JPrevost

Can somebody explain to me why the 8746 ecm doesn't have a full table for the accel enrichment vs tps table!
I looked and it only goes up to 12.5%. Anybody find that strange considering the 7747 goes to 25%.
Does anybody know the value formula for the stoich value. I see that the value is 8 bit, so only 255, it has a 147 as the value right now. I guess that equals 14.7 afr, so is 255 = 25.5 afr and 4 = .4 afr?

Grim Reaper

I haven't dug much into the 8746, but if you are referring to some of the tables that seem to be limited to an RPM of 3,600 (IIRC), I believe a lot has to do with GM's original design was for a limited HP engine that was not conceived for high performance use.

With the TPI BINs ($8D and $6E), you have fuel correction via to 6,400 RPM. I believe that this was to ensure there was "growth" for the code since the ECM was used in GM's top performing cars at the time. For a stock TPI, you don't really need any correction beyond 5,200 rpm. This probably explains why GM has the main spark and VE tables limited to 4,800 rpm and then the extended tables to 5,600 rpms; probably an after thought.

If you were to get into developing some Source Code for your ECM, you should be able to extend the tables to handle higher RPMS. Again, I don't know much about the 8746, so I can't tell you if there are any "space" problems with your EPROM. But, a lot of the eproms has a lot of "useless junk" (IMO) because it was designed to run on a wide variety of vehicles. You could customize the programming to only deal with your car and eliminate the stuff that aren't used to freee up some space.

Ken73

You're talking about Accel Enrichment vs. *Differential* TPS, right?

Notice what the table represents though - a delay in adding enrichment. Does it really need to be messed with at all?

As for the stoich value - you've got it right. 147 = 14.7 AFR. Obviously you wouldn't want to set it at .4 or 25.5 - I'd leave it where it's at.

Ken

fast_broker

iTrader: (1)

Accel enrichment vs diff TPS is like the accelerator PUMP SHOT in a carb... ie, move the TPS (throttle) x amount, add Y fuel enrichment. EDIT: in a 7747, anyways

[This message has been edited by fast_broker (edited November 30, 2001).]

JPrevost

yeah yeah yeah, I know not to mess with that 14.7 value but I still don't understand the accel enrichment (aka pumpshot in the $61 tdf file) vs *diff* tps position.
I would think that having the values going to 25% would be much better for tuning than the 12.5%.
Could it be because the 7747 doesn't have the intake air temp corrections in the eprom, and since both the 8746 and 7747 use a small 4k bin!?!?
I might end up going to a 7747 ecm just because the 8746 eprom seems to be full of too much crap.