Fuel pressure?

[exgmguy]

I made fuel pressure changes between dyno runs.

[poopstang]

Anybody heard of C&L's new 76mm?any good?I'm thinking about getting one?need $

I'm starting to think my low end miss is my EGR valve?

[jimberg]

poopstang, I won't dispute what you're at, so if you think you're at your fuel limits, maybe an adjustable FPR will help. Your initial message, though, doesn't really fit with a fuel starvation issue. You'd be hitting your limits at high rpm, not low rpm.

Have you replaced your O2 sensors recently? If they're not working properly the computer could be incorrectly adjusting your air/fuel ratio.

exgmguy, since you changed your fuel pressure between runs, it's a good bet that your computer has adapted by now. What more likely has happened is that the computer was adapting from run to run to get the most power.

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351W 89 Mustang GT Convertible

[poopstang]

I check the O2 heater's(turned on the key, felt them with my hands)they were warm, so i guess they work.

I can't seem to get any codes out of my car?
I think the wire harness is f@#ked, the diagnostic lights in dash don't even work?

Any advise on the EGR or the C&L 76mmMAF
I'm go'n to take the vacuum line and harness off and see if it runs better at low rpm?

Maybe i just need a gear?

[jimberg]

Taking the vacuum line off the EGR would be good to determine if there is a bad EGR vacuum control solenoid. If it doesn't make a difference, though, the EGR may still be stuck open. The only way to really test that is to remove it all together and bolt on a plate.

Crane recommended 3.55 gears for my E303. I'm sure you are probably in the same boat.

Do you have a specific code reader or are you using jumpers? If one doesn't work, try the other.

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351W 89 Mustang GT Convertible

[poopstang]

i used a snap-on code reader and multimeter with jumpers, nothing works?

Any advise on a MAF?

oh well my car is a pos!but she's fast so i'll keep her for now.

[red82gt]

Originally posted by jimberg:
exgmguy, since you changed your fuel pressure between runs, it's a good bet that your computer has adapted by now. What more likely has happened is that the computer was adapting from run to run to get the most power.

Under this logic then shouldn't his car have made peak power with the original fuel pressure if he had driven it at all on the way to the dyno?

[withamc]

jimberg - based on the number of posts you've made, you've obviously been around a while, and your posts are intelligently written so you've obviously got some experience. It's just that your position on fuel pressure contradicts my own experience and the opinion of a significant percentage of this and many other message board members, as well as magazine articles and dyno shops. I know that my car put more HP to the ground dropping the fuel pressure to 33 PSI and it felt faster, and it still feels faster than when I had it tuned.
So I'll respectfully disagree with you for now. If I should get my hands on some information that convinces me otherwise (BTW I've got the book, I'll read that page first chance I get), I'll be the first to admit you were right. Until then...

Chris

[jimberg]

Red82GT, no, since the computer has learned to drive on the street. Once you start doing WOT runs the computer will relearn to make peak power. It's kind of cool and kind of a pain. We'd all like to be able to lock in our best performance settings and tune it between runs. That's just not how it works.

withamc, as far as the page goes, it covers adaptive strategy. Mach 1 and I disagree as to whether or not adaptive strategy applies to open loop operation. We both agree that it does in closed loop. I'll try to point you at specific passages.

Example: suppose the oxygen sensor keeps sending rich mixture (go-to-lean) signals as short-term correction under certain rpm/load signals. The control module notes these repeated short-term corrections, and shifts the base calibration for that rpm/load combination toward lean.

I added emphasis to "base calibration" because these are the numbers that are used in the formulas to determine how long to open the injectors. These same base calibrations are used in the open loop mode, too. I think we can all agree that you're running in open loop mode when you're doing the 1/4. If adaptive strategy doesn't apply why would the author say this in a sidebar?

Drivers who drive their adaptive-system cars to the drag strip are often puzzled about their high Elapsed Times. The system adapts to street driving. When they run the strip a few times, the control module re-adapts to the strip and their E.T.s improve.

Sorry for repeating that one.

This statement supports my response to Red82GT. It also clearly states that adaptive strategy even works during open loop mode. The computer doesn't simply revert to a bunch of hard coded tables at WOT. It uses different lookup tables, but they're still adapted to the base calibrations that are changed during closed loop and even open loop mode.

There are other things that will change with fuel pressure that I really haven't mentioned in the past, but it's already difficult trying to get people to believe the stuff we've been discussing above. Let's say you have 30# injectors and are having trouble passing emissions (especially HC and CO). You should lower your fuel pressure down to a point that they perform like 24#ers (about 31psi). The reason you would do this is that the injectors have physical limits as to how fast they open and close. The bigger the injector, or higher the fuel pressure, the less control the computer will have at idle. When the computer attempts to open and close the injector at a faster rate than the injector can handle, it will simply meter more fuel than the computer wants, and, therefore, run rich at idle. Too low a pressure may actually affect the spray pattern.

Like I've already said, I have my fuel pressure at 47psi because I am making more HP than the 24# injectors can support. I had definite fuel starvation problems at 39psi. Even at 45psi it seemed to lean out a little too much. 47 seems just right. The thing that hasn't really changed is my gas mileage. If I were to accept what you guys are saying, why wouldn't my gas mileage be significantly worse? Do you get better mileage at 33psi vs 39psi?

Dyno shops probably don't tell people that tweaks of computer controlled cars are worthless because they want your business. Also, some of the older computers may not use adaptive strategies, or at least ones that are as strict.

Didn't magazines start all the BS about adjusting the TPS to .999 volts? Our experiences, however, are different, aren't they (.94 to .98 is sufficient)? I suppose some will still swear by TPS adjustment still, but it's clear to me that if they can be wrong on the TPS they can be wrong on other things, too.

I don't know if you guys can tell, but I really love these types of discussions. The most important thing that any of us can do that will help us make our cars go faster is by knowing how they work and what we can change to improve them. It will also save us from spending money on gimmicks.

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351W 89 Mustang GT Convertible

[Mach 1]

Jimberg -While your logic is sound, and I read the book that you are referencing, the results seem to be different in real life.

How many people have drove to the strip, ran a few times, and thier e.t.'s improved, without touching the fuel pressure setting? Not many I would guess.

Although the book states the theory, perhaps it just doesnt work as well as it is supossed too in actual conditions?

Why is your computer not adapting? Are u saying your pressure is so high, that it runs good there, because your computer can not open your injectors any slower to compensate, or else it would?

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1993 GT/AOD
'93 Mustang GT

[QUIN]

well, i personally see better times the more i run,,,,, (but that is probably more from lack of experience than anything!!!!) LOL

Q

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Quin, 87 GT,306,forged/cut pistons,edelbrock head\intake,steeda#18cam,1.7rr,MSD Blaster tfi coil,A9L,pro-m75mm,24#inj,accufab65mm,2.5"pipes,hooker headers,dynomax exhaust,3.73 gr,110 lph fp,moroso cold air,ASP pullies, weld rims

See my engine on user rides.

I see your shwartz is as big as mine, now lets see how well you handle it!

[jimberg]

I have my fuel pressure set high since the computer can't open the fuel injectors long enough to provide the amount of fuel I need at WOT. Injectors must open and close so they cannot possibly run at 100% duty cycle. If they only can run at 90% duty cycle, and I think that number may be lower, that means that 24# injectors can only realisticly supply 21.6# of fuel in an hour at 39psi. That's enough for about 346hp( Assuming .5 #/hr/hp). By increasing pressure, more fuel can be delivered per injector pulse. At 47psi the injectors essentially become 29# injectors able to support about 417 hp at a 90% duty cycle.

As a side note, people have to make sure that their fuel pump goes with their injectors. A liter of fuel weighs about 1.5625#s. Multiply your pump capacity times that number and then divide by 8 to figure out what size injectors it'll support.

As for improving after each fuel pressure tweak on the dyno or at the track, there's still the fact that the computer hasn't adapted yet. It may be that the O2 sensors are reporting a leaner condition that really exists and moving fuel pressure down compensates fot that for a while. Then the computer adapts again and you're back to running rich. I know this from experience. When I bumped up my pressure it ran a lot harder throughout the powerband. That power is gone now since it has adapted.



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351W 89 Mustang GT Convertible

[Mach 1]

ok, after a little more thought, I think you are right and wrong at the same time. You say that you need an adjustable regulator because your injector size can not support your fuel needs at the factory 39 psi. This is correct and makes perfect sense. Crank the pressure, and you will get your increased fuel.

But why wont this also be beneficial to people with minor or moderate mods? I guess it comes down to defineing moderate and minor mods, horsepower numbers, etc...,

but, if for example, a car needs 26 lph to run ats its best power, and they have 24 lph injectors at 39 psi, it wont perform its best.
So, they slap on a adjustable regulator, crank it up a couple psi (the exact desired psi number is based on formulas, specific fuel comsumption, blah, blah, blah, etc...) to experiment, and the car performs better. Now, everythings cool, the car needs slightly more fuel for its particular combination, and now it has it, why would the computer even attempt to change anything? The car runs good, and maybe it is at the desired air/fuel ratio determined by the computer, so it has no need to revert back or change anything. Possibly the desired air/fuel ratio wasnt available with the factory computer programming, injector size and fuel pressure, but now it is. So, in essence, you are just "helping" the computer, not "tricking it" or "changing it", and it likes it, why would it try to change anything?



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1993 GT/AOD
'93 Mustang GT

[jimberg]

I think we're almost on the same page. If you increase pressure, you increase the amount of fuel that the computer expects to deliver with a certain length pulse. The computer will see this as a rich condition and reduce the length of the pulse until it gets the air/fuel ratio it is programmed to keep. You still have the extra fuel you need at maximum load but the computer has adapted to the extra fuel that it doesn't need at lower load conditions.

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351W 89 Mustang GT Convertible

[Dark_5.0]

Ok "JIMBERG" the only time I ever drive my car is at the strip. So does that mean that my cars computer is adjustd for WOT or what or is it different on a speed density system.

I have been afraid to do any mods to my car other than bolt ons cause I hear if you modify a speed density system it will run like sh!t. Someone on this board told me that I can just bump up my fuel pressure to compensate for mods is this correct in your opinion.

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88 mustang gt convertible bored to 306 BBk equal length headers mac cold air fender kit cowl hood nitto drag radials ford racing clutch flow masters h-pipe 160* thermostat 16 degrees of timing electric fan off 94' t-bird jacobs electronics cap and wires.
best 60 ft 2.14, best 1/8th 9.65, best 1/4 15.2 @89mph

[jimberg]

I only have a mass air system and haven't done any research related to speed density systems. I've read stuff like you have that pretty much say that they are less adaptive to major modifications. If that's the case, maybe it's true about bumping up the fuel pressure. I can't really give you answer any more than that. Sorry.

Upgrading to mass air would probably be a good idea, though.

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351W 89 Mustang GT Convertible

[QUIN]

sorry, i just found this funny,,,
by JIMBERG "a liter of fuel weighs 'about' 1.5625 #'s"
"ABOUT"???? I dont think you can get much more precise than tens of thousandths!!!!!
lol
Q

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Quin, 87 GT,306,forged/cut pistons,edelbrock head\intake,steeda#18cam,1.7rr,MSD Blaster tfi coil,A9L,pro-m75mm,24#inj,accufab65mm,2.5"pipes,hooker headers,dynomax exhaust,3.73 gr,110 lph fp,moroso cold air,ASP pullies, weld rims

See my engine on user rides.

I see your shwartz is as big as mine, now lets see how well you handle it!

[Dark_5.0]

Thanks for trying does anyone know how much $money$ the conversion from speed density to mass air will run me?

How much time can you knock off with a larger mas air sensor.?



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88 mustang gt convertible bored to 306 BBk equal length headers mac cold air fender kit cowl hood nitto drag radials ford racing clutch flow masters h-pipe 160* thermostat 16 degrees of timing electric fan off 94' t-bird jacobs electronics cap and wires.
best 60 ft 2.14, best 1/8th 9.65, best 1/4 15.2 @89mph

[QUIN]

my costs for converting to mass air.
A9L~ 100$
Pro-m 75mm 150$ (used but basically new)
wiring harness~ 30$
24# injectors~ 225$ (optional)
saudering kit~ 10$ (if you dont have one)
thats all i can think of.
cant tell you and specific #ers on performance gain from mass air meters. speed density is quicker for stock applications though, (you probably already know that)
i think its more about matching your combo than specific meters and their dyno #ers.
everyone seems to really like the pro-m77mm though. i might switch some day in the future to that one. good bit more expensive though.
Q

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Quin, 87 GT,306,forged/cut pistons,edelbrock head\intake,steeda#18cam,1.7rr,MSD Blaster tfi coil,A9L,pro-m75mm,24#inj,accufab65mm,2.5"pipes,hooker headers,dynomax exhaust,3.73 gr,110 lph fp,moroso cold air,ASP pullies, weld rims

See my engine on user rides.

I see your shwartz is as big as mine, now lets see how well you handle it!

One thing that I haven't seen anyone mention, and I'm a little surpirsed, is that the lack of his low end torque and popping sound, might be caused by his Crane ignition not being setup properly. A very similar thing happened to me when my MSD box was installed. I would suggest checking your wiring for correct set up - your problem might be as simple as that!

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'90 LX 5.0; 12K original miles (no sh*&); 3.55 gears; pulleys;Edelbrock Performer Heads; BBK shorties; MSD 6AL box w/ blaster 2 coil; Motorsport E303 cam; Pro-M 75mm MAF; BBK 70mm TB; Eibach spring kit; Southside welded subs; K&N cone filter charger; Hurst shifter; fiberglass turbo hood; A/C-less; rear seat-less; cat-less; 2 chamber Flos; Corbeau racing seats (fronts);
30# injectors; JMS Chip; 190 lb fp; TFS track heat Intake (12.299 @ 113)