As you're probably already aware, a bad fuel pump will cause your 3.9L Dodge Dakota to not start.
The cool thing is that testing the fuel pump, on the 2000-2003 3.9L Dodge Dakota, is a piece of cake.
In this tutorial, I'll show you how to confirm that your Dodge Dakota's no-start is due to a lack of fuel (from the fuel pump).
Contents of this tutorial:
Symptoms Of A Bad Fuel Pump
Over the years I've worked as an automotive diagnostic technician I've noticed that fuel pumps usually fail in one of two ways. They either fail completely and the engine refuses to start.
Or the fuel pump fails and dies a very slow death. To be a bit more specific: I mean that the fuel pump still functions but it does not send enough fuel pressure and/or volume to the fuel injectors.
Here are some specific symptoms of when a fuel pump completely fails.
- The engine turns over but will not start.
- All 6 spark plug wires are sparking (confirming it's not an ignition system problem).
- The PCM will still pulse (activate) all 6 fuel injectors (as confirmed by a Noid light test).
But when the fuel pump fails slowly, your 3.9L Dodge Dakota will start and run but with engine performance problems. You'll probably see one or more of the following symptoms:
- Rough idle.
- Engine starts after extended cranking.
- Lack of power when accelerating the vehicle down the road.
- Back-fires thru' the intake manifold when accelerating your vehicle down the road.
- Lean air/fuel mixture trouble codes: P0171 or P0174 or both.
Whether the fuel pump is the cause behind your 3.9L Dodge Dakota's no-start problem or engine performance problem, you can find out with a simple fuel pump pressure test. Alright, with this info under our belts, let's get testing.
Where To Buy A Fuel Pressure Test Gauge
You can buy a fuel pressure test gauge just about anywhere and is one of the most important tools any serious DIY'er should have in his/her tool box.
The following fuel pressure test gauge kits are pretty good deals and will work with your 3.9L Dodge Dakota:
All of the fuel pump pressure test kits above have the fitting that will connect to your Dodge's Schrader valve.
TEST 1: Checking Fuel Pressure With A Fuel Pressure Gauge
Testing the fuel pump on the 2000-2003 3.9L Dodge Dakota is a breeze due to the fact that it comes equipped with a Schrader valve.
This Schrader valve is located on the fuel injector rail (see photo above). And it's to this Schrader valve that we can easily connect a fuel pressure gauge to.
NOTE: If you don't have a fuel pressure gauge, take a look at the section: Where To Buy A Fuel Pressure Test Gauge.
OK, let's get started with this test:
- 1
Place a shop towel around the Schrader valve. The shop towel's job is to absorb any fuel that may leak when doing step 2.
- 2
Connect the fuel pressure gauge to the Schrader valve on your 3.9L Dodge Dakota's fuel injector rail.
- 3
When ready, ask your helper to cycle the key ON and OFF but don't crank the engine while you observe the fuel pressure tester's gauge.
Check the connection at the Schrader valve for fuel leaks and if any tighten the fuel pressure a bit more (by hand only) to eliminate them. - 4
Crank and start the engine and check the fuel pressure gauge. Your fuel pressure gauge should register:
44-54 PSI: 2000, 2001, 2002 3.9L Dodge Dakota.
47-51 PSI: 2003 3.9L Dodge Dakota. - 5
If the engine doesn't start, crank the engine enough to get the fuel pressure up. Your fuel pressure gauge should register:
44-54 PSI: 2000, 2001, 2002 3.9L Dodge Dakota.
47-51 PSI: 2003 3.9L Dodge Dakota.
Let's take a look at what your results mean:
CASE 1: The fuel pressure gauge registered 0 PSI. This test result lets you know that the no-start problem is caused by a lack of fuel from the fuel pump.
I recommend that you take one more precaution, before condemning the fuel pump as bad, and this is to make sure 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: The fuel pressure gauge registered the indicated PSI. This is the correct test result.
With this test result you can conclude that the fuel pump is working and delivering enough fuel to the fuel injectors. You can also conclude that your 3.9L Dodge Dakota is not starting due to another reason. The fuel pump is OK.
