voltage vs. pulse

[racerron]

today i stated my car after putting the alternator in. the battery voltage went from 12 volts to 14 volts in turn for some reason the engine went lean with more voltage. i have never touched the injector dead time voltage %. i am runing 500 lb injectors because i use methanol for fuel but for cold in Michigan temperatures i fill the fuel tank with e85 and the required fuel number ends up to be 1.2 (ms). so to get the afr back to normal (13.5) i had to add around 8 on the VE table. this is at a idle.

[elaw]

i have never touched the injector dead time voltage %.

And that would be the explanation for your problem!

The dead time vs. voltage needs to be tuned just like many other things.

In this case the easiest thing to do probably would be to set everything back to how it was when it ran well without the alternator. Then fire the engine up with the alternator connected, and edit "dead time voltage % curve 1" at the 14.4-volt point so the AFR matches what it was with the alternator not connected.

The above is a bit of a hack since it doesn't cover any other voltages, but it's better than nothing.

[racerron]

i did not adjust those because i figure the guy writing the code knows better.

[elaw]

Ooh... no, no, no!

The dead time vs. voltage curve is a characteristic of the injector, and no two are the same (well, no two *part numbers* are the same). The driver circuit can be a factor too, so it's really the injectors you're using in combination with the Megasquirt itself.

The above also applies to the basic dead time... if you haven't set that, you could run into trouble tuning. If you do a search here there's a ton of discussion about setting dead time.

[billr]

Also, the MSQ indicates using MS3X injector drivers; so the injectors are either high-Z or dropping resistors are being used. Either is more fussy about voltage comp than low-Z with P&H drive.

[racerron]

i am driving these billet atomizers with a versa fueler p&h .

[billr]

OK, I somehow ignored the possibility you weren't using the MS3X drivers direct! Sorry.

[racerron]

That's okay.

[jeffmarsh750]

Billet atomizers ? Do you have the correct dead time charts to use for voltage compensation ? The extra volts really snaps those big injectors open.

[billr]

Hmm... I'm looking for Jean B's input here:

It seems to me that there is really very little in the way of "extra volts" when using a good P&H driver and low-Z injectors. The drivers are always current-limiting, regardless of supply voltage (assuming it is above some fairly low minimum, like 9-10V). That's the main reason I feel they are "less fussy" about DT voltage comp.

Am I correct in thinking the standard (mainboard) drivers are not true P&H? They apply full voltage, needing comp, before starting PWM current-limiting after the specified period

[racingmini_mtl]

Hmm... I'm looking for Jean B's input here:

It seems to me that there is really very little in the way of "extra volts" when using a good P&H driver and low-Z injectors. The drivers are always current-limiting, regardless of supply voltage (assuming it is above some fairly low minimum, like 9-10V). That's the main reason I feel they are "less fussy" about DT voltage comp.

Am I correct in thinking the standard (mainboard) drivers are not true P&H? They apply full voltage, needing comp, before starting PWM current-limiting after the specified period

The main board drivers are P&H but they are not current sensing P&H. So they won't give you the same current for the peak and hold phases for different voltages since they are only controlled by time and duty cycle; a higher battery voltage will give higher peak and hold currents and a lower battery voltage will give lower currents. So under extreme conditions, you may not get fully open injectors or you may get warm/hot injectors. And you can get the same if you don't set the injector parameters correctly.

The "true" P&H drivers use current sensing circuits that will always give you the rated peak and hold current regardless of battery voltage. If the voltage is not high enough to reach the peak current, you get a time out value after which the hold current will be applied. By the way, during the peak phase the full battery voltage is applied as with other driver types but the current is monitored so that this is only done until the peak current is achieved.

Jean

[billr]

I think I know the answer, but gotta ask...

Jean, are your P&H boards "true" P&H; is voltage comp for DT (using 2.4 ohm injectors) minimal using your boards? Again, assuming supply voltage is up in the normal 12.5-15V range.

[racingmini_mtl]

I think I know the answer, but gotta ask...

Jean, are your P&H boards "true" P&H; is voltage comp for DT (using 2.4 ohm injectors) minimal using your boards? Again, assuming supply voltage is up in the normal 12.5-15V range.

They are current sensing P&H drivers. However, that doesn't mean that DT voltage compensation is minimized; that's mostly an injector characteristic based on electrical and mechanical aspects and it can also be affected by fuel pressure and other fuel characteristics.

So both DT and voltage compensation need to be characterized with those drivers using a setup as close as possible to the actual running setup (or better yet using the actual running setup if possible).

Jean

[billr]

OK, thanks. I'm a bit confused now, but will mull it over some more...