D4 7u low fuel pressure

I have low fuel pressure on my D4 and was wondering What would the first thing I should look at to see why the pressure is low have put a new gauge on it. But was wondering if fuel filters could be the problem. Thanks

check the check valve and spring on the inlet to the transfer pump

make sure you have good flow from the tank to the transfer pump

Thanks for the reply

The gauge is tapped in AFTER the filters, so dirty filters will show a lower pressure.

I have never understood why the gauge was not turned so you could see it from the seat while the engine was loaded and drawing maximum fuel, but I guess sooner or later you will began to feel the effects of restricted filters and get off to look at the gauge for confirmation.