ACE1252

For those who have just found this, please read the entire thread. There are some assumptions by me in my earlier posts where it turned out I was wrong(concerning additional time additions to the short pulse adders). I corrected my mistake later on, but do please read the entire thread.

I've been doing some homework on tuning FI systems. I started with buying these two books(off Amazon) authored by Greg Banish....

http://www.calibratedsuccess.com/Media.htm

There is a ton of good information in these books, but I think the Designing and Tuning High Performance Fuel Injection Systems is the better of the two from an engineering standpoint.

The book is well written and shows the 8 operation regions of the VE table and explains how the VE table is used in engine operation. The interesting thing is that where he shows the tip in region(region #2 on the VE table) is exactly at the KPA level that I'm having bucking problems(bucking when applying light throttle around 7mph). Based on what I've read so far, it appears that my VE table is somehow out of whack in this region.

I've learned that one of the first steps in tuning is to get the injector settings correct. Not only the pressure, but the offsets. Using this offset data from Ford SVO on the 30# redtop injectors.....
http://www.fordracingparts.com/parts...-9593-b302.pdf

I found that link here....
EECTuning.org • View topic - FMS :: Injector offset vs Battery Voltage:: Where ?

...and the data for other Ford SVO injectors is here.....
FORD RACING 24 LB/HR FUEL INJECTOR SET | Part Details for M-9593-AA302* | Ford Racing Performance Parts

Using the m-9539-b302.pdf, the 30# injector offset data is in the FNPW_OFFSET table. This table is rated at 39.15psi and there is a correction factor when raising and lowering the pressure. The correction factor is in table FNPW_OFFCOMP.

I first created a table of just the FNPW_OFFSET data @ 39.15psi. That data only goes from 6 volts to 15 volts in well spaced steps. To give it more resolution, I subtracted the differences between the each of the voltage steps and divided it by the number of tenths of a volt between each of the points. This gave me a linear value by which to step up(or down depending on how you look at it) to the next values in the LT1 injector offset tables(there is much more resolution in the LT1 injector offset table than data given for the SVO injectors).

For example, the offset value @ 6volts is 3.253mS and the value @ 8 volts is 1.669mS. There are 20 tenths of a volt between 6 and 8 volts. The difference between the offset values is 3.253-1.669 = 1.584

1.584/20 = 0.0792 which is the tenth of a volt step value for the 6-8 volt range. So if you want to know the value for 7.2 volts(working up from 6 volts) you do the following....

7.2 - 6 = 1.2V or 12 tenths of a volt.
12 * 0.0792 = 0.9504, then....
3.253 - 0.9504 = 2.3026 or 2.303mS
So the offset data for 7.2V is 2.303mS

You can come at it from the other way it you wish(calculate from the 8V end). Just pay attention to the math.

[Edit 2-26-15]I think you can also use a line equation for this, so I took the long way around to get the value.[End Edit]

Now, the values below 6 volts I kinda pulled out of my rear because I just didn't know what to put. Above 15 volts, I just used the stepping value from the last extrapolation step and kinda followed the stock injection pattern(but at a higher time).

After getting the base values, I used a multiplier of 1.0375 to get my final offset values(per the FNPW_OFFCOMP table...extrapolating as in the other steps). EDIT 4-28-12: Found a slight error..the FNPW_OFFCOMP multiplier @43.5psid should be 1.042957. I used a value of 43psi to get the 1.0375...off slightly, but GM LT1 rail pressures are based 43.5psi and not 43....just needed to correct this.

I do not know how well this will work as I have not programmed it in yet. I expect this will invalidate the current VE tables, but I have to start somewhere and trying to get the injector settings correct is one of the first steps.

Just wanted to forward on what I have learned so far(LOL, right or wrong).

Here is an excel spreadsheet of what I done with a curve compare vs the stock LT1 offset values. The battery voltages and 24# injector data came directly from my stock LT1 PCM. Pay attention to the unit values....my DST software displays the injector offset values in uS not mS as in the Ford data sheet. However, for my spreadsheet, I converted the values to mS. The new curve looks reasonable based on what I've been told about the SVO injectors(slower reacting than the stockers).

Edit:4-28-12 Do read on....I think the values in my above spreadsheet are wrong. The GM offset and Ford offset are slightly different in their definition(see Alvin's chart below). I do plan on trying to make a better explanation of what needs to be done for this later....along with posting a much better spreadsheet.

Link to old spreadsheet removed. See post #20 in this thread for new spreadsheet.

Ricardo

Injector offsets will have a major effect at idle, where PCM calculated injector pulses are at their minimum.

ScottKnight

Nice to see someone else rolling up their sleeves on injector data (even though Greg already did the really hard work for us ). I made the same journey earlier this year and found using spreadsheets tedious and eventually landed on SciLab to handle the numbers:
http://www.impalassforum.com/vBullet...d.php?t=236016

MikeGyver

Here's an online injector service shops that can test and graph your injector latency for $25.
http://www.witchhunter.com/injectorserv1.php4

ByByC5

I realize this is an older thread, but believe there may be others trying to tune and not using the offset tables.

I for one fell into this category, running 36 lb. Ford SVO injectors on my car.
And with a manual transmission, and the GM 847 cam had some bucking issues when I first began tuning my PCM.

Aware of offset tables, and unable to find the offsets for the old style SVO injectors. (the big bulky ones) Until recently I was running the stock offsets.

I was actually happy with it running with an open loop tune, and all the timing, fuel changes and a few maf tweaks here and there, and finally got it driving better than the old motor I had with the hot cam running closed loop.

I found a set of tables for the older SVO injectors and used these in my tune.

http://carprogrammer.com/Z28/PCM/Injector/injectors.htm

Now running closed loop, and so smooth I can honestly cruise 40 mph in 6th gear. ( 4:33 gears in the differential helps too)
Idle is really smooth, compared to what it was.

In fact idle quality is so good now I am setting the idle lower.
I'm at 950 now and it seems to high with the offsets in place.

Fuel pressure varies between 36 and 44 ( have the vacuum hooked up to an adjustable regulator)

Wide band is showing better A/F ratio's at idle and part throttle cruise, 14-16:1

Really happy I found this old thread

Thanks to the OP and all other contributors
HTH

Keith

ACE1252

I did put these(injector offsets) in at one point and it threw off my fuel trims big time. Too much to leave them in....

I suspect that it was due to the short pulse adders being incorrect(could be a VE thing as well...or combo of both.....programmer left the short pulse adders stock along with Injector voltage offsets).

Recently, on the Monodax(edit: oops, it was hptuners) forums, I ran across a post by Alvin of PCMforless.

http://www.hptuners.com/forum/showthread.php?t=37803

They were talking about the short pulse adders. I, myself, have struggled with what GM was doing vs what Ford was doing. I've got a good handle on how Ford was doing the adder....

Low slope for the non linear range of the injector(which actually has a "higher" slope value).
High slope for the linear range of the injector(which actually has a "lower" slope value).

My problem was understanding what GM was doing.....well Alvin posted up a picture that made it crystal clear for me.



I don't know why Greg never had this in his DVDs or books(and to my knowledge, I have them all). Anyway, this has given me the tools to figure out what I need for my short pulse adders. I just did get them calculated tonight. I'll post up later on how they work out.

In summary, the short pulse adder is the subtraction of the X axis values for the non-linear flow and "theoretical" extension of the linear flow. Again, this is for Ford injectors on a GM application.

The actual flow of the injector(in the nonlinear region) - the extended linear flow(slope of the injector) = short pulse adder.

Keep in mind the linear flow in the low region of the injector is not real(blue line). It's just an extension of the linear flow ("high" slope) to the bottom of the graph.

ByByC5

Eric,
Are you using the 96 OBD2 pcm in your car for tuning?
Or have you switched out for a 94-95 OBD1 pcm?

I am using a 95 OBD1, and TunerCat, latest revision.
I am running SVO 36 lb. EV1 style injectors, and am in search of calibration data for these injectors.

I could be wrong on this, but the OBD1 pcm does not use VE tables as long as the Maf sensor is working with no faults.

I can unplug the map sensor, and see no difference in engine operation at all, except the check engine lamp illuminates almost immediately.

Greg is tuning OBD2 pcm's and these may use VE along with the Maf?

I have searched the internet, gone to the Ford Racing Website mentioned above to find all but my 36 lb. (EV1 body style) injectors listed

M-9593-D302 is the part# for these. If anyone has the calibration summary, I would greatly appreciate it!

I worked for Ford dealerships (3) for over 25 years as a master tech, and later as a shop foreman. Now not working for them.
I tried my Ford hotline access and not being currently part any affiliated company, could not acquire the necessary contact id# to get in to speak with an engineer.
Tried the Ford Racing web site "help" line, and was told if it isn't posted, we don't have it.
Final try was to email a Ford instructor I know for all the years I went to training classes and work shops.
He searched and emailed me back with no luck.

So outside of asking for them from a professional tuner, and I know none personally, I am asking here for the data.

I do have the voltage offsets, and as mentioned above, it helped my driveability in a huge way.
But now that I have set those, I would like to dial it in even more!!

Thank you!

Keith

ACE1252

Keith,

I'm using '96 OBDII PCMs for my tuning. Still running full OBDII hardware.

As I understand things, GM is using a blended model for all 4th gen MAF F-bodys....OBDI and OBDII(this excludes '93..only offered with speed density).

MAF works well for steady state flow, but when you get to snapping the throttle around, transients are introduced into the air flow that the MAF can't handle well. Thus the need for a blended model of MAF and speed density. As such, it's important to get both the MAF and speed density setups right in the PCM.

Did your 36lb injectors come stock on any Ford vehicle? I'd try to lift the calibration values from that vehicle if they did. You will not have the pressure multipliers, but to get the high and low slopes is one step closer.

From my casual observation, Ford is a little better than GM when it comes to helping us out on the tuning side of things. So if they say they don't have it....that is not good. In just looking over the posted Ford calibration summaries, they skipped over the D302 for some reason....A302, B302, C302, and F302 are all there....

The folks over at Injector Dynamics might be able to help you. I don't know how much it would cost to characterize them. In the end, it might cost less to pick up a set with a published calibration summary. To email or call them up would not hurt at all.

ACE1252

Adding in some useful information from Injector Dynamics site...

Injector Dynamics - Technical Articles
Injector Dynamics - GM Data
Injector Dynamics - Ford Injector Calibration

ACE1252

Ohhhh....it just hit me by staring at the picture above as to why my injector voltage offsets caused such a drastic shift in the fueling(fuel trims waaay out). Don't get me wrong, I expected a shift but nothing like what I got. Notice at the bottom of the graph where Alvin has the Ford offset and the GM offset.

In addition to doing all the work with the Ford Injector summary in my first post for the pressure changes(39.15psi vs 43.5psi), there will need to be an X value offset subtracted from all the voltage offsets to convert the "Ford Voltage offsets" to "GM Voltage offsets".....This offset will be the difference of the Low slope - the High slope at Y=0......

I'll try it and post up later.

ByByC5

So are you saying that the voltage offsets for Ford injectors are interpreted differently in the GM pcm?
If so, how do you calculate the difference to get the correct data?

I know some of the offset values are in milliseconds, and some in microseconds. That easy to convert either way, but getting the Ford data into GM usable values is where I am confused.
Aside from the pressure offset differences (I can drop my fuel pressure to 39.15 easy enough), how would one calculate the pulse adder area from the Ford low slope data?

I went to the HP tuner site, and some of that thread is difficult to interpret.
And I am still in search of the calibration data sheet for my 36 lb. SVO's.

The car is actually running very well, super smooth given the cam it is. Not a big cam, but not known for smooth sailing! I am enjoying the learning, and want to see just how smooth this cam can be.

I did drop my idle to 900, and it is still very stable. And will drop it to 850 and see how that does.

Thank you,
Keith

ByByC5

I am still looking for the calibration data for my injectors.

I am beginning to think the fuel pressure offset calibration not as critical due to the vacuum controlled fuel pressure regulator system used on the LT1 fuel system.
The fuel pressure can vary almost 8 to10 psi up or down depending on the amount of vacuum applied to the regulator, or lack of it.

Maybe if you get much over or under the design specifications of the "window" of fuel pressures a stock LT1 system see's, these pressure offsets may be more important.

I removed the vacuum to my adjustable regulator, and maintain 39 psi now, and have seen no noticible change in driveability.

I'll have to data log and see if my trims are out now.

Also would like more information on how to tune the low rpm pulse adder.
Thank you,

Keith

Injuneer

While the rail pressure may vary by up to 10psi, the pressure that affects the flow of the injectors is not the rail pressure, but the DIFFERENTIAL pressure - the mathematical difference between the rail pressure and the intake manifold pressure. The injector is like an orifice - the flow is dependent on the difference between the inlet and outlet pressures of the device. That's the whole purpose of the vacuum compensating fuel pressure regulator - to hold as close to possible a 43.5psi DIFFERENTIAL pressure.

ACE1252

It appears they are handled differently. Look at Alvin's chart. The Ford offset is based upon where the bottom of the low slope is on the X axis when Y is 0. The GM definition is based upon the theoretical linear high slope at y=0. So, in order to use the Ford offsets in a GM controller, you need to subtract difference of those positions at Y=0 for all the Ford offset values.

My initial tests look promising. The tune currently in the car is +10% on the fuel trims. With the new settings the swing was -10%. It was not the gross over correction as before...I mean they didn't look good at all. However, I need to buy a wideband and some steady state dyno time before I go any further. I also need to install my stock air intake to take changes in the MAF calibration out of the equation when I do the tuning. Yeah, I actually kept all that stock stuff when I put on my K&N CAI years ago. Thankful now that I did that.

I'll try to explain the offsets in more detail later, but I don't have the time to draw up what I would need to show you. If you look at Alvin's picture, it should become clear, but more elaboration may be needed(a review of slope calculation, etc in algebra does not hurt either...they are needed to work with this stuff).

Don't remove the vacuum from the regulator. As Injuneer stated, it's there to compensate for the reduced pressure in the intake(it's lower than atmosphere...when running...have to compensate for it). With the engine off, make sure the rail pressure is 43.5psi.

He has multiple threads around here outlining the pressure calculation(in fuel and ignition section I think....) to use when using Ford injectors on GM applications. For example, the SVO 30# units are set as 31.68# units in the GM controller vs just 30#. It's because Ford benched them at a rail pressure 39.15psi vs the LT1 pressure of 43.5psi. Most people just change this setting and forget about the short pulse adder and injector voltage offsets.

I think your going to be out of luck on finding reliable data(offsets and low/high slope values) for those injectors without getting them characterized on a bench. Why Ford skipped posting the information I'm not sure. However, I am thankful for all the other data they have posted.

ByByC5

That is a very good explanation of vacuum regulator function. I now understand why Ford and GM got away from that system. Or I am speculating. The need to regulate fuel pressure VS load (or pressure differential) still remains even with the single fuel line and pulsed fuel pumps.
It must be cheaper to control the rail pressure with software programming in the PCM, and a fuel pump control module, eliminating the extra fuel lines and the regulator.
Not to mention one less fuel line to worry about leaks.

Also the mechanical regulator is subject to variations in production tolerances, equating to slight pressure variances between units. My stock regulator was almost 50 psi, key on and engine off.

The addition of a wideband will really aid your tuning for sure.
I am using the LC-1 wideband controller and a digital readout for continuous monitoring.
It would be interesting to see if the 450mv center swing of the factory O2 would read about 14.7 on the wideband display.


However I am unsure of the need for dyno tuning for drivability. I don’t see how it could be better than normal driving with a data logger running.
Even WOT on a dyno is not the same as a run at the track for data logging and tuning for that. Maybe it’s just easier and safer on a dyno. Maybe Greg addresses this in his books or DVD?

The maf tables are another area that I tweaked. My car is a 96 Ram Air car from the factory and slp. So obtaining the correct maf table for a 95 PCM and the ram air set up was not possible for me. So I found a maf table from a stock 95 LT1 Vette and substituted those values in place of the ones that came in my 95 pcm. There were substantial differences.
As the air intake system is similar to the ram air set up. Just no nostrils in the hood.

I do have my stock 96 pcm, and would like to pull the maf tables out. But have no way to do that.

So you think setting my base fuel pressure back up to 43.5 with the vacuum hooked up, and adjusting the injector flow setting from 36 to 38 (rounding up from 37.947…….. would be better to get closer to a better tune for these injectors in my PCM?

I will give it a try and do some data logging.

Thank you Fred, and Eric!!

Keith