Nissan Engine Diagnostics – UnderhoodService

Nissan Engine Diagnostics

You don’t have to be an import specialist to know that Nissan cars and trucks have a good reputation for reliability and longevity. Nissan, under the Datsun name, was one of the first Japanese automakers to break into the U.S. market. They did it right, by establishing a strong dealer network and offering a quality product at the right price. In doing so, they have built a loyal group of customers.

In this article, we’ll take a look at some the common mechanical problems that have cropped up on this line of cars. “Common” is probably the wrong word, but with the amount of miles these cars deliver, some problems will inevitably show up.


Over the years, Nissan has used both timing belts and chains. Currently, in most of its vehicles, the valve train is controlled with a chain. If you had to pick a problem area with these engines, it would be in the valve timing area. And most of these problems are leaks. On GA16-equipped Sentra models, front crank seals are a common failure. It’s hard to miss this one with its tell-tale trail of oil being whipped off the pulley. They’re easy to replace by simply removing the pulley, popping out the seal, and installing a new seal and fresh drive belts. Be sure to inspect the seal contact area on the pulley for wear. If it’s deeply grooved, let it protrude slightly so the lip will contact an unworn portion of the pulley, rather than install the seal flush.

The K24 series of engines used in the Altima and Nissan trucks doesn’t have as big of a problem with the seal, but that’s not to say you won’t be confronted with a leak in the front seal area. Often mistaken for a crank seal, leaks from the front timing chain cover are a more common problem with this engine. The culprit is the passage where the oil travels from the cover-mounted oil pump into the block. Located on the rear of the engine, it’s easy to spot when you’re aware of it. While there have been some reports of the same problem on Sentras, it seems to be more prevalent on the bigger four.

Chain noises are another problem that will require removal of the timing chain cover. In the early ’90s, there were some problems with chain guides breaking, allowing the chains to stretch and contact the cover. The resulting noise has been described as sounding like a diesel at idle. These engines use two timing chains: A lower chain that runs from the crankshaft to an intermediary or jackshaft, and an upper chain from the jackshaft to the camshafts. It’s safe to assume that most of these problem cars have been taken care of and any noisy chains encountered today are probably the result of poor maintenance practices, high mileage or both. It’s a pretty big job to remove the timing cover. If you’re going in to repair a leak or noise on a high-mileage vehicle, it’s a good idea to replace the chains, guides and tensioner. Inspect the idler gear closely for wear. If there is any sign of deterioration in the teeth area, replace the gear. You don’t want to do this job twice.

Don’t be overwhelmed when looking at this job. It takes a solid five hours, but it’s not as bad as it looks. Keep the bolts in order as they’re removed, making note of the different lengths. Your repair information system may have you removing the cylinder head, but experience has shown that isn’t necessary. The oil pan will have to be removed to gain access to the oil pump pickup and you can then remove the front cover, taking care not to damage the head gasket. Be sure to thoroughly clean the pan by removing any bits of plastic from the broken chain guides. The chain guides from Nissan have been updated, so be sure to use them.

If you’ve completed a job on one of the four cylinders and find yourself without oil pressure, try to recall if you supported the engine with a jack under the pan. If so, you probably dented it slightly. The K24 engine has little tolerance in this area – the slightest dent will move the pan up to the pump pickup, closing it off.

The real strength in Nissan’s engine lineup is its V6. Originally built as 3.0-liter SOHC with a timing belt, this engine has powered the Maxima model to the top of the affordable sports sedan list. Now it’s grown in displacement and breathing capabilities to a 3.5-liter DOHC four-valve timing chain engine. But it hasn’t lost any of its reliability and the performance increase has kept pace with its competitors. You’ll still find the single-cam version in trucks and the popular Quest minivan. Now at 3.3 liters, this is the only Nissan engine still using a timing belt.


Like the four-cylinders, there are very few mechanical problems with these engines, but the most common issues are related to the timing chain area. In the early ’90s, Nissan went to a variable cam timing system that used a solenoid to open an oil passage, applying oil pressure to the cam gear and changing the timing. Some of these gears had problems with noise and/or leakage. Both of these problems can trick you into a misdiagnosis.

The noise is often mistaken for a valve lifter or timing chain problem, while the leak will have you blaming the cam seal. Like so many problems, this one should be easy to diagnose once you’re aware of the issue. To access the gears, only the top chain cover has to be removed, making it a relatively easy job. Mileage and maintenance history will have to be considered when deciding whether or not to change the timing chain and its related components.

The only problems the single-cam V6 has had could hardly be called mechanical engine issues. The most common of these is when an exhaust manifold stud breaks, causing an exhaust leak. Since the exhaust is only leaking out of one port, it can be mistaken for a valve or knocking noise. The difference with the exhaust leak is it will usually quiet down once the engine warms up and the manifold expands.

Be sure to check the manifold for flatness when it’s removed to drill out the stud. I can’t say why the stud breaks, but I would guess it’s caused by expansion, although the manifold on a V6 is pretty short. We simply replace the stud, reinstall the manifold and torque to spec – and haven’t done the same car twice. You would think if expansion were the cause, the problem would recur, but that doesn’t seem to be the case.

Removing the timing belt pulley from the crankshaft can also cause problems. It’s always a good practice to replace the water pump crank and camshaft seals when doing a timing belt, or you may have leakage from the crankshaft front seal that will require removing the pulley.

There are a couple of suggested ways to remove a stubborn one; both processes will have you drilling a couple of holes on the face of the pulley. One method is to drill and tap the holes to 8 mm allowing the use of a crossshaft-type steering wheel puller, while the other is to drill the holes and split the pulley with a chisel. Of course, splitting the pulley will require a new part. While it’s inexpensive, you’ll have to get one before the job can be completed. The drill and tap method will take longer, but it will allow you to reuse the pulley and get the vehicle back in service.

The last problem is oil leaks at the rear main seal area. If a leak is evident in the rear seal area, don’t be too quick to simply replace the seal without removing and resealing the seal housing. Although this problem seems to be most evident on the Quest, it’s a good practice on any Nissan engine that’s getting a new seal.


With so few mechanical problems to be concerned with, we should take a quick look at some of the other underhood problems that you might see.

Starting with the Sentra, be careful if a “towed in, no start” cranks like the compression is low. Remove the spark plugs and check for signs of flooding. If it’s started and runs for only a few minutes (for example, if the car is moved in the driveway), the plugs will get wet and the car won’t start the next time. When it’s tried, it will only flood worse. By the time the customer gives up and has the car towed, it will be so loaded with fuel that the plugs will be soaked and the oil will be overfull from the fuel in the crankcase.

To get started, remove the plugs, drain the oil and put a little oil in the cylinders as if you were doing a wet compression test. Crank the engine to oil up the rings, install fresh plugs and start the engine, allowing for a thorough warm up. To prevent a recurrence, be sure the base idle is set properly by unplugging the throttle switch and setting the idle with the air-bypass screw on the throttle body. Refer to your service information for details.


There are also some problems with distributors on the Sentra. The early models with E-16 engines would suffer from intermittent failures, causing the engine to quit while driving. Many times the engine would restart immediately, while other times it would require a couple of minutes of cool down time to refire. This can be a tough one to diagnose since the problem can’t always be duplicated. We’ve found this to be a common enough problem that we’re comfortable replacing the distributor when faced with it.

Later-model cars don’t seem to suffer from the photo-optical problems that the early cars do, but they’re having problems with the internally mounted ignition coil. For an experienced tech, diagnosing a dead coil shouldn’t be a problem. I find it easiest to simply hook up a tach and dwell meter to the negative lead of the coil and crank the engine, looking at the RPM signal. If you have a signal and power to the positive side, it should make spark. On these models, the coil is serviced with the distributor; rebuilt units are available from the dealer.

Look at the distributor if you’re faced with a “poor-running” problem on an Altima. On these vehicles, look for oil contamination that blocks off the slots in the reluctor, preventing the photo optics from functioning. The worst cases will be leaking oil from the distributor housing. We’ve had good success with cleaning out distributors that have built up oil over time and don’t have severe leakage problems. Units that have severe leaks will need to be replaced with a rebuilt unit.


The V6 engines will have us looking at a couple of problem areas, the most common of which is the air mass sensor. If you’re faced with a car that runs poorly and you suspect the air mass sensor, refer to your service information on how to retrieve codes. If you get a code for the sensor, it’s a safe bet to replace it. We’ve had good luck with aftermarket rebuilt units that will save the customer some money.

Most of the other problems we see are dead cylinders, which are most common on twin cams that use the coil-on plug system. Coil failures are common. While it’s not difficult to run tests on the coil, it’s hard to argue with the ease of simply switching the coil from an adjoining cylinder.

Recently, we’ve gotten in the habit of checking compression and spark plug condition while switching the coils in anticipation of the coil being good. That way we know that the engine and ignition system are up to the job and if the cylinder still doesn’t run, we can take a hard look at the fuel system.

Vacuum leaks don’t seem to be an issue with this engine but we’ve had some bad injectors. Using your stethoscope, compare the sound of the injector in the bad cylinder with a good one; you’re listening for a sharp clicking noise. The offending injector will have a “dull” sound to it. As luck would have it, the problem is usually with the injectors on the rear bank that require removal of the upper plenum to gain access.


We all should be familiar with retrieving check engine lights and codes, and finding definitions in our service information systems. If you’re lucky enough to have software for your scanner that allows you to get more than generic OBD II codes and data, take the time to look for and explore the functional tests that will make your diagnostic process much easier.

With the proper software, many tests can be performed using the scanner and will save you a great deal of time. From cylinder balance tests to triggering the fuel pump relay, this feature will make quick work of some of your diagnostic challenges.

I’ll share some tips on the scanner and codes that may save you some time or prevent you from heading down the wrong path. Knock sensor codes are common, but they won’t set the CEL, nor do they seem to cause any driveability problems. If you’re working on a “poor-running” complaint, it’s safe to say the knock sensor isn’t the cause of the problem.

If you’re checking a “no-start” condition and spark is present but there’s no sign of flooding, the ability to trigger the fuel pump from the scanner is a big help. Just by listening closely, you can hear the relay close and can tell if the pump is running or not. Sometimes, all it takes is a gentle tap on the bottom of the tank to get a stubborn pump going, while a quick check for voltage and ground going to the pump can confirm that it needs to be replaced – not an uncommon problem with the Nissan line.

The final tip involves an EGR flow problem on the Quest. If faced with a code, go no further until you check that the exhaust pressure sensor line going to the top of the EGR modulator isn’t burned through. Mounted at the top of the engine under the cowl, the hose isn’t easy to see, but it’s easy to reach. You’ll have no problem feeling a damaged one.

Of course this short article won’t make you an overnight Nissan expert. But I do hope it will make you more comfortable when one of these popular vehicles finds its way into your bay. There’s no reason you shouldn’t be able to tackle any job that these cars might bring.

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