Duty Cycle over 100, AFR goes lean

[g-snoop]

Hello,

I'm running on a 1272cc supercharged car (4 cylinder) with 245cc injectors.
It runs pretty well under 5800rpm but It goes lean over. Even if I put some higher value on high rpm, result is same.
First, I was thinking that my fuel pump was out of order, but when I check the datalog, I see that duty cycle 1 is over 100, near 150 at full load (210kpa) !
Very strange for me...

So, before changing my fuel pump for an other, I would like your opinion on this problem !
I put my MSQ and datalog as attached file.

CurrentTune.msq

(26.02 KiB) Downloaded 80 times

[g-snoop]

Oops, here is the datalog !

2010-09-14_17.17.31.zip

(676.64 KiB) Downloaded 88 times

[g-snoop]

Ok, after looking at the log, I understand that the AFR goes lean when the duty cycle goes over 100%.

But, my problem is that 245cc injectors are pretty good for this set-up, I'm sure of that. They are often used on the same engine, with more boost without problem.
So, is there any bad setting wich limit my injectors ? I tried up a lot of setting without any major change

[Bernard Fife]

g-s,

The only setting that could do what you are seeing is if you have low impedance injectors, and the PWM% is marginal. The time threshold opens the injectors, and then the PWM% holds it open. If the PWM is a bit low, it may eventually close the injectors before the pulse width ends.

However, since this is happening only when the duty cycle is over 100%, it seems that one of the following is much more likely:

- the injectors are not flowing the amount you think. They may be the wrong injectors, they may have crud in them, or the spec may be optimistic,

- the fuel pressure is lower than it should be (and lower than the rating for those injectors). This could be because the regulator is inaccurate, or inaccurately set (and any gauge used to set it may itself be inaccurate). It could be because the fuel pump is insufficient for the task at hand (the volume and pressure requirements - the pressure may be dropping at the highest volumes - i.e., max horsepower). Or it could be that the fuel supply lines are too small, kinked, or otherwise limiting flow.

Lance.

[g-snoop]

Thanks Lance,

My Injector (high impedance !) chars seems to be correct:




The PWM time treshold is not the same as injector Opening Time but Megamanual says:

If you are running high-impedance injectors (greater than 10 Ohms), then set the:

* PWM Time Threshold to 25.4 msec, and the
* PWM Current Limit (%) to 100%.

So I think this is a hardware problem. Injectors was used on a similar project so I really don't think they are bad, but if fuel pressure is good, I will change them.
Maybe the fuel regulator is out of order. I am puzzled

[Bruce Bowling]

Check the injector resistance that the microsquirt sees - use a multimeter to check, even if these are Hi-Z just make sure something is not wrong.

If the resistance is approacing the 2 ohm point the drivers will go into current limit which is still OK. For really low injector impedance loads (like 1 ohm) the drivers will get hot and go into shutdown. This will look like a lean situation that you cannot tune out no matter what you do. The drivers cool off so fast that they are ready for the next pulse, just to go into thermal protection mode again - so this effectively shortens the applied pulsewidth.

- Bruce

[g-snoop]

Sorry for the late !

A friend lent me an other fuel pump and it works better. I'm now waiting for a Walbro 255l/h. I think it will works better !