: surging under WOT



Dubya
01-29-04, 04:19 AM
i noticed this 2 days ago, my car is surging kinda bad under WOT, almost like its starved of fuel. in the low and high rpms, when i get on it.

could it be a bad tank of gas? wishful thinking???

95 aurora 4.0 "northstar" the FPR is about 1 year old.

Geno Castellano
01-29-04, 02:02 PM
i noticed this 2 days ago, my car is surging kinda bad under WOT, almost like its starved of fuel. in the low and high rpms, when i get on it.

could it be a bad tank of gas? wishful thinking???

95 aurora 4.0 "northstar" the FPR is about 1 year old.

Buy a fuel pressure gauge and screw it onto the schraeder valve on the fuel rail and watch the pressure when the surging starts to confirm that you're chasing a low fuel pressure situation. That's what it sounds like to me. It could be the pump, the FPR, the fuel filter, the sock at the pickup, etcetera.

If the fuel pressure does drop then the next thing to do to confirm that the FPR is not the problem is to block the return line and do the WOT thing. If the fuel pressure drops with the return line blocked (no fuel going back to the tank) then you can rest assure that the FPR is not causing the problem. Next would be the fuel filter. Maybe you got a load of trash on that last fillup or the sock - maybe a load of trash or water at that last fillup. The sock will block the water and could cause fuel starvation if completely plugged or coated with debris.

The first stop is a fuel pressure gauge, though. Find an old R12 recharging line somewhere (that is the same shraeder fitting on the fuel rail). Find a cast off 60 or 100psi gauge and put it on the refrigerant line with the fitting. Instant fuel pressure gauge. Even if you have to buy all the parts I made one like this recently for about $12.

ernie50
01-29-04, 10:57 PM
I'm having the same problem at WOT. It happens in the 4000 rpm range for me very consistantly... Which leads me to believe it might be electrical in nature

Geno Castellano
01-29-04, 11:16 PM
I'm having the same problem at WOT. It happens in the 4000 rpm range for me very consistantly... Which leads me to believe it might be electrical in nature

Not necesarily. If the fuel system is restricted or compromised in some way it will usually run out of fuel supply or fuel pressure at about the same demand point. I'd get a fuel pressure gauge on it, gather some information and stop guessing.:yup:

Dubya
01-30-04, 02:13 AM
thanks Geno, ill stop at checkers tomorrow and pickup a fuel pressure gage, can't be to much $$$. what should the pressure be at? no idle problems at all, seems like its being starved for fuel, never changed the filter. i had a SLIGHT surge before at certain rpms, but it seems like it got alot worse out of nowhere

not sure what you mean by sock though

if it is the pump, how hard are those to change? i heard you have to drop the tank and its HARD and EXPENSIVE, hope things changed!

btw its a 95 aurora

Dubya
01-30-04, 02:15 AM
i noticed too, its not just high rpms, its when i get on it, low to mid to high, when i push it hard enough for it to shift at about 4.5k or higher

Geno Castellano
01-30-04, 12:06 PM
i noticed too, its not just high rpms, its when i get on it, low to mid to high, when i push it hard enough for it to shift at about 4.5k or higher

Get a fuel pressure gauge on it first. What you are loooking for is constant fuel pressure regardless of load and RPM. If the fuel pressure drops suddenly, concurrent with the loss of perfromance, then that's what you're looking for.

The fuel pickup has a mesh strainer on it, commonly called a "sock", that's the first line of defense against water and dirt in the fuel. If it becomes clogged or coated with debris then it'll often collapse as it's on the suction side of the system.

The pump is inside the fuel tank. Dropping the tank is required to replace the pump. It's really not that difficult as long as the tank is nearly empty.

Dubya
01-30-04, 03:14 PM
thanks for all the help, but thankfully i don't need it (good info to know, thanks!)

i filled up today, with the old tank almost empty. drives completly normal. i didn't think a bad tank of gas could be THAT bad. the car drove like crap, and i used holiday 93octane. guess that blue planet gas is as bad as ive heard.