As you're already aware, the throttle body fuel injection system on your 1987 to 1995 4.3L, 5.0L, or 5.7L pickup (or SUV) uses a low pressure (12 PSI) electric fuel pump located in the gas tank.
And although GM did not include a Schrader valve to which you could connect a fuel pressure gauge, it can be tested with one to find out if the fuel pump is producing the correct pressure (or not).
In this tutorial, I'm going to show you two different methods to verify if the no-start condition on your 4.3L, 5.0L, or 5.7L throttle body fuel injection (TBI) GM vehicle is due to a lack of fuel, which usually means that the fuel pump has gone bad.
One method involves using just starting fluid and the other involves using a fuel pressure gauge. One method is a very accurate way of diagnosing a lack of fuel condition causing a no start, the other method is not that accurate.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Verificar La Bomba De Combustible En Los Sistemas TBI (at: autotecnico-online.com).
IMPORTANT: Gasoline is extremely flammable. Be careful and take all necessary safety precautions. Use extreme care when using starting fluid since it ignites as easily as gasoline. Accomplishing both tests indicated in this article, without any unhappy consequences, is more than possible if you're careful and use common sense.
NOTE: This tutorial covers only the TBI equipped 4.3L, 5.0L, and 5.7L pickups (SUVs). If you need to test the ‘spider’ equipped GM pickups or SUVs, the following tutorial will help:
Symptoms Of A Bad Fuel Pump
A bad fuel pump will make your 4.3L, 5.0L, or 5.7L throttle body fuel-injected pickup or SUV crank but not start. Here are some more specific symptoms:
- The ignition system is creating and delivering spark to the spark plugs. So you know that the ignition system is not at fault (in other words: the ignition control module is OK, the ignition coil is OK, etc.).
- You've sprayed starting fluid (or carburetor spray) into the throttle body and your vehicle started, even if only momentarily.
- You don't hear the fuel pump making a buzzing sound as you turn the key to the ON position or crank the engine.
- You don't see the fuel injectors spraying gasoline.
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
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.
TEST 1: Using Starting Fluid
The first step is to see if a ‘no fuel’ condition is actually the cause behind your pickup or SUV's no-start problem.
And the fastest/easiest way to do this is to see if the fuel injectors are spraying fuel while a helper is cranking the engine. If the injectors are not spraying fuel, then the next step is to coax the engine into starting using starting fluid.
CAUTION: You'll be working around a cranking engine, so take all necessary safety precautions and think safety all of the time.
OK, to get this show on the road, this is what you'll need to do:
Remove the top cover of the air filter assembly.. You don't have to completely remove the assembly, just the cover.
Spray starting fluid down the bore of the throttle body. When you have sprayed a good squirt of starting fluid, quickly place the air filter assembly's cover back on.
IMPORTANT: Placing the cover back on the air filter assembly is important because it'll prevent any back-fire, that may occur, from spouting flames out of the throttle body.
Have your helper crank the engine once the intake cover is back on the air filter assembly.
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: The engine started and ran for a few seconds. This means that the reason your pick up (or SUV) is not starting is due to a lack of fuel.
Now that you have confirmed that the ‘no-start’ problem is due to a lack of fuel, you now need to actually confirm how much pressure the fuel pump is producing with a fuel pressure gauge. For this test go to: TEST 2: Fuel Pressure Test With Gauge.
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 remove the fuel line that connects to the fuel injector rail and place it in a container. Then have a helper bump the starter while you check to see if fuel comes out of the Line and into the container. This way, you can visually see if there is or there isn't fuel coming out of the fuel line.
Quite a few things can cause a ‘no-start’ condition and if you have ruled out the fuel pump as the problem, this tutorial may be of help: How To Troubleshoot A No Start (GM 4.3L, 5.0L, 5.7L).