erummel

iTrader: (2)

I was curious about the relation of fuel pressure to pulse width of the fuel injector. I have heard (depending on who you talk to) that increasing the fuel pressure causes either a lean condition or a rich condition (more so than the way GM designed the fuel system) based on the existing pulse width of the injector.
I would think that for a given setup, an increase in pressure would not cause a rich condition based on the fact that the pulse width has not changed. I could see a lean condition as WOT but not a rich.
Does this seem right.

Grim Reaper

Increasing fuel pressure increase the amount of fuel flow in a given period of time, similar to adding a larger injector.

erummel

iTrader: (2)

True, but how does that relate to the pulse width of the injector?

Grim Reaper

Simple, unless you modify the eprom the injector will use the SAME pulse width as it did prior to the increased fuel pressure. Thus it will flow more fuel in the same amount of time...exactly like what happens if you put a larger fuel injector in...more fuel in a given length of time.

If you do this to an engine that was already getting the proper amount fuel, you would have to shorten the injector pulse width if you either 1) increased the fuel pressure or 2) installed larger injectors.

Injectors are rated in #s/hr @ a given fuel pressure. Pulse width is the length of time in mSecs per revolution of the engine. Unless you modify the eprom, there is no way the ecm when it is in WOT mode or Open loop mode will know that it has to shorten the pulse width to compensate for 1) increased fuel pressure or 2) larger fuel injectors.

In closed loop, the O2 sensor MAY compensate by shortening the pusle width to maintain 14.6. I say MAY, but there are limits how far it can compensate even in closed loop. You could get a Code 45 (O2 rich) error code if the amount of fuel is excessive for even the ecm to compensate in closed loop.

Starting to make sense?

Kyle F

We just had this discussion on Adjustable Fuel pressure regulators on the V6 board. You might want to check it out. It may answer you question a little further. The basic idea of increasing pressure is to add more fuel to an engine that needs it, or reprogram your prom to shorten the pulse width so you get the same amount of fuel, but a larger and finer spray so the fuel mixes better with the air. This does tow things. Makes a quicker burn, and cools the air because of the heat absorbed by the gas to change phase from a liquid to a gas.
Hope this helps

------------------
86 Trans Am 355 TPI Rebuilt 700R4 with Corvette servo, modified valve body, and a B&M Torque Converter (2000 rpm stall w/ lock up), 87 350 block bored .30 with new crank, bearings, rings, and magnafluxed rods. Reworked 305 heads with 3-angle valve job. Added in the rebuild was an SLP TPI cam, BBK 58mm Throttle Body,SVO 24# injectors,MSD 6A, Hypertech Power Coil, 1.5 Crane roller tipped rocker arms, SLP Intake Runners and Port matching in upper intake including fully ported plenum, TPIS adjustable fuel pressure regulator @ 46psi, Hooker shorty style headers w/ Thermotech heat wrapping, Custom 3” exhaust with Flowmaster muffler and chrome quad tips, Hypertech Thermomaster Computer chip, K&N open element cone filter on modified MAF per TPIS specs, MSD Wires, removal of A/C hardware and a 1LE firewall cover installed. Also there has been a PST front suspension kit with Hotchkis strut tower brace
http://geocities.com/SunsetStrip/Garage/9548/kyle.html

Kills:
95 Talon TSI, 96 Probe GT, 91 T/A L98, 89 RS, 86 Mustang GT, 88 Mustang LX 5.0, 92 Thunderbird V8. couple or ricers that I think were Civics or Preludes not sure what year, 95 Celica GT-S, 94 Chevy 1/4 ton 350, one of those NASCAR F150's ..... **** on Monkie
SOON TO BE A SUPER CHARGED TURBO WITH NOS ON A 500000 CU. IN engine

vettenuts

Not sure why you would want to re-program. The ECM should try to maintain the stochiametric optimum that is programmed into the PROM which is 14.7:1 air to fuel ratio when in closed loop. When you go open loop (WOT), then on the TPI if the pressure is higher you can control the amount of fuel to some degree. On the LT-1, especially the later years, the PCM will compensate and the additional pressure won't buy you anything.

------------------
1990 Roadster

Grim Reaper

Vette, when you increase the fuel pressure, in closed loop your BLM/INT counts will drop (to indicate the ecm is leaning the injecor pulse). Unless you have altered the max/min BLM in the eprom, you can only go down to a BLM value of 108 and an INT value of 80. If the ecm cannot go lower than that and it needs to to attain 14.6, you will get a code 45. Been there...done it.

As for WOT, how do you propose to shorten the pulse width after you increased the fuel pressure (and fuel flow)? You either have to get more air into the engine (good reason for more mods), reduce fuel pressure (kills the idea of increasing fuel pressure) or shorten the pulse width (eprom is the most effective).

This is all assuming that your engine DID NOT need addtional fuel in the first place due to mods. For a stock or basically stock (no heads or cams) engine, a lot of people bump up their fuel pressure to 50 psi from the stock 37-42 (depending on the year on your FPR). Increasing from 42 to 50 psi, this represents a 10% increase in fuel. From 37 to 50 psi, this is a 16% increase.

People keep forgetting that "lean is mean" and "rich is a bitch". You want to be a lean as possible without detonating. For safety, people generally run 13:1 at WOT. A 10% increase in fuel would drop that to 11.7:1 which is going to make your slower...not faster.

A 10% increase would be great IF you were stuck at 14.6 @ WOT. That would drop you to just above 13:1. But trust me, if you were at 14.6:1 you would know it, you would have a lot of knocking going on @ WOT.

Grim Reaper

PS: The formula for calculating the change to fuel flow is: (FPnew/FPold)^(1/2). That's the square root of (New Fuel Pressure/Old Fuel Pressure).

It really does have a dramatic effect on the total fuel flow.

RP1987GTA

raising the fuel pressure over stock(assuming it was in spec to begin with)will with stock injectors lean things out.I found that the stock injectors flow more in time @39psi...than @49psi

------------------
87GTA,350,Auto,MAF screens removed,195 thermostat,cold start injector UNPLUGED,K&N,modified air intake,ADSchip,3:70s,3inch cat back Flowmaster single outlet,TPS.54,Bosch Plat plugs,base timing 6BTDC,22 MPG,what a ROACH,Bilstiens in the rear....,don't let yer meat loaf

Grim Reaper

If everything is proper working order, that is wrong RP. It defies the laws of physics. Increasing fuel pressure increase flow as per the formula : (FPnew/FPold)^(.5)

I suspect you had problems with either your injectors, regulator or fuel pump. But on a properly working fuel system, increased fuel pressure WILL increase fuel flow.

At 49psi, you are getting a bit high for the stock system as a whole; it will shorten the life of your fuel pump at least.

[This message has been edited by Glenn91L98GTA (edited January 11, 2001).]

vettenuts

Understand, but is this something you would want to do? As the pulse width is reduced in an effort to maintain 14.7, the ECM starts losing control dues to injector rise time, etc. Seems to me that if you need to reprogram the lower boundary of your BLM, then you are just too rich to start with. Am I missing something?



------------------
1990 Roadster

RP1987GTA

there is alot more going on than what you realize ......raising fuel pressure changes how fast the injectors respond.

erummel

iTrader: (2)

Glenn, yes that is starting to make sense.
So basically an increase in fuel pressure is not needed for an engine with stock heads and cam unless you find that your fuel pressure low to begin with. Correct?

erummel

iTrader: (2)

Guys, I just finished reading the post on the V6 board. I would have to say that that is one of the better posts I have seen. It certainly explains a great deal about the fuel pressure and pulse width relation ship and the need to really do a prom upgrade if you raise the fuel pressure more than a couple of psi if you want to keep from losing power. Thanks

Eric

Grim Reaper

Isn't great when people can keep their emotions out of the posts and keep it strictly to facts?

Once the fact about the relationship between fuel pressure/pulse width became apparent to me, it completely altered my method of tuning. Instead of "try various fuel pressures until you find an optimum time"...I am now selecting a fuel pressure I want to run at (46-48 with 48 my preferred pressure...high for good atomization but not so high as to dramatically shorten my fuel pumps, injectors or regulator's life). From that, I adjust the pulse width to attain the optimum performance.

The tuning technique is pretty simple (having a fast baud rate ecm, lots of information and a scan tool really helps). Once I set my fuel pressure, I then adjust the injector constant to attain the best idle possible. From there, I set my BLM to 128 to force all ecm adjustments to the INT. I then drive around recording all this information on my Diacom. When I return, I take all the gdf files from Diacom, and translate them into DBF files which I import into Excel.

I then load ALL those DBF files into Excel and sort on RPM/MAP/INT values. Then I just scroll down the file calculating the average INT value for a given RPM/MAP reading (just like the VE tables are). I then have a set of Excel Spreadsheets that I have the same VE values as my eprom which I apply a factor based on my INT values to derive new values for my VE tables. This then makes all my part throttle readings as close as possible to 128/128 (you'll seldom get exactly perfect 128, but I am damn close on almost all RPM/MAP values).

Lastly, I work on my WOT values (because you are effectively in open loop mode or WOT mode and can't really use a scan tool there) which I rely on my times (and other factors like my spark plugs and knock retard etc). The WOT is the part that requires the greatest time, but the rewards are well worth it.

As a side note, if your ecm is off on its tables, it is the open loop mode that causes problems. The ecm uses open loop a lot more than most people think (warm up, idling, coasting downhill, WOT, etc). If your tables aren't right, you just waste gas or run the risk of running lean. And if you want to invoke "Highway mode", you MUST have those tables right, or it won't perform as you are hoping...lean out the engine on highway cruising to save gas.

As I said before, the actual mechanics of eprom buring is really easy...eprom writers are ripping off the public, it is so easy. BUT, to tune it right, that just takes time and patience...that's where the eprom writers are earning their keep. But that is where a "canned eprom" falls down. How can the eprom writer account for the fuel pressure you are running (especially if you don't know or adjusted it) and the general condition of your engine, fuel pump or injectors. They do a good job of getting you close thanks to the great job the GM programming works over a very broad range of operating conditions. But if you tune your engine "tighter" for a specific elevation, temperature, etc...you are rewarded with more "free" hp than the other guy.

vettenuts

I understand your approach. How are you tuning WOT? I wouldn't be confident in time slips providing enough data or did I mis-read what you are doing. Also, where did you get the equipment for burning the PROM and reading the PROM? Cost?

------------------
1990 Roadster

erummel

iTrader: (2)

Glenn, is there any books that you can recommend that deal with burning proms for fuel injection. I have the equipment to burn the proms (perk of my job), but I would like to have a reference for the finer points of the fuel mapping process.

erummel

iTrader: (2)

Glenn, is there any books that you can recommend that deal with burning proms for fuel injection. I have the equipment to burn the proms (perk of my job), but I would like to have a reference for the finer points of the fuel mapping process.

Guest

In reference to the injector flow ratings..

If you take an injector rated for, say, 15psi max, then set the fuel pressure at 45psi, the injector will lock and not flow at all. But, if you have an injector rated for 55psi and change the fuel pressure from 45-50psi, then the amount of fuel flowing from the injector increases based upon the formula Glenn gave. Each injector has its limit that it can handle, and sometimes that varies based upon production tolerances and what kind of shape the injector itself is in, like if its clogged or something like that.

I dont know of any book for programming proms for fuel injection, its probably something banned by the US government. There is alot of GOOD information on the net however, especially on the gm ecm and related sites. Check out TRAX's article, and go from there is what I would suggest. Print it all out and bind it if you really want something in a book form

Grim Reaper

Here's the link to Traxion's article... www.thirdgen.org/newdesign/tech/promintro.shtml

Check out a post on the PROM Board of where to start. I started with Traxion's article and went to every link that it had..and every link within those links.

And then I started by setting the "TOPIC display" to 1 year and started to read every post from the oldest to the most recent on the PROM board. Many are the same question asked over and over.. so you pass on those.

But I had virtually every question answered that I had by those posts (after reading Traxion's article). Hope to see you guy's on the PROM Board.

As for WOT tuning...that's the tough part. But it is no different than just tuning for higher fuel pressure. Without having my own personal dyno, "time" is really the best you can do...besides, isn't that the "ultimate" goal of everyone? I could care less what HP I have at a certain rpm and compared to the other guy...I just want to beat the guy.

I am definitely a hell of a lot "crisper" than my stock eprom and my ADS eprom. But I still have more "playing" to do...only have the weekend to play with it and balance that between family and obligations.

I do use my scan tool while tuning for WOT...to ensure I am not encountering knocks and that my O2 reading is not totally out to lunch...but the stock O2 that are on our cars are not "fine enough" to accurately tune by them. You would need a Wide Band O2 sensor that has much greater resolution. So I rely on performance increases, scan data, plug readings etc. I will probably schedule a dyno session to assist in some tuning.

GTech is useful for quantifying the WOT improvements. It is fairly accurate for the et, but within your own vehicle it is quiet consistent...and that's what you need to quantify.

All I need to do is win the "big one", so I can buy my own personal dyno and race track...and then I will be set.

[This message has been edited by Glenn91L98GTA (edited January 12, 2001).]

Grim Reaper

Well, if you think that fuel pressure and adjusting the injector pulse width is confusing; I have another wrinkle to add.

After getting a near perfect VE table for my engine, I decided to test the effects of higher fuel pressure through out the load (MAP/vacuum) range and RPM range.

I am still analyzing the RPM range, but I can tell you that the effect on the load range is not linear or constant. It is exponential.

I added 5 psi of fuel pressure, and set my BLM min/max to 128 so I could see the direct effects by the INT reading. My VE tables were nearly 128 perfect on the INT values before I raised the fuel pressure.

When I have adjusted the Injector Flow Constant, this always resulted in a near idential drop or increase to the INT values through out the RPM and LOAD range. Which is what you'd expect.

But when you increase the fuel pressure, the drop in the INT values at low load (low MAP/high vacuum), the drop is minimal for the amount of fuel pressure change I have made. However, as the load increased (higher MAP/lower vacuum), the drop in the INT constantly increases with ever increasing load.

The reason for this is easily explained when you realize that the fuel pressure regulator is also controlled by vacuum. At low load, you have high vacuum, so the fuel pressure is lower. Thus increasing the fuel pressure at 5 psi is done by measuring with the vacuum line off. With the vacuum line on, the increase in fuel pressure is substantially less than 5 psi. Thus it has a minimal effect on the amount of fuel it increases to the injectors at low load.

Conversely, at high load (low vacuum) you are getting the full effect of the 5 psi difference and this results in a far greater amount of fuel going to the injectors. To effectively compensate, you cannot just simply correct it by altering the Injector Flow Constant. You must reduce the values in the VE tables with the greatest reduction occurring at the high load/MAP part of the table.

Effectively, you end up with a much flatter VE table as you increase the fuel pressure.

SMasterson

In searching for WOT tuning, which is where I'm at with my 730 PROM tuning and Stealth Ram 383, I found this!

Thanks guys!