Thoughts on cam phasing and ECU tuning

[brn12345]

Since the high pressure fuel pump is driven off the exhaust cam and the shape of the lobe (triangle) has an impact on the timing of fuel discharged from the direct injectors, would changing the exhaust cam angle (lets assume we can tune this via the ecu) mess up the direct injection timing?

[Grishbok]

you have a window for which you can inject fuel through the DI. The stock map is pretty conservative, but you can tell the system to inject fuel earlier in that window to sneak more fuel in but you are limited to the confines of that injection window.

[serialk11r]

No, it wouldn't. The injectors are electronically controlled.

[brn12345]

Originally Posted by serialk11r

No, it wouldn't. The injectors are electronically controlled.

Measuring the fuel that goes into the cavity before the injection nozzle is electronically controlled, but the actual injection is performed by the cam lobe acting on the plunger, so if the cam phase shifts, it should have an impact on the timing of fuel injected. That's how I understand this system to work.

[serialk11r]

Originally Posted by brn12345

Measuring the fuel that goes into the cavity before the injection nozzle is electronically controlled, but the actual injection is performed by the cam lobe acting on the plunger, so if the cam phase shifts, it should have an impact on the timing of fuel injected. That's how I understand this system to work.

Where are you getting this idea? There is only injector pulse duration and fuel pressure regulation. The cam lobe does not act on the plunger, that would be a disaster. The plunger is activated by a solenoid. I'm 100% positive on this. There is no fuel measurement that happens, the "measurement" is done by how long the plunger is open.

Just think about it, if the exhaust valves control the fuel injection, then fuel is injected in the exhaust stroke. That makes no sense.

[ElectronSpeed]

Originally Posted by brn12345

Measuring the fuel that goes into the cavity before the injection nozzle is electronically controlled, but the actual injection is performed by the cam lobe acting on the plunger, so if the cam phase shifts, it should have an impact on the timing of fuel injected. That's how I understand this system to work.

I see your point. It is not exactly how I think of it. I think of the exhaust cam position has having a bigger impact on pumped volume than timing.

In many current direct injection systems (this one included?), the ecu needs to know the cam position to determine when to close the inlet valve on the pump and get the right volume. Thankfully, the ECU can typically monitor fuel pressure at the fuel rail to understand if they have pumped the right volume toward the fuel rail.

Eric Schieb
Electron Speed

[ElectronSpeed]

Originally Posted by brn12345

Since the high pressure fuel pump is driven off the exhaust cam and the shape of the lobe (triangle) has an impact on the timing of fuel discharged from the direct injectors, would changing the exhaust cam angle (lets assume we can tune this via the ecu) mess up the direct injection timing?

The "triangle" shaped lobe would be a clue that this is not a fuel injection timing thing. There is little in the engine that happens 1.5 times a crank revolution.

[Calum]

Originally Posted by serialk11r

Where are you getting this idea? There is only injector pulse duration and fuel pressure regulation. The cam lobe does not act on the plunger, that would be a disaster. The plunger is activated by a solenoid. I'm 100% positive on this. There is no fuel measurement that happens, the "measurement" is done by how long the plunger is open.

Just think about it, if the exhaust valves control the fuel injection, then fuel is injected in the exhaust stroke. That makes no sense.

His explanation seems like he probably knows diesels well. Don't beat him up, it's just a misunderstanding of the difference in the injection systems even if they are both are DI.

[gmookher]

DI on this car is nothing like a diesel

ECU can control rail pressure

[SkullWorks]

yeah, sounds like you guys got this sorted out,

There is a mechanical pump which is acted upon by the Cam shaft via a 3 lobe profile, the solenoid on the mechanical pump controls how much of the fuel is trapped (it is called a spill valve for a reason) in the mechanical pump and therefore affects the rail pressure,

The direct injectors are then triggered electronically, via a peak and hold driver box of sorts that is under hood on the passenger side.

[benster]

Originally Posted by serialk11r

Where are you getting this idea? There is only injector pulse duration and fuel pressure regulation. The cam lobe does not act on the plunger, that would be a disaster. The plunger is activated by a solenoid. I'm 100% positive on this. There is no fuel measurement that happens, the "measurement" is done by how long the plunger is open.

Just think about it, if the exhaust valves control the fuel injection, then fuel is injected in the exhaust stroke. That makes no sense.

I know it doesn't work like that anymore even in most diesels, but I would like to know why on earth would it be a disaster if the injector would be activated by a cam lobe? that lobe would just be different than the valve lobes and not at the same angle either. it worked for decades, it is old tech, but did work.

[Aza]

Originally Posted by benster

I know it doesn't work like that anymore even in most diesels, but I would like to know why on earth would it be a disaster if the injector would be activated by a cam lobe? that lobe would just be different than the valve lobes and not at the same angle either. it worked for decades, it is old tech, but did work.

This tech pre-dates variable cam phasing - if you were to create a setup like this your injector timing would be in a fixed relationship with the valve timing, which would remove one aspect of modern engines' adjustability.

Also the tech (when applied to diesel engines) didn't have to cope with the ~8000rpm redline that many engines see today.

[benster]

i know that, I'm not saying it should be still used, just that it was working back then. and btw there are p-pumped cummins engines turning 6500rpm with injectors like that, and that make over 2000hp.

again, this should not be used on cars like the brz or any new engines for that matter, just stating facts. it would still work with cam phasing as the injector lobe would be affected the same as the valves.

[Coheed]

So much debate on how the fuel injection pump works. It's just a high pressure pump. The timing is still controlled by the injector driver and ECU. They are independent, and cam phasing has nothing to do with the injection timing.