I've been studying the lo3 and lo5 fuel tables since I am new to this and trying to learn. How come in general as the RPM's increase and the MAP number increases the fuel increase except in the last column. Map=100. This would be WOT right? Wouldn't higher RPM's need more fuel? Instead it goes leaner? I'm sure theres a logical explination, I just want to know it.

Also how does the ECM decide which table to use. Say MAP=45. The tables are only 40 and 50. Does it average the fuel values in both or does it round up to 50? Same with RPM's?

 

It's because of restrictions. In oem form the engine will only need so much fuel, because there are so many limits to it making any serious HP. Lots of totally stock cars barely get over 90 K/Pa, so there is no use adding fuel above that.

The oem injectors in general are way oversized, so that the corrections that the ecm makes are rather large.
With properly sized injectors, you'll never see any 100 values in the VE table. Generally 88-93 is all you want there. Also, you have to leave a little some in there so when the ecm does the baro correction, there is still some head room injector wise.

then also, GM doesn't want you over spinning your engine so they start limiting the timing and fuel so that you don't make enough power to hurt the engine.
then we can toss in the CAFE and EPA stuff for a whole new set of issues

 

How does the 2nd fuel table (vol eff. adder) fit into the equation?

 

Which ecm?

 

Sorry, little too early! 1991 TBI 8746

 

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