Will An In-Line Fuel Pump Help?

[wlingle92lx]

I recently got my car dyno tuned and don't like the very lean A/F ratio. Is was pretty lean N/A but I later found out they had the fuel pressure set at only 40psi. I bumped it up to 45psi just to be a little safer. When I sprayed a 150 shot on the dyno it had a very unsafe 15.2 A/F and ended up making 500 RWHP. I havent sprayed the car since because of fear of blowing it up.

I have no idea what part of the fuel system is maxed out but mabey you guys can tell me what is. I have stock rails, stock lines, 255lph (high pressure) pump, adjustable regulator and 30lb injectors.

If I were to install an in-line fuel pump would this help allow me to spray the car safley. If so, whats a good in-line pump to get? How much should it flow?

[1989GT]

When you posted up that you made 350 at the wheels a little while back your A/F was lean even in NA form, this leads me to believe that it's a tuning problem. What was used to tune the car? And is the nitrous kit a wet or dry kit?

[wlingle92lx]

It was a tuning problem. Because the car used to fall on its face at 5500+ Rpms because of fuel starvation. I them bumped the fuel pressure from 40psi up to 45psi and it stop doing it.

It is a nitrous express plate wet system.

[Jeff Chambers]

30# injectors are maxed for 350 at the wheels; in fact over-maxed. That's why bumping to 45psi has helped a little. The wet system is hurting you even more, unless you've got it on a dedicated fuel pump. It'll steal fuel that should be making it to the injectors. An inline pump may help the situation a little, but IMHO you've still got some fuel system issues that need to be worked out if you're going for 500 at the wheels on a regular basis.

It has been my experience that the stock fuel lines and rails become a real problem above 400rwhp. There may be plenty of people that make it work, but there are also plenty that don't. Trying to push that much fuel through the dinky lines from the tank to the engine bay is a real problem. Replacing those lines with something capable of moving 255lph of fuel (or more) without huge pressure drops will make the fuel system sooooo much happier.

[1989GT]

I don't think the 30# injectors are maxed out. 350 rwhp with a 15% drivetrain loss would be about 411 bhp. 30(8)=240#'s of fuel/hr. Should be more than enough to support that. Also the 255lph should support over 500 rwhp. Now maybe the lines aren't up to the task for the nitrous shot, I could see that, but there's no reason for you to be running lean when on motor. Obviously your tuner pulled fuel, when tuning the car, and I think by bumping up the pressure you're temporarily tricking the computer to add more fuel. But as soon as you drive the car for a little bit the computer will "learn" and pull the fuel back out and you'll be back to square one. I say go get it retuned, and look to upgrade your fuel lines if you want to be safe about the nitrous shot.

[Dark_5.0]

Originally Posted by Jeff Chambers

30# injectors are maxed for 350 at the wheels; in fact over-maxed.

I was hoping my stroker would put out over 350RWHP so would you suggest I go with 36# injectors Jeff?

The fuel system analyzer on this site says for 420HP at the flywheel.

24# injectors 63 psi in the safe zone.
30# injectors 40 psi
36# injectors 28 psi over injected

So naturally I was about to buy some 30# injectors.

I know you have seen alot of dyno pulls and I am not doubting what you say. Just trying to better educate myself before I buy more injectors to replace my 24#ers.

[Jeff Chambers]

Originally Posted by 1989GT

I don't think the 30# injectors are maxed out. 350 rwhp with a 15% drivetrain loss would be about 411 bhp. 30(8)=240#'s of fuel/hr. Should be more than enough to support that. Also the 255lph should support over 500 rwhp. Now maybe the lines aren't up to the task for the nitrous shot, I could see that, but there's no reason for you to be running lean when on motor. Obviously your tuner pulled fuel, when tuning the car, and I think by bumping up the pressure you're temporarily tricking the computer to add more fuel. But as soon as you drive the car for a little bit the computer will "learn" and pull the fuel back out and you'll be back to square one. I say go get it retuned, and look to upgrade your fuel lines if you want to be safe about the nitrous shot.

Let's go with your 411bhp at a BSFC of 0.5. That's 205 #/hr fuel requirement. That means the injectors are running at 85%+ duty cycle right now, with all our assumptions. Too close for comfort. In the real world, depending on the A/F commanded/delivered, with losses, inaccuracies of the dyno, etc that 15% overhead may be gone. I've had 331 cars on my dyno max out 36# injectors at 365 RWHP. Even worse is the fact that I see quite often fuel systems that aren't totally maxed on the dyno easily get maxed out on the street. The dyno pulls are short and rarely do we have full electrical load on the vehicle while on the dyno. I've datalogged many vehicles on the dyno that are at that 85% duty cycle (on pump or injectors) that once we make the road test and datalog are maxed out and in danger.

Then let's not forget that fuel pump output is dependent a few parameters that take that 255lph rating and throw it in the trash. The pumps are normally rated at 14-volts; don't get that full 14 volts and the output drops dramatically. Pump output also varies dramatically with the line pressure. The pump may be rated at 255lph at 0-psi load, but put the line pressure at 50 psi and that 255lph becomes 180lph. Take for example the gool ole tried and true Holley Blue fuel pump (I know, its a carburetor pump but bear with me for the sake of demonstration). Its rated at 100gph, fantastic thats what, 375lph? Whoah, but that's at 0psi. Set your regulator to 9psi and now that same pump is rated for only 50gph or round about 189lph. Do some mis-figuring and cause a boatload of problems. Alot of people forget that when they read fuel pressure at the rail, that the fuel had to travel through some pretty restrictive lines to get to that point. 40psi at the rail/gauge may actually be 55 psi at the pump. I've stalled pumps rated for 90psi with 70psi at the gauge/rail. I attached a fuel pump performance curve for a Walbro GSS341. Also don't forget that as these pumps age, their performance degrades. There's some good information out there on the internet on studies done to really quantify fuel system performance.

Do you really think the tuner would have pulled fuel if he was seeing the car run lean? What exactly do you think the computer is learning at this point? I think you need to learn/understand the roles of adaptive learning and how the fuel & MAF curves work in the logic. Sure, tuners can and do make mistakes, but no amount of tuning can solve underlying mechanical faults/weaknesses. Bring the car to me and I'll datalog both fuel pressure and injector duty cycle during the run and show definitely that's there's a problem.

[Jeff Chambers]

Originally Posted by Dark_5.0

I was hoping my stroker would put out over 350RWHP so would you suggest I go with 36# injectors Jeff?

The fuel system analyzer on this site says for 420HP at the flywheel.

24# injectors 63 psi in the safe zone.
30# injectors 40 psi
36# injectors 28 psi over injected

So naturally I was about to buy some 30# injectors.

I know you have seen alot of dyno pulls and I am not doubting what you say. Just trying to better educate myself before I buy more injectors to replace my 24#ers.

I'd go straight to 42# injectors and be done with it. They can be had for less than 36# nowadays and give you the margin to not only be safe, but to grow on down the line. There's plenty of deals out there where you can get the injectors and a 90mm LMAF for less than retail on the 36# injectors alone. Remember, that there's really no such thing as too big of an injector (within reason). When properly tuned, the delivered pulsewidth is only going to be whatever is required to meet the commanded lambda.

[1989GT]

1st run (Base Pull) 326 RWHP/ 311 RWTQ (11.2 A/F) (15* timing)
2nd Run: 346 RWHP/ 320 RWTQ (13.8 A/F) (15* timing)
3rd Run: 353 RWHP/ 319 RWTQ (14.5 A/F) (16* timing)
4th Run (150 Shot) 502 RWHP/ 511 RWTQ (15.2 A/F) (13* timing)

Do you really think the tuner would have pulled fuel if he was seeing the car run lean?

Sure looks like someone pulled fuel out to me My question is if the tuner new the car was running lean and that it was a fuel problem why did he release the car back to the owner in an unsafe condition? Or give some sort of advice as to how to fix the problem, as opposed to having the owner come on here trying to figure out what his problem is? Look Jeff I'm not trying to argue with you, I just posted how I see/understand things and if I'm wrong then by all means help me understand. I have a great deal of respect for you and your opinions.
I had a good friend of mine make 365 rwhp with 30 lb injectors a little while back, combo was a stock lightly ported heads, trick flow intake, stock cam and 1.7rr and a procharger with 8 psi. 40psi base pressure and a 1-1 fuel/boost sensitive regulator. 11.5-12:1 A/F across the board.
Also my point about the fuel pressure is that you can turn it up as high as you want but the computer will shorten the pulse width of the injector to compensate for the pressure increase, because of the commanded A/F ratio, but until the computer takes in all of it readings (o2, MAF etc) the car will run richer, and better in this case until the computer "learns" what is going on. Or atleast that's the way I understand it.

[Dark_5.0]

Originally Posted by Jeff Chambers

I'd go straight to 42# injectors and be done with it. They can be had for less than 36# nowadays and give you the margin to not only be safe, but to grow on down the line. There's plenty of deals out there where you can get the injectors and a 90mm LMAF for less than retail on the 36# injectors alone. Remember, that there's really no such thing as too big of an injector (within reason). When properly tuned, the delivered pulsewidth is only going to be whatever is required to meet the commanded lambda.

Thanks Jeff,

I have a local guy here where I live that is well known in the modular mustang world that is going to street tune my car so it should be all good.

Is there a plug adapter for the lightning mass air meter. If I remember correctly the plug is shaped differently.

[Jeff Chambers]

mass-air.com has a connector. Motorcraft also has a new style pigtail but I don't have the number handy.

[Jeff Chambers]

[QUOTE=1989GT]1st run (Base Pull) 326 RWHP/ 311 RWTQ (11.2 A/F) (15* timing)
2nd Run: 346 RWHP/ 320 RWTQ (13.8 A/F) (15* timing)
3rd Run: 353 RWHP/ 319 RWTQ (14.5 A/F) (16* timing)
4th Run (150 Shot) 502 RWHP/ 511 RWTQ (15.2 A/F) (13* timing)

Sure looks like its out of pump and injectors to me. That 15.2 with the wet system sure tells me that something is maxed.

Tuned two Porsche cars yesterday heading to the 24 Hours of Daytona. Second car was drifting lean beyond 5200rpm. Replaced the pump with a brand new pump of the same size/type (stock replacement) and the car perked up and continued to make power to 7200rpm. All the MW analyzers in the world can't take in to account all the variables. If this guy is really concerned about the health of his motor, he'd get it back to a professional that can diagnose what's happening.

[Jeff Chambers]

Originally Posted by 1989GT

My question is if the tuner new the car was running lean and that it was a fuel problem why did he release the car back to the owner in an unsafe condition? Or give some sort of advice as to how to fix the problem, as opposed to having the owner come on here trying to figure out what his problem is?

Do you really think the tuner could deny the customer his car because its running lean? Sounds like to me that the dyno shop told Winged that he was out of fuel but HE chose to take the car and figure it out himself. As a shop owner, I know that I can only recommend to the customer. I can't force the customer to do squat. I can't tell you how many times I've had a customer leave the shop with something less than ideal because his buddy has a similar set up or because some internet jockey on the Corral said it was OK. Can't tell you how many times I've seen those same customers hurt their equipment or struggle with less performance than they really have the capability of.

[1989GT]

Sure looks like its out of pump and injectors to me.

So what happened between the 1st and 2nd run? (with the info we have) it looks like the car picked up 20 rwhp and went really lean with no changes. Then with the car running out of fuel the tuner decided to add timing for the 3rd run. Now here's a question for ya, if the car was running out of fuel making 350 at the wheels why would anyone try to spray a 150 shot on it?

[Jeff Chambers]

Good question on the NOS run....only Winged or the tuner could answer that.

[Dark_5.0]

I want to see a dyno graph. First he asked what parts he should buy and a week later hes at the dyno for the second time.

I am sure I am not the only one that thinks this is a little fishy. Especially since a week earlier he also had 24# injectors if you look at his other thread.

I was interested in his results but I am having a hard time finding them credible.

[~The Jester~]

Originally Posted by Dark_5.0

I want to see a dyno graph. First he asked what parts he should buy and a week later hes at the dyno for the second time.

I am sure I am not the only one that thinks this is a little fishy. Especially since a week earlier he also had 24# injectors if you look at his other thread.

I was interested in his results but I am having a hard time finding them credible.

Forgot one of my all time favorite sayings:

"If it walks like a duck, looks like a duck, and flies like a duck, do you really have to wait to hear it quack?"

Someone has some wires crossed, not telling us the whole story, or is just flat out playing games with us.