Current Trends for Ignition Systems

Current Trends for Ignition Systems

As automotive technology moves forward, ignition systems are becoming more and more entangled with other systems on the engine. The current generation Nissan Maxima 3.5L V6, which was introduced in 2004, has a fairly conventional coil-on-plug (COP) ignition system. The individual coils are driven by the powertrain control module (PCM) using the input signal from the crankshaft position (CKP) sensor as the primary timing trigger. But what makes this system different from others you may be familiar with is that the PCM also uses input signals from the two camshaft position (CMP) sensors (one for each cylinder bank) to modify spark timing. Nissan also refers to the camshaft position sensors as “PHASE” sensors (for cam phasing, I assume).

Spark timing on the 3.5L engine is nonadjustable and is controlled by the computer. You can read the timing on a scan tool, or if you prefer to do things the old fashioned way, you can actually check the spark timing on this engine with a timing light. The catch is you first have to remove the #1 COP ignition coil (the first cylinder on the rear bank) and insert a plug wire between the coil and spark plug. Then you can clamp your inductive pickup onto the plug wire and observe the timing marks on the crankshaft pulley. The timing spec for this engine is 15° plus or minus 5° BTDC (Before Top Dead Center). The idle spark timing can vary quite a bit depending on what the PCM thinks the engine needs based on operating conditions.

So what happens if you check the timing and see that it’s outside the specs? Nissan has a special procedure for this called the “Idle Air Volume Learning” procedure. The 2004 and newer 3.5L V6 engines are throttle-by-wire, so the PCM will vary spark timing according to throttle position, idle speed and airflow into the engine. Nissan says the Idle Air Volume Learning procedure must be done anytime the PCM or electronic throttle control actuator is replaced, or anytime the ignition timing or idle speed are not within specifications. Nissan also recommends doing this procedure anytime an engine has a stalling problem or an erratic idle issue.

Before you can do this procedure, the engine and transmission fluid must be warm. The coolant temperature should be above 158° F, and the vehicle should be driven for 10 minutes or more to warm up the transmission fluid. The charging system must be putting out 12.9 volts or more at idle, the gear shift selector must be in Park or Neutral, and all the lights and accessories (A/C, heater, radio, etc.) must be off. On vehicles with daytime headlights, applying the parking brake before the engine is started will prevent the headlamps from turning on.

The easiest way to do the Idle Air Volume Learning procedure is with the Nissan Consult-II factory scan tool. All you do is select the test, touch Start and wait until the scan tool displays “CMPLT” for test complete. You can then rev up the engine a couple of times and recheck the timing and idle speed to make sure they are now within specifications.

There is also a manual procedure for doing the Idle Air Volume Learning procedure if you don’t have a Nissan factory scan tool handy:

  1. With the engine and transmission warmed up, turn off the key and wait at least 10 seconds.

  2. Confirm that accelerator pedal is fully released, turn on the ignition switch and wait three seconds.

  3. Repeat the following quickly five times within five seconds:

    – Fully depress the accelerator pedal.

    – Fully release the accelerator pedal.

  4. Wait seven seconds, then fully depress the accelerator pedal and hold it for approximately 20 seconds until the MIL stops blinking and turns on.

  5. Fully release the accelerator pedal within three seconds after the MIL turns on.

  6. Start engine and let it idle.

  7. Wait 20 seconds.

  8. Rev up the engine two or three times and make sure that idle speed is 625 rpm plus or minus 50 rpm, and that spark timing is 15° plus or minus 5° BTDC.

If idle speed or ignition timing are not within specs, you’ve got a problem. Inspect the throttle valve to make sure it is fully closed. Check the PCV valve (make sure it rattles and is sucking vacuum). Check for any air leaks downstream of the throttle. If no problems are found, check all the wiring harness connectors to the throttle actuator, and check throttle position sensor and airflow sensors for possible faults.

Misfire Codes
If the MIL is on and you find a P030X misfire code for a specific cylinder, the fault may be a fouled spark, a bad ignition coil or even a burned valve. See coil locations in Figure 1. Chances are the misfire might be a bad coil since Nissan has had a history of coil issues on the previous generation Maxima.

On the 2001-’03 Maximas, coil failures at relative low mileages (60,000 to 70,000 miles) are not uncommon. Nissan has not recognized the problem and has not issued a technical service bulletin about the coil failures. But they do recommend replacing all six coils if one fails. Why? Because when one coil fails, chances are another will fail not too far down the road. The coils cost about $85 each, and the part number is 224488J115.

These earlier generation coils also have had a problem with RFI (Radio Frequency Interference) causing static on the car radio. Nissan issued a bulletin NTB01-073B, dated March 1, 2002, covering 2002 Maxima, Altima and Sentra models.

The bulletin says the cause of a steady, rhythmic ticking or popping noise in the radio speakers that follows engine speed on certain FM radio stations can be caused by the ignition coil resistors (which are located inside the ignition coil tube that fits down over the spark plug).

To get to the coils on the 2002 engines, it is only necessary to separate the intake collector from the intake manifold as shown in Figure 2 on page 18. You do not have to remove the throttle body from the intake collector or drain the radiator. The resistors inside the coil tubes can then be replaced by pulling the rubber boot away from the ignition coil. Then twist and pull the ignition coil tube to separate it from the coil. The old resistor assembly inside can then be replaced with the new resistor as shown in Figure 3.

On the current generation Maximas, a different style of COP coil is used and failures have not been an issue (at least not yet) — which is a good thing because the coils are harder to replace. If you have to change one (or all six), here’s the procedure:

  1. Remove the plastic engine cover.

  2. Drain the radiator.

  3. Disconnect the mass air flow sensor electrical connector and remove the air cleaner assembly and air intake tubes.

  4. Remove the intake manifold collector, gasket and electric throttle control actuator.

  5. Replace the coil(s).

The ignition coils for the current Maximas are also about $85 each, and the standard labor to replace all six is 2.2 hours according to Nissan. The part number is 224488J115.

Spark Plugs
The factory-installed spark plugs in the 2004 and up Maximas are PLFR5A-11 NGK platinum plugs with a 100,000-mile service interval. The electrode gap is 1.1 mm (0.043”). If a cylinder misfire is due to a worn, fouled or shorted spark plug, you still have to go through the same coil removal procedure because the plugs are buried down under the coils. You’ll need a magnetic spark plug socket and a long extension to extract them from the holes in the valve covers.

Reading the plugs is still a useful diagnostic practice for seeing what’s actually going on inside the combustion chamber. And, Nissan’s 3.5 V6 engines have a pretty simple firing order. See Figure 4. If a plug is wet, it means the coil isn’t firing. If the electrodes and insulator on the plug are covered with black soot, the cylinder is running too rich (possibly a leaky fuel injector, or maybe a sticky fuel pressure regulator or bad O2 sensor if all the plugs are carbon fouled). If the plugs have wet, oily carbon deposits, the engine is burning oil. The most likely cause would be worn intake valve guides and seals, or possibly worn or broken piston rings. Oil burning can not only foul the plugs, but also cause a buildup of heavy carbon deposits on the intake valves and inside the combustion chamber. This, in turn, may cause hesitation problems when accelerating, or possibly spark knock (detonation).

Knock Sensor
The Maxima engine requires premium fuel, but will also run on lower octane gas because it has a knock sensor (located in the middle top of the engine under the intake plenum). If the knock sensor detects spark knock when the engine is under load, it will send a signal to the PCM to retard spark timing. There shouldn’t be any spark knock if the knock sensor is doing it’s job and there is not too heavy a buildup of carbon in the combustion chambers or on the tops of the pistons. If an engine has a spark knock issue, therefore, the problem might be a defective knock sensor or a heavy buildup of carbon in the engine. If switching to 91 octane gas doesn’t eliminate the problem, and the knock sensor is generating a signal, the carbon needs to be removed from the engine with a Top Cleaner treatment.

You can check the knock sensor by looking at the scan tool to see if is generating a signal, or by measuring the resistance between knock sensor terminal 1 and ground. A good knock sensor should measure 532-588 kOhms at room temperature. Nissan says to handle the knock sensor carefully because it can be damaged if it is dropped onto a hard floor. If you need to replace a knock sensor on a 2004 or newer Maxima, the part number is 220607S000. The part costs about $95 and takes 2.6 hours labor to replace because of its buried location (the top of the intake manifold has to come off).

No Start, No Spark
If you encounter a Maxima that won’t start, the fault might be no spark or it might be no fuel. A quick way to find out is to spray some starting fluid into the throttle or air intake and see if the engine starts. If it starts and runs a few seconds, then dies, the problem is no fuel (bad fuel pump, fuel pump relay or a leaky fuel pressure regulator). If it does not start, the PCM may not be getting a good rpm signal from the crank position sensor.

The crank sensor, which Nissan refers to as a “POS” (position sensor), is located on the oil pan, is a magnetic sensor with a Hall effect chip inside that converts the AC signal to a digital rpm signal. There are no resistance specs for this sensor other than zero (on) and infinite (off). You can use your scan tool or a scope to see if the sensor is generating an rpm signal when the engine is cranking, or a noid light to check for a digital signal output. If the sensor is bad and you need a new one, the part number is 23731AL60C and the cost is about $70.

Another component in the ignition system that may cause a no start because of no spark is the ignition system relay (located in the underhood relay center along with the fuel pump, cooling fan, starter, PCM and headlight relays). An open relay will kill power to the ignition coils.

The ignition system also has a condenser in the circuit that runs from the PCM relay to the ignition coils. A shorted condenser could also ground out the ignition circuit causing a no start. The condenser can be checked by measuring the resistance between terminals 1 and 2. A good condenser should have 1M Ohms or more of resistance.

Nissan has a bulletin out for a hard hot starting problem on the 3.5L V6 in the early 2004 Maxima and Quest, and 2003-’04 Altima models. The symptom it describes is an engine that starts OK cold, but is hard to start after it has been driven. The check engine light may or may not be on, and DTC codes P0340 (CMP sensor bank 1) and/or P0345 (CMP sensor bank 2) may be present. See Figure 5. In any event, Nissan says the fix is to replace one or both camshaft position sensors. The part number of the rear bank (bank 1) CMP sensor is 23731-65906, and the front bank (bank 2) CMP sensor is 23731-Al616. The CMP sensors are the same type as the CKP sensor, and also cost about $70 each.

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