Fuel Pressure Problem

[86 TR]

It probably sounds like a broken record but here it goes. I was out tuning my car today and when the boost would come on my fuel pressure would start dropping off to about 50psi. I have the reg. set at 44psi vac. line off. I increased the press. to 48 psi and still would drop off. Boost is set at 20 psi I got 009's. My 02 numbers started about 820 and dropped to 740's then I lifted. Luckily I had zero knock. What the hell would cause this?? I've got a new XP pump from Red, hotwired, adjustable regulator, volt booster. I was watching my scanmaster to see if the voltage was dropping but it held steady at 15.2 volts at WOT. Changed my fuel filter just in case but nothing.

It runs like a bat out of hell but hows that saying go: Leaner is meaner till you blow it up!

What gives??

 

[turbofabricator]

Sounds like one of two things. Bad regulator hose (not getting corrrect boost signal). Or a bad fuel pump or hose between the pump and sending unit is leaking at higher pressure.

 

[86 TR]

Im sure that the reg. is working fine. There's no pinched vac. lines or hoses. The next thing might just be drop the tank and check everything out again.

I don't like how the fuel pump connects to the hanger with a piece of rubber hose and hose clamps.

Maybe I'll just end up getting a new pump again.

 

[MyBoosta]

It probably sounds like a broken record but here it goes. I was out tuning my car today and when the boost would come on my fuel pressure would start dropping off to about 50psi. I have the reg. set at 44psi vac. line off. I increased the press. to 48 psi and still would drop off. Boost is set at 20 psi I got 009's. My 02 numbers started about 820 and dropped to 740's then I lifted. Luckily I had zero knock. What the hell would cause this?? I've got a new XP pump from Red, hotwired, adjustable regulator, volt booster. I was watching my scanmaster to see if the voltage was dropping but it held steady at 15.2 volts at WOT. Changed my fuel filter just in case but nothing.

It runs like a bat out of hell but hows that saying go: Leaner is meaner till you blow it up!

What gives??

Heck dude, I'm running 740's O2 readings, 25psi of boost with 117 race fuel and NO KNOCK. After many, many testing, I learned that O2 readings numbers are just that...numbers! Each car is different...some may like O2's in the 800's while others in the mid to low 700's and not hurt a thing. I had the same problem you have and it was my fuel line gauge acting up (it read a certain psi cold and something else hot). So even after a new gauge, my O2 readings were close to the same.

Thanks

 

[MyBoosta]

It probably sounds like a broken record but here it goes. I was out tuning my car today and when the boost would come on my fuel pressure would start dropping off to about 50psi. I have the reg. set at 44psi vac. line off. I increased the press. to 48 psi and still would drop off. Boost is set at 20 psi I got 009's. My 02 numbers started about 820 and dropped to 740's then I lifted. Luckily I had zero knock. What the hell would cause this?? I've got a new XP pump from Red, hotwired, adjustable regulator, volt booster. I was watching my scanmaster to see if the voltage was dropping but it held steady at 15.2 volts at WOT. Changed my fuel filter just in case but nothing.

It runs like a bat out of hell but hows that saying go: Leaner is meaner till you blow it up!

What gives??

Heck dude, I'm running 740's O2 readings, 25psi of boost with 117 race fuel and NO KNOCK. After many, many testing, I learned that O2 readings numbers are just that...numbers! Each car is different...some may like O2's in the 800's while others in the mid to low 700's and not hurt a thing. I had the same problem you have and it was my fuel line gauge acting up (it read a certain psi cold and something else hot). So even after a new gauge, my O2 readings were close to the same.

Thanks

 

[TurboDave]

Heck dude, I'm running 740's O2 readings, 25psi of boost with 117 race fuel and NO KNOCK. After many, many testing, I learned that O2 readings numbers are just that...numbers! Each car is different...some may like O2's in the 800's while others in the mid to low 700's and not hurt a thing. I had the same problem you have and it was my fuel line gauge acting up (it read a certain psi cold and something else hot). So even after a new gauge, my O2 readings were close to the same.

Thanks

He's not so much concerned about the O2's right now as he is about the fuel pressure NOT rising with boost.

 

[TurboDave]

Im sure that the reg. is working fine. There's no pinched vac. lines or hoses. The next thing might just be drop the tank and check everything out again.

I don't like how the fuel pump connects to the hanger with a piece of rubber hose and hose clamps.

Maybe I'll just end up getting a new pump again.

On occasions the hose between the pump and hanger is sometimes damaged sliding it onto one or both fittings, and a piece of hose ends up hanging out in the fuel stream internally. Sometimes one of the connections comes loose, etc.

 

[86 TR]

Pulled the tank out today. I found the problem. The hose clamp that secures the hose to to hanger was loose!! The hose was loose on the sending unit. Going to take it out tonite yet and do some testing.

Thanks for the info.

 

[86 TR]

Just did some WOT testing. Fuel press. problem fixed my next question is why do my O2 reading start at 830's in the midrange and then drop off to about 760's at WOT. Is this normal. No KR boost is set at 20psi with some 110 octane race gas. I increased fuel press. and the wot numbers came up a little. And the midrange 02#s jumped to 860's. It was a new O2 sensor when I took the car out. Feels great but the O2 milivolts have me wondering why they fall off at WOT. Well at least the fuel press. is going up with the boost now.

Any input??

 

[TurboDave]

Just did some WOT testing. Fuel press. problem fixed my next question is why do my O2 reading start at 830's in the midrange and then drop off to about 760's at WOT. Is this normal. No KR boost is set at 20psi with some 110 octane race gas. I increased fuel press. and the wot numbers came up a little. And the midrange 02#s jumped to 860's. It was a new O2 sensor when I took the car out. Feels great but the O2 milivolts have me wondering why they fall off at WOT. Well at least the fuel press. is going up with the boost now.

Any input??

Because most if not all switching O2 sensors react adversely to extreme heat and pressure (the worst of those two conditions exist where the sensor is mounted).