Injector Duty Cycle Reporting with 16197427 PCM

[FSJ Guy]

I am using the $0D bin. It appears that the my XDF computes the Injector Duty Cycle via the injector Base Pulse Width and Tachometer readings.

The conversion in TunerPro is this:

X * Y / 60000 * 100

where X is the Injector BPW and Y is the Tachometer input.

But why the 60,000 * 100?? Isn't that the same as 6,000,000?

The reason I'm interested in this is because at WOT, my fuel tables are as close to 100 as possible but my injector duty cycle is reporting at most, 30 %.

I'm wondering if I'm not understanding something right (quite likely) or of there is some other parameter that I'm not seeing. Thanks!

[gregs78cam]

60000 is the conversion factor needed to get PW (msec) to play nice with RPM (minute) since there are 60000 msec in one minute. I would say that the " *100" is to get rid of the decimal point in the output.


But if you are at 100 on the VE table I would say to change your injector flow constant slightly to get a better usable range. Lower the injector constant by 10% and the VE table by 10%. I think that is the right direction. I am sure someone will correct me if I am wrong.

[FSJ Guy]

I was thinking of adjusting the lbs/hour setting in the bin, too. Cheaper than getting an adjustable fuel pressure regulator!

To force the injectors open longer, I'd want to tell the PCM that the injectors' rating was LOWER than the actual rating, right?

So if I have 80 lb/hr injectors, I'd want the PCM to believe that I'm running 70 lb/hr injectors. That way, the PCM thinks it needs to open the injector longer for more fuel in order to offset the lower lb/hr rating.

Yes?

[gregs78cam]

That is what I am thinking then you will have to re-adjust your ve table.

[dave w]

I was thinking of adjusting the lbs/hour setting in the bin, too. Cheaper than getting an adjustable fuel pressure regulator!

To force the injectors open longer, I'd want to tell the PCM that the injectors' rating was LOWER than the actual rating, right?

So if I have 80 lb/hr injectors, I'd want the PCM to believe that I'm running 70 lb/hr injectors. That way, the PCM thinks it needs to open the injector longer for more fuel in order to offset the lower lb/hr rating.

Yes?

I agree with the explanation of lowering the injector flow to get the injectors to flow more fuel. A change of 3 lbs / hr is a HUGE change! The entire VE Table can be adjusted to correct for an injector flow change, but 3% is a HUGE change!

I like to get a VE table with the low numbers no lower than the low 40's, and the upper numbers no higher than the mid 90's. It's rare, but the use of a vacuum referenced pressure TBI pressure regulator is required. http://www.ebay.com/itm/220698940400...84.m1423.l2649

The vacuum reference will have low fuel pressure at high vacuum (near idle vacuum). When the vacuum is low, (near 100 Kpa) the vacuum reference regulator will increase the fuel pressure.

dave w

[FSJ Guy]

Great! Thanks for all the help!

Time to burn more gas $$ out the tailpipe! LOL!

[EagleMark]

Lot's of great ideas but wouldn't just raising fuel pressure do the trick?

[FSJ Guy]

Yes, but that would require buying a $75 adjustable fuel pressure regulator. I've tried the "DIY" way of adjusting the OEM ones and have not have success.

[EagleMark]

I think the spring is only capable of 15 psi... springs are available... or I think I read a guy added a washer?

But if your above way works all the better.

[JeepsAndGuns]

I have read many times that 15 psi is the most the stock will do. But on mine, with the regultor adjusted all the way up, 13 psi was the most I could ever get. That was with a brand new diaphram and spring.

Nice find on that vac refrenced FPR, I never knew they made one for tbi's. If I had known how they worked, what their function was, and the advantages were, I probably would have got one for mine back when I was setting up my system. I have the huge 90 lb/hr stock injectors in my 454 tb. My bpw at warm idle is somewhere around 1.08 (IIRC) and I am running 12 psi.

One thing that is confusing me, because I am still learning, is how can the VE table be near max and the injector duty cycle be no where near max? If the injector flow is programmed in, why is it not calculating all the the injectors useable range? I can watch my DL dash and my bpw goes up as rpm goes up. So I know it varies the bpw, but if I am reading it correctly, why is is not proprotinate to the fuel table? If the VE is getting close to 100, why is the bpw not also higher? If it automaticly calculates and adjusts the bpw, then why would it not see that its getting close to 100 ve and raise the bpw?
So if the ve is at 100, and it still needs more fuel to keep from funning lean, what happens? Does it just run lean because ve is at 100, even though the injectors can flow enough?

[dave w]

The 16197427 does not have a VE Adder table like the older '7747 ECM.

Basically, I've never looked at the VE Table as a direct relationship to Injector Duty Cycle. Basically, I've always counted on that a VE Minimum of low 40's and a VE Maximum of mid 90's was a good rule of thumb to follow when tuning a VE Table. Using the rule of thumb (keep VE's above mid 40's and below mid 90's), the VE Tuning I've done has produced excellent results. When VE Numbers are below mid 40's and / or above mid 90's I change the injector flow, and re-tune. The best solution I've found to fixing a VE table when 80 lb ~ 90 lb injectors are absolutely required for a +1 horsepower per cubic inch TBI engine is the Vacuum Reference Pressure Regulator.

I can't remember ever reading a detailed explanation on how the changing the VE number relates to the injector duty cycle (I sure it does though). I would also be very interested to know more about the relationship between the VE Table and the Injector Duty Cycle. Sometimes I get so focused on the VE Tuning results, I over look the basics for the theory of operation on injector duty cycle.

dave w

[FSJ Guy]

But AFAIK the OEM style adjustable vacuum referenced pressure regulator is no longer available.

I agree, it is weird that at 100% VE, the duty cycle isn't close to being maxed out. Maybe it's a built in safety feature to prevent the engine from going lean at WOT? <shrug>

[gregs78cam]

Being at close to 100 on the VE table and not seeing your PW max out, is not an issuethe VE table is just one part of the entire fueling equation. Remember you have a lot of adders like AE, and PE, that come in to play at high load areas of the table. and others like the Coolant temp adders, and battery V correction. I think some where on TGO a guru posted the equation for how the '7747 computes PW. I have a feeling that to make one up for the '7427 it would take hours and pages, because the '7427 has so many adders.

I know in the Camaro, my cruising PW is only slightly higher than my idle pw. Idle is around .488msec, and cruising at 60 is somewhere around .5xx-.6xxmsec. But my highest DC that I have seen, is around 35% at WOT @ I want to say ~3.4msec.

[EagleMark]

I'm guessing your VE is getting close to 100 in the WOT area? Have you looked at the PE? We just had a big discussion on that and basically PE is disabled on stock chips. Delay is 70 seconds!!! Get your PE working and see what happens. There's a PE.zip folder in $OD, $OE, $31, $E6 ECM information threads.

Here's the thread that started it:
http://www.gearhead-efi.com/Fuel-Inj...PE-not-working

[FSJ Guy]

Mine goes into PE mode all the time. It seems instant, too. If it's over a certain MAP (70-80 or so, depending on RPM) as well as if the accelerator is floored, PE is active.

As an update, I dropped the fuel tables by 20% and changed the lbs/hr rating from 81 to 70. That got my close enough that it would run and drive well enough to do some datalogging. A few tunes later, and my BLM's are back to where I like them.