Car is an '03 Ecotec with M62 supercharger. Recently installed new injectors, soldered the connections in my harness, new spark plugs.

I disabled closed loop so I could work on getting my new injector constant. My idle and low rpm ve tables are all stock. When I start the car I get a random misfire. I wasn't misfiring before new injectors and I can't get my afr to idle at a 14.7 area. I can get it to idle at 13:1, but if I lower the constant, it bounces around above 14.7. I'm attributing my changing afr to the misfire that's sporadically on every cylinder (mostly 4). It's strange. I can start the car, and #1 will misfire. Turn off the car, restart it, #1 and #3 will misfire, turn it off, start it again, #4 will misfire like crazy. I've swapped plugs around, I've swapped injectors around, there's nothing that seems to be wrong wit the installation.

I re-enabled closed loop (fuel trims) and started the car with the same injector constant, my wideband would not give me a reading, it was beyond the gauge's lean side and my short term fuel trim was at 100%.

What do I need to do?

What injectors are you running (size), and what constant are you using?



FU Tuning

440cc injectors and my current constant is .08050. It idles at a 13:1 afr and anything higher makes it run far on the lean side. I think the misfire is affecting the afr.

New plugs are SRT4 plugs. They're already dirty run idling a little rich.

My problem now is solving this misfire. Suggestions?

your injector constant is .08050?? weird.. my constant with 380cc is 0.27000 . i calculated my new constant for when i put the 42# injectors in, i got 0.231429 with the formula new constant = old constant * (old injector size/new injector size) . when i divided instead of multiplied i got 0.315000 .. which seems more reasonable to me since in the fake 2.5 bar thread john mentioned having to raise the constant even though the injectors were bigger.. so i dont know.

using that formula assuming you had 380cc injectors before hand with the injector constant you listed above, i got your new constant to be 0.069523 using old const * (380/440). if that seems funny, try 0.093211 which was found with old const / (380/440) .

hope that helps lol, bout to go out and tweak some of that stuff myself.. hope my car doesnt wake the neighbors

no idea about the misfire.. could it be related to the incorrect constant not letting enough fuel in or something along those lines?



12.33 @ 111.67 mph [Oct 2009]
Dyno'd on 08/02/09 - Mustang Dyno:
327.6 WHP 333.6 WTQ [10.1 AFR]

injector constant is .08050?

stock constant is what .18333 or somethign like that> I could be wrong here

24lb stock injector size/42lb (440cc injectors) = .57 x current constant thats like = .10475ish, im pretty sure your constant is low



1989 Turbo Trans Am #82, 2007 Cobalt SS G85

stock constant (in my stock tune file) is 0.17800

im still confused why your constant is so low.. i tried using the result from that formula today which was 0.118042 (0.178 * (252/380)), and my car wouldnt even start.. so i just went back to 0.27000



12.33 @ 111.67 mph [Oct 2009]
Dyno'd on 08/02/09 - Mustang Dyno:
327.6 WHP 333.6 WTQ [10.1 AFR]

chris, by disabling closed loop you shut off the fuel trims. if you're moving the injector constant to try and get the idle AFR to 14.7 when the computer is reading the raw VE table thats the problem and why your VE tables are so screwed up.


alpha-n (especially ours) won't work that way. just tune WOT, smooth the crap out of the low and high rpm tables and try your best to leave the rest alone. the offset VE sometimes needs to be adjusted which automatically scales everything.. bring idle and coast down VE tables back down as close to stock as you can (if you need a 50 VE offset, subtract 30 from the idle and coast down tables (stock is 20. whatever the difference is from the old offset to the new, subtract that number from idle and coast down tables. In otherwords if you need a 60 VE offset, subtract 40 from those tables.)

fuel trims is what gets you to stoich. DO NOT TOUCH your main VE tables to try and tune low TPS for stoich you're going to want to kill yourself.
HPT just can't tune our ecu properly for anything other than high TPS stuff (ie. WOT)

what I think you're doing is adjusting the injector constant to try and get 14.7:1 when you have the computer reading the VE map that wants WOT values.. when you turn off closed loop, its going to run rich ALL the time.

put your table (both low RPM and high RPM VE tables) back to stock, and tune only for WOT. Change nothing but the constant when you install the injectors to the calculated amount. LEAVE THE VE TABLES ALONE.

Get back to me on how you're seeing misfires (in other words, is it activating a CEL?)

im not understanding how you can not touch the main VE table and have the car run half decent



1989 Turbo Trans Am #82, 2007 Cobalt SS G85

I haven't touched the VE tables for anything under 50% throttle. Nothing at all. Now coastdown, main, idle, nada.

I disabled closed loop, and changed my constant hoping to achieve a 14.7:1 afr at idle. I've tried eleventy billion different constants, and now I'm at one that idles the car well at idle with fuel trims enabled. (PJ supplied it)

My afr still jumps a lot because I'm misfiring. I'm misfiring mostly on #2 and #4. Occasionaly #3. I've checked the resistance in my harness and there isn't any.

I'll get a blinking cel if I let it go long enough. I can see it with HPT.

chris.. you can't turn off closed loop then adjust your constant to get a stoich mixture.. if you're in open loop, its supposed to be rich, not stoich. do you understand what I mean?

you're turning off fuel trims, then adjusting the CONSTANT to try and get a stoich idle? that makes no sense.
I see what you're trying to accomplish but I don't think our VE tables are programmed that way. The idle and low rpm tables overlap, but the values from one to the other do not cross over. There's other tables that we can't see that effect idle.. its useless to try and alter that stuff.

Rodimus wrote:
im not understanding how you can not touch the main VE table and have the car run half decent

what I said was:

Pj wrote:DO NOT TOUCH your main VE tables to try and tune low TPS for stoich

In other words, don't disable closed loop then try to tune the low TPS cells for fuel economy. Its a waste of time.

Pj wrote:put your table (both low RPM and high RPM VE tables) back to stock, and tune only for WOT.

Build off a stock VE table, and tune only for WOT stuff (when the bypass valve on the charger is closed). Let the fuel trims do the work of getting stoich.
The parameters that get us to stoich values aren't viewable in HPT. There's most likely some other multiplier or hysteresis that needs to be manipulated in order to truly be able to fine tune the stoich performance of the car (cruise).

Change the constant for the size injector you're running, and just build off the stock low and hi rpm VE table for boost. You can also use the IPW multiplier table to help with boosted fueling. VE offset also needs to be changed.. how much so can be indicated by logging VE error % using a wideband, and if you max the tables out, you'll have to raise the offset. stock is 20 (which means lowest is 20, highest is 120) I'd imagine 50 is a good place to start (lowest VE value on any of the tables is 48 in the idle table).. just remember to take the idle, and coastdown tables back to their values before you changed the offset.. whatever you add to the stock 20, subtract from those tables.

I really want to tune another s/c L61

I get what you're saying now. Should the constant be changed until the fuel trims are close to 0% at idle?

come over PJ and you can assist in the tuning of mine
spark maps are so touchy.. im getting the KR down, but not to 0 quite yet.


i dont think that is necessarily true admiral jedi, my long term fuel trim is at 0 at idle, but the short term is not.



12.33 @ 111.67 mph [Oct 2009]
Dyno'd on 08/02/09 - Mustang Dyno:
327.6 WHP 333.6 WTQ [10.1 AFR]

If you really want to you could try to do that, but I don't think you're going to accomplish anything other than frustrating yourself. I've tried to tune before for fuel economy/ get the trims to zero but since we're using alpha-n its a whole other ballgame then what is put up in FAQs and in the help file in HPT.. it really just doesn't apply to us.

there's way more tables used for closed loop and open loop, we just can't see them. the idea of getting your trims as close to zero as possible is sound, but the stuff we need to see in order to do the job right isn't there.. if I were you I'd just worry about getting the AFR good for whenever you hit boost (figure out what the minimum TPS value is that makes the bypass valve close, and just add fuel from that TPS percentage and higher in all your tables. Anything below that can be stock. Maybe make a custom histogram that compares TPS with boost pressure in one of the user programmable inputs. That way, you have solid numbers that show you where the TPS closes the bypass and you get the needle on the boost gauge past atmospheric).

Your problem is the constant.....

You sound like you are wrestling with the EXACT same thing i was untill yesterday... Now my car is tuned in perfectly and runs like a champ.

I have an LD9 and a true 2Bar.... and im not Alpha-N... and i am not doing any "faking" So we might be in a different place on some of the details...

But basically... the main thing is nailing down that constant...

.08050 is INSANE.... that is lower than i use on my 750cc's (lower numbers are for higher flow injectors) So the constant you have there is almost telling the car you have 1000cc injectors... no wonder you wont idle. (at least that is how it would be on my LD9, yours may be different)

You are running 440cc injectors now right? what size were stock? and what was your stock constant?

use the New Constant = Old Constant * (Old Injector size / new injector size)

I was going to put different injectors in my car, when i did the math it was showing up as
.10873 for 750cc
.18532 for 440cc
.26305 for 310cc

So I just cant imagine you running a .08 being close at all...

Even Shifted himself runs 440cc....

Shifted wrote:New Constant = Old Constant * (Old Injector size / new injector size)

So...

.32359 * (252/310) = .26305 for the 310cc injectors

.32359 * (252/750) = .10873 for the 750cc injectors

My constant for 440cc injectors is a lot less than .2, and I haven't touched my idle VE tables, my car idles fine.

My constant didnt work perfect right from the get go... But i did notice it was evenly off across the board... so i adjusted the VE offset to compensate for the total skew... then that put me right in the ballpark, and i did my tuning from there.

be sure to PASTE>ADD. (multiply will screw you big time)

^^^ constant takes into account engine displacement. therefore constants for the 2.4 do not cross over to the ecotec.

if you want chris, I can email/ PM you the constant I used on the skwirl for the 440cc.

i wouldnt mind seeing the constant you are using PJ. i came up with one based off of what i already had and it runs, but it wouldnt hurt to compare



12.33 @ 111.67 mph [Oct 2009]
Dyno'd on 08/02/09 - Mustang Dyno:
327.6 WHP 333.6 WTQ [10.1 AFR]