How To Troubleshoot The Fuel Pump (GM 3.8L)

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).

Here are the contents of this article at a quick glance:

  1. Symptoms Of A BAD Fuel Pump.
  2. FUEL PUMP TEST 1: Using Starting Fluid.
  3. FUEL PUMP TEST 2: Fuel Pressure Test With Gauge.
  4. Which And Where To Buy A Fuel Pressure Gauge.
  5. Related Test Articles.

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:

  1. 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.
  2. You've done a fuel injector Noid Light test and all of the fuel injectors you tested are getting their activation signal.
  3. 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.

FUEL PUMP TEST 1: Using Starting Fluid

How To Test The Fuel Pump With Starting Fluid (3.1L, 3.4L GM)

Testing a no start condition, to see if it's being caused by a lack of fuel can be very rapidly done with starting fluid. Now, let me tell you that this is not the most accurate way of testing the fuel pump... but it doesn't mean it's not effective.

I personally have used this starting fluid test with a lot of success, along with a few other tests, to verify if the vehicle I'm working on is not starting due to a lack of fuel.

OK, to get this show on the road, this is what you'll need to do:

  1. 1

    Remove the intake air duct from the throttle body. You don't have to completely remove it, since you'll have to reconnect it in one of the next steps.

  2. 2

    Open the throttle, manually, and spray starting fluid down the bore. When you have sprayed a good squirt of starting fluid, quickly reconnect the air duct to the throttle body (you don't have to tighten the hose clamp).

    Reconnecting the intake air duct is important as a safety precaution.

  3. 3

    Once the intake air duct is back on the throttle body, have your assistant, inside the vehicle, crank the engine.

  4. 4

    You'll get one of two results with this test:

    1.) The engine will start momentarily and after a few seconds will die or.

    2.) The engine will only crank but not start at all.

OK, let's find out what your results mean:


CASE 1: If the engine started and ran for a few seconds: This means that the reason your 3.8L equipped car or mini-van is not starting is due to a lack of fuel.

Usually, this also means that the fuel pump is BAD. But since we don't live in a perfect world... this could also mean a few other things like: the fuel pump fuse is blown, or the fuel pump relay is BAD or the factory anti-theft system has activated and is disabling the fuel injectors. Now, don't worry about this too much, because you can test this by:

  1. Checking fuel pressure with a fuel pressure gauge. Go to: Your next step is to go to: FUEL PUMP TEST 2: Fuel Pressure Test With Gauge.
  2. Making sure that the fuel pump is getting power (12 Volts) when you crank the engine.
    1. You can accomplish this by locating the wire (circuit) that feeds power (12 Volts) to the fuel pump and with a multimeter in Volts DC Mode, verifying that 12 Volts are reaching the fuel pump when you crank the engine.

CASE 2: The engine did not start, not even momentarily: This usually means that a lack of fuel IS NOT the reason your car is not starting.

Now, remember what I said about this test not being very accurate? Well, I suggest you do one more test...

... This is to get yourself a fuel pressure gauge at your local auto parts store and check fuel pressure with it. If you have an AutoZone or an O'Reilly auto parts store nearby, you can rent one for free (after leaving a cash deposit which you'll get back when you return the tool). Your next step is to go to: FUEL PUMP TEST 2: Fuel Pressure Test With Gauge.