Please help me to understand injector BPW with an L98 7730 ecu. I have a recording of a 1/4 mile run where max BPW is 9.6ms at 5900rpm. Am I calculating correctly that there is only 10ms at 6000rpm? This is basically saturated operation 100% duty, controlled only by fuel pressure? On the other end of the recording is pulse widths of 1ms or less, which I'm not sure is controlled operation either.

 

My math... at 6000 RPMs each injector has to fire on the intake stroke only, so 60000/2 = 3000 pulses per minute. 60s/1min*1min/3000pulses=.020000sec or 20.00ms.

Now, I am only starting to cut my teeth on tuning. So I can't provide you specific answers yet. Some things i have read though...

At some point when you go to 100% Duty Cycle (Static) you will see a jump in flow output because the injectors satay open and there is no latency to open them. I believe tuners use this by changing the target AFR, but I would have a lot more reading to do to fully explain their use of this. However, I have always seen you want to stay at or below 85% duty cycle to maintain control.

 

Trouble with batch fire is, which cylinder's intake stroke if you're pulsing 4 at a time? Pretty sure there is an injection pulse for every crank revolution in batch fire. Which is double the frequency of sequential. Thats really the root of my question is to confirm that 10ms open is saturated. It looks to me like i have to use math to calculate duty cycle table unless there is a direct measurement of "off" injector timing that i can't find.

Then i'd also like to confirm that my injectors can operate with as little as 1ms commanded. I think i'm losing control at both ends. Car is running pretty well however.

Sorry if i didn't state this explicitly but this is a 1990 corvette L98. Speed density, batch fire 7730 computer, ANHT bin.

 

Again, not an expert here, but I believe there is a time that TPI goes into 1 time per revolution. Or maybe that might be just the EBL that is derived from TBI.... but you should be able to search on both of those points. In the end, you will have to go with what the ECM is telling you. If you are running out of injector you can try bumping your base fuel pressure or you will need to go with larger injectors. I would think the best answer is to look at your BLMs and actual AFR feedback versus commanded.

The algorithm for the base PW is pretty complicated. It looks at tables for temperature, TPS, TPS Delta %, INJ Voltage offsets, Injector Constants, feedback from O2 (BLM/INT), VE tables... and a few more I am sure I am leaving out to calculate the PW. So to your question of 1ms, yes it can... but it has to take other considerations into the actual pulse width. It may need only 1ms of flow, but it will need to add in the latency to calculate total time. You can get a good idea of if this is realistic based off the voltage offsets in your .BIN.

Another way to look at it is this. You said you have data from a 1/4 mile run. Your MPH should tell you roughly how much power you are making. Do you have enough injector to support that? Based off VE of an ICE or BSFC, to make a certain amount of output you need a certain amount of fuel (including losses). There are charts out there that will aid in size selection of injectors based on this.

I am here for more specific answers as well as I am going down the path of tuning my own TPI. With a Supercharger bolted to it, I am sure I will be facing some similar questions.

 

According to my EBL at 6000rpm's and 8.1mS I am at 80% duty cycle. I have 35# bosch EV14's from DeatschWerks and the documentation flow data shows 2.0 ms through 8.0ms then static.

 

Also note that is rated at 3BAR or 43.5PSI. So be mindful of your fuel pressure.

 

i'm not looking to pick out injectors and i'm not trying to calculate the pw. I'm logging WB AFR and mixture is not the concern either. I'm trying to calculate how much injector I have left, and trying to see if I will be able to control the injection with different fuel or different air. The online injector calculators confirm that my application is probably tapped out at very near 100%. What i'm trying to correlate is the observed 10ms at 6000rpm is 100% duty cycle, meaning that the injection window is 10ms at that engine speed and the injector is on the whole time. This would be different than the expected 20ms from a sequential injector at the same speed. To calculate duty cycle you have to know the time off as well as time on. In the chart from DW, the length of injection is arbitrary, its the resting time in between that determines duty cycle . This injector can operate at any duty cycle at 8ms. Meaning if you spray 8ms on, just rest 8ms off and you're down to 50% duty.

 

The feedback from your ECM is practical, hands on information. Your calculations are theoretical and your ECM will be what matters in tuning. If you are having no issues controlling your WOT AFR, you are still OK on injector.

With some reading, because as I said I am learning to tune that TPI as well... I found the following:

So it would appear the math I put up is wrong. The injectors do fire each cycle and all 8 at once, not 4/4 like I thought. I guess with the long runner and air velocity this works, primitive... but it is what it is. If you look at the wiring diagram, both circuits have a shared ground.

So , at 6000 RPMs, you have 10ms per revolution. My math was wrong I see based off an improper understanding. That is latency + needed pulse width. You will see a sudden jump in flow once they go static since latency will disappear. However, if you are seeing 9.6ms pulse width, yes... you are about to hit the wall with your injectors, but they haven't went static. You would have a bit more power supported by them.

 

Correct - 6K = 10 ms
10 ms / rev
What we tend to forget is that on 4 strokes we have 20 ms to get fuel in, i.e, 4 stroke = 720 degrees

 

Interesting.... so the cylinder will actually experience two pulses form the fuel injector per intake valve opening.... hence the doubling of the PW at low speed. So... if you are still trying to get two pulses in 20ms, you still only have 10ms/pulse?

 

At WOT duty cycle will go to 100% O2 reading is in a sense ignored. ECM fuel map is dictating fuel control. Bumping fuel pressure also increases volume and can reduce duty cycle during part throttle operations when feedback is influencing fuel control. If your wide band is leaner than you want, does it match fuel map? If yes, adjust map. If not increase available fuel = pressure, pump, and /or injectors.

 

Yes because in essence the commanded AFR at WOT would be off the charts to a NB 02 Sensor and why WBs are used for tuning. So the ECM wouldn't really get data worth adjusting for?

Are you saying at WOT the injectors go to 100% DC by default? Expand on that thought. I thought they were still commanded by the PW calculation and if you have enough injector they don't have to run static.

 

I'll start with OEM engineers engine management to the tight emissions standards. Yes, it's default TPS@5.0 v MAP @ 0 kpa ECM will command maximum fuel. During the engineering process all the calculations were done to know how much fuel will be available. Programming is also designed to run reasonably well without feed back. The O2 still operates ECM justs ignores it. If it reads .000 while duty cycle is 100 there's not enough fuel. .999 could be, fuel management is designed to overfuel to a point, too much available fuel, fuel pressure regulator set at 60psi + or larger than necessary fuel injectors and ECM hasn't been programmed for them. Typically over fueling shows up during part throttle operation also.

 

Yes, this would be tuning with a WB 02 and setting you VE tables and PE... I think. But yes, runs off set values or... an open loop.

Yes, cooler combustion chambers means you can hold on to a bit more timing (or boost), plus overlap in the cam and such... you want to be rich as it has been demonstrated engines make more power at WOT while running rich.


Let me be a bit more clear about my question. Say I dropped a set of 36# injectors into my L98. Even with the Supercharger there is no way I am going to use that much fuel. Say the injector constant was changed in the .BIN (EBL uses a nice tool to calculate needed values based off #'s/hr, fuel pressure, #of Injectors), voltage offsets are done and the VE table has been set and so forth.
Will the ECM automatically go to 100% Duty Cycle just because of WOT. Doesn't it still calculate on the VE table with PE enrichment? In the example above with the 36# injectors, it just wouldn't take a 100% duty cycle.