Inj Offset and AFR

[thehemi]

My truck is the first time that I've ever used a WB sensor.
At idle and part throttle the AFR seems to vary wildly. Is
this normal, perhaps due to the narrow band o2 sensors?
(For instance at idle my truck's AFR is roughly mid 15s but
can bounce between 14s and 16s while I'm sitting idle.)
Should my idle AFR be lower? Should the AFR be stable?

My truck had stock 23# injectors, but now I'm running 60#.
It has a bog off idle which I'm led to believe is because I'm
running the 23# inj offset values and the 60# injectors likely
need more time to open/close.

So I'm starting to slowly increase the inj offsets to see what
happens to driveability. Can I expect any change in the part
throttle AFR values, or are they simply what they are?

[awillis98]

AFR will bounce around at idle Because of the Narrowband correcting fuel. the WB will really on read constant when you hit PE (powe enrichment). but is defenly a must to fix the Injector table for your bigger injectors.

[thehemi]

AFR will bounce around at idle Because of the Narrowband correcting fuel. the WB will really on read constant when you hit PE (powe enrichment).

Not to sound too naive, but why does the AFR run more constant
when the truck is running in PE mode? I thought PE was basically
just a way to command a lower AFR, but aren't the same narrow
band o2 sensors still in charge of adjusting the fuel?

I'm sure it's much more complex than I pretend to comprehend.

but is defenly a must to fix the Injector table for your bigger injectors.

My bog is off idle or off a real slow roll, and people tell me it sounds
like a lean bog from the injectors not opening up enough, which they
say isn't necessary an issue at higher RPMs (due to the pulse width?).
Does that sound like a fair assumption?

I currently have 20% added to my 23# injector offsets and, while I
do think it runs better, the bog is not completely gone. So I'm going
to adjust it higher some more.

Before I go to 30%, 40%, or whatever it takes, I just wanted to see
if there's a value at which people might say "woah, way too much" of
a change to the offset values. If 20% is not much, obviously I can try
30-40% or more, but if 20% is a lot, I must be on the wrong track.

Does that question make sense?

From 4.5V to 17.5V, here's the stock 23# table...

2.42432 2.23389 1.45703 1.16650 1.02393 0.92627 0.83496 0.76074 0.70117 0.65283 0.61133 0.57764 0.54736 0.54883

Here's 4.5V to 17.5V adjusted with 20% increase...

2.90918 2.68066 1.74854 1.39990 1.22852 1.11133 1.00195 0.91309 0.84131 0.78320 0.73340 0.69336 0.65674 0.65869

Thanks for your help!

[thehemi]

Well, I did some more test and tuning tonight and ended up at 40%
above stock and it feels like its running pretty good. I did not have
any hesitation from a stop or from a slow roll. I will perform a few
more test drives before I consider part throttle resolved.

My fuel trims, however, are really going deep. -15 to -20 at times.
Both my long terms were red when I got back from my test driving.

I suppose that's a subject for a different post...

[awillis98]

Have you tried setting up the LTFT+STFT Histogram and done a Maf Tune yet?

[thehemi]

Have you tried setting up the LTFT+STFT Histogram and done a Maf Tune yet?

You're speaking German to me!

I found a "Guide to VE tuning using fuel trims" document on LS1tech.
It explains the LTFT and STFT purposes and goes through removing
the MAF and, apparently, some tedious tuning to adjust the VE table.

Is that what I should do next?

Would adjusting my inj offset values do anything to change what the
VE table is going to look like? They seem kind of depending on each
other, one being air and the other being fuel. Although there's much I
don't know, so maybe I will go ahead and do the MAF/VE tuning and
see where I stand...

[awillis98]

from my understand is you have to have the Injectors set to the correct setup up before any tuning. because if you make any changes to the injectors after starting tuning it will throw your tune all out of whack.

Ok, i'm not sure what all things can be modified in your computer. but for my car there's hardly anything. so For me it was just set the injectors the a MAF tune based on the LTFT+STFT. this gave me steady 0 LTFT. then from there i used my wideband and tuned the Maf for the WOT. but maybe you can post up your HPT file so i can look it over and see that you have going on.

[thehemi]

I'm going to get my baseline fuel pressure tonight and see what I can find about these Mototron 60s to see where my flow rate should be. Then I need to scavenge around and find out what the offsets are suppose to be for these injectors. I think the offset table details for the Mototrons are classified, as far as I can tell from my current searches!

[jmoody66]

I'm going to get my baseline fuel pressure tonight and see what I can find about these Mototron 60s to see where my flow rate should be. Then I need to scavenge around and find out what the offsets are suppose to be for these injectors. I think the offset table details for the Mototrons are classified, as far as I can tell from my current searches!

I agree with you....if you purchase injectors it would seem that you would be given every piece of info needed to set them up correctly but you gots to pay again to get that info I guess......America the great

[thehemi]

I agree with you....if you purchase injectors it would seem that you would be given every piece of info needed to set them up correctly but you gots to pay again to get that info I guess......America the great

I finally found some others with the Mototrons and a PDF document
with the specs. Using either of those offsets, the truck won't even
idle. The PCM is my truck is very limited in tuning parameters, so I'm
thinking about going with smaller injectors and maybe they will work
better.

[awillis98]

I finally found some others with the Mototrons and a PDF document
with the specs. Using either of those offsets, the truck won't even
idle. The PCM is my truck is very limited in tuning parameters, so I'm
thinking about going with smaller injectors and maybe they will work
better.

the reason it wouldn't idle is because you messed with the maf transfer function before you got the injectors set right. get the injectors set to what info you recieved then tune the maf. it shouldn't take long for you to get it to idle correct once the injectors are set.

[thehemi]

the reason it wouldn't idle is because you messed with the maf transfer function before you got the injectors set right. get the injectors set to what info you recieved then tune the maf. it shouldn't take long for you to get it to idle correct once the injectors are set.

My MAF/VE tables are stock. I have not touched them yet.
The only variables changed so far has been the flow rate and
injector offset vs volts table.

Some people suggest I get a "0411 PCM" which I guess is more
modern PCM which will allow Accel Enrich and more parameters.
Although I may try some smaller injectors to see if m PCM just is
not capable of handling injectors this large. I know people have
used smaller injectors (33-36#) on the marine intake, and I guess
they don't have this bog problem.

[awillis98]

My MAF/VE tables are stock. I have not touched them yet.
The only variables changed so far has been the flow rate and
injector offset vs volts table.

Some people suggest I get a "0411 PCM" which I guess is more
modern PCM which will allow Accel Enrich and more parameters.
Although I may try some smaller injectors to see if m PCM just is
not capable of handling injectors this large. I know people have
used smaller injectors (33-36#) on the marine intake, and I guess
they don't have this bog problem.

i wish i know more about your engine and PCM so i might help more. but us 3800 guys come stock with 32 pound injectors and i've seen people run 60+ with turbos. i have a set or 42.5's.

[murphinator]

if you need a set of L67 injectors (GM 33's) I have several engines in different states of disassembly just shoot me a pm.

[thehemi]

I downgraded to 33# injectors (33# @ 58psi) from the huge Mototrons.
To my surprise, there's still some bog in the throttle and getting rich trims.

I'm an amateur for sure, but looking through a scan after a drive it would
appear that the truck gets low lean conditions during accel (3-4) but the
problem is cruising or decel when it gets really rich (-15-18+).

I can adjust the injector size and/or offsets to remove the off idle bog but
it only makes the rich decel condition even worse.

As far as adjusting the VE table, in part throttle driving the only difference
in my truck from stock is the K&N air filter, no air box and larger injectors.
Does a VE tune really seem like its that necessary? Maybe the injectors
cause it to be a good next step?

Or are there some decel (DFCO?) parameters that I should try tweaking
to in an attempt to lean up the cruising and decel instances?

I guess it comes down to if I need to "cut fuel" or "adjust air" in the tune?