Tool Briefing: Look and Listen

Diagnosing internal engine noise with sound and sight


Direct Hit: 295581

Vehicle Application: 2004 Nissan Maxima, 3.5L engine

Customer Concern: Timing chain rattling noise.

Average Reported Mileage: 96427

Tests/Procedures:

  1. Check oil level and condition. Change the oil and see if the noise goes away.
  2. With the engine idling, energize the intake valve timing control solenoids by grounding the Red wire for the bank 1 and the Yellow wire for the bank 2 and see if the noise goes away. This indicates faulty intake camshaft sprockets.
  3. If the noise does not go away, check the timing chain tensioners per the Nissan TSB NTB07-042d.

Tools Used

  • Oil pressure test gauge
  • Stethoscope (mechanical and electronic)
  • Video inspection scope

Noise coming from inside an engine means something is broken or worn. Engine wear is controlled by supplying oil pressure to the bearings and valve train components. On this engine, oil pressure also operates the timing chain tensioners. Measuring the wear on any of these parts requires at least partial disassembly of the engine. However, with a few special tools and just a little bit of diagnostic time, it’s possible to learn more about the noise described here before committing to hours of engine surgery.

Oil condition and pressure testing

It’s not really possible to determine the condition of the oil just by pulling the dipstick, especially in this situation. It’s faster and ultimately less expensive to just change the oil and eliminate that as a possible cause. Don’t forget to catch the oil in an open pan and look for the tell-tale swirls of metal or other contaminants. If there’s nothing obvious, or even if there is, the next step is to check oil pressure.

An oil pressure gauge on the instrument panel is generally not accurate enough or doesn’t have enough resolution for diagnostic purposes. Better to measure oil pressure directly with an external mechanical gauge. Remove the oil pressure sensor or sending unit, and install a gauge or adapter directly into the same hole. Many domestic models use SAE straight thread or pipe thread for the oil pressure sending unit, while imports generally use ISO metric thread or a banjo bolt fitting.

 

There are test kits available with adapters for all the different threads and sizes, and a quick-connect fitting for the gauge. Some have fittings that allow the gauge to be used for checking transmission pressures too. Some are also suitable for use with fuel systems, but they should not be used that way unless instructed to do so. If the kit includes an extension hose, the gauge can be temporarily taped to the windshield to check engine oil pressure or transmission fluid pressure while driving the vehicle.

What's that sound?

This engine has variable intake camshaft timing, operated by oil pressure and controlled with a solenoid valve on each camshaft. In Step 2, the control valves are driven fully open, and if the intake cam sprockets are faulty, the noise should go away. However, this engine has three timing chains: a long main timing chain and a short one on each cylinder head. Each has its own tensioner, and the water pump is also driven by the main timing chain. With so many items that could cause timing chain noise, you’ll need a way to isolate each component to pinpoint the source. An electronic stethoscope is the answer.

Most techs are familiar with using a long screwdriver or socket extension as a stethoscope, but an electronic listening device is far more precise and effective, especially in a noisy shop environment. An electronic stethoscope has an extremely sensitive microphone that tightly focuses the ‘listening area,’ and the headphones block out ambient noise so you only hear what the mic picks up. The amplifier has a volume control, and some also have an adjustable noise filter.

 

There are two basic types of electronic stethoscope. One type has a flexible wand that must be in direct contact with the subject, just like a mechanical stethoscope. It’s ideal for pinpointing a bad bearing or a dead injector, or in this case a slack timing chain. Some have a light at the tip of the wand, providing an easier point of reference in dark, tight spaces.

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