I have an 89 camaro with a 406/miniram. I am losing fuel pressure towards the top end, I have hot wired the fuel pump to the alternator terminal still have the same amount of drop. The fuel pump is a walbro 255lph, with stock fuel lines. Can anyone suggest where to look for the problem. fuel pressure is @50# no vacuum at idle. Thanks, Chad

 

Sounds like your injectors might be staying open at WOT (static)

 

How can I check for the injectors going to 100%? I don't know if it would be that, due to how soon it starts going into fuel pres. drop. Thanks

 

Check your injector duty cycle with a scanner, injector P/W.

 

How about a simple clogged fuel filter.

Did you tape a gage to your window? With it coming right off the fuel rail? How much gas do you have in your tank when racing. In my vette I have to have at least 1/2 tank or it will bog super bad and FP drops.

That pump with those injectors is way more than you need.

Make sure you have the correct voltage at the pump. As the pumps output is directly related to the voltage it receives

 

I replaced the filter when I first noticed it. I have an autometer electronic FP gauge, I also connected an regular FP gauge and taped to the window. Fuel tank is full. When I hot wired the pump I'm sure it had good voltage even though I didn't measure it. I'll have to hook up and see if snap-ons scanner reads duty cycle. Thanks

 

you ran 11.2 @ what mph? could you go into some more detail on your combo?

 

Update on problem:
Raplaced intank pump. Still same problem. tried T-rex in-line with Walbro. Same problem. Anyone have ideas. Tried the basics, and threw some parts. no fix. No crimps in the fuel lines.

Duty Cycle approx. 75% WOT.

Please give ideas.

 

Is the in-tank strainer clogged? Also, maybe you have a bunch of crap floating around in the tank, and when you start sucking alot of fuel, it pulls all the stuff towards the strainer which blocks fuel flow. You could also have some crap clogging your actual lines. Maybe drop the tank and leave just the pickup hanging, pull the fuel filter off, disconnect the lines at the motor, and blow some air through the lines to get rid of any gunk.

I know the stuff is basic, but sometimes that's the stuff that causes the most grief

Good luck with your problem,
Matt

 

The tank is clean, checked while it was down doing the other pump. As far as the lines I didn't blow through them while I had it apart. Still can I guess. Do the rubber hoses ever colapse?

 

Hey, combo details? And how are you determining that you are going lean? or are you?

 

some fuel lines, where they turn into rubber, will have a plastic inner core, if pinched, it will colapse and give grief..
stock fuel lines? maybe they arn't adequate? i'm just shooting that last one in the dark.. some restriction somewhere.. flare nut not in properlly, or one of those clip nuts.. (can't remember the trade name for it)....

 

If you have not replaced the rubber lines might as well, they are not that expensive. What is your voltage reading when the pressure drops?

 

One item to remember is that the fuel pressure is intake manifold pressure referenced. If the intake pressure drops due to a restriction the fuel pressure will also drop. A restriction can be anything from the duct work being too small, air filters getting clogged, incorrect placement of the intake to the outside of the car.

A common problem is the intake duct work actually collapsing. Stock Camaro TPI setups will do this.

RBob.

 

Rubber lines are on their way. Voltage is 13.3 at pump. I have ran WOT with and without vacuum to pressure regulator to eliminate reference vacuum. Thanks for all the replies

 

Aren't those SVO injectors rated at a different pressure than TPI injectors? They also have a different resistance (ohm) too, if I remember correctly.

As vacuum goes down, fuel pressure goes up. That's why the pressure is set with the vacuum line off and plugged.

Try taking a pair of pliars and squeeze the vacuum hose leading to the fuel pressure regulator and see if the pressure doesn't rise.

Jake