TEST 2: Checking Fuel Pressure With A Fuel Pressure Gauge
The best way to check the fuel pump's condition is with a fuel pressure gauge and Dodge has made it super easy to test the fuel pump with a fuel pressure gauge.
The fuel injector rail, of the 4.7L V8 engine, is equipped with a Schrader valve. It's to Schrader valve that you and I can connect a fuel pressure test gauge and check the fuel pump's pressure output.
NOTE: If you don't have a fuel pressure gauge, take a look at the section: Where To Buy A Fuel Pressure Test Gauge.
OK, let's get started with this test:
Place a shop towel around the Schrader valve. The shop towel's job is to absorb any fuel that may leak when doing step 2.
Connect the fuel pressure gauge to the Schrader valve on your 4.7L Dodge's fuel injector rail.
When ready, ask your helper to cycle the key on and off but don't crank the engine while you observe the fuel pressure tester's gauge.
Check the connection at the Schrader valve for fuel leaks and if any tighten the fuel pressure a bit more (by hand only) to eliminate them.
Crank and start the engine and check the fuel pressure gauge. Your fuel pressure gauge should register: 44 to 54 PSI with the engine running if the fuel pump is OK.
If the engine doesn't start, crank the engine enough to get the fuel pressure up. Your fuel pressure gauge should register: 44 to 54 PSI if the fuel pump is OK.
Let's take a look at what your results mean:
CASE 1: If the fuel pressure gauge registered 0 PSI This confirms that the no start problem is caused by a lack of fuel.
Now, I usually take one more precaution, before condemning the fuel pump as BAD... and this is to check that the fuel pump is getting 12 Volts as the engine is cranking. This is just to make sure that the fuel pump relay and fuse are OK and doing their job.
What you'll have to do to accomplish this is to attach a multimeter in Volts DC mode to the wire that supplies this voltage to the fuel pump and while a helper cranks the engine... verify that the fuel pump is getting this power. If the 12 Volts are being supplied to the fuel pump... you have now 100% verified that the fuel pump is fried and needs to be replaced.
CASE 2: If the fuel pressure gauge registered 44 to 54 PSI: This fuel pressure gauge result let's you know that the fuel pump is working and delivering enough fuel to the fuel injectors. The reason your 4.7L Dodge is not starting is due to another reason. The fuel pump is OK.
Where To Buy A Fuel Pressure Test Gauge
You can buy a fuel pressure test gauge just about anywhere and is one of the most important tools any serious DIY'er should have in his/her tool box.
The following fuel pressure test gauge kits are pretty good deals and will work with your 4.7L Dodge:
All of the fuel pump pressure test kits above have the fitting that will connect to your Dodge's Schrader valve.