FUEL PUMP TEST 2: Fuel Pressure Test With Gauge
GM has made it super easy for you and me to test the fuel pump (with a fuel pressure gauge), since they have installed a fitting (called the Schrader valve) on the fuel pressure regulator to which you and I can connect the fuel pressure gauge to (see photo above).
Using a fuel pressure gauge is one of the most accurate ways to make sure that enough fuel is reaching the fuel injectors. If you do own a fuel pressure gauge, this is the test for you.
If you don't own one, I'm gonna' make some recommendations to you as to which one to buy and where to buy it in the section Which And Where To Buy A Fuel Pressure Gauge.
As mentioned in the previous page, you can run down to your local AutoZone or O'Reilly auto parts and rent one too.
OK, let's get started with this test:
Connect the fuel pressure gauge to the Schrader valve on the fuel rail.
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 35 PSI, or
2.) The fuel pressure gauge will register 0 PSI.
OK, let's analyze your test results:
CASE 1: If the fuel pressure gauge registered 0 PSI. This confirms that the cause of your 3.8L equipped GM car or mini-van is caused by a lack of fuel.
Now, I'm going to make one more recommendation to you... Before I condemn the fuel pump as bad, I 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 35 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 3.8L GM vehicle is not starting is due to another reason. The fuel pump is OK.
I suggest you take a look at the section Related Test Articles to see more testing options.
Which And Where To Buy A Fuel Pressure Gauge
Owning a fuel pressure gauge is now becoming a must. All vehicles now use an electrical fuel pump to deliver fuel (under high pressure) to the fuel injectors and the best way to diagnose this fuel pump is with a fuel pressure gauge.
As mentioned earlier (in fuel pump TEST 2), in all of the GM 3.8L V6 equipped vehicles, GM was kind enough to put a Schrader valve on the fuel injector rail where you can tap into the fuel system and check its performance.
A fuel pressure gauge can cost you as little as $40 (US) or as much as $200 (US). The price difference depends on whether you're buying a non-professional technician grade tool or a professional technician grade tool. Whichever one you buy, it's an investment that will pay for itself many times over.
Your local parts house will have a fuel pressure gauge set to sell you, although you'll pay more for it and it won't be a professional grade tool (if that's what you're looking for).
The Actron CP7838 Professional Fuel Pressure Tester is a good tool but not a professional technician level fuel pressure gauge although the name used by Actron to describe it has the word ‘professional’ as part of its name.
Why do I know this is a good tool? Well, I own one (I also have a professional level grade fuel pressure gauge set) and I used it regularly and I can tell you that it works. The only things I don't like about it is 1.) No molded case to put the fuel pressure gauge and the fittings that go with it and 2.) You can't buy the fittings, that you may lose or break, separately. But for the price it's a great deal.
You'll be able to test most of the GM vehicles, most Ford vehicles, among several makes; although this isn't that important if you're only worried about testing your GM vehicle.
The OTC 6550 Master Fuel Injection Kit will have the adaptors for Asian and Domestic (USA) vehicles. So, if you work on cars for a living and you work on a variety of Makes and Models, this is the fuel pressure gauge set that you need to have in your tool box.
Since this fuel pressure gauge set is a professional grade technician tool, you can buy most of the components, that make up the set, separately. This comes in handy, because you're able to buy whatever fitting you lose or gets damaged. Also, and probably the last consideration, is that this is an OTC tool, and OTC has been around for a long, long time and makes a ton of automotive specialty tools known for quality.
Related Test Articles
If you enjoyed and/or found this ‘How To’ article helpful, I've written several more 3.8L specific test articles. You can find a complete list of 3.8L tutorials here: GM 3.8L Index Of Articles.
- How To Test The Fuel Injectors (GM 3.8L).
- How To Do A Fuel Injector Noid Light Test (GM 3.8L).
- How To Test The 3.8L GM Crank Sensor With a Multimeter.
- How To Test The Camshaft Position Sensor -P0341 (GM 3.8L).
- How To Troubleshoot A No Start (GM 3.8L).
- GM 3.8L Ignition Control Module and Crank (3X, 18X) Sensor Test (at: easyautodiagnostics.com).