calculating injector offsets

[Vasquezz1228]

I been tuning my car for a few weeks already on 60s and havent figured out the injector offsets. I have them zero'd out and i get a really bad surge on cold starts and on warm starts the car cranks longer to start. I already adjusted my fueling and timing but car still has those small issues. Im thinking it due to the offsets but not sure.

When i had the lsj injectors i used a log of my car running my trifecta tune and used those offsets on my new tune and it worked great. But when i used the same table on the 60s it was running rich even after correcting the MAF. I know if it stays rich that means the numbers in the table are too high and lean means too low.

My question though is how can i calculate the offset tables for these injectors without just inputting different numbers and correcting fuel everytime? Can i log them and then just copy paste? Or is there more involved?

[cobaltssoverbooster]

i have a file somewhere at home that explains how to tune them but it is a long process.

basically it comes down to setting a set of base offset values. tune the ve in with a wideband the best you can. then multiply fuel table by fixed percentage say 10%. if the error from this ve change comes back anything different than damn near 10% you will have to adjust the offsets related to those ve cells until switching between your base ve and 10% ve net a 10% change all the way through.

[cobaltssoverbooster]

Adjusting Injector Offset table
Determining the proper amplitude is done by adding an exact percentage to the base injector pulse width and ensuring that the result is the same percentage increase in AFR.
The injector offset value is added to the injector pulse width as the very last item before the total pulse width is sent to the hardware. The purpose of the offset is just to account for the opening time - closing time of the injector. The offset is not affected by temperature and other engine trims and that is why it is added after all the trims have been applied to the base fuel value.
Prior to calibrating your injector curve, set up a physical switch on one of the inputs to request the auxiliary maps. In the auxiliary fuel map, select the entire map and set all cells to +10% fuel. Set all the auxiliary ignition map to zero trim on all cells.
For calibration, set up the variable voltage supply and let the engine warm up until the point where the coolant and air temperatures reach steady-state. This is probably best done on a cool day. If the day is warmer, turn off the car's thermal fans and use a couple large dyno fans to keep coolant temperature constant at a safe point. What you don’t want is for the car's fans to cut on and off so that the coolant temperature is moving up and down.
Turn off closed loop fuel trims and zero out all your fuel trims. Now set the voltage at a good starting point like 13.0 volts. Adjust the base fuel table so that the AFR stays at a steady 14.70 AFR. If your AFR is not staying fairly steady, you have to figure out why. Make sure that no fuel trims are affecting the AFR and if so, zero them. Fuel temperature and humidity can affect AFR a bit, but the fuel temperature should reach a steady state after 30-minutes of idling the engine and humidity usually stays constant unless the weather is changing quickly or it is early in the morning or late in the day. It is important to try to keep as many factors that affect AFR constant as possible so that you can focus on the injector offset.
With the AFR steady at 14.70 and voltage steady at 13.0, hit the aux switch to instantly add 10% base fuel to the engine. The AFR should settle out in a couple seconds to 13.23 (since (14.70 - 13.23) / 14.70 is 0.1). If the AFR ends up richer than this, then you had more of the pulse width coming from the base fuel map than you should have and the 10% trim actually gave you a larger trim. This means that you need to increase the injector offset at 13.0 volts (so your entire curve moves up) and decrease the base fuel by the same amount across the board (if you add 0.2ms to the offset, subtract 0.2ms from all the cells in the base fuel table). If the AFR settled out leaner than 13.23, then you had too much in the offset table and not enough in the base fuel table and you need subtract from the offset curve and add the same amount to the base fuel table.
Repeat the experiment again until switching in and out of the auxiliary map produces exactly a 10% change in AFR. Once you have this, you know that your injector offset curve at 13 volts is right where it needs to be. If you have already programmed the rest of your curve, you can switch to a different voltage and verify that the aux switch still gives you exactly a 10% change in AFR. Once you verify this you know you have the proper curve at the proper amplitude. Now you can copy the final offset curve to a normal map and start tuning the car for real.

[Vasquezz1228]

Wow sounds like a lot of work 😅

So for base numbers i can input any numbers? Or is there somewhere i can get those??

Can i log the car and then just paste the offsets in?

I think i will try to figure the offsets out because i cant stand the studder my car does on cold start. I think its because of this

[cobaltssoverbooster]

start with a close file first

[Vasquezz1228]

Thanks, ill give it a shot this weekend and see how close i can get

[eronq9]

I been tuning my car for a few weeks already on 60s and havent figured out the injector offsets. I have them zero'd out and i get a really bad surge on cold starts and on warm starts the car cranks longer to start. I already adjusted my fueling and timing but car still has those small issues. Im thinking it due to the offsets but not sure.

When i had the lsj injectors i used a log of my car running my trifecta tune and used those offsets on my new tune and it worked great. But when i used the same table on the 60s it was running rich even after correcting the MAF. I know if it stays rich that means the numbers in the table are too high and lean means too low.

My question though is how can i calculate the offset tables for these injectors without just inputting different numbers and correcting fuel everytime? Can i log them and then just copy paste? Or is there more involved?

Are you talking about offsets or short pulse adders, if you zero out the offsets then im suprised the car actually ran well at all.

Offsets (Which are not part of the INJ PW as reported by an LSJ PCM) is the time in ms that the injector takes to operate and the minimum amount of time the PCM can give a signal where any fuel is released. If your offsets are 0 then your idle pulsewidth wil end up higher because it has to make up for the time for the injector to operate. That is why the offsets are very large at lower voltages, and smaller at higher voltages, because the injector can operate quicker. Generally the offset will change with fuel pressure differential across the injector as well.

If you don't have the correct offsets, you'll never be able to dial in your MAF because the PCMs calculated Pulse Widths will have very nonlinear flow and lower load regions will be super lean in the same MAF cell.

[Vasquezz1228]

Are you talking about offsets or short pulse adders, if you zero out the offsets then im suprised the car actually ran well at all.

Offsets (Which are not part of the INJ PW as reported by an LSJ PCM) is the time in ms that the injector takes to operate and the minimum amount of time the PCM can give a signal where any fuel is released. If your offsets are 0 then your idle pulsewidth wil end up higher because it has to make up for the time for the injector to operate. That is why the offsets are very large at lower voltages, and smaller at higher voltages, because the injector can operate quicker. Generally the offset will change with fuel pressure differential across the injector as well.

If you don't have the correct offsets, you'll never be able to dial in your MAF because the PCMs calculated Pulse Widths will have very nonlinear flow and lower load regions will be super lean in the same MAF cell.

I only have the MAP table zero'd out. The other table i had made changes to and seemed to help with being too rich or lean and now it looks like im pretty close on with the AFR everywhere except cold starts for the first 30 seconds. I made changes last night but did not have time to wait for the car to cool down and start it up to see if it starts better

[steelmesh]

I been tuning my car for a few weeks already on 60s and havent figured out the injector offsets. I have them zero'd out and i get a really bad surge on cold starts and on warm starts the car cranks longer to start. I already adjusted my fueling and timing but car still has those small issues. Im thinking it due to the offsets but not sure.

When i had the lsj injectors i used a log of my car running my trifecta tune and used those offsets on my new tune and it worked great. But when i used the same table on the 60s it was running rich even after correcting the MAF. I know if it stays rich that means the numbers in the table are too high and lean means too low.

My question though is how can i calculate the offset tables for these injectors without just inputting different numbers and correcting fuel everytime? Can i log them and then just copy paste? Or is there more involved?

Can you provide info on the engine, ECM?

[Vasquezz1228]

Can you provide info on the engine, ECM?

It is a 2009 Pontiac G5 with the e37 ECM

It is a 2.2 LAP engine with VVT, m62 supercharger with 2.9 pulley, dual pass endplate, 60lb injectors, and aem cold air intake. Pretty basic setup

[Vasquezz1228]

After a few days of messing with the offsets, i finally found some that work pretty good. I get my AFR matching commanded spot on when on open loop. But during closed loop it dips a little rich during PE and goes a little lean on idle if i havent gone WOT in a while. Feels like a small misfire. I changed spark plugs and its still there sometimes.

Do i have to tune closed loop with fuel trims and not wideband? Or am i doing something wrong?

[cobaltssoverbooster]

if your wideband is setup properly then it doesnt matter which method you choose. you will on the other hand always have to tune PE with a wideband as the ecu ignores the o2 during this stage. the only motors to use the wideband in pe are the DI engines with factory widebands.

[Vasquezz1228]

if your wideband is setup properly then it doesnt matter which method you choose. you will on the other hand always have to tune PE with a wideband as the ecu ignores the o2 during this stage. the only motors to use the wideband in pe are the DI engines with factory widebands.

I see, so i should tune PE in closed loop now? It was perfect open loop. My previous setup on stock m62 supercharger and lsj injectors, i tune part throttle and idle with fuel trims and WOT with widband and worked great. But i was having trouble with the new setup. Maybe its because of the crazy weather changes in texas at the moment lol

[cobaltssoverbooster]

you missed the point. closed loop means O2 sensor is used. when you WOT this ecu your ecu will IGNORE the O2 sensor. this means it auto defaults to OPEN loop during wot.
you can only tune wot using a wideband because of this case. if you tune it in open loop with the wideband then when you activate closed loop control you should have the same afr.
any tuner here that tunes all the way down to the base tables will tune wot in open loop then leave it alone when in closed loop because there shouldn't be any difference between the two modes. i can tune both ve and maf in open loop and then when i activate closed loop i wont have to make any adjustments since the ecu has already been pre-programmed and is only making corrections for atmospheric or density issues.

there are two reasons there is an error once closed loop is initiated.
1) (most common) the wideband being used does not report back the same values in the software as the gauge unit does. This is usually due to grounding voltage offsets and can be adjusted by re-configuring the gauge offset value.

2) some ecu's have a value called o2 switch points. These values are the voltages that are to be used to determine a rich/lean value in the ecu. If your gauge matches your scanner afr value then you need to look for these values and tune them to match your gauge. the gauge is way more accurate than the stock o2 will ever be so if your reading the correct values on the wideband; the factory o2 calibration must be at fault.

if you fix these issues then switching between closed and open loop will not net any major errors.

[Vasquezz1228]

I see, thanks a lot for clarifying the proccess. That will help me a lot.

Im sorry for all the questions, i really appreciate the help