The problem with that is with large injectors and very small PW at idle, and small changes in temp and voltage mean your AFR's are way off.

See Jasons 1st post in this thread for why they're important.

I disagree totally with guessing the deadtime. getting it correct is key in achieving a consistent setup specifically at idle.

 

I didnt say guess, he has published rates.

 

"Just pick a number and go with it"

Aka guess :P

 

now ladies......

 

technically it's subtracted from the necessary pulsewidth...

if the ECU calculates you need 1.7ms, it will inject .9ms and let the dead time take care of itself. the injector will then be open for a total of 1.7ms.

 

Well in fairness, he was referring to the previous post where there was a choice between 2 dead times for the RX-8 injectors

Back to the RX-8 injector- how do we get the battery correction curve right if there are no published rates?

 

I'm running 550cc RX7s, but didn't see any specific info on them, so I tested my own. Looks pretty close to Brain's (RX7 460s), but again, there's 2 different slopes so I'm not sure what to set. Depending on values I'm looking at, I can see anywhere between 1.0ms to 1.6ms.

To relate this to real world tests on my car...until today I have ran a dead time of 1.0. I needed values in the 60s in my VE table to get a 14.7 idle...always seemed high to me. Today, when changing dead time to 1.5ms, VE values in the 30s gives me the same idle. I'm thinking I ought to just keep my 1.5ms setting, but not sure...what do you all think?

Another question I have is.... the "open time" setting under "injector characteristics" in MS2- is that asking for the dead time at a certain voltage? Because the parameter after "open time" is the battery correction in ms/v. I understand that the dead time will change with voltage and that's the value we use to define the 'slope'...but what voltage is going to be referencing that from? 13.2V seems to be some sort of common value?

 

just 'figured out ' that it does indeed reference that value @ 13.2V... (MS2)

http://msextra.com/forums/viewtopic....oltage#p285337

so, assuming I'm going to with 1.5ms dead time at idle @ 14 volts batt voltage, and .2ms/V slope in MS.... I should set about 1.3 in the "open time" field, correct?



edit: i got it backwards....probably a setting of 1.6ms and .1ms/v would get me 1.5ms dead time at 14V. is this the idea?

 

That injector may not have a .2 ms/V correction. For instance, my RC750 is .13 from 12 to 15V from 11v to 12v it's .16ms/V I'm using the .13 ms/V because it is in my useful range.

 

DIYPNP has a base map for a car with 460cc RX7 injectors... they used 1.2V and .1mv/S.

I ended up just going with those setting and moving on- close enough

 

Here is the plot for my RX8 Yellow injectors.

Measured dead time is 0.75ms.

 

your data is too messy

 

what's it mean if my AFR goes to 17:1 when my voltage drops from 14.2 to 12.5?

 

voltage compensation is wrong. Does it to do instatnly then recover?
Sounds like more deadtime needs to be added for 12.5V.

 

I thought I would share some more of my data. I am using the published injector data, but never went back and collected any experimental data to compare. Here it is. The first graph is a large dataset. The calculated deadtime is very close to the theoretical for the battery voltage in which the data was collected. However ther is a very tight group of points that a y intercept of 1.1 fits rather nicely.

The lower graph has the excel calculated y intercept,a nd then a couple that I selected just to see how they fit. During the data collection the battery voltage held steady at 14.2V with the injector deadtime set to .734ms at 13.2v. Publish data would suggest a deadtime of .604 at 14.2V

Please post your opinions about what you see.

Should be using published data or experimental data?

 

Eyeballing the *upper* graph above shows 3 major trendlines. You can't just take a single trendline from the above. You have to find out what is making the trendline change - e.g. did battery voltage change due to fans turning on, or was part of it after a hot restart, etc.

Having 3 different distinct trendlines is different than getting a single trace with a curve in it. In the latter case, you look at the trendline where accurate afr control is most critical - idle at min RPM with min loading (no fans, no ac, charged battery), in the region of about 15:1 afr.

How did you vary the AFR to generate the dataset in the upper plot?

 

The afr in the top graph ranges from 13.6-14.2 iirc. I believe the afr change is due to the change in AIT. What is a sufficient number of datapoints to plot. Obviously 60s as opposed to 10min of points will remove most affect of IAT change. I'll play with it again after I make some ecu changes.

 

How did you force the afr to change?
Is the plot of MAP/AFR?

I took a few minutes of logs where I raised and lowered inj dead-time.

 

I did take a log where I adjusted the pulsewidths, but I don't believe this this data was taken from that log. Adjusting the pulsewidth resulted in an idle of 17:1. I didn't think this was possible.

It's a graph of pw vs map/afr

I wonder if I used a log where I was adjusting the injection timing table. I'll take another one when I get my computer sorted.

 

Btw guys the dead times should not have a linear value...