TEST 2: Fuel Pressure Test With Gauge
Testing the fuel pump's fuel pressure may seem impossible on the 4.3L, 5.0L, or 5.7L TBI equipped pickup or SUV since they don't come equipped with a Schrader valve.
But the fuel pressure can be tested using a special adapter that either fits between the throttle body and the pressure line or fits in place of the fuel filter.
If you don't own a fuel pressure gauge, you can rent one from your local auto parts store (AutoZone, O'Reilly Auto Parts). You just have to make sure that they have the TBI system adapter.
If you're interested in buying your own, check out my recommendations here: Which And Where To Buy A Fuel Pressure Gauge.
OK, let's get started with this test:
Connect the adapter to the fuel line.
With a shop towel, mop up any fuel that was released during the process of connecting the fuel pressure gauge adapter to the fuel line.
When ready, ask your helper to crank the engine while you observe the fuel pressure tester's gauge.
Your fuel pressure gauge will register one of the two following results:
1.) The fuel pressure gauge will register 12 PSI, or
2.) The fuel pressure gauge will register 0 PSI.
OK, now that the testing part is done... let's take a look at what your results mean:
CASE 1: If the fuel pressure gauge registered 0 PSI. This confirms that the cause of your TBI equipped pickup's ‘no start’ condition 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 12 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 4.3L, 5.0L, or 5.7L GM vehicle is not starting is due to another reason. The fuel pump is OK.
The following tutorial may have some helpful testing suggestions: How To Troubleshoot A No Start (GM 4.3L, 5.0L, 5.7L) .
Which And Where To Buy A Fuel Pressure Gauge
There are two ways to tap into the fuel line to see how much pressure the fuel pump in producing.
One method involves removing the fuel filter and using an adapter, that has a Schrader valve on it, in its place. You then connect your fuel pressure test gauge to this adapter.
The other method is to use an adapter between the throttle body assembly and the pressure line. Once this adapter is installed, you then connect your fuel pressure gauge to it.
Below you'll find the adapter (that's use in the fuel filter's place) and the fuel pressure gauge kit that comes with the adapter that fits between the throttle body assembly and the fuel pressure line.