Injector Offset ?'s vs LS1 edit

I have with my offset values met a bit of a problem.
I have been trimming and trimming my VE table and having trouble getting some cells to become lean enough. I have even tried reducing the low map offset values eg the ones at 80-55 manifold pressure ie 14-45map.
It helped a bit but some cells dont want to lean out.

The culprits are
1200rpm at 25map 0.922
1600rpm at 20map 0.87
1600rpm at 25map 0.90
1600rpm at 30map 0.92
2000rpm at 20map 0.89
2400rpm at 20map 0.94
3200rpm at 20map 0.88


All other cells are fine. Including
2800 at 15 map and
surprizingly 3200 at 15 (when 20 was bad??)

I am wondering if i need to tweak the minimum pulse width settings or something?? What can i do.

The car is set at the moment with DFCO turned off. Should i turn the DFCO and not worry about it or maybe even just go back to the stock offset figures. I had the AFRs good everywhere before???

Good if someone can help - i am technically stuck.

Ok, I installed my 60 lb mototron inj. IFR table from spreadsheet etc. When I hold the rpms constant at 2K, the car misses and I can see the AFR go from 14 to about 15 or 16 momentarily. I am thinking that the 60 lb inj require more time to open. So I start increasing the offset table in 10 % increments. At 30 to 35% increase, the miss is gone. However, I am running very rich at higher rpm (no load so far). So, for for my application, it seems the offset table needs to be tweeked. I will now reduce the lower manifold vacuum values to probably 15% then do some logging to dial it in further.

I have heard that some people only adjusted the IFR table for these injectors and they run fine. It is a little frustrating if this is true and why would it be diff. for my application? I question if I am compensating for a bad injector.

I have found out the problem is that SVO 30 injectors use older technology and cant open any shorter than what mine are now. So the problem is unsolvable with these injectors. I have gone back to the original offsets at the moment....

Quote:

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Originally Posted by hpcubed

Ok, I installed my 60 lb mototron inj. IFR table from spreadsheet etc. When I hold the rpms constant at 2K, the car misses and I can see the AFR go from 14 to about 15 or 16 momentarily. I am thinking that the 60 lb inj require more time to open. So I start increasing the offset table in 10 % increments. At 30 to 35% increase, the miss is gone. However, I am running very rich at higher rpm (no load so far). So, for for my application, it seems the offset table needs to be tweeked. I will now reduce the lower manifold vacuum values to probably 15% then do some logging to dial it in further.

I have heard that some people only adjusted the IFR table for these injectors and they run fine. It is a little frustrating if this is true and why would it be diff. for my application? I question if I am compensating for a bad injector.

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You need to adjust the IFR table and the VE table to get the mixtures right , adjusting the injector pulsewidth voltage table is not the right place to be looking, its a offset for varying voltage and needs some special equipment to get it right

Quote:

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Originally Posted by Delco

You need to adjust the IFR table and the VE table to get the mixtures right , adjusting the injector pulsewidth voltage table is not the right place to be looking, its a offset for varying voltage and needs some special equipment to get it right

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what kind of equipment?

Quote:

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Originally Posted by TAQuickness

what kind of equipment?

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A full injector test bench with variable voltage , pcm simulator etc

I have a few comments on this topic and may be completely wrong, but may not...

The way I understand the injector offset, its an adder to the total pulsewidth used to make up for the time it takes the injector to fully open and close. So once the PCM calculates the needed fuel and determines the injector time, it looks up the offset and adds that value to get the final pulsewidth. This value is unique to each injector and should be supplied by the manufacturer, not calculated or scaled.

The offset becomes very important in idle / low rpm tuning. At idle when pulsewidths are small, the offset is a much larger percentage of the total than at high rpms. If the offset is .5 milliseconds at 14volts and the pulsewidth is only 2.5 milliseconds, the offset is 20% of the total. Compared to only 3% of a 15ms pulsewidth at higher rpms.

Now some will say you can just adjust VE to bring idle fueling back in line, which is true. ... but only for that specific voltage. Once there is a voltage difference (under loads, cruise, idle, etc...) and the PCM uses a different offset, the fueling is off a little again. Get the correct offsets input first, then tune VE and fueling should be very similar under those different conditions.

To take it beyond the normal thinking - You could add a fixed amount of fuel to every pulsewidth by increasing the offset table. In effect, that would make a greater percentage change to idle fueling.

From my personal experience just last week -

I installed a set of Bosch green top injectors, a set of TEA heads and a new cam. I took my PCM completely back to default values in timing, MAF, VE, idle airflow, etc... I plugged in the new IFR, new offset values, and set idle at 700 rpms. Idling for 10 minutes, one bank showed +1.95 the other was a solid 0. Cruising trim values were between -2 and -4.


For the offset, I found a few posts on the internet referencing the offset values from Ford PCMs that basically matched the post by ChrisB with the values. There seemed to be some confusion as the same offset values were posted for the red top and green top injectors, both claiming to be from the lightning truck. Finally, I hit paydirt and found offset numbers for the green tops that had just been independently tested. The numbers were slightly smaller than those I had previously found, but more than double the original values my PCM had to begin with.

please send me the green top's offset numbers to marcinpohl at gmail dot com
thanks

Quote:

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Originally Posted by BigTex

I have a few comments on this topic and may be completely wrong, but may not...

The way I understand the injector offset, its an adder to the total pulsewidth used to make up for the time it takes the injector to fully open and close. So once the PCM calculates the needed fuel and determines the injector time, it looks up the offset and adds that value to get the final pulsewidth. This value is unique to each injector and should be supplied by the manufacturer, not calculated or scaled.

The offset becomes very important in idle / low rpm tuning. At idle when pulsewidths are small, the offset is a much larger percentage of the total than at high rpms. If the offset is .5 milliseconds at 14volts and the pulsewidth is only 2.5 milliseconds, the offset is 20% of the total. Compared to only 3% of a 15ms pulsewidth at higher rpms.

Now some will say you can just adjust VE to bring idle fueling back in line, which is true. ... but only for that specific voltage. Once there is a voltage difference (under loads, cruise, idle, etc...) and the PCM uses a different offset, the fueling is off a little again. Get the correct offsets input first, then tune VE and fueling should be very similar under those different conditions.

To take it beyond the normal thinking - You could add a fixed amount of fuel to every pulsewidth by increasing the offset table. In effect, that would make a greater percentage change to idle fueling.

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True to a degree but hopefully you have a fully functing alternator regualted properly so the voltage the injector normally sees is nice and constant the table is to account for changes in this offset.
Yes GM did a very good job on this part of the calculation and changing the injectors is going to affect it slightly BUT unless yopu have the right test equipment you are going to make the problems worse rather than better.