6 MAF tables (as you've done) and for now, set the ICCU to 100% across the board. Also set your timing to something modest.

Go through the procedure I outlined above and tune in the IFR. Just please, as you're tuning, don't go to WOT. Go up to 60% or 70% TPS. That will exercise the entire IFR table and should not push your MAF frequency high enough to be a problem. Once you get the IFR dialed in, start applying more throttle (slowly) and take note of your peak MAF frequency. If the MAFF is getting too high, you will need to scale the ICCU down (try setting it all to 95% at first). In order to compensate for that, you will also have to scale your IFR table down as well. Move the entire table down by a fixed multiple (i.e. 0.98%). This is going to be an iterative process. Once you get a feel for how things are moving, you will be able to make changes faster. You want to get to the point that under the most airflow you will ever see (smallest pulley), and in the coldest temps, your MAFF should not go past 11,000. That's how I've tuned my car so I know that I'll never overrun the MAF table.

Once all the fueling is adjusted, we'll be in a much better position to see what's happening when your friend goes into gear too early, before the PCM gets into closed loop.

John
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Old 01-01-2005, 09:40 AM
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latest version will show it to you in lb/hr if your units preference is set to "imperial".

The PCM actually stores it as sec/gram we just thought it was easier to understand it in a format everyone is used to.

Chris...
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Old 01-01-2005, 10:04 AM
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Chris,

FWIW, I like the new way of using lb/hr.

John
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Old 01-02-2005, 12:33 PM
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Jason, for cold start you need to do something completely different then just tweak the IFR table. Not knowing what software you are using, I am just guessing here. Usually, there is a crank VE table that the car uses during cold start. Tweaking this table can help it alot. You'll have to experiment to get it right, but don't be scared to go +/- 20% on the first couple tries. I think you have to lower it, but don't quote me on that. If there is not a crank VE table, then look for a startup air table. You can add or subtract fuel in this table based on temp and a couple other things.

Get your injector table dialed in first, though, since all these other tables use it calculate fuel based on the MAF (which is why you shouldn't tweak the MAF table either).

-Geoff
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