There is a method to the madness of diagnosing an engine no-start problem and in this article, I'll explain what I did to diagnose a no-start condition on a 2002 1.8L Nissan Sentra that belongs to some friends of mine.
As you'll see, as I spin this yarn, the camshaft position (CMP) sensor was the component that had failed and was preventing their 1.8L Nissan Sentra from starting.
Contents of this tutorial:
- The Complaint: Nissan Sentra Cranks But Does Not Start.
- STEP 1: Making Sure That The Fuel Pump Is Working.
- STEP 2: Checking All Ignition Coils For Spark.
- STEP 3: Checking That The Fuel Injectors Are Being Activated.
- STEP 4: Checking For Trouble Codes.
- STEP 5: Testing The CMP And CKP Sensors.
- More 1.8L Nissan Sentra Tutorials.
You can find this tutorial in Spanish here: Resolviendo Un Arranca Pero No Prende -Estudio De Caso (2002 1.8L Nissan Sentra) (at: autotecnico-online.com).
The Complaint: Nissan Sentra Cranks But Does Not Start
As I mentioned earlier, the 2002 Nissan Sentra would crank but not start. My friends were under the impression that the fuel pump was bad and were preparing to have it replaced when they called me for my opinion.
Testing the fuel pump pressure with a fuel pressure gauge is a piece of cake on this Nissan Sentra, so I offered to go over and check it for them.
STEP 1: Making Sure That The Fuel Pump Is Working
Since the concern was that the fuel pump had failed, the first thing I did was check the fuel pressure with a fuel pressure test gauge.
On the 2002 Nissan Sentra, testing the fuel pump is easy because all you have to do (to test fuel pressure) is connect the fuel pressure test gauge in series with the fuel hose that connects the fuel filter to the fuel injector rail.
If you look at the photo above, I disconnected the fuel hose where it connects to the metal fuel line at the top of the intake manifold plenum (the orange arrow points to this location) and installed the fuel pressure test gauge there.
Here's a breakdown of what I did:
- I disconnected the fuel hose that connects to the fuel pressure line at top of the intake manifold plenum (the arrow in the photo points to the hose).
- I connected the fuel pressure gauge to this hose with a T fitting (which is included in the fuel pressure gauge kit).
- Using the fuel hose included in the kit, I connected the other end of the T fitting to the metal fuel line going to the injectors.
- I tightened all of the hose clamps and then cranked the engine while observing the fuel pressure gauge needle.
Well, it turned out that the fuel pump was producing the correct pressure. Now that I knew the fuel pump was not the cause of the engine's no-start issue, I needed to make sure the ignition coils were sparking.
STEP 2: Checking All Ignition Coils For Spark
After checking and confirming that the fuel pump was not the cause behind the Nissan Sentra's no-start issue, the next step was to make sure the ignition coils were sparking.
I performed this test using a dedicated spark tester. The spark tester I use is the HEI spark tester. This spark tester is the only one I trust to give me an accurate spark test result.
Basically, if the ignition coil makes the HEI spark tester spark, then that ignition coil is working properly.
You can check out this spark tester here: HEI Spark Tester (at: easyautodiagnostics.com).
Here's the breakdown of what I did:
- I unplugged and removed the #4 cylinder ignition coil.
- Once the coil was removed, I reconnected it to its connector.
- I connected the HEI spark tester to the ignition coil.
- I grounded the HEI spark tester directly to the negative (-) battery post with a jump start cable.
- I asked my friend to crank the engine while I observed the spark tester.
The result was that the #4 ignition coil did not spark. I tested the other three ignition coils and none sparked.
Since it's almost impossible for all four coils to fail at the same time, these test results told me the problem wasn't caused by failed ignition coils.
So far, having eliminated the fuel pump and ignition coils as the cause of the engine's no-start issue, my next test was to see if the fuel injection computer was activating the fuel injectors.
STEP 3: Checking That The Fuel Injectors Are Being Activated
So far in my tests I had ruled out the fuel pump and the ignition coils as the cause of the engine's no-start issue.
Now I was curious to see if the fuel injection computer was activating the fuel injectors.
To find out, this is what I did:
- I disconnected the #4 cylinder fuel injector from its connector.
- I plugged the appropriate Noid light into the fuel injector connector.
- I had my friend crank the engine while I observed the Noid light.
What I was looking for here was for the Noid light to blink ON and OFF while the engine is cranked.
Well it turned out that the Noid light did not blink ON and OFF (connected to the #4 fuel injector connector), so I checked the other three. None made the Noid light blink ON and OFF.
These four test results confirming that the injectors were not receiving an activation signal and the lack of spark from all four ignition coils told me that the most likely cause of the engine's no-start problem was probably a bad sensor of the crankshaft position (CKP) sensor.
But before testing the crankshaft position sensor, I took out my generic scan tool and checked the Nissan Sentra's fuel injection computer's memory for diagnostic trouble codes.