When the fuel pump goes bad on your GM 3.8L equipped car or mini-van, it's going to crank but not start. Although it stinks that your vehicle is not starting, the cool thing is that testing the fuel pump is not hard.
I'm going to show you two different methods that you can use to verify if the no-start condition on your 3.8L GM vehicle is due to a lack of fuel.
Now, in case you're wondering, in this tutorial I'm gonna' show you 2 specific tests. One fuel pump test involves using just starting fluid. The other involves using a fuel pressure gauge (which is the most accurate of the two).
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Bomba de Combustible (GM 3.8L) (at: autotecnico-online.com).
IMPORTANT: Gasoline and starting fluid are extremely flammable! Be very careful. Take all necessary safety precautions and stay alert. You'll be able to accomplish both tests, indicated in this article, without any unhappy consequences, if you're careful and use common sense.
Symptoms Of A Bad Fuel Pump
I mentioned at the beginning of this tutorial that a bad fuel pump will cause your 3.8L equipped car or mini-van to ‘crank but not start’. Well, there are a few other specific symptoms you'll see. These are:
- All of the coil packs, sitting on top of the ignition control module (ICM), are creating and delivering spark to the spark plugs. So you know that the ignition system is not at fault.
- You've done a fuel injector Noid Light test and all of the fuel injectors you tested are getting their activation signal.
- You've sprayed starting fluid (or carburetor spray) into the throttle body and your car (or mini-van) started, even if only momentarily.
Although the above list is a not a very complete list of symptoms, the theme that runs thru' them, and any other related symptom, is that the engine will crank and crank, but not start.
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.
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 with a fuel pressure test gauge.
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).
All of the fuel pump pressure test kits above have the fitting that will connect to your vehicle's Schrader valve.
FUEL PUMP TEST 1: 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:
- 1
Connect the fuel pressure gauge to the Schrader valve on the fuel rail.
- 2
When ready, ask your helper to crank the engine while you observe the fuel pressure tester's gauge.
- 3
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 you condemn the fuel pump as bad, 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 lets 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 More 3.8L V6 GM Tutorials to see more testing options.
