Injuneer

The vacuum compensated regulator does not "regulate fuel pressure VS load".... it's regulating the differential pressure. Those are two different things.

Not sure where you are going with that. Take the LS1's dead ended system. The fuel pressure regulator is a bypass unit, at the tank. The PCM fueling tables are adjusted based on load. The PCM doesn't control the rail pressure. For high HP applications, that's not a good way to do it. The recirculated system is far superior in maintaining a constant rail pressure (or a vacuum compensated rail pressure if you choose to program that way). You do not want the rail (or differential pressure) to vary, even from cylinder to cylinder - hence the benefit of a large diameter rail. Controlling the pressure at the tank leaves the system susceptible to increasing pressure loss in the line to the injectors as flow increases.

Hence the use of higher quality adjustable pressure regulators in high HP applications, particularly power adder applications, where minor variations in fuel pressure can cause serious engine damage.

ByByC5

[QUOTE=Injuneer;6892734]The vacuum compensated regulator does not "regulate fuel pressure VS load".... it's regulating the differential pressure. Those are two different things.]

I always thought of a change in engine vacuum and load closely related. Like the old speed density systems using a map sensor for PCM load input?
And when engine vacuum at the regulator changes, so does the fuel pressure within it's designed parameters, be it a 10 psi variance or whatever it's designed difference is.


[Not sure where you are going with that. Take the LS1's dead ended system. The fuel pressure regulator is a bypass unit, at the tank. The PCM fueling tables are adjusted based on load. The PCM doesn't control the rail pressure. For high HP applications, that's not a good way to do it. The recirculated system is far superior in maintaining a constant rail pressure (or a vacuum compensated rail pressure if you choose to program that way). You do not want the rail (or differential pressure) to vary, even from cylinder to cylinder - hence the benefit of a large diameter rail. Controlling the pressure at the tank leaves the system susceptible to increasing pressure loss in the line to the injectors as flow increases.]

Well I know this may be a GM site(I drive a GM car though!), but I used to work on Ford products for many years (25+), and Ford does use pulsed fuel pump control on many of their products, performance vehicles included. Duty cycle control of the pumps can vary line pressure from 25lbs. to 60lbs. in single line systems, and yes there was a max pressure bypass on the pump, and a fuel rail pressure sensor for feedback input to the PCM.
This was as of 2010 (Last Ford I worked on )
As far as a dual line system being better? Yes I agree. And I always looked at some of the things Ford did over the years and had to wonder what the engineers were thinking sometimes. Ha Ha.

[Hence the use of higher quality adjustable pressure regulators in high HP applications, particularly power adder applications, where minor variations in fuel pressure can cause serious engine damage.]

Agreed!
Also in high HP applications the need for a good steady voltage present at the fuel pump. Not sure how the LSx cars are wired, my car is an LT1. But in stock wiring configuration, voltage drop in that circuit creates varying pressures. Not good! I ran separate 14g wire and a Bosch relay to mine.

ACE1252

The vacuum control on the fuel pressure regulator is simply to get accurate fuel delivery. Shooting pressurized fuel into a vacuum will yield more fuel delivered than shooting it into a space at atmospheric pressure at a constant pressure. As such, pressure must be reduced in a vacuum to get the same expected volume. At least, I think that is the deal. I know just enough about mechanical engineering to get me into trouble.

ACE1252

Something had to be wrong. Productions tolerances should not be that gross. Sounds like to me you had some kind of issue with the regulator....or maybe a fuel pump that was on steroids.

Edit: Scratch my above statement. The key on, engine off pressures the F-body manual states should be 41-47psi. 50psi is a little high, but not as bad as I was thinking. Still, that might cause negative fuel trims(too much fuel delivery).

ACE1252

Here is my new Injector Offsets and Short Pulse Adder spreadsheet for the FMS 30# fat top injectors. It accounts for the Ford/GM offset difference according to Alvin's diagram. Also included are the line equations for the low and high slopes. The sheet also outlines how I got the values. Any questions, just let me know. I'll do my best to answer them.

http://www.ace1252.com/LT1_Tunes/LT1...s_02232013.xls

Edited file....added in two injector offset tables. First one adjusted to Alvin's drawing(subtracting slope difference), Second one adding back in the slope difference.

ACE1252

I got the chance to try out the injector settings again. For some reason I was seeing split long term fuel trims. Much more so than with my other tune. For some reason my bank 2 trim with autotap is always almost steady. Makes me wonder if the software is not looking at the correct parameter in the PCM. I'll have to do some more checking.

There may also be the possibility that I have a slight vacuum leak on the passengers side. It is constantly calling for more fuel than the drivers side. Most of the time the injector pulse widths are always 0.5mS greater for the passengers side.

Just wanted to report what I have seen so far.....hopefully I'll get a wideband in the very near future.

ACE1252

Just looking at the numbers tonight. The fuel breakpoint for these injectors@43.5psi is around the 2.5mS range. It appears that the LT1 PCM has a hard cutoff for short pulse adders at around 2mS. Wonder if that could be playing into things....

Still, it's not doing what I expected of it. I'll keep working to try and find out why, but it is discouraging to see such a "split" in the fuel trims and injector pulse widths.

ACE1252

I'm now wondering if the voltage offset definition is the same between Ford and GM.

I think the short pulse adders are calculated correctly, so I'll add back in the offset I took out based on Alvin's drawing(assuming that the GM and Ford definition of offset are the same) and see what happens.

ACE1252

I'm still not having any luck. The fuel trims are split badly at idle. LTB1 is -15% while LTB2 is 2% with the new settings. With the settings of the stock injector offsets and adders @32.12# LTB1 is 5% while LTB2 is 10%. I don't understand why such a greater unequal split with the new settings. I can live with a 5% split but not a 17% split.

32.12# is the current programmed fuel pressure.

I made a plot(with "Graph"...free graphing software...good stuff) of the 32.12# line @13.6V(offset of 214uS) and the stock adders, vs the 31.62#line@13.6V(offset of 580uS) and the new calculated short pulse adders. The new short pulse adders parallel the low slope...so I'm not sure what is going on and why the much wider split fuel trims with the new settings.....

File for the plot(right click, save link as)...
http://www.ace1252.com/LT1_Tunes/inj...ings_plots.grf
Link to the software....
http://www.padowan.dk/graph/

The dotted crosshairs sit on the breakpoint @43.5psi


Here is the plot with the pressure 32.12#, stock offsets, and adders, vs Stock pressure 24.9#, stock offsets, and adders.


To add to the confusion even more, in looking up the part GM part number for my stock injectors(17124248), Summit has them listed as GM performance injectors 22lbs/hr. I've always read that they were 24lbs/hr....curiously, the stock program is set at 24.9lbs/hr.

The driving force for getting the injectors correct is that, if you don't, it bakes in errors to what you do down the line in the tuning process. If I can't nail down what is causing the problems, I will install my old stock injectors(along with the stock air intake system and stock injector settings) for dialing in my VE table. That will insure the injectors and MAF are correct moving forward for the tuning process.

I am in the process of making sure that the O2's and injectors are not to blame for this issue. I have already swapped sides with the O2's...no change. I'm going to swap the injector banks next(injectors from 1,3,5,7 to 2,4,6,8 and vice versa). This will make sure that I don't have a malfunctioning injector giving me issues. I don't think that any of them are bad....but just to be sure....

Update:Swapped injector banks and fuel trims stayed the same...so the injectors are fine. After a fuel pressure test, looks like my stock pump is down on performance@WOT. I don't think it has anything to do with the above, but the car has been slowing down from when I got it together and I hope this is the reason why. I'm still working on the injector issue and will report back with anything I find or figure out.

ACE1252

Just a little update. I've made no progress on why the "correct" FMS data splits the fuel trims so badly. However I think I've found why my fuel trims were split on PCMforless's tune. It had nothing to do with the tune. It was hardware I added to my Z28 long ago.

It appears that the metal airfoil I put in the stock throttle body was causing the split at idle. I removed it, replaced the top plate gasket with a new one, and the fuel trims are now within 1% of each other. Not the 5-7% spilt I was seeing before. I need to do some more data logging, but I almost passed out after removing the foil, driving a little, and saw the LTFTs at 9.4% and 9.0% at idle.

Another observation.....for some reason Bank 1's long term fuel trim adjusts quite a bit faster than Bank 2's. Just speculating, but I think it may have something to do with where the stock cat's were mounted. The Bank 1 stock cat was very close to the head, while the Bank 2 cat is much further down stream compared to Bank 1. This might be the reason why Bank 1 LTFT always "comes in" faster than Bank 2 LTFT. They both always get to the same repeatable value, just bank 1 does it much sooner than bank 2. It's not the O2's either....I have swapped them between banks with no change in the level of LTFT response.

Edit:After further testing, I don't think the airfoil was playing that big a deal in the split trims. Autotap being jacked on reporting the bank two LTFT value may have fooled me.

ByByC5

Very glad to see your committed to finding a path to success!
I have my car tuning on hold at the moment, but not finished yet.
I'm close, but not finished.....are we ever finished?

I too had issues with an air foil in my stock throttle body before I switched to a 58 mm one. I had enlarged the air passage in the throttle body (383 needed more idle air) to get my IAC position back down to a normal window at idle. The the air foil was restricting that extra air needed for a good idle quality and IAC positioning.
Removing the air foil brought the IAC in proper positioning, and idle quality increased.

The bank 1 vs. bank 2 speed of response "may" be related to when the PCM looks at the O2 sensor relative to where it "thinks" it is in relation to how far down stream it is located.
I am not sure if GM engineers used this strategy, but I know Ford used it years ago in OBD1 EEC IV systems (not sure about the OBD2 EEC V systems, as I never asked this in training schools) and bet they still do.
The PCM knew when to look to see if a commanded control had a desired result. And moving the location of that sensor up stream or further down stream skewed this process.

With the install of long tube headers, both bank 1 and 2, O2 sensors are at different locations than factory placing.

Again, not sure if any of this is true with GM, but it does give another look outside the box, so to speak.

Please continue your research and posting here......

I THANK YOU!

Keith

ACE1252

I've been tweaking with this stuff on and off for several years. However didn't really get the knowledge on how to do the injector stuff until purchasing Greg Banish's DVD's. His method's for how to handle the injector data(and open loop tuning), from an engineering standpoint, seem spot on. There still must still be something I'm missing.....not sure if it's unique to the LT1 as opposed to LS1(he works only with LS1/LS6/LS9 engines on the DVD's). Just makes no sense to me that swapping around the injector data split the fuel trims so badly. I don't understand why they don't shift together....but I will keep looking answers. However, it's nice that I seem to have found one issue(the airfoil).

I honestly wonder if the driver circuitry, in the PCM, could not be driving the injectors as the Ford circuitry would. This would certainly have an effect on tuning. I may have a look from that angle next....compare the commanded pulse widths with the actual pulse widths(and duty cycle) to see if all is in sync. I'll use a Fluke scopemeter to have a look at what is going on.....examine things injector by injector. I may even go as far to check the FMS injectors, with a LRC meter, compared to the stock injectors.

I take spells where I'll sit down with it for a few hours, learn something, then not come back to it for a few weeks depending on what is going on at home.

Your statement on "Are we ever finished?" is very very true.

ACE1252

Just a few more notes to add to the thread.

I've been looking at this problem again. I decided to convert all my data values based on 58psi(LS1 rail pressures) to see if I could match Greg's data.

Our short pulse adders don't match, but our voltage offsets match(@ 0 Kpa) when you subtract the difference between the "Ford offset" from the "GM offset". I made a note on Alvin's picture in my spreadsheet on this and was not sure if I was right or not....I can't say if I'm right, but the data does match. Based on the difference on how GM and Ford are handling things, this does make some sense.

I still have no answer on my split fuel trims with the new data. Still too cold for me to work outside with it.

The latest thing that concerns me is relating to the fuel breakpoint(FUEL_BKPT).

Based on the multiplier for going to 43.5psi, the break point to switch to the low slope is 0.01038973g. If you trace that out on the graph(31.62psi high and low slope), that puts switching to the low slope at ~3mS(depending on which voltage offsets you use). The hard cutoff in the LT1 PCM for short pulse adders is 1.952mS. So we have a no man's land between 1.952mS and ~3mS. So the Ford data is stating that the nonlinear region is beyond what the GM LT1 PCM can deal with(until the pulse widths get beyond 3mS...then you are on the high slope which is the linear region).

This could mean that we have no chance of getting these injectors characterized "correctly" in the LT1 PCM. The LS1 PCM has short pulse adder ability going all the way to 4.8mS(based on Greg's worksheet).

ACE1252

Reading back through Banish's speed density book.....

I'm not so sure about my previous post on subtracting the difference between the GM and Ford offset.

In reading, there is not only the opening of the injector to overcome, but the closing to consider as well. I had really only been thinking about the opening.....but I should know better with my background.

An inductor(coil of wire) by it's nature resists a change in current. If the current is at zero, when you apply voltage to it, there is an inrush of current and as this current builds, a magnetic field is simultaneously cutting across the wires opposing the in-rushing current. This slows down the current "charging" the coil but only until the magnetic field is fully established. Once fully established, the field does not oppose the current.

So, the inductor resists a change in current by trying to hold it at zero for a brief time. All of the previous description is for DC....AC gets a little more involved(frequency(Hz) comes into play) because the voltage/current is constantly changing directions.

The opposite is true when turning off an inductor. When you remove voltage, the current starts to stop, as such, the magnetic field around the wire starts to collapse. When this happens, the field induces or charges the wire with more current....this keeps the current flowing after the voltage is remove....but only for a brief time.....however the inductor again, has resisted a change in current by trying to keep it going.

Greg defines injector offset as the following time....

Injector Offset = Injector Opening delay - Injector Closing delay

This makes sense because of an inductor's very nature(as I described above). On the front end of the injector pulse, the injector resists opening(resisting a change from zero current to full load current as the field expands) and on the back end of the injector pulse the injector resists closing(resisting a change from full load current to zero current as the field collapses). The opening delay is much more pronounced than the closing delay.

On the front end of the pulse, most of the opening delay does not come from the coil inductance(what I described above), but from the injector spring and differential gasoline pressure between the back and front side of the pintle. However coil inductance does play into it on both sides.

Unless there are some code tricks going on related to the linear and non-linear flow(as in when to apply the offsets to one or both flows), I don't see how the injector offsets could be any different between Ford or GM. As of right now, I consider my "matching data" to be more of a fluke than anything else.

My thinking was that there may be differences between the offsets in the high and low slopes. All of my reading to date states that the offsets are constant across both regions. So I will update my excel sheet to omit this idea(updated 02-23-2013...Alvin's drawing included(credit given on drawing) because it's important to understand the short pulse adder relationship).

I'll continue "blogging" as I make more progress.

ACE1252

Since Ford has modeled the non-linear flow all the way to ~3mS, my next experiment will be to input the Ford injector offsets(without any subtraction nonsense), set the short pulse adders to zero, then program in the low slope value as the "injector flow rate". This will bypass the hard coded limit of the short pulse adders. This, of course, will jack up any flow above ~3mS, but this is just to see how the PCM reacts when the low slope is input properly.

I'll then only let the engine idle and maybe do a couple of tip in tests. We will see what the LTFTs do then.

I'm also going to take the MAF and SD fuel equations I've learned and try to calculate the fuel delivery request(using sensor data). Once done, I should be able to strip the injector pulse width down to just the "add-ins"(fuel trims, offset, etc.). I don't think I'll be able to get all the add-ins correct short of viewing the GM source code, but I need to at least have a good idea of the base pulse that the system needs. I'm interested in this because increasing the offsets didn't appear to increase the pulse widths....they decreased(in my old logs). Something I didn't expect....however more testing is needed.