Fuel pressure problem that i cant make heads or tails of

[ttribejr]

My factory return lines are not damaged. It may be from those factory (saginaw? however you spell it) fittings. They neck down way smaller than 1/4" inside. Looks like 1/8 or 3/16" at most. Or it may be an obstruction. I don't know and don't plan to diagnose it further, i am going to put a larger line on as this problem would only be amplified when I get a stronger pump.

Ttype6, i was on the same thought process as you. I thought surely this 255 LPH pump is not overpowering stock fuel lines. Thats why i was checking everything else first. But the problem is somewhere between the lower fuel fitting in the engine bay and the other one above the rear suspension cross member. And no signs of a dent or kink in the lines. Rubber replaced.

 

[BEATAV8]

He said neither crush nor damage. He was commenting on the ID of the Saginaw fitting at the front of the return line.

is 1/8" good then?

 

[ttribejr]

In other words, I bypassed those fittings completely. Hope this makes sense. You could not fit a a Q-tip inside them, they are small inside.

I this fuel line was the only line on the car when i got the pressure down as low as 30psi. I took the return side and just let it drain into a empty fuel jug i had. the fitting that attaches to this one is the one that is very small.

 

[ttribejr]

I did take the flex fuel sensor out of the equation. it made no difference. Its 3/8" ... the inside diameter is larger than the outside diameter of the oem return line.

 

[Ttype6]

[QUOTE="ttribejr, post: 3722184, member: 5130] the problem is somewhere between the lower fuel fitting in the engine bay and the other one above the rear suspension cross member.[/QUOTE]

Yes,and one of the most likely restrictions was or is staring you in the face. Stick a spinning drill bit into the front of the steel return line and report back. Again,it would be wise to remove the sensor and re do your first test. This will tell you if you have e restriction between the front of the return line and the sensor. If you don't,there is no need to drill the front Saginaw fitting and you'll know the restriction is farther back. It is also worth sending some compressed air through the return line to the tank. Remove gas cap for this.

 

[Ttype6]

You could not fit a a Q-tip inside them, they are small inside.
the fitting that attaches to this one is the one that is very small.

That is the hole that you will enlarge. There is another Saginaw fitting like this where the rubber return line attaches to the regulator. I think it is a little larger,but I'm not sure.

 

[Ttype6]

I did take the flex fuel sensor out of the equation. it made no difference. Its 3/8" ... the inside diameter is larger than the outside diameter of the oem return line.

So you removed the sensor and started the engine and ran fuel through a hose into a bucket?

 

[Ttype6]

is 1/8" good then?

It's normal at the necked down area of the return line that houses the o-ring. Mine is this size. What the OP is seeing,is typical.

 

[ttribejr]

No. Specifically. I complete removed it from the car and ran larger rubber hoses. Like I said, im 100% positive that its the section of fuel line I mentioned. I just don't know if its the fittings or something inside the lines that shouldn't be there.

I am going to be running 500+ LPH of fuel in the near future. I may as well upgrade the return line now and kill two birds with one stone.

 

[Ttype6]

No. Specifically. I complete removed it from the car and ran larger rubber hoses.

So,you removed the sensor and replaced it with a piece of hose connecting the two steel lines together then started the engine?

 

[Mr.Spool]

Usually if you loose fp while your driving into it you don't have enough pump.if you can't lower fp there is a return restriction somewhere.

 

[Mr.Spool]

No. Specifically. I complete removed it from the car and ran larger rubber hoses. Like I said, im 100% positive that its the section of fuel line I mentioned. I just don't know if its the fittings or something inside the lines that shouldn't be there.

I am going to be running 500+ LPH of fuel in the near future. I may as well upgrade the return line now and kill two birds with one stone.

Check the return line for kinks

 

[Mr.Spool]

A 255lph pump will not max stock return line and won't feed 120 lb injectors which is why I believe it goes down when you drive it.I also believe there is something wrong with the return line and you have 2 things going on.

 

[ttribejr]

Car is fixed

I cut off the oem restrictive fitting and used the larger 5/16 vapor line. I now have full control all the way down to mid twenties psi fuel. The modifications took about an hour.

 

[Reggie West]

Car is fixed

I cut off the oem restrictive fitting and used the larger 5/16 vapor line. I now have full control all the way down to mid twenties psi fuel. The modifications took about an hour.

Glad to hear it but you will run out of pump on the top end so be careful. Watch the duty cycle on your injectors.

 

[ttribejr]

Glad to hear it but you will run out of pump on the top end so be careful. Watch the duty cycle on your injectors.

Thanks Reggie. One thing I know is tuning. I have been EFI tuning for over a decade. Today ended with a street tuning session that resulted in 18psi boost with less than 4% correction in 1st-3rd gear. Duty cycle peaked at 44%.

There is a misconception some people have about fuel systems. As long as you have a fuel pump and injectors that can meet or *exceed* your max power, you are good.
I have read that the stock turbo runs out of breath around 22psi (assuming stock heads/cam etc). I am at 18psi boost and 44% duty cycle (consistent). I have injectors that are good for over 700HP and a fuel pump that is good for (guessing) 350 e85 horsepower. As long as you don't go over 350hp (in this scenario) you are fine. Too big of a fuel injector is nearly never a problem as long as you can tune idle and light load stuff with it. I could have gotten away with a 60 or 80# injector. But I bought 120s so I can grow into them. There is almost zero drawback to this.

I doubt I will max out my fuel system until I change the turbo and raise the boost.

 

[Reggie West]

Cool sounds like you know what you are doing.

 

[ttribejr]

It's the car I am learning. I'm greatful for those who have been there, done that and share their experience with the rest of us. It takes a lot of guesswork out for people like me who are on their first buick.

Thank you, everyone, for the tips and advice to speed up the diagnosis of my problem.

For anybody wondering. The inside diameter of the oem fuel fitting on my car measures 5/64"... even smaller than the 1/8" I anticipated.

 

[Mr.Spool]

Car is fixed

I cut off the oem restrictive fitting and used the larger 5/16 vapor line. I now have full control all the way down to mid twenties psi fuel. The modifications took about an hour.

Ok that part is fixed.now the Majic question does fp rise 1to1 with boost?and do you see fp rise and not drop as you describe?

 

[ttribejr]

No way to be sure about 1:1 until I get a log kit. But I can tell by the adjustments I had to make to the VE table that fuel pressure is rising with boost. The higher the KPa, the more I had to lean out the car. Light load and idle, I had to add fuel to compensate for the new lower fuel pressure in those loads. It all makes sense.