Minimum Injector Pulse

[Wnts2Go10O]

when dialing in new injectors, do you subtract the percentage of difference between the stock injectors and new ones? it makes sense in my mind anyways.

example: minimum pulse is 1.25 with stock 28lb injectors. going to 42lb injectors means an injector 50% bigger so take away that same amount from the pulse dropping it to .625.

would i be correct to do it this way or am i completely off?

[Frost]

You either use known data or (I) tune backwards to solve for them.

[Wnts2Go10O]

You either use known data or (I) tune backwards to solve for them.

ok i found this from ls1tech by redhardsupra:

"i usually set the minimum and default pluse widths to 1.0 and so far no problems.
i was just tuning a F10+mac mids car, and it at 850rpm it used to idle with 50-52kPa MAP. after playing A LOT with spark, i got it down to 45-47kPa, and much less jumping around spark-wise. it idles smoother, and the idle pulse width dropped from 2.3 to 2.0-2.1ms. the idle was decent before, it's really nice now. so if you're interested in dropping it farther down, up the idle spark table and the regular spark table but in the idle range to about 30-34 and you should."

another question, how does the MPW actually effect the car beyond idle?

[keith42]

ok i found this from ls1tech by redhardsupra:

"i usually set the minimum and default pluse widths to 1.0 and so far no problems.
i was just tuning a F10+mac mids car, and it at 850rpm it used to idle with 50-52kPa MAP. after playing A LOT with spark, i got it down to 45-47kPa, and much less jumping around spark-wise. it idles smoother, and the idle pulse width dropped from 2.3 to 2.0-2.1ms. the idle was decent before, it's really nice now. so if you're interested in dropping it farther down, up the idle spark table and the regular spark table but in the idle range to about 30-34 and you should."

another question, how does the MPW actually effect the car beyond idle?

Anyone have a answer, I'm trying to understand mpw,also just because you set a mpw in the ecm doesn't mean the injector can do it. is that correct?

[MNR-0]

Yes, you are correct

High impedence injectors usually go down to 1.6ms. Low impedence around 0.9-1ms. Again, it depends on the quality of injector, but that is a rule of thumb I have observed over the many years

If you do not have any injector calibration data then you *always* start with your stock calibration (adjusted for flow rate of course) and tune from there to reach your desired results

For example,

I recently fitted 60lbs injectors to a factory stock car (exhaust and intake only) with an outcome of reducing the idle pulsewidth from 2.8ms (factory) to 1.6ms (60lbs). I would not think a factory car could handle anything bigger

I had no injector data short of the flow rate

With factory calibration, it would flatline at 1.8ms. Idle AFR was 11:1 and if left alone would foul the plugs and wash bores

I reduced the minimum IPW to 1, zeroed out the short pulse adder. That got me to 1.7ms - still too rich. I then re-scaled the offset table 20% lower at a time until I reached 1.6ms. At this AFR I now had bi-directional control around the stoich point (richen it up it would go richer and lean it off it would go leaner) and that was my goal. Now I had fuel control back, I tuned the VE map from there

The car now idles at 14.5AFR when warm and does everything it is supposed to when cold (starts nice) with a startup AFR of 11:1 (what I want) and leaning off from there

This was done with a wideband before the CAT

You can tune any injector (within reason) on an LSx without injector data

[keith42]

What does rescaling the offset table do in this situation?

[MNR-0]

The offset adds to the base IPW. If you need a lower IPW, this is the last resort to achieve that

[Frost]

I can usually get them down without touching the offset. I have needed to go as low as 1.2-1.3mS on some larger units to get idle to clean up. besides the normal tables, HPTuner's has a transient fuel tab that seems to be labeled incorrectly.

The transient fuel min mg is actually an IPW floor since it seems that it is active at idle. I made a few bins for 5.7ute to check out and this is what he found in compare (this is his work). To get from min fuel mg in transient to actual IPW multiply by 31.124308. Try it on an OEM file.... 1.4mS. That's not low enough to clean idle 80s on many applications. I have had to get it down to 1.3/1.4mS for some sets of 60s on some applications.

[MNR-0]

I can usually get them down without touching the offset. I have needed to go as low as 1.2-1.3mS on some larger units to get idle to clean up. besides the normal tables, HPTuner's has a transient fuel tab that seems to be labeled incorrectly.

The transient fuel min mg is actually an IPW floor since it seems that it is active at idle. I made a few bins for 5.7ute to check out and this is what he found in compare (this is his work). To get from min fuel mg in transient to actual IPW multiply by 31.124308. Try it on an OEM file.... 1.4mS. That's not low enough to clean idle 80s on many applications. I have had to get it down to 1.3/1.4mS for some sets of 60s on some applications.

Was that with high impedence injectors? Ive only ever believed low impedence injectors would get that far down

I'll look into that next time I see the car or there is another 60lbs setup to be done. The numbers available to me in the tune still don't add up though, as this one already was set at 0.035 as the min. fuel which equates to 1.09 IPW (according to your math). The only adder that I could see was the offset adding 0.3662 and 1.6ms was the lowest I could get them to before idle quality suffered

[Frost]

Some of the files have a different value for OEM fuel min mG. I use the 156 OS the most for swaps and it definitely has the value I mentioned.

Those were indeed High Z injectors. The 83lbers flow 9X at our rail pressure and need to go that low. The 60s need to sometimes as well.

[5.7ute]

Was that with high impedence injectors? Ive only ever believed low impedence injectors would get that far down

I'll look into that next time I see the car or there is another 60lbs setup to be done. The numbers available to me in the tune still don't add up though, as this one already was set at 0.035 as the min. fuel which equates to 1.09 IPW (according to your math). The only adder that I could see was the offset adding 0.3662 and 1.6ms was the lowest I could get them to before idle quality suffered

The Australian calibrations as you have noticed run a much lower value than the US cars. This may have something to do with emission control under decel conditions.
One thing I have found is that if this value is higher than min pw, the default pw table is ignored & this then becomes the injector floor. All this work was done with "other "software, but thanks to Frost we have been able to work out the corresponding table in HPT so you guys no longer need to rape offset & small pulse adder tables.

[zl1killer]

The Australian calibrations as you have noticed run a much lower value than the US cars. This may have something to do with emission control under decel conditions.
One thing I have found is that if this value is higher than min pw, the default pw table is ignored & this then becomes the injector floor. All this work was done with "other "software, but thanks to Frost we have been able to work out the corresponding table in HPT so you guys no longer need to rape offset & small pulse adder tables.

LOL. I'm tweaking all of this now to sort mine out... it is coming along quite nicely.

[nikon1999]

very interesting information... Wish I only understood how to apply it better. My car is seeing around 2.0-2.1ms at idle, sometimes 1.8ms on decel, but I feel like it should be less.
Will be playing with these ideas.

[zl1killer]

feel like or it needs to be? what is your AFR? what are the trims doing? is the car trying to pull lots of fuel?

[Zero4488]

This thread answered alot of my questions....thanks to all that posted....

[98Camarod]

Back from the dead!

I can usually get them down without touching the offset. I have needed to go as low as 1.2-1.3mS on some larger units to get idle to clean up. besides the normal tables, HPTuner's has a transient fuel tab that seems to be labeled incorrectly.

The transient fuel min mg is actually an IPW floor since it seems that it is active at idle. I made a few bins for 5.7ute to check out and this is what he found in compare (this is his work). To get from min fuel mg in transient to actual IPW multiply by 31.124308. Try it on an OEM file.... 1.4mS. That's not low enough to clean idle 80s on many applications. I have had to get it down to 1.3/1.4mS for some sets of 60s on some applications.

I'm confused. Are you saying the table that many people say to have as .002 should actually be 0.06224816?

[98Camarod]

bump

[STLWS6]

Hi guys dug this old thread up cause i had problems with the siemens deka 80 pound injectors
part number 110324... ev1... f351l00649 on the body of injector. i tried for 2 weeks to keep them idling and ns158sl helped when he said 1.87 was the lowest these would go. Put in 1.87 in all 3 injector bottoms fired right up thank you!! if i tried to lower them past 1.87 they would start the motor and it would rev then die. it makes my 5.3 ls6 cam motor at 750rpm idle rich at 12.5 afr is the leanest i could make it. Here is my tune maybe i am doing things wrong???