A/F mix

[beaukz28]

I'm looking for info on commanded a/f ratios. On an accel gen 7 there is a map where I can put in the exact a/f mix that I want the pcm to achieve. Is there a map like this that i'm not seeing? When logging I see the commanded a/f on the dashboard. How do I change that commanded a/f. What I would like to do is set the commanded a/f's all to 14.7. Then tune the VE until there is little to no correction. I have read a few threads about IFR's (not sure what that stands for). But not really understanding what exactly your doing. Can someone point me in the right direction. Thanks.

[joecar]

For commanded AFR in open loop mode, see table B3605.

IFR = Injector Flow Rate, see table B4001.

What year/model vehicle...?

Some vehicles have the FPR in the tank, so they don't have a return line from the fuel rail... "unreferenced FPR"... these vehicle have a sloped IFR... the horizontal axis for B4001 is MANVAC which is BARO - MAP... this is how IFR is calculated, if you're calculating it (vs tweaking it): showthread.php?t=4821 (http://forum.efilive.com/showthread.php?t=4821)


Also see the AutoVE tutorial in C:\Program Files\EFILive\V7.5\Doc\Tutorials.

[SSpdDmon]

Careful with the commanding 14.7:1 everywhere. Best to try and keep MAP's under 80~85kPa assuming you're close to sea level (lower kPa's the higher up you are).

[joecar]

14.7 at WOT (high MAP) and/or high load will induce/allow detonation/knock which is very damaging to the motor.

[beaukz28]

I'll work on processing this and messin around over the weekend. Thanks for the info. I'm sure I'll be back on monday with more questions.

[joecar]

Have a read of the AutoVE tutorial: http://store.efilive.com/download.aspx#downloads7 (http://www.efilive.com/downloads)

The AutoVE procedure goes like this (assumes you will be calculating your IFR from your injector rated flowrates):
1. calculate your IFR B4001 using the spreadsheet;
2. do the AutoVE procedure (dials in the VE table B0101 based on wideband AFR);

Then, when done with AutoVE, you have these next options:
a. go to OLMAF;
b. go to CLMAF;
c. go to CLSD.
d. stay in OLSD;

You may want to configure the CFOL B3605 and PE B3618 to give you suitable AFR (to make power/torque, and prevent ping).

To dial in the MAF after doing AutoVE, reenable the MAF and set B0120 to zero, and do the same procedure as AutoVE except that your BEN table will now look like the MAF table B5001, and you will be paste-multiplying into this instead of the VE table.

When you enable CL, check the LTFT trims.

Finally, you may want to reenable DFCO, COTS (cat conv overtemp prot), and any other safety measures.


Also note that there are other methods of tuning.

[ChipsByAl]

beaukz28 take note that the commanded air fuel ratio table is only used in open loop. Once the vehicle warms up and goes into closed loop it will run at 14.7. If you enter PE mode (WOT), that commanded AFR will be what the PCM is trying to achieve. Your engine does not have a wide band O2 sensor connected to the PCM, only narrow band sensors. If the tune is off, the commanded AFR could be 12.80 and not even close to it. The PCM's O2 sensors will not correct at WOT, they are ignored. The Accel Gen 7 system uses wide band O2 sensors to achieve the desired AFR at all times in closed loop, the factory PCM does not.
Al

[critter]

Some vehicles have the FPR in the tank, so they don't have a return line from the fuel rail... "unreferenced FPR"... these vehicle have a sloped IFR...

Joe, are you suggesting that a fuel rail mounted pressure regulator with return line to tank have a flat graph? ie y is constant for all values of x????

[ForcedTQ]

Joe, are you suggesting that a fuel rail mounted pressure regulator with return line to tank have a flat graph? ie y is constant for all values of x????

Critter, I believe that is exactly what Joe is saying. Reason being that the fuel rail mounted FPR references manifold vacuum and acts like the sloped IFR table to compensate for fuel pressures under various levels of vacuum to 100 kPa MAP (Atmosphere). The fuel rail FPR operates by restricting rail pressure at lower MAP and allowing full pump pressure at 100 kPa aka Naturally Aspirated W.O.T. :cheers:

[joecar]

Yes, that is correct.

With a MAP-referenced FPR, the FPR keeps a constant pressure difference across an injector... MAP pressure is present on the manifold and is added to the fuel rail base pressure...

the pressure difference across an injector cancels MAP out, leaving base FP (which is really FP + BARO).

More info: showthread.php?t=4821 (http://forum.efilive.com/showthread.php?t=4821)

[critter]

Yes, that is correct.

With a MAP-referenced FPR, the FPR keeps a constant pressure difference across an injector... MAP pressure is present on the manifold and is added to the fuel rail base pressure...

the pressure difference across an injector cancels MAP out, leaving base FP (which is really FP + BARO).

More info: showthread.php?t=4821 (http://forum.efilive.com/showthread.php?t=4821)

Also to ForcedTQ ...

I was well aware of using MAP referenced FPR in boosted applications but never considered it in NA applications. I completely missed "unreferenced FPR" above. Or it didn't compute so I ignored it ... :(

I can see where it would be handy to MAP reference my rail mounted FPR and flatline the table. I don't remember if the Fast has any place I could get manvac.

In thinking about this, that table should really curve (in the usual non referenced case) because flow across an orfice is a square law function. And the lower your rail pressure, the more that would be the the case.

[joecar]

It does curve, but it's so slight that it appears straight.

[critter]

It does curve, but it's so slight that it appears straight.

Yeah. But the table I found for my Lucas 42# injectors a couple years ago was all jagged, and thinking that could not be right, I made a best fit straight line. Having thought it through now, it is really trivial. 0 MANVAC is the nominal injector rating (converting from one test pressure to another if necessary) and the other entries just scale with (p+manvac/p)^0.5

DUH!!!