injector flow rate table

[hpcubed]

Just wanted some clarification. The injector flow rate table is a correction for the injector flow rate as a function of pressure (MAP). This correction is because injectors are calibrated at atmospheric pressure but in the engine, they are under varying levels of vaccum?

[Ira]

That would be correct.

Ira

[PSWired]

I am guessing IFR tables are only used on returnless fuel systems where there is no vacuum references FPR?

[joecar]

My understanding of this subject (...ha...)...

The IFR table tells the PCM how much fuel mass the injector flows as a function of vacuum (i.e. BARO - MAP).

Injector flow rate depends on the pressure difference accross the injector: on one side of the injector there is manifold pressure (MAP), and
on the other side is [constant] fuel pressure plus atmospheric pressure (since fuel pressure is measured relative to atmospheric pressure);
i.e. diff = FP + BARO - MAP, where FP = constant

At WOT, injector flow rate is less (MAP is high), and to spray a specific mass of fuel, the PCM needs to keep the injectors open longer;
At idle, injector flow rate is more (MAP is low), and to spray a specific mass of fuel, the PCM needs to keep the injectors open shorter;
i.e. time(s) = mass(g) / flow_rate(g/s)

Since the pressure regulator is not MAP referenced (in our case, "returnless system"), the PCM uses the IFR table to compensate
for the variation in injector flow rate caused by the variation of MAP;

But, if the pressure regulator were MAP referenced, the regulator would increase fuel pressure as MAP increased, causing the pressure
difference across an injector to always be constant regardless of MAP variation, and in this case the IFR table would be flat with no slope;
i.e. diff = FP + BARO - MAP, where FP = constant + MAP, so diff = constant + BARO
:?

[dfe1]

The IFR table is simply the electronic equivalent of a vacuum line running between the intake manifold and the pressure regulator. Trucks have a vacuum referenced pressure regulator so the IFR table is a straight line.

[joecar]

dfe1 wrote:

The IFR table is simply the electronic equivalent of a vacuum line running between the intake manifold and the pressure regulator.
Spot on, that's the best summary I've seen.
:)

[daveb]

I am wondering why the configs only go from 0-80 Kpa in the ifr tables, which is less than 1 bar.

What do you do when using forced induction?

[Delco]

I am wondering why the configs only go from 0-80 Kpa in the ifr tables, which is less than 1 bar.

What do you do when using forced induction?

Thats 0-80kpa of vacuum , for forced induction the whole maps need to be rescaled.

[joecar]

VAC = BARO - MAP

where
VAC = vacuum
BARO = barometric pressure (1 ATM, 1 bar, 100kPa approx, 15psi approx)
MAP = manifold absolute pressure

and since when MAP goes below 20kPa (VAC goes above 80kPa) the PCM cuts fuel (...correct me if I'm wrong...) so the PCM does not need the the injector flow rate below MAP 20kPa (which is VAC above 80kPa).

[daveb]

Thanks, I thought that might be the case.

I assume injectors come with these ratings so the ifr table can be altered to suit.

If we have a 2bar FI setup, I assume we scale this table as the 2 bar MAP sensor will report to the PCM the same voltage range as a 1 bar although it is covering 2 bar of pressure. Is that correct?

Thanks,

[Rich Z]

But, if the pressure regulator were MAP referenced, the regulator would increase fuel pressure as MAP increased, causing the pressure
difference across an injector to always be constant regardless of MAP variation, and in this case the IFR table would be flat with no slope;
i.e. diff = FP + BARO - MAP, where FP = constant + MAP, so diff = constant + BARO
:?


The IFR table is simply the electronic equivalent of a vacuum line running between the intake manifold and the pressure regulator. Trucks have a vacuum referenced pressure regulator so the IFR table is a straight line.

Sorry about bringing this old thread back to life, but I'm a RAW newbie at this tuning stuff and am sticking my toes into the water (timidly, I might add) by looking over the tune that was done on my car and then comparing the tables against a stock tune.

Now if I understand the above quotes, then a car using a fuel pressure regulator that is MAP referenced (which mine is), then the IFR table should be a flat horizontal line. Is that correct? Well, I'm looking at the IFR table in my tune, and I see this:

http://www.corvetteflorida.com/pics/ifr_table_c5z_01.jpg

So obviously I am confused. The car seems to run fine except for some low RPM issues, but I would think that a MAP referenced fuel pressure regulator combined with changes in the injector pulse width forced by such an IFR table would give me some substantial issues.

What am I missing here?

[joecar]

Hi Rich,

The stock FPR on the Corvette has a hose on it, but the other end of the hose sees BARO not MAP...

( the hose disappears under the plastic coil cover, but it is not connected to the intake manifold )

so it is un-referenced...

so your IFR table is correct in being sloped.

[Rich Z]

Hi Rich,

The stock FPR on the Corvette has a hose on it, but the other end of the hose sees BARO not MAP...

( the hose disappears under the plastic coil cover, but it is not connected to the intake manifold )

so it is un-referenced...

so your IFR table is correct in being sloped.

Sorry, I was not clear about this. Been in the trees for so long that I forget that I am in a forest. :)

My car is anything but stock. Custom 427 based on an RHS block done by LME, STS rear mounted twin turbos, dual in tank fuel pumps by Lonnie's Performance, etc., etc. I put in a vacuum manifold block myself which is fed from the brake booster and connects to the secondary fuel pump enable switch, blow off valve, and runs to the Aeromotive fuel pressure regulator mounted right next to it behind the driver's side front wheel. I have a fuel pressure gauge and can watch the fuel pressure change during driving, so I am pretty sure it is working.

http://www.corvetteflorida.com/pics/vacuum_block_10.jpg

The tuner is pretty highly respected and did an excellent job of getting my car running when the local guy who tried for about a year pretty much claimed that my car was untunable. So is it possible that he is using both the mapped FPR and the IFR table somehow? I know I told him about the FPR, and the car certainly runs fine enough as far as I can tell. Just some issues I have to tackle with the low RPM running and idle, that I know he didn't mess with much at all.

So what the heck am I looking at here? I'n trying to contact the tuner, but so far haven't gotten any responses to my earlier emails. But heck, this time of year no one seems to take work seriously.

I've decided I want to get into this tuning stuff, since I've been forced to do my own wrenching anyway (basically an ongoing nightmare for most of the past 3 years), and I might as well try to tackle this aspect of it as well. I'm retired and got some time on my hands.

But seriously, this stuff is a really big gulp to try to take. I have a background in computer programming and been tinkering with cars since I was a teenager, but this is a whole new world behind this door I cracked open.

[eficalibrator]

The tuner is pretty highly respected and did an excellent job of getting my car running...

Looking at your hardware and the screen shot of the injector setup, I'd say your highly respected tuner missed a few things.

1) You should never have a straight diagonal line for IFR. If the regulator is not manifold referenced (yours IS), then this table should have a slight bend in it as it follows Bernoulli's law for change in flow versus pressure. It should be a square root function, so NOT a straight line. Straight lines mean he took a shortcut that does NOT always work out nice when trying to fix AFR issues.
2) Manifold referenced regulators (like yours) need a HORIZONTAL straight line.
3) With any change in injectors there are also changes to a few other tables (short pulse adjust, offset vs voltage) that MUST be changed or you will have more problems like I said in #1 above.

[Rich Z]

Well, to me it was a huge step forward just getting my car driveable. When I drove it back home from the second shop "working" on it, I wasn't sure I was going to be able to make it the 50 miles back to my garage. And yeah, when I saw that IFR table in this tune, an alarm went off. I did know enough about it to think it didn't look as it should. When I was rebuilding my fuel system (you wouldn't believe what the guy who installed it had done) I looked into the issue of using a mapped FPR versus an unmapped one, and about half of the people (pretty much par for the course with anything I have ever asked about concerning my car) said mapped was the way to go. Logically it seemed to make sense to me, so that is the route I decided to take. Certainly doesn't mean I was correct in my decision, though. :)

Actually my car drives pretty well (aside from an intermittent and nagging drive train squeal on clutch engagement), but the issue upppermost in my mind at the moment is if things are worse that I think (or hope) with the fuel delivery.

I started wrenching on my own car because I stopped trusting nearly everyone else to touch it. I'm hoping this IFR thing is just a minor mistake by the tuner, but I am not willing to blindly trust someone when my engine could be in jeopardy. So if I have to learn this tuning stuff now, then that is just what I have to do.

I am a raw newbie with this. Read some books (actually, Greg, some of yours) but my retention is not what it used to be when I was younger. Lately I have been looking over the tables in the tune the tuner did for me and reading some threads here, as well as the tutorials. Quite honestly, everyone seems to know what most of the acronyms stand for but me. So it's tough going at the bottom of this learning curve I am at.

Can I get some help here? The top priority, in my opinion, is to make sure the tune in my car right now is SAFE. If the IFR table AND the mapped fuel pressure regulator are both controlling fuel pressure to the fuel rails, well that does make me somewhat nervous. Can I start a new thread in the proper forum here, post my tune, and have someone look at it and give me advice? I did a log of a drive I took back on 12/07, but I just let the log capture the entire time. Therefore it is quite a large file. But I can attach it here if it will help and there are no limits on the file size. I think it's 800K or so, if I remember correctly. I can see that running at 10 mph (I live on a dirt road) the engine RPM and spark advance is jumping all over the place. But things leveled out once I got up to a normal speed. It's a 2 bar map speed density tune, I believe.

What I would like to do is to first make certain my engine is in no danger, and then afterwards get some handholding, when needed, to learn this stuff. Heck, I've got to figure out how to hook up the wideband REAL SOON, I guess. I am in NO hurry with this, and want to take the time to learn this. Heck, my car has been tied up for three years now, so what's several more months? I just want it to be RIGHT when the smoke clears.

Thank you.

[eficalibrator]

You may not like this answer, but the proper solution is to re-enter the injector characterization correctly and start over on the MAF and VE tables. The injector flow AND offset AND short pulse adjust all need to be correct before touching the MAF/VE to avoid baking in weird errors and driveability quirks. Ideally, this would get calibrated on a load bearing dyno in steady state before heading to road tuning. Trust me when I say that 2hrs on dyno can get more work done than 2 weeks on the road in most cases. You just need to follow a valid calibration method and things almost fall into place. Done correctly, there's really no need for a custom operating system.

[Gordy M]

What year is your Corvette, if I recall 97-98 were the return style and the 99+ Corvettes were returnless. If it is a 99+ then the builder would have had to install a return line to the gas tanks for you to be MAP referenced and this was often done when a turbocharger was added.

[Rich Z]

You may not like this answer, but the proper solution is to re-enter the injector characterization correctly and start over on the MAF and VE tables. The injector flow AND offset AND short pulse adjust all need to be correct before touching the MAF/VE to avoid baking in weird errors and driveability quirks. Ideally, this would get calibrated on a load bearing dyno in steady state before heading to road tuning. Trust me when I say that 2hrs on dyno can get more work done than 2 weeks on the road in most cases. You just need to follow a valid calibration method and things almost fall into place. Done correctly, there's really no need for a custom operating system.

Oh, I've gotten a lot of answers I haven't liked over the past couple of years, so this is nothing new to me.

The tuner sent me an email this morning, so I'm going to work with him. I don't have a dyno available anywhere near me that I am aware of (at least none that are owned by shops that I would trust taking my car to), and I've got the time to spend here doing this on the road. Luckily I'm in the boonies, so long stretches of road with no traffic are not hard to come by.

I could always run the car up to the tuner, if I wanted to do a 6 hour drive to get there, I suppose. He seems like a good guy and if he is willing to stand behind his work and give me the opportunity to learn this stuff somewhat myself doing this remotely with my being the hands and eyes, then that is OK with me. He's probably too busy to be an actual mentor to me, but I'll take what I can get at this point. And heck, I spent a good chunk of change for this tune, and quite honestly I can't just throw that away.

Guess I'd better get cracking to hook up that wideband.

Thank you.

[joecar]

Looking at your hardware and the screen shot of the injector setup, I'd say your highly respected tuner missed a few things.

1) You should never have a straight diagonal line for IFR. If the regulator is not manifold referenced (yours IS), then this table should have a slight bend in it as it follows Bernoulli's law for change in flow versus pressure. It should be a square root function, so NOT a straight line. Straight lines mean he took a shortcut that does NOT always work out nice when trying to fix AFR issues.
2) Manifold referenced regulators (like yours) need a HORIZONTAL straight line.
3) With any change in injectors there are also changes to a few other tables (short pulse adjust, offset vs voltage) that MUST be changed or you will have more problems like I said in #1 above.+1.




You may not like this answer, but the proper solution is to re-enter the injector characterization correctly and start over on the MAF and VE tables. The injector flow AND offset AND short pulse adjust all need to be correct before touching the MAF/VE to avoid baking in weird errors and driveability quirks. Ideally, this would get calibrated on a load bearing dyno in steady state before heading to road tuning. Trust me when I say that 2hrs on dyno can get more work done than 2 weeks on the road in most cases. You just need to follow a valid calibration method and things almost fall into place. Done correctly, there's really no need for a custom operating system.+1.

[Rich Z]

What year is your Corvette, if I recall 97-98 were the return style and the 99+ Corvettes were returnless. If it is a 99+ then the builder would have had to install a return line to the gas tanks for you to be MAP referenced and this was often done when a turbocharger was added.

It's a 2002 Z06. Oh you wouldn't believe what the "builder" did to the fuel system. When I got it back home, I discovered that there was no fuel filter in the system at all. Not sure what sort of fuel line fittings he used, but they were disintegrating and sending metal particles into the fuel. Completely trashed the fuel injectors, of course. The external Aeromotive fuel pump was not only installed completely wrong, but it was positioned right above the wastegate for the turbos. And my passenger side fuel tank wasn't even hooked up. I had to completely redo ALL of that. Heck, rather than going into all of the details about what these guys did to my car and drive this way off topic, here's a complete blow by blow description -> http://www.corvetteflorida.com/forums/showthread.php?t=44697. Any of you that frequent CorvetteForum might have seen a similar thread over there as well. But when the mods closed it down because I called Pfadt to the carpet for sending my builder a carbon fiber drive shaft that was TOO LONG, well, I didn't need to continue the discussion any longer over there anyway.

But back on track, yes, the fuel system is pretty much all custom. Dual pumps from Lonnie's Performance. F.A.S.T. fuel rails, etc. I'm not a Corvette tech by any stretch, but after having two shops nearly destroy my car, I brought it back home and figured it was up to me to save it. So yeah, I'm learning a LOT. All things considered, I believe I need to learn this tuning stuff now. I'm just hoping that some of you guys here will lend me an ear and provide advice so I don't do something stupid based on ignorance of the dangerous waters I might want to jump into.

[joecar]

What year is your Corvette, if I recall 97-98 were the return style and the 99+ Corvettes were returnless.
...Hi Gordy,

Yes, the stock 1997/1998 has a FPR with a return line at the fuel rail, but the reference hose is open (i.e. not connected to intake manifold)...

:) don't assume the reference hose is connected to MAP... take a closer look when you get a chance (it surprised me too).

[Gordy M]

Your correct, it is baro referenced, always thought they manifold referenced.