A bad fuel pump will cause a ‘cranks but does not start’ condition. A fuel pump that's failing and not creating enough pressure will cause engine performance problems.
So, if you suspect that the fuel pump is bad and behind your 4.7L equipped Dodge's problem... this tutorial will help you test it!
Contents of this tutorial at a quick glance:
- Symptoms Of A Bad Fuel Pump.
- TEST 1: Using Starting Fluid To Confirm Lack of Fuel.
- TEST 2: Checking Fuel Pressure With A Fuel Pressure Gauge.
- Where To Buy A Fuel Pressure Test Gauge.
- Where To Buy The Fuel Pump And Save.
- More 4.2L Ford Diagnostic Tutorials.
You can find this tutorial in Spanish here: Cómo Probar La Bomba De Gasolina (4.7L Dodge Dakota, Durango) (at: autotecnico-online.com).
Symptoms Of A Bad Fuel Pump
Fuel pumps usually fail in one of two ways. They either completely fail or die a very slow death. By a ‘slow death’ I mean that they still function but don't send enough 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 8 ignition coils are sparking (confirming it's not an ignition system problem).
- The PCM will still pulse (activate) all 8 fuel injectors.
But when the fuel pump fails slowly, your Dodge 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 has failed completely or is still barely hanging on... you can check the state of the fuel pump with a fuel pressure gauge. Alright, with this info under our belts, let's get testing.
TEST 1: Using Starting Fluid To Confirm Lack of Fuel
Using starting fluid, to test a no start problem, is probably one of the most common tests performed to acertain the problem is caused by a lack of fuel/bad fuel pump condition.
Now, having said that, using starting fluid to diagnose a bad fuel pump is not the most accurate way. Still, it's an effective test.
NOTE: To get an accurate test result from the starting fluid test, it's a good idea to check that the ignition coils are sparking. You can easily accomplish this by using a spark tester to check for spark.
IMPORTANT: This is a very fast and easy test but you do have to take one very important safety precaution and this is to reconnect the air intake duct after spraying starting fluid down the throttle bore (although you don't have to fasten it). This will prevent any backfire, that might occur, from scaring the heck out of you when cranking the engine.
This is what you have to do:
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.
Open the throttle plate and spray starting fluid down the bore.
As a safety precaution reconnect the air duct after you have sprayed a good squirt of starting fluid (but you don't have to tighten the air duct's hose clamp).
Crank the engine once the air duct is back on and you're clear of the engine compartment.
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 test result tells you that the no start problem is due to a lack of fuel.
Your next step is to check to see what the fuel pressure is with a fuel pressure test gauge. Go to: TEST 2: Checking Fuel Pressure With A Fuel Pressure 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 and this is to check the fuel pressure with a fuel pressure test gauge. Go to: TEST 2: Checking Fuel Pressure With A Fuel Pressure Gauge.