Injector dead time.

[DaveEFI]

Having read a couple of posts on the MegaSquirt Forum on this, it looks like mine may not be spot on.

Does anyone have the figures from the original Bosch as used on the flapper 3.5 - driven PWM from MS2, ie no resistors? Or can give a link to a site with tables? Can't find one which gives details of those.

I initially set it using the MS instructions and arrived at 1 ms which was the default anyway. But have read it's more likely to be 0.6-0.8 for low impedance injectors driven directly.

[volospian]

I presume you have already seen this.... http://blog.nsfabrication.com/2010/02/0 ... me-part-1/

Doesn't tell you what you want, but it does suggest a method for testing your own.

Rich

[volospian]

Double post..

Rich

[DaveEFI]

Thanks for that - I'd not seen it. Yet another method.

Was hoping someone had already done the hard work.

[volospian]

I didn't know if some of those listed as tested were the same injectors as yours. What injectors are they, exactly? Part numbers etc. may help the search for folks who have already done this.

[DaveEFI]

Injectors are the standard Vitesse low impedance types.

Bosch part is 0.280.150.105

[dnb]

Unfortunately, there's no guaranteed way of not having to do some working out yourself - there are lots of variables such as fuel pressure and what ECU drive electronics you have and what voltage everything runs at. Someone with the same ECU would get pretty close, but it's not going to be perfect.

The good news is that it doesn't have to be perfect. The VE table is there to take out all of these unmodelled errors if you make them small enough.

Do you have a problem with running at low loads and low RPM when the injectors are only opening at low duty? If not, I would not worry overly about it unless you have a really odd shape VE table.

If you look at the VE table it can indicate which way you need to change things, but not by how much since we tend to not know what the VE of the engine really is. The error is largest when you have lots of short pulses (high RPM, low load) and lowest when you have fewer long pulses (low RPM, high load) so if the table looks suspiciously low or high at the end with the highest error, the opening time correction needs to be decreased or increased respectively.

[DaveEFI]

It is more about idle. I like as slow an idle as practical. it will do it all day in drive, but not in neutral. No matter how much I play with the VR table, it's the same.

I used the method given in the MS manual initially - but ended up back at the default setting of 1mS. A post on the MS forum (not about mine) suggested that generally low impedance injectors driven PWM are more likely to be 0.6-08 mS. Which got me wondering.

Trouble is I don't know of anyone else using Vitesse injectors driven PWM, to compare. Most seem to stay with the series resistors.

[Quagmire]

Dave,

I did some testing aaaaages ago (4-5 years?) on my Landrover when it had Flapper injectors - however I was using a resistor pack, not PWM.

The Landrover uses MS1 so no test mode - using the 2 squirts/ 4 squirts method I got a deadtime of somewhere around 0.6ms (I can't remember exactly what I got but I seem to remember that I thought it was improbably quick!). This would seem to tie up with what you have read.

I believe that if you don't have the right deadtime then your tune will drift with changes in air temp etc.

What kind of idle speed are you aiming for? I am using the standard hotwire injectors on my MS2 powered Rover 3500s with a guesstimated deadtime of 0.9ms and it currently idles at 600rpm, which I think is probably a tad too slow - its easy to stall when parking!

I keep meaning to get off my bum and work it out properly, is it too late to make a new years resolution?