I was asked,

>Would you mind expounding a little on what and how
>to recalibrate the offset tables.

Curious to see what others think about this.



If you knew what the idle trims were prior to the
injector swap, and believed the original offset and
flow table and your new flow table, then the easiest
thing might be to back into it using the LTFTs. The
injector offset matters most at minimum injector
pulse widths (it's making up for all of the actuation,
mechanical vs electrical, time-skew).

You may see that the injector is operating right up
against the minimum pulse width value. That would
bind your hand. Need that value to be sane, but
below the operating idle pulse width delivered.

Then if your idle trimming is fatter than before, figure
that can be attributed to the offset error. Like if the
idle cell LTFT moved from -4 to -8, 4%, the injector
offset error has contributer -to the total- a -4%
drift by swapping. Take the delivered pulse width
apart, it's the sum of (offset+airflow_calc). Or now
(offset+error+airflow_calc). The offset presently
being fixed and known, you can get the old airflow_
value known and be left with the error in mS. Go
subtract that from the present table (if trims went
more negative) and you should see the idle trims
move back to original (the delivered PW will stay put
at least in the closed loop area, but cold idle PW will
skinny up some).

If I were going at it like science, that would be a good
pulse train generator, a good fuel pressure gauge and
a variable pressure regulator, and a gram scale plus
plumbing. Run the injector at 10% and 80% duty on a
10mS period and take the two data points' line-fit
down to the axis. Then you'd be wanting the voltage
mapped out (coil and pintle-mass differences) and
the fuel pressure (pintle area). That's a mess o' data
to take, I can see why nobody does it (flow sells
parts, clean idle is for pussies ).

But if you can get to happy by just shaving on the
offset table based on the car, in relative terms, it's
good enough, right?

 

Does anyone have any further knowledge about Injector Offset they can add to this post!

 

Jimmy - that's quite possibly the best explaination i've heard yet. thanks for sharing

 

Interesting Jimmy. Ever since I changed over from 30s to 60s for the blower my car has been dumping fuel at idle (hard to get it above +6). So maybe I screwed myself by making the inj # too big down low. I was told 60s were hard to make idle because they pump a lot of fuel at very low duty cycles, so I pre-adjusted the lower cells up. Maybe I didn't need to.....

 

Jimmy,

Heres a question; Doesn't each injector have its own offset values as determined by the manufacture? If this is the case, why can't we readliy get this information? I am working with a set of Motron 60's that are giving me some idle issues.

Seems to me that IFR's and IOS should be a set values per injector......No??

Thanks for your post!

 

"If this is the case, why can't we readliy get this information?"

That's the question no one can get an answer for, I've been looking for a year, on many many sites. No luck.

 

Some years back when I used to be envolved in injector flow testing, we took a few different brands of different flow rate injectors and graphed the results of flow by changing their pulse width and RPM. I posted the results, now lost, on the Vettenet and it created alot of interest. There were several percentages of differences, which should be expected, because of the different styles such as a disc, pintle or ball valve style and the differences in weight or movement traveled with any given style from brand to brand. Thus, like most aftermarket mods, it is not an exact science computing IFRs or IOTs which also tends to explain why our MAF, VE, PE etc tables don't always work out like we think they should.

 

Oops, on my previous post it should read, "we took a few different brands of GIVEN flow rate injectors"

 

Ok. Now what do we do?? This is crazy that all these people like us into the tuning and we can't get this info!

Makes me want to go out and get an injector flow bench and figure it out once and for all! The injector offset sounds like we need to do a flow test but at varying voltages.

 

Some people have already done some of this, such as AEM who is a large supplier of a very advanced stand alone engine management system. Within their software they have an initial setup wizard that allows you to select the brand of injector of a given flow and it automatically sets up your IFR, IOS and voltage tables (hint, hint, GM software suppliers). That's all we would have to do is download their FREE software from http://forum.aem.power.com/downloads/AEMrelease060404 do the wizard for each injector, find the tables and copy them, (hint, hint, again) wouldn't that be a nice competitive feature from one of our suppliers.

 

Link is down but I like your idea!

 

Oops, try this, http://forum.aem.power.com/downloads...ease060404.zip

I seen some people on the forum complaining that they couldn't find it so there may be a problem. It's around 47 MB, I'll test it when I get to the shop where I have broadband later.

 

I think forum.aem.power.com is down as a whole for now...

 

Oops again, dam period key stuck, it's always the computer, it's early, http://forum.aempower.com/downloads/...ease060404.zip

 

Sorry, last try, http://forum.aempower.com/forum/index.php?board=7.0

Then go to "Download Updated V1.19 Software" etc.

 

ttt ttt

 

I pulled down the AEM software, it has some injectors
but not the ones I plan to use (Delphi 32#). It might
help some folks. I may end up sending mine out to get
cleaned & flow-tested if I can find a shop that will do
dynamic flow testing at multiple pressures and voltages.
If anyone has a reliable, cooperative contact of that
sort I'd like to know; the places I've turned up on the
Web don't seem to be science-project-oriented (or at
least, not according to what they present). PM me, if.

 

anyone found any luck on the motron 60#ers , they are also giving me hell at idle. seem to be fine up in the rpms tho(at least to a certain extent)

 

Downloading now. Hopefully they have the info on the motron 60's in there. I believe that they are Siemens built so either should work.

 

ttt............