Trouble after forged

[evo400]

Hi, my friend has cracked stock pistons, and changed to forged internals. This pistons are lower so he has less copression now. And the problem is, he has now leaner AFR at all conditions, aprox 10-12% leaner. How can i easy and clean add this percentage of fuel, and lett the values in the base AFR map stay ? Nobody wants to see wanted AFR 13:1 and real AFR 15:1 ..... My idea was lower the offset of the Injectors so the ECU will calculate more opening time.... is it right, can it work ?

Thank you for any ideas.

[06rexwagon]

Did he change his intake when he built the engine? Pistons won't change the afr. Something else changed. Clean the maf first, then if you're still off in fueling rescale the maf sensor.

[absubtle]

Less compression will change the a/f ratio... it would make a less-complete burn...usually.
Absubtle
CO
PS-THings do change. When taking an engine out, and even installing the same engine back in, or throwing in a different one, w/ diffetent specs, things will change. You have to do what the car wants, not what you think it should be at.

[06rexwagon]

Less compression will change the a/f ratio... it would make a less-complete burn...usually.
Absubtle
CO
PS-THings do change. When taking an engine out, and even installing the same engine back in, or throwing in a different one, w/ diffetent specs, things will change. You have to do what the car wants, not what you think it should be at.

So according to you the afr should be rich, since it would be a less complete burn with lower compression. He's seeing the opposite.

[evo400]

Lower compresion on this engine is made by lower pistons, so there must be increasment of volume at lower piston position too, or not ? So my idea is, higher volume of air commes in and more fuel is needed , or not ?

[06rexwagon]

If more air comes in, the MAF will read that air, and if tuned properly the necessary fuel will be added. I just don't buy it. I built my motor and lowered my compression too. I tuned the car myself.

[korhan]

i understand that you dont want to make changes in the afr map and just want to make a compensation through another place for changing afr.

i dont understand why it goes to lean, it has to be gone to rich area.
also i dont understand why you dont want to change afr map.

but as a result if you write the injector scaling 500 instead of 552 you gone %10 richer. it is also the method of lazy tuners who dont want to work on whole afr map, they just write the injector scaling less and boom the afr goes richer for all map.

[evo400]

Why not to change base map ? I has tryed that. This must be 11,5:1 to achieve 14,7:1 and the ECU stops to do short + long trims. Why ? Who knows ?

The trims are very high if i stay on stock fuel map. But yes i was wrong on my idea about lower compresion.... because more likely the map has been damaged or smudged at the rime of rebuild. Ill try to check all this.

[todd-w]

it is now a completely different engine therefore a completely different tune ,you will have to re map no ifs no buts.

[evo400]

I am sure i need to retune, but if i put so much different low-load values for AFR the ECU stops to du short and long therm corrections..... understand ?

[todd-w]

no i dont , what values for short/long term trims