Fuel pressure?

[poopstang]

I have a 90 GT with a b303, 70mmTB, 1.7's, pullies, cranefireball

I was wondering if an adjustable regulator
would make my car run better? I always seem to have a miss at low rpm and sometimes it seems like i get a pop sound(lean?)out of the exhaust? With the mods i have i'm flowing alot more air than stock, so i think i need more fuel?

Any advise?

[TheSloAod]

my car liked more fuel pressure
@ 42 lbs the car went 13.56
@ 44 lbs the car went 13.42
all with 19 lb injectors, you will just have to play with it one day at a track and see what your car likes

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My slo aod- 3.73s, pullies, flowmasters, h-pipe, bbk cold air, and 13.42 in the 1/4 @ 103 mph

[jimberg]

Unless you're pushing 300 hp, which you aren't with just a cam, TB and pullies, fuel starvation isn't your problem.

Fuel starvation wouldn't be an issue at low RPMs, either.

As far as running better with a different fuel pressure, it will only happen immediately after you bump it up or bump it down. After driving it for a while, the computer will recalculate its adjustment tables and compensate to go back to the computer controlled air/fuel ratios.

I'm assuming that you still have stock heads and a stock intake? A 70mm TB is way to big and the cam is a mismatch.

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351W 89 Mustang GT Convertible

[LX XLR8R]

jimberg..what is ur basis for that information??what u r basically saying is that no matter what pressure i set my car at the computer will learn this and go back to the stock settings???well i can say that is wrong at least on my cars and ones that ive worked on...my car with heads, intake, cams, exhaust 24#ers and 77mm mass air will not run at the stock FP no matter how many weeks i drive around at 38psi..my car will cut out up top and my plugs will be glazed...i have 24# injectors but i still need to bump up the FP to keep up with the incomming air..my car will run good at 42-45 psi depending on weather..now people running EGT gauges(serios tuners IE tropphy stock) and running 1340deg constant run after run..day after day, do they reset thier computer every day???and why make adj regualtors at all if the computer will reset it anyways??

i do agree that 70mm TB is too big also..i run one cuz A) i have at least 3.73's if not 4.10's in my rear at all times, and B) my cam although big makes increadible tourque and needs to breathe wll up top

does the pop come when ur getting on it or when you are decelerating??

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1987 black notch(ex 4 banger)
DSS 306 w/ main support...Elderbrock 6028 heads..gt-40 intake..24# injectors...70 mm tb..77 pro-m...accel 300+..mac full legnth..tremec w/ pro5oh...full MAC exhaust,off road h-pipe,long tubes, catback...ron davis radiator..subframes, control arms...CFDF II..o yea holley FPR sucks..dont buy one..
AIM=onesillynotch

[jimberg]

LX XLR8R, the way you are using your FPR is correct. I have mine set at 47 psi for the same reason. The only effect setting it has is increasing or decreasing the amount of fuel available at the top end. The computer cannot control fuel pressure. That's strictly mechanical.

I was responding more to TheSloAod's message so I didn't cover all of the nuances of adjustable FPRs and how the computer works. I guess I'll go over it again.

The computer has preprogrammed air/fuel settings that it sticks to. It uses the MAF and O2 sensors to keep it at those settings during closed loop operation (normal cruise). While it adjusts the amount of fuel delivered into the cylinders it keeps track of how long it's opening the injectors to keep the correct air/fuel ratio. This information is stored in adjustment tables and is used at WOT when the computer is just using MAF to figure out how much fuel to deliver. If you don't have fuel starvation problems, adjusting your FPR does nothing. That's why it's a waste to put it on a stock engine.

If you're leaning out on the top end like you were, that means you have reached the throughput limits of your injectors running at stock pressure. By increasing the pressure, you are increasing the throughput limits of the injectors and, therefore, making it possible for the computer to do its job by delivering more fuel at WOT.

Our computers are programmed to balance power with cleanliness. If cleanliness wasn't an issue, we would probably have a richer air/fuel mixture for more power. This is why TheSloAod saw positive results as he bumped up his fuel pressure at the track. The computer will see that fuel increase and start to adjust back down to the clean running air/fuel ratio. The next time he goes to the track it will be back to what it normally runs unless he resets the computer before his runs.

If he was having fuel starvation problems, that's a different matter as explained above.

I hope this is clearer now.

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351W 89 Mustang GT Convertible

[poopstang]

I motor will only suck(air) to it's capability.
It will suck the same amount of air with a 65mm TB as with a 70mm TB. A 70mm is less restrictive.

It's like flowing a gallon of water through a 1 inch pipe vs. flowing a gallon of water through a 4 inch pipe. Less resistence

You act like TB's are forced induction.

[jimberg]

It's not just as simple as opening up the breathing. If it were, why would runner length be such an issue? We would all have box intakes. By having too big of a throttle body, you are reducing your air velocity and, therefore, the momentum of the air moving into your plenum. With less momentum, you get less of a bounce in the runners, and less air being bounced into the cylinders. You do, by the way, get more into your cylinders than you would if you just let the cylinders suck air into them without an intake.

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351W 89 Mustang GT Convertible

[86GT]

jimberg is right about the throttle body. If you don't have enough velocity you'll kill bottom end torque. Same idea as putting huge heads and open exhaust on a stock engine. It'll pull up top, but what happens to that snappy, torque? Its not there anymore, at least not as it used to be. 65mm is plenty for stock applications.

[Mach 1]

70mm tb's dont show any improvement unless you are making over 400 hp N/A.

Jimberg- whats this about the computer using tables it has built at W.O.T? I thought open loop was all preprogrammed.

And I have heads, intake, cam, etc...and my car runs much better on the lean side, like 35 psi. Dont know why you all run better richer? Maybe running a cooler water temp. has my computer trying to run it rich? I usually dont get over 180 degrees.

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1993 GT/AOD
'93 Mustang GT

[poopstang]

oh well it seems to work fine on my ride and top end power is ten times better than stock.

you guys are right about the low end, it sure does slack in that department.

And back to the regulator why do so many people use it if it doesn't do anything(ecu corrects for extra pressure)?

[jimberg]

Mach 1, Open loop just means that it isn't making adjustments based on feedback from O2 and other sensors. If you reset your computer and never run in closed loop mode, yes, it will run with preprogrammed settings. While it's in closed loop operation, however, the computer is determining the length of the injector pulses that go with the sensor signal feedback. It uses this information to build adjustment tables. These adjustment tables are then used at WOT to figure out how long to open the injectors to provide a fairly rich air/fuel ratio.

If your engine never gets warm enough, it will stay in open loop mode. That's why you should never get a thermostat below 180. Maybe that's why you see a difference with your pressure turned down. I find that hard to believe, though, since the leaner you run, the hotter the engine. Do you have a really good cooling setup? Aluminum radiator, water pump, etc.?

As far as running richer for better performance, the SVO extender will go to a maximum air/fuel ratio of 14:1. That's still on the rich side. I read an article in one of my magazines that referred to that as a piston melting ratio. A some of the sample cars in that article were running best with 10:1 ratios which is very rich.

Poopstang, this is where the benefit of adjustable FPRs is gained. If the amount of fuel being delivered by the computer is too much at WOT, then you drop the pressure so that the computer cannot deliver what it wants. Or, if your injectors can't deliver the amount of fuel that your engine needs, you can increase their overall capacity by bumping up the fuel pressure. I don't believe that you are in either situation so saving the money to buy something else is more beneficial.

I hope you at least have a 77mm MAF sensor to go with that 70mm TB.



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351W 89 Mustang GT Convertible

[Mach 1]

Yeah., my cooling set up rocks. Fluidyne rad., high flow water pump, hi flow 180 stat, I needed it because I was having problems with running hot. I have an AOD car with high stall converter, A/C, live in hot climate,etc... I try to keep it between 180 and 195. In the winter, it wont go to 180 though, but close.

I know what open loop and closed loop means, you dont have to repeat yourself.

What I never heard of was that the WOT open loop tables were based on information built when the car was running in closed loop, and Im still not sure I believe it. Where did you get this information?


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1993 GT/AOD
'93 Mustang GT

[jimberg]

Page 108 section 5 of Ford Fuel Injection and Electronic Engine Control covers adaptive strategy.

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351W 89 Mustang GT Convertible

[red_90_gt]

I know a pretty good mechanic who told my friends dad that i can trick my stock 5.0 computer to reprogram for more performance. He said to disconnect the battery, then reconnect it and start the car and immediately rev to about 2000 rpm. Anyone heard of this? Would this be possible with the entire stock fuel system?

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90 Mustang GT. K&N air filter, completely stock. Purchased at 107,000 for $3500

[exgmguy]

Some of you guys are running 302's with 24 lb injectors @ 47 psi?

Have any of you been dyno tuned with a wide band? I have aftermarket heads/cam/intake/etc... and made the best safe power at 35 psi.

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1988 Mustang GT
12.0 @ 122
1992 BadAzz Wrangler
1993 Explorer

[jimberg]

I have a 351W that I'm using 24# injectors at 47psi.

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351W 89 Mustang GT Convertible

[Mach 1]

Jimberg - ill have to glance over the book when I have time, I have the book.

exgmguy - i agree with you, 35 psi rocks, and you proved it on a dyno.Of course , other combinations will be different, but a common mustang beginner mistake is to crank up the fuel pressure, thinking they are helping, but in reality, killing performance.

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1993 GT/AOD
'93 Mustang GT

[poopstang]

so an adjustable regulator is no good for what i'm currently running?

[jimberg]

An FPR is not a good purchase at this point. It will be when you start making more power than your injectors can support.

19# injectors at 39psi can support about 270 hp at 90% duty cycle. This is based on .5 #s of fuel per horsepower per hour. Some engined do better and some do worse. .5 # is a good average.

exgmguy, how did you go about tuning your fuel pressure on the dyno? Did you set your pressure, drive around for a few days and then go to the dyno, or did you set your pressure at the dyno between runs?

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351W 89 Mustang GT Convertible

[poopstang]

I think i'm at the 260-270 hp mark?