Fuel pump replaced, now another fuel problem comes up with engine missing/bucking under load.
 

I just replaced the fuel pump in my ’96 Discovery because it wouldn’t hold pressure after shut-off causing hot start problems. It starts up fine now but after taking it for a drive it bucks and misses with moderate or stronger acceleration. Feels like it’s starved for fuel. I hooked up my fuel pressure gauge and snaked the hose out the rear of the hood and secured the gauge under a wiper arm for a test drive. Sure enough, as soon as I put the engine under a moderate load, the gauge needle started to drop and around 10psi the engine stated to buck and miss at which point I let off the gas and the needle went back up to around 30psi and it ran fine.

Could it be the new fuel pump is bad right out of the box? I didn’t notice this problem with the old fuel pump. Or could the new pump just bring to light the next weakest part down the line such as the pressure regulator. I pulled the vacuum hose off the regulator but that made no difference. I’m trying to envision how the regulator works and what would happen if for example it was stuck. If it was stuck, and at idle the pressure was 30psi, and you put the engine under load with the injectors requiring more fuel, the pressure would drop but since the regulator was stuck, it couldn’t raise the pressure back up to the required 30psi. Does this sound logical? Should I just replace the regulator? It does have a new fuel filter.

RE: Fuel pump replaced, now another fuel problem comes up with engine missing/bucking under load.
 

it is always possible the fuel pump could be defective..the pressure regulator is attatched to the pump. do you have acheck engine light on?

RE: Fuel pump replaced, now another fuel problem comes up with engine missing/bucking under load.
 

No, the pressure regulator is under the hood on the fuel rail. And no check engine light on.

RE: Fuel pump replaced, now another fuel problem comes up with engine missing/bucking under load.
 

ooopps sorry thinking about my 03 yes that is correct, check to see if the vacuum line is o.k.again it may be a bad fuel pump..if you didnt have this problem before you replaced it. but the regulator regulates the fuel pressure and if you are only getting 10 psi under load then it could point to either the pump not delivering enough fuel or the regulator failing under extreme demand from the injectors/vacuum pressure.