Understanding Injector Data Sheet

I have upgraded injectors in my truck that I'd like to understand how to tune for. I also have the associated data sheet and am little confused by some of the numbers that I'm seeing. There are parts of the map that show that the fueling is basically identical for my new injectors compared to the stock tune file and other places require less duration for the same amount of fuel as I would expect, but specifically the EM test shows that it would require a longer duration for the same fuel quantity which I don't understand. I will try to post files that will show what I'm talking about.

Bringham,

It's not uncommon for 'oversized' injectors to flow equal to stock or even less than stock at low rail pressures and durations. The phenomenon has more to do with opening and closing dynamics than orifice size. Luckily you have a flow sheet for some direction. You may choose to widen the pulsewidth in the EM area by 10-15% up to about 50mm3 to account for this effect or you may choose to simply leave the table stock up to 50-60mm3 and then adjust based on the VL data from there. Have you tried running the stock PW graph? Is the truck exhibiting any frustrating symptoms?

Nick

If you buy aftermarket injectors, i suppose they they are not flowing exactly the same (not oem do it either), but how can you compensate for this? Or will they flow almost exactly equal, so no internal calibration is necessary?

Many of the OEMs use injector calibration codes which are printed on the injector and can be adjusted using the factory scan tool. If you're using an aftermarket supplier you're at the mercy of their bench test data.

A wideband O2 sensor can be used to catch and adjust to some degree but it's not as delicate as a good bench tested set. Ideally the injector supplier can give you a sheet that matches the table posted above. (perfect world).

-Nick

Nick, What is the difference between, EM and VL data on the sheet?

Simply fitting a bigger nozzle will throw the injector off balance as there will be a bigger pressure drop under the Pintle lifting it slower. So yes smaller mm2 stoke @ low coil on time and fuel pressure. This is OK as adding time injector on duration can be done and even not doing this could help as well as fuel injected quality will not be better in most cases fitting an aftermarket nozzle making smoke a lot faster.

Flow number can look great on some bigger aftermarket injector but please do not fool your self. Is the Pintle lifting it slower it also closes to injector slower ending up with a lot longer injector opening time than you will be expecting. We seen over 800 microsecond after end of coil on time when real injection stopped.

We always look @ the Design nozzle flow @ 100 bar ml/m for example and compare this to the stock nozzle flow so we know how good or bad the injector really is handing fuel.

Nick, I got a wideband O2 sensor and have been logging data with it. My theory was that I could log the commanded lambda (calculating it in efilive by using commanded mm3/stroke and converting it to grams from diesel density and per second from rpm then comparing it to the measured maf g/s) and compare it against the measure lambda to figure out if injectors needed to be adjusted. In doing so I've shortened the pulse width by quite a bit. I think I've probably gone too far by trying to use this method. My truck used to be very smokey and now it doesn't smoke at all which I'm happy about, but it is probably running excessively lean.

In your experience, have you ever been able to do this same thing with a stock LBZ or earlier truck to see how closely the measured lambda follows the calculated lambda that the computer is commanding? I might be wasting time trying to figure out the main injection pulse table this way. In my mind, as long as the maf sensor is reading correctly, this should get me a good idea of how much fuel my injectors are injecting.

Also, do you know if the S&B intake for LBZ would necessitate a remap of the maf sensor? I don't have a stock intake to compare to to know for sure.

Thanks for all of the great insight so far from everyone!

Brigham,

I support your method of wideband based adjustment to the pulsewidth table. Remember, there's no such thing as too lean on a diesel. As long as your adjustments get you the drive-ability you're looking for I think you're on the right path.

With regard to your question of the calc lambda vs. actual, I have watched and usually they're very close on a properly calibrated truck. Just remember that the lambda table on a diesel is a "Lambda Limit", meaning you may well see leaner values than those in the table but you should not see richer values. The table is usually only active during transient fueling.

With regard to the S&B intake, you should not have to re-cal the MAF as the S&B is designed to maintain close-to-factory MAF scaling. It's the only way S&B (or any airfilter manufacturer) can get a CARB E.O.