Calculated Fuel Rate

Hey! Its my first post and slowly working through all the info. One thing I have been thinking about is calculated fuel rate, primarily at idle. My build has 30% overs and is a bit hazy at idle. I captured 30 sec idle log at temp in park and CFR average is 11.1. These are name brand remans with 1000 miles on them, and trying to figure out if I have a tune issue or a injector issue. If I use a stock average of 8 mm3 and factor the 3.1mm3 difference into the balance rate averages form same log file 5 injectors are out of spec. Is my thinking correct or is the 11.1 CFR with 30% reasonable and I should keep working on tune?

Thank you,

Jake

Jacob,

It's not uncommon for larger injectors to have more latency at low fuel pressure near idle, thus requiring a longer duration to sustain idle and reporting a higher CFR. 30% injectors will only flow more fuel as pressure and duration come up into the midrange. I would not be concerned about it. In fact, I'd take that intel into account when deciding how much more timing/fuel pressure the injector might like in order to clean up at low load. Try an put an extra 1.5-2 degrees of main timing in at idle along with 10 mPa and see if things clean up.

Nick

Hey Nick, thanks for your help! I will give it a try. Im glad you mentioned latency, as that is another area I have been thinking about. Long story short, the guys who originally tuned my truck is no longer available, and I decided to take on the task myself but am having to start fresh with a stock file I acquired. I for now am working towards developing a very solid stock file that will work well with my set up, and I can build power once I have a solid platform. I have been researching how to scale the pulse width table for 30% overs, and wanted to confirm my thinking. Using the injector flow data provided with my injectors, I was able to compare that flow data to my stock file, and mathematically calculate that I needed to subtract 20% form the entire table to effectively achieve the same flow rate with 30%'s. To do this I subtracted 100US from the table before I made the changes to account for latency, subtracted the 20% then I added the 100US back into the table. I did this for all Pulse tables including pre and post tables. Am I close, and can I assume 100US is an acceptable latency for 30%'s, assuming the fuel pressure will support it? Is this factor necessary to consider? Any advise is much appreciated!

Thanks you,

Jake

Jacob,

Unfortunately injector latency cannot be approximated with a single value as it changes with pressure. They closest approximation I've found for it is the .1 or 1mm3 row of the pulsewidth table. On an LBZ for instance, the delta between the .1 row and 1mm3 row represents the actual on-time dedicated to spraying 1mm3 of fuel, the rest of that time is latency. Copy this row into all other rows and call that new map the 'latency map', subtract the latency map from the original map and you'll arrive at 'actual fueling time'. From there you can adjust by percentage (avoid the rows below 40mm3). When you're done, don't forget to add back the 'latency map' before saving.

Nick

Ok, I think I understand just want to clarify. Per snapshot below. If for example at 100 MPA and .1mm3 the injector latency is essentially 180us and the injector on time for 1mm3 of fuel would be 212-180=32us of fueling time? Correct? So I can essential use the .1mm3 row as a rough latency figure as mentioned.

Thank you,

Jake

You got it!

Awesome great thank you!

Next question, far as injector trim codes, these injectors I have are balanced to +-2%, and I was told to keep the trim codes that are already in the ECU, which to my knowledge are for the original motor and stock injectors. Does this sound correct? How will these trim codes affect tune/ balance rates etc. if left alone? Would you recommend changing the trim codes in any way? Any advise is much appreciated!

Jake

I typically do not worry about trim codes on oversized injectors. FWIW

-Nick

Thanks again for your help!