TEST 3: Making Sure The Engine Has Good Compression
If your tests have confirmed that all 8 cylinders have spark and fuel injector pulses and that the fuel pump is OK, then I suggest testing your Dodge Dakota or Durango's engine compression.
I've written a detailed ‘how to test the engine compression’ tutorial for the 4.7L Dodge Dakota and Durango, and you can find it here: How To Check Engine Compression (Dodge, Jeep 4.7L V8) (at: troubleshootmyvehicle.com).
Alright, let's get started:
Remove the ignition coils and the spark plugs from all 8 cylinders.
Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder. Hand tighten the compression gauge only! Do not use any type of tool to get it tight.
Have your helper crank the engine till the needle on the compression gauge stops climbing.
Now, record the value on a piece of paper and repeat steps 3 and 4 on the remaining cylinders.
Let's take a look at what your compression test results mean:
CASE 1: All cylinders have compression above 120 PSI. This is the correct and expected test result.
If all cylinders have at least 120 PSI of compression, then you can conclude that the engine does not have a compression problem (causing it not to start). Now, if your Dakota or Durango's engine is not starting, the next step is to see if you have a blown head gasket on your hands.
CASE 2: All cylinders have 0 PSI compression. This tells you that 0 compression is the cause behind the no start problem on your 4.7L Dodge Dakota or Durango.
The most likely cause will be a broken timing chain or the engine threw a rod.
CASE 3: Two adjacent cylinders have 0 PSI. This usually indicates a blown head gasket. Specially if your Dodge Dakota or Durango overheated before the no start problem occurred.
For more testing suggestions, take a look at this tutorial: How To Test For A Blown Head Gasket (4.7L Chrysler, Dodge, Jeep) (at: troubleshootmyvehicle.com).
TEST 4: Checking For A Blown Head Gasket
A blown head gasket (and the 4.7L V8 engine has two of them) can cause the engine to not start.
In case you're wondering, a blown head gasket is usually caused by severe engine overheating.
Testing for a blown head gasket involves 3 to 4 specific tests. None of them are hard to do and you can find them explained in detail in this tutorial: How To Test For A Blown Head Gasket (4.7L Chrysler, Dodge, Jeep) (at: troubleshootmyvehicle.com).
No Start Troubleshooting Summary
Testing a ‘cranks but does no start’ condition all boils down to a process of elimination.
The most important thing you should remember is that the engine is not starting due to a lack of spark, or a lack of fuel, or a lack of compression.
By checking these basic things (spark, fuel, air), you'll save yourself the frustration of replacing components that won't solve the problem.
As you noticed, I started out the troubleshooting tests with a spark test (at all cylinders). This is due to the fact that the culprit behind most no start problems is the ignition system, specifically a defective crankshaft position sensor.
Once you've confirmed that you've got spark at all cylinders, there isn't any need to spend time testing the crankshaft position sensor. The next step is to make sure the fuel pump is working and so on and so on.
Where To Buy An HEI Spark Tester And A Fuel Pressure Gauge
As I mentioned before, the HEI spark tester (OTC 6589) is an accurate spark tester and it doesn't cost and arm and a leg. The fuel pressure gauge that connects to the Schrader Valve on the fuel rail (of your 4.7L Dodge Dakota or Durango) is a reasonably priced tool too:
More 4.7L Dodge Tutorials
You can find a complete list of 4.7L Dodge tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The MAP Sensor (2000-2001 4.7L Dakota, Durango).
- How To Test The Throttle Position Sensor (2000-2007 4.7L Dodge).
- How To Test The Fuel Injectors (Dodge, Jeep 4.7L V8) (at troubleshootmyvehicle.com).
- How To Test For A Blown Head Gasket (4.7L Chrysler, Dodge, Jeep) (at troubleshootmyvehicle.com).
- How To Test The COP Ignition Coils (Chrysler, Dodge, Jeep 4.7L) (at troubleshootmyvehicle.com).
If this info really saved the day, buy me a beer!