I've got a theory, and a question.. First my theory:

1) On a boosted car (such as mine), under boost you'll be in PE,
so ae is only for.. non-wot, mild throttle accelerations.. Right?

2) The PE table(s) change the AFR, by a percentage.. Percentage of fuel to the air? I don't get it.


% change
54.7
48.8
43.8
33.6
22.7
22.7
22.7
22.7
34.4

So what, a higher positive # means more fuel? And is it a recalculation each time? This is specifically important in the
pe % change by RPM:

-2.0
-2.0
-2.0
-5.9
-5.1
-5.1
-2.0
6.6
3.1
12.5
8.6
8.2
0.8
0.8
0.8
0.8
0.8

12.5 then 8.6.. Is it 12.5 + 8.6, or did the % added just go down??


3) On a 730 ECM running $8d, the MAX injector pw you can run at 6,000rpm is 10ms correct? So I should get the fuel pressure so my max PW at full boost, and 6k is 8ish ms?


-- Joe

 

~10ms@6K is true to all engines reguardless of code. BW

 

Don't some code's run double fire, SFI, etc? Or is most everything pretty much the same deal, batch fire, once per rev?

-- Joe

 

Different fueling schemes may have different PW's, however all still have only 10ms max to inject fuel at 6K. Any longer PW's and the injectors are considered static.

BW

 

OK.. Heres the deal. I get good o2 at 4400RPM under full boost. like .800.. But at 5500rpm under full boost, we're talking like .070mv.

Now looking at those tables above, 4400rpm gets 8.2 % pe, but 4800 and higher is .8.

So I guess this makes sense, that I should up my PE from 4800+ to at least 8.0% to compare? or am I wrong?

-- Joe

 

Doesn't the $8D ALDL output the commanded AFR? I believe it does, but may be wrong. If it does you can check that for the change in AFR according to PE%'s.

One aspect of boost is that the fuel pump has to keep up with the increase in boost pressure. So a stout pump is required.

RBob.

 

Good point.. Based on your note, I changed my PE so it should reflect a commanded AFR of 11.20:1.

-- Joe

 

YES - the $8D does provide commanded AFR. In fact - this value DIRECTLY follows a value calculated via the PE coolant and RPM modifiers. I have proven this via a program that I wrote. I hate changing the PE fueling via the coolant and RPM modifiers because this is done by using a percetage that is inaccurate. I posted about this inaccuracy a long time ago ...

https://www.thirdgen.org/techbb2/sho...threadid=37236

Thus, I wrote a program to change the AFR by ... well ... changing the AFR See the attached screenshot. This program makes dynoing your car much easier because if you need to change the AFR via 1.25 points then you change it by 1.25 points. Easy. I have verified that the commanded AFR values follow the table values. They do. I have also verified that if you modify the commanded AFR (via coolant and RPM modifiers) that the WBO2 will display the change.

Tim

 

1)
It depends.
PE is primarily a function of TPS. There are other qualifiers, but TPS is the main one. Boost is usually rom related. So it's a combo of rom and tps the dictates when you use PE. AE is used for increasing loads, as a function on throttle setting. A large TPS change will generally use AE and enable PW. You can have one without the other under various circumstances, but sweeping statements about who oerates where, aren't always true.

3)
You can have the code calculate a 130% duty cycle. So you can see all sorts of PW's at 6K RPM. BUT, anything over 10 msec means the injector is static.
And, FWIW, The problem with static, is getting there, since the injectors get erratic as they close in on going static. To avoid this, means running in the neighbor hood of 85-90% DC.

 

GM used 3 strategies in the 3rd Gens.

TBI, which alternates firing the injectors on each ref pulse.

SEFI, on the 89 TTA. SEFI fires each injector once every second revolution, at a specific cylinder.

And then batch fire, all the injectors once per crank revolution.

 

Thanks guys. I think i'm on the road to getting this thing running correctly now.

-- Joe