AfterMarketNews AfterMarketNews Auto Care Pro AutoCareCareerHub Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

Diagnostic Dilemma: The Case of the Missing Code

When doing mobile diagnostic work, no-code stalling complaints are a major part of your agenda. In most cases, the client shop is simply too busy to duplicate the failure or, in some cases, a long test drive will yield nothing in the way of useful...

Read more...

Secondary Ignition: The Art of Spark

What is a coil? From the beginning of the internal combustion engine, several different ignition systems have been used to create a high-energy spark. The most popular system, and the one that’s in use today, is a step-up coil. A coil is nothing...

Read more...

Diagnosing Catalytic Converter Failure Symptoms

Although construction can vary according to engine application, the common three-way catalytic converter contains a reduction and oxidation stage. To create maximum surface area, each stage is generally a ­ceramic or stainless steel honeycomb substrate...

Read more...

Electronic Proportioning Valve: Doing More With Less Hardware

Anti-lock brake systems (ABS) and the HCU are replacing proportioning, combination and other valves to change the braking forces in the front and rear. This is called Electronic Brake Distribution (EBD) and it can dynamically change the proportioning...

Read more...

NHTSA’s GM Brake Line Corrosion Investigation: Reading Between the Brake Lines

There will be no recalls on some GM vehicles for brake line corrosion. Instead, we received an advisory from the National Highway and Traffic Safety Administration (NHTSA) about brake line inspection and car washes. What was not discussed was the corrosion...

Read more...

2007-2011 Ford Expedition and Navigator Air Suspension

The Ford Expedition air suspension does more than just lift and raise the vehicle. The system levels the vehicle under loads and when a trailer is attached. The system uses only two air bags on the rear axle unlike previous models with air bags on all...

Read more...

MAZDA: Timing Belt & Chain Replacement

This month, we’re going to be looking at the ­timing components on the Mazda line of vehicles. We’ll be focusing on timing belts since they are considered a service item and will present the greater amount of opportunity for replacement. Then, we’ll...

Read more...

Honda Element Brake Job

It may look like a car that was never removed from the box it came in, but the Honda Element isn’t boxy when it comes to the brakes. Based on the CR-V platform, there is also nothing tricky when it comes to service. But, its brake system is hardware...

Read more...

The Changing Maintenance Market: New Technologies Mean More Opportunities

Most of us wake up each morning, not ­realizing that our professional world has changed even as we slept. Our first job of the day is to service a ­vehicle equipped with an oil life monitor. Not only do we discover that modern oil life monitors can...

Read more...

Converter Codes: How Long Will the Light Stay Out?

OBDII systems with faulty catalytic converters will normally store a diagnostic trouble code (DTC) when the converter begins to fail. The OBDII converters use an upstream and downstream oxygen sensor to measure the differences in oxygen content between...

Read more...

Maintaining Your Spray Guns

If there’s one piece of equipment that epitomizes the painter and the paint shop, it’s the spray gun. Over the years we’ve seen many spray guns. Although there are operating principles and functions that remain the same, some have been improved...

Read more...

Wheel Bearing Adjustment Tools & Equipment

A recent survey showed that more than half of the bearings on the road today are adjusted incorrectly. A wheel bearing that’s out of adjustment can reduce bearing life and can affect more than just the bearing. An out-of-adjustment bearing affects...

Read more...

Print Print Email Email

By Larry Carley
Technical Editor

Question: My engine burned a piston. What does that mean and why did it happen?

Answer: It means the piston failed due to excessive heat in the combustion chamber. A burned piston will typically have a melted appearance, or a hole burned completely through the top of the piston. Aluminum can only withstand so much heat, and when it gets too hot, it melts. The underlying cause is usually detonation and/or pre-ignition.

Detonation occurs when the temperature and pressure inside a cylinder exceed the fuel’s octane rating. Instead of igniting when the spark plug fires, the air/fuel ignites spontaneously much like a diesel engine. This creates multiple flame fronts within the combustion chamber that collide and hammer the top of the piston, producing a metallic knocking noise called “spark knock.”

Common causes of detonation include a buildup of carbon deposits in the combustion chamber and on the top of the piston that increase compression, no EGR (exhaust gas recirculation), overadvanced ignition timing, a bad knock sensor, a lean fuel mixture, low quality gasoline that does not meet minimum octane requirements, or any cooling problems that causes the engine to run hotter than normal (coolant leak, low coolant level, bad water pump, stuck thermostat, restricted radiator, defective cooling fan, even exhaust restrictions that back up heat into the engine.

Pre-ignition occurs if a hot spot develops in the combustion chamber that ignites the air/fuel mixture before the spark plug fires. The hot spot may be the spark plug itself, an overheated exhaust valve, carbon deposits in the combustion chamber, or a sharp edge in the combustion chamber.

Common causes of pre-ignition include the wrong heat range spark plugs (too hot for the application), carbon deposits in the combustion chamber and on the tops of the pistons, a lean fuel mixture, detonation or anything that makes the engine run hotter than normal.

On engines that are turbocharged or supercharged, too much boost pressure and/or not enough fuel can burn a piston very quickly. Check the operation of the wastegate and boost control system. If the turbo system has been tweaked to deliver higher than stock boost pressure for more power, the turbo may be pushing more air into the engine than the stock injectors can handle, causing the fuel mixture to lean out and burn the piston.

An often overlooked cause of piston burning is a weak or dirty fuel injector. If an injector is not spraying enough fuel into the combustion chamber, the air/fuel mixture in that cylinder may become too lean increasing the risk of detonation, pre-ignition and piston damage.

Diagnosis requires using a scan tool to check for lean codes and to look at fuel trim values. If a P0171 or P0174 code is found, or the long term fuel trim readings are 10 or higher (indicating a lean mixture), the engine may have one or more weak or dirty injectors.

The only way to know for sure is to remove the injectors, clean them on a fuel injector cleaning machine, then flow test all the injectors and compare the results. Any injector that does not flow within 5 to 8 percent of the rest should be replaced.

Question: What is a ‘scuffed’ piston?

Answer: A scuffed piston is one that has been damaged by rubbing against the cylinder wall. The metal-to-metal contact smears the metal on the skirt on the piston and damages the piston.

Scuffed pistons can be caused by too much heat in the combustion chamber, engine overheating or inadequate lubrication. The piston-to-cylinder clearances in most late model engines is much less than it used to be to reduce piston rock and noise. Consequently, if the piston or cylinder gets too hot, the clearance goes away and you get metal-to-metal contact.

In instances where piston scuffing occurred due to a loss of lubrication, the underlying cause may be a low oil level in the crankcase (due to a lack of maintenance or an oil leak), low oil pressure (a worn oil pump), poor oil quality, or oil breakdown (not changing the oil often enough).

When diagnosing a scuffed piston, note where the piston is scuffed. If the cause is overheating, the scuffing will mostly be on the upper ring lands and on the sides near the wrist pins.

There may also be oil carbon and lacquer burned onto the underside of the piston indicating it got too hot. Scuff marks on the lower skirt area often indicates a lack of lubrication (check the oil pump and pickup screen). Scuff marks on the edges or corners of the thrust sides of the piston may be the result of bore distortion. Scuffing on both thrust sides would indicate binding in the wrist pin.

Some original equipment pistons and many aftermarket performance pistons now have special anti-scuff skirt coatings to reduce the risk of scuffing.

The following two tabs change content below.
Latest articles from our other sites:

Ultimate Underhood: From Mechanical Fuel Injection to Putters

Mechanical constant stream fuel injection is the pinnacle of pure mechanical engineering. The mechanic setting up the system must optimize the amount of fuel for a given throttle position, rpm and engine...More

Induction Cleaning Service For Direct-Injection Vehicles

You may have seen it before: misfire codes, stumbling and suspicious fuel trim numbers. On a scan tool, the engine may show a loss in volumetric efficiency. The driver may complain about a loss of power,...More

Electronic Proportioning Valve: Doing More With Less Hardware

Anti-lock brake systems (ABS) and the HCU are replacing proportioning, combination and other valves to change the braking forces in the front and rear. This is called Electronic Brake Distribution (EBD)...More

NHTSA’s GM Brake Line Corrosion Investigation: Reading Between the Brake Lines

There will be no recalls on some GM vehicles for brake line corrosion. Instead, we received an advisory from the National Highway and Traffic Safety Administration (NHTSA) about brake line inspection and...More

Tips For Spark Plug Removal

Removal or installation of spark plugs on modern vehicles requires extreme precision and care. Before removing a spark plug, check to see if it’s still working properly and whether the engine itself...More

Oil Service for Today’s Vehicles

You have most likely been made aware over the last few years that you need to be diligent in which oil you choose when servicing today’s modern vehicles. Hopefully your team is trained to look up the...More

Beta Tools Offers Double Swivel End Socket Wrenches

Beta Tools of Italy offers #80 double-end, swivel socket head wrenches, which are made to swivel 180° on a single-plane axis to allow access to confined spaces. They are bright polished chrome vanadium...More

Electronic Specialties Introduces Its Automotive Test Lead Set

Electronic Specialties introduces a new product, #635 CATIII Automotive Test Lead Set. This kit includes a basic assortment of accessory test leads, which are in compliance with IEC Safety Rating of...More