Hypothetical FPR question

[Calan]

Assuming some hypothetical conditions:

1. Engine running in open loop at 4000 rpm
2. Some steady amount of airflow
3. Good working injectors etc.

Would increasing or decreasing the fuel pressure change the amount of fuel entering the cylinders, or is this clamped by the ECU and injectors?

In other words... is the amount of fuel delivered by the injectors dependent on fuel pressure, or are they going to inject a fixed amount for any given set of conditions (as commanded by the ECU) regardless of the pressure in the rail?

 

[FORMONTOYA]

Assuming some hypothetical conditions:

1. Engine running in open loop at 4000 rpm
2. Some steady amount of airflow
3. Good working injectors etc.

Would increasing or decreasing the fuel pressure change the amount of fuel entering the cylinders, or is this clamped by the ECU and injectors?

In other words... is the amount of fuel delivered by the injectors dependent on fuel pressure, or are they going to inject a fixed amount for any given set of conditions (as commanded by the ECU) regardless of the pressure in the rail?

Yes, changing fuel pressure will change the amount of fuel entering the cylinders.

 

[coreyr]

yes it will change it. while the ECU controls fuel injectors it has no way of knowing how much pressure is actually in the rail so it assumes its got the correct amount of pressure and injects what it thinks is the proper amount for the given pressure. hence the reason cars run like shit when pumps are dying - lack of fuel pressure.

 

[Calan]

Ok... kind of figured this... so....

I'm thinking that my tuning problems have been with the delicate balance between timing and fuel. If I lean out my MAFT to get a decent AFR (measured with WB), then I get into agressive timing and start hitting knock, which crashes timing... car goes pig rich.. etc etc.

I'm wondering if I can approach this another way... leave the MAFT a little richer to bring timing back a little, and then adjust AFR by lowering fuel rail pressure. Or vise versa if needed.

So basically, I'm trying to get a balance of MAFT base correction factor and fuel pressure. Then use the Idle/Mid/WOT controls to fine tune the AFR.

Seems logical. Am I way off base here?

 

[jongreene]

Or ditch the MAFT and go with a 2g MAF.....that was your next step eh?

 

[Calan]

What is a "good" timing range to see at WOT? Before I get flamed, I understand that it depends on a LOT.

I guess it may be easier to ask what would be "abnormal" and likely to cause problems?