FUEL PUMP TEST 2: Fuel Pressure Test With Gauge

Fuel Pump Schrader Valve Test Port Location. How To Troubleshoot The Fuel Pump (GM 3.1L, 3.4L)

Testing the fuel pressure with a fuel pressure gauge can be very easily done on your 3.1L or 3.4L Monte Carlo (Venture, Beretta, Corsica, Lumina, Monte Carlo, Grand Prix, Grand Am, Cutlass Supreme, etc.). This is due to the fact that GM has included a Schrader valve on the fuel rail to which you and I can attach a fuel pressure gauge to.

Using a fuel pressure gauge to make sure that enough fuel is reaching the fuel injectors is the most accurate way to diagnose the fuel pump in your car or mini-van.

If you don't own a fuel pressure gauge, you can rent one from your local auto parts store (AutoZone, O'Reilly Auto Parts). 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:

  1. 1

    Connect the fuel pressure gauge to the Schrader valve on the fuel rail.

    With a shop towel, mop up any fuel that was released during the process of connecting the fuel pressure test gauge.

  2. 2

    When ready, ask your helper to crank the engine while you observe the fuel pressure tester's gauge.

  3. 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, 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 Venture's (Malibu, Impala, Lumina, Grand Am, Cutlass Supreme, etc.) 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 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 3.1L or 3.4L GM vehicle is not starting is due to another reason. The fuel pump is OK.

For more testing suggestions, I suggest you take a look at the following tutorial How To Troubleshoot A No Start (GM 3.1L, 3.4L) .

Is the Anti-Theft System Causing the No Start Condition?

PASS-Key/Passlock system failures are very common (especially the ignition key lock cylinder malfunctioning and not sending the correct key signal to the PCM or BCM).

The end result of these failures activating the anti-theft system is a no-start condition. This no start condition can seem like it's due to a bad fuel pump.

To explain this a bit further... the anti-theft system is designed to disable the fuel injectors (when it activates) the 3 seconds after the engine starts. This causes the engine to stall and if you use starting fluid... the engine will start (and of course die when the dose of starting fluid you just sprayed gets consumed).

This may lead you to believe that the fuel pump has failed (when it hasn't). To help you tell the difference between a bad fuel pump and an anti-theft system problem... take a look at the following chart:

Anti-Theft Versus Fuel Pump
Symptom PASS-Key / PassLock Fuel Pump
engine cranks but won't start YES YES
engine starts with starting fluid (momentarily) YES YES
Ignition system delivers spark YES YES
Anti-theft MIL flashes on instrument cluster YES
Engine starts momentarily then stalls YES
Fuel pressure at spec (as checked
w/ fuel pressure gauge)
PCM disables fuel injectors a few
seconds after the engine starts

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 3.1L and 3.4L 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 what type of fuel pressure gauge set you buy... this means either buying a non-professional technician grade tool or a professional technician grade too. Whichever one you buy, it's an investment that will pay for itself many times over.

In the next page, I'm going to review two different fuel pressure gauge sets that will shed some light into which one is the one you may want/need to buy.

Alright, now, which one and where to buy it in the next page...