By the release of the restyled version of the BMW X3 Facelift in 2014, a new generation of diesel engines was introduced, which in subsequent years may become an integral part of the European BMW car fleet. The B47 engine, like its N47 predecessor, has four cylinders and a 2.0 liter displacement. Numerous improvements were aimed at reducing fuel consumption and improving the sound of the engine. In an interview, Christian Bock, head of the new engine development project, revealed many of the technical features of the new 4-cylinder diesel unit, which is offered in 150 and 190 hp versions.
The importance of an economical yet powerful diesel engine to the European market cannot be overestimated. For example, the 520d engine has not only dominated the BMW 5 Series for a long time, but is also very popular in the 3 Series and X1 and X3 off-road models. With the release in 2014 of the restyled version of the BMW X3 F25 LCI, the previously used N47 engine will retire and will be replaced by the new BMW B47.
Like its predecessor, the B47 has four cylinders in line, common rail injection, 1,995 cubic centimeters of displacement and a single variable geometry turbocharger.
While the N47 in the x18d and x20d versions had 143 and 184 hp, the new B47 offers 150 and 190 hp. The maximum torque in the case of the 150-horsepower version remains at 360 Newton meters at 1500-2250 rpm (previously: 1750-2500 rpm). In the more powerful series, this figure has increased from 380 to 400 Nm at 1750-2250 rpm (previously: 380 Nm at 1750-2750 rpm).
The increase in engine power and torque significantly improved the driving characteristics of the BMW X3. Thus, the X3 xDrive20d is able to reach the mark of 100 km / h in 8.1 seconds, which is four tenths of a second faster than before. In addition, the optimization also affected the indicators in the intermediate sprint.
The new B47 meets the Euro 6 environmental standard and is characterized by reduced fuel consumption in the Euro cycle. Depending on the type of transmission and series of production, the reduction in fuel consumption is 0.1-0.4 liters. However, whether a four-cylinder diesel engine will always show moderate appetite in practice remains to be seen. In the case of the X3 sDrive18d, the low rolling resistance tires ensured the car's standard consumption of 4.7 liters per 100 km and the status of the most economical SUV in its class.
One thing is certain: the B47 engine will gradually replace the N47 and will provide high performance and reduced fuel consumption not only for the restyled version of the X3, but also for many other Bavarian cars for a long time to come. However, from the point of view of BMW, its main advantage lies elsewhere. Compared to the N47, the new B47 uses a lot more unified parts, which allows them to be purchased in large quantities, significantly reducing purchase prices.
An article about the best BMW engines - their technical specifications and important features. At the end of the article - an interesting video about how BMW engines are made in China.
The content of the article:
The opinion that the quality and productivity of the engine depends on its volume is long gone - modern engineering trends are based on reducing the volume of the motor while increasing its power.
BMW has been a leader in the automotive market for many years. Engines designed by engineers of a well-known representative of the German automotive industry meet all modern requirements. Back in the middle of the last century, the creators of the brand formulated a concept that reflected the meaning of their existence as the creators of cars. It sounded like this: "The car is for drivers."
Brand history
The BMW company dates back to 1913. In the then small German town of Munich, two small companies engaged in the production of engines for the aviation industry merged. The new enterprise was named Bayerische Flugzeugwerke (BFW).
In 1917, the logo was created, which today is a sign of high quality. But not everyone knows its meaning. Since the history of the brand began with the aircraft industry, the created logo is also directly related to aircraft - it depicts an aircraft propeller against the blue sky.
The name BMW, under which the company is known to the modern consumer, appeared in 1920, after the production of any aircraft was prohibited under the Treaty of Versailles in Germany. For some time, the BMW factory produced brakes for aircraft. But the founders of the company decided not to linger in the aviation industry - in 1923 the first BMW motorcycle was created.
It must be said that the two-wheeled vehicles produced by the German automotive giant still win the hearts of lovers of extreme sports and high speeds. The first car rolled off the assembly line in 1929.
Since the birth of the BMW automotive brand, the company has experienced several major failures. But despite this, they were able to climb the "auto-Olympus" and take their place of honor there. The engines produced by the concern have been holding leading positions in the most authoritative world competitions for several years. What motors of the German manufacturer are rightfully considered the best in the world?
First of the first
1999 was a significant year for all representatives of the automotive business and production. It was in that year that a competition was held for the first time to identify the best automobile engine. Among the nominees were the largest companies from around the world. The first place was absolutely deservedly taken by diesel engines produced by BMW:
The device was produced in two versions: 3.9 and 4.4 liters. The cylinder block and crankcase were made of cast iron, which significantly increased the weight of the engine, but at the same time gave the engine parts high strength.
The best among gasoline engines
Among motorists, cars with an engine running on gasoline are very popular. Such demand is explained by the simplicity in production and, as a result, the relatively low cost of the motor.
Another important advantage of the unit is the ability to develop high speed in a short period of time.
Gasoline engines are not considered too economical, but recently the installation and use of LPG, which works perfectly in tandem with a gasoline internal combustion engine, solves this problem.
Among the gasoline engines produced by BMW, the following models can be noted:
The innovative VANOS gas distribution system allows you to significantly increase the performance of the device, while significantly reducing fuel consumption.
The use of aluminum alloy greatly facilitates the design of the motor. This engine model is characterized by the complexity of the lubrication process.
best diesel engine
Cars with a diesel engine have long and firmly entered the hearts and garages of motorists around the world. This is a truly versatile unit. He "perfectly" copes with "traction" loads and is able to withstand the transportation of large loads on an ongoing basis. At the same time, he copes well with the "urban" mode of operation.
Endless braking and abrupt starts are tolerated by a diesel engine without any problems. But for high-speed tracks and racing cars, this is far from the best option.
Economy is also a clear advantage of diesel - diesel fuel is cheaper than gasoline.
What diesel engine from BMW was recognized by international experts as the best?
16 valve N47, which quite successfully replaced its predecessor - the diesel M47. 4 cylinders, 2 camshafts, injection system reaching 2200 bar pressure, aluminum crankcase - these are not all the technical advantages that allowed it to take first places in the categories "Best New Developments" and "Best Engine from 1.8 to 2.0 liters ".
This engine is presented in two configurations - 1.6 and 2.0 liters. But it was the two-liter power unit that won the above awards. The engine is installed on most models of E and F classes.
Achievements of recent years
Modern society dictates more and more new rules. This also affected the requirements for internal combustion engines. The motorist of the 21st century wants to get maximum power from the motor with a minimum of financial investment.
An important factor is the environmental friendliness of transport.“Less emissions, more clean air” is what consumers are demanding from car manufacturers. And the BMW concern gave fans of their cars the opportunity to "make the world cleaner."
bmw b58- a gasoline 6-cylinder turbocharged engine, which appeared to the eyes of car owners in early May 2015. In such a short period of existence, he managed to receive several awards of the highest category at international competitions. Among consumers, it is called "Breakthrough in engine building" and nothing else.
The use of aluminum alloys and polymer composites has significantly reduced the overall weight of the engine. The difference with the N55, which is gradually being replaced by the B58, is in the order of 100 kg. The level of carbon dioxide emissions fully complies with the Euro-6 category. That cannot but please the fighters for the environment.
To minimize fuel consumption, the B58 uses an innovative pump control map and a direct line in the injection system. The concept of TwinPower Turbo refers to the use of several technologies at once: VANOS, Valvetronic, Turbocharging and Direct injection.
Conclusion
The combination of the letters BMW has long been a sign of high quality and innovative manufacturability in the automotive world. This applies to all products coming off the assembly line of the German brand factories. Like the first models created in the early 19th century, modern turbocharged engines surprise with their technical characteristics.
From the inception of the first 303 to the present day, the Car for the Driver concept has remained relevant. Both designers and brand designers are guided by it. Stylish design and manufacturability - a combination that gives BMW cars the right to bear the proud title of leader in the global automotive industry.
Video about how BMW engines are made in China:
BMW N52B30 engine
Characteristics of the N52B30 engine
| Production | Munich Plant |
| Engine brand | N52 |
| Release years | 2004-2011 |
| Block material | magnesium aluminum |
| Supply system | injector |
| Type | in-line |
| Number of cylinders | 6 |
| Valves per cylinder | 4 |
| Piston stroke, mm | 88 |
| Cylinder diameter, mm | 85 |
| Compression ratio | 10.7 |
| Engine volume, cc | 2996 |
| Engine power, hp / rpm | 218/6100
218/6100 231/6500 258/6600 258/6600 265/6600 272/6650 (see modifications) |
| Torque, Nm/rpm | 270/2400-4200
280/2500-3500 270/2750 300/2500-4000 310/2600-3000 315/2750 315/2750 (see modifications) |
| Fuel | 95 |
| Environmental regulations | Euro 5 |
| Engine weight, kg | ~160 |
| Fuel consumption, l/100 km (for E87 130i) - city - track - mixed. |
13.6 6.6 9.2 |
| Oil consumption, g/1000 km | up to 1000 |
| Engine oil | 5W-30 5W-40 |
| How much oil is in the engine, l | 6.5 |
| Oil change is carried out, km | 10000 |
| Operating temperature of the engine, hail. | ~95 |
| Engine resource, thousand km - according to the plant - on practice |
- ~300 |
| Tuning, HP - potential - no loss of resource |
350+ n.a. |
| The engine was installed | |
Reliability, problems and repair of the BMW N52B30 engine
The first engine in the new N52 line (which included and) with six cylinders in a row. Unlike its predecessor, the N52B30 is a completely new engine, with a new lightweight magnesium-aluminum cylinder block, a different crankshaft and a lightweight connecting rod and piston group.
The engine uses a new cylinder head using a variable valve timing system on the intake and exhaust camshafts Double-VANOS, and, for even greater efficiency, a Valvetronic II valve lift change system has been added. Their height varies from 0.18 mm to 9.9 mm. Exhaust valves - 9.7 mm. Phase 255/263. The diameter of the intake valves is 34.2 mm, exhaust 29 mm. Injectors have now moved to the cylinder head, the intake uses a DISA variable length manifold, Siemens MSV70 engine management system,Timing chain applied.
The N52B30 engine was used onBMW cars with index 25i, 28i and 30i, depending on modification.
The 3-litre N52 engine was used until 2011, despite being supplanted by a modified engine since 2007.
BMW N52B30 engine modifications
1. N52B30U1 (2004 - 2011) - strangled 218 hp engine. at 6100 rpm, torque 270 Nm at 2400-4200 rpm. Power is reduced by using a different intake manifold and ECU firmware. For versions with index 25i and 28i.
2. N52B30 (2007 - 2011) - analogue for the North American market. Power 231 hp at 6500 rpm, torque 270 Nm at 2750 rpm. For versions with index 28i.
3. N52B30O0 (2004 - 2011) - base engine with 3-Stage DISA intake manifold. Power 258 hp at 6600 rpm, torque 300 Nm at 2500-4000 rpm. For versions with index 30i.
4. N52B30O1 (2006 - 2009 onwards) - power 265 hp at 6600 rpm, torque 315 Nm at 2750-4250 rpm. For versions with index 30i.
5. N52B30O1 (2006 - 2010 onwards) - power 272 hp at 6650 rpm, torque 315 Nm at 2750 rpm. For X3 and X5 crossovers and BMW 30i models.
Problems and disadvantages of BMW N52B30 engines
N52B30 engine malfunctions are similar to those that can be encountered on the younger one, with the exception of the underlying rings and their attendant troubles. The N52B30 uses other Mahle oil scraper rings, so there is no oil burning problem.
As a result, the resource of the 3-liter N52 engine is much higher than its younger brother and, in general, it can be recommended for purchase.
BMW N52B30 engine tuning
Chip tuning. Inlet
It makes sense to modify the younger, artificially strangled versions of the N52B30 with 218 hp. and 231 hp To get it back to factory 270 hp, you need to buy a 3-Stage DISA intake manifold and flash the ECU for 272 hp. in an office specializing in N52B30. For a more complete disclosure of potential, we do not buy a sports air filter and a sports exhaust system. Such manipulations will increase the power to 280-290 hp.
You can install a 6-throttle inlet, but you will have to configure it on third-party brains.
N52B30 Compressor
As for the younger N52B25, you can buy a compressor kit from ARMA (or another manufacturer) for a 3-liter N52 and get about 300-350 hp. to the stock piston. This is good, but it is much better and cheaper to buy and make chip tuning up to 400 hp.
In the ranking of the best motors, it is no coincidence that M series: although they are complex for their time, they are powerful and reliable units. And here ruler N, which replaced them, as if created for queues in the service. So, for example, all N-series motors do not have an oil dipstick. The sensor often lies, while the oil consumption is on average 1 liter per thousand km. Result - oil starvation. Other typical problems - timing chain stretch already by 80 thousand km, the resource of valve stem seals is only 30 thousand km. Many components and parts are capricious even before the wear of the CPG. There is no need to talk about the high cost of original spare parts for BMW engines and the cost of engine overhaul.
And at the same time, it was the N-series motors that were repeatedly recognized as the best in prestigious competitions in various categories. Marvelous.
N45
This motor was produced from 2004 to 2011 and was installed on the BMW 116i, BMW 316i (E90), BMW 320si.
He is known for his gluttony with a relatively modest return, especially in the 1.6-liter version. Intermittent operation and trouble with the timing chain, too, unfortunately, have become its characteristic features. And the problem chain stretching and jumping on several links could not be solved before the termination of serial production of the N45. In addition, owners of the 320si series with this engine encountered cracks in the cylinder block - due to insufficiently dense wall between them.
N47
A common engine has been produced since 2007 and installed on BMW 118d, 120d, 123d, BMW 318d, 320d, BMW 520d, BMW X1 18d, 20d, 23d, BMW X3 1.8d, 2.0d. Volume - from 1.6 to 2.0 liters, power - up to 218 "horses".
At first, diesel N47s behaved very well: acceptable fuel consumption and excellent traction. But after several years of operation, signs of chronic diseases began to appear with characteristic noise - sprains and even timing chain break, wear of shaft sprockets. As a result, the engine goes into emergency mode, at best. At the same time, the chain on the first N47 went only 50-60 thousand km! And to replace it, it was necessary to remove the motor. The problem with the chain was solved only in the spring of 2011.
Another typical N47 sore that does not manifest itself in any way is cracking of the cylinder block from the inside. The icing on the cake is the wear and tear of piezoelectric injectors, which have a limited resource, but are stunning. Yes, still intake manifold flaps in the event of a breakdown, they fell directly under the valves and cylinders, the consequences - until the replacement of the internal combustion engine.
N46
Gasoline engines with a volume of 1.8 and 2.0 liters replaced the similar N42 in 2004 and were installed on many models of 1-series and 3-series, 5-series, as well as X3 crossovers.
The full list of victims is as follows: BMW 120i, BMW 318i, 320i, BMW X3 2.0i.
It seems that nothing foreshadowed - 4 cylinders, a modest 156 hp, naturally aspirated. But the desire to increase efficiency while maintaining power did not lead to good. The designers screwed into the N46 all the achievements of the automotive industry at that time. Here you have a throttleless intake, a phase control system, and extreme operating temperatures. The result is predictable: coking of oil in the grooves of the piston rings and wear of the valve stem seals. The result is excessive gluttony and engine oil starvation. At the same time, the plastic guides and washers in the timing drive are destroyed, they simply crumble into the crankcase. Let's add a quick failure of the hydraulics - we will get a major overhaul after 3-4 years of operation. Best case scenario.
The owners tried to prevent trouble in advance by filling AI-98 and changing the oil as often as possible. But it helped only at some stage.
N63 4.4 Biturbo
These "hot" engines have been installed since 2008 on many models: BMW 750i / Li, BMW X5 / X6 50i, BMW X6 ActiveHybrid, BMW 550i, BMW 650i.
The main trouble with the N63 4.4 Biturbo is the problem with cooling the collapse of the V-shaped block. As a result - a zone of thermal stress between the two turbochargers, sintered oil, increased wear of the camshaft cams and a change in valve timing. Hence the drop in compression in the cylinders.
By 2012, the designers presented a modified N63B44TU with a capacity of 450 hp. But it is even more complex structurally, which inspires certain suspicions.
Do not miss the review of the most popular BMW models:
- E60 - watch
- E83 - watch
- X5 - watch
- E90 - watch.
03.04.2017
- a compact car produced by a German automaker BMW AG. BMW "treshka" has always been one of the most popular cars among young motorists. Addictions to this car are quite understandable, since it is pleasant in all respects: current appearance, good equipment, powerful power units, a high level of comfort and excellent handling. Adds to the popularity of this model and the reasonable price of the car in the secondary market. And, here's how things are with the reliability of a used BMW 3 series, and what you should pay attention to when choosing a three-ruble note with mileage, I'll tell you in this article.
Some interesting facts:
The presentation of the first BMW 3 series, which had the E-21 index, took place in June 1975, and marked the beginning of the history of BMW's three-series. In 1980, a sports version of the car was introduced, which was called " BMW M3". At its core, this is a BMW 3 series in the back of a “coupe”, but modified by the BMW tuning department and equipped with only the most powerful engine. To date, six generations of this car have already changed, but today we will talk about the fifth generation of the model, the world premiere, which took place at the Geneva Motor Show in 2005. Depending on the body type, the car is assigned the appropriate index: sedan - E90, wagon - E91, coupe - E92, convertible - E93. When developing the design of the fifth generation of the three-ruble note, the manufacturer did not dare to radically change the style, but limited itself to evolutionary changes, bringing the appearance of the three-ruble note in line with the design of older models.
Half a year after the debut of the sedan, the BMW 3 Series station wagon appeared on the market, and in September 2006, mass production of the car in the coupe body began. Since 2007, all BMW 3 series began to use the system " Dynemix”, which showed how driving pleasure can be combined with exemplary low fuel consumption and emissions. The BMW 3 Series is the company's best-selling model - in 2008, about 40% of sales came from the 3 Series. Models of this series periodically fall into the list of the best-selling cars in Europe. In total, during the period of production of a car of this model, 2,147,247 copies were produced.
Disadvantages and common malfunctions of the BMW 3 Series with mileage
The body of the BMW 3 Series corresponds to the image of the brand and is not subject to corrosion. The metal of the body elements can withstand our reagents, and even in the places of chips, after several years of operation, in most cases, there is not even a hint of rust. But, the body equipment cannot boast of exemplary reliability. So, for example, after 2 years of operation, the front optics begin to become cloudy. Over time, door handles begin to wedge, this ailment is unpleasant because when it appears, you have to change not only the handle, but also the door lock. Another nuisance that is characteristic of aged cars is that the seal falls out between the rear window and the trunk lid. In most cases, the owners fix the problem on their own by putting the gum on the glue. For the winter, you need to fill in a high-quality anti-freeze for glasses, otherwise, in severe frost, when you try to wash the headlights, the washers will fail.
Engines
Traditionally for BMW, the “treshka” has a large number of available power units, but in our secondary market, cars with such power units are most often found: gasoline - 2.0 (136, 150, 168 hp), 2.5 (215 hp .), 3.0 (254, 268 hp), 3.5 (302 hp). Also, diesel engines are quite common - 2.0 (120, 141, 167, 177 hp), 3.0 (194, 201, 228, 242 hp). BMW power units have always been associated with power and reliability, but not everything is so simple with “three-ruble note” engines. One of the most problematic areas of engines is considered to be increased oil consumption - up to 2 liters per 10,000 kilometers, and the more mileage the car has, the more often you will have to add oil ( up to a liter per 1000 km). When servicing engines, it is necessary to fill in the recommended oil, otherwise the valve stem seals wear out prematurely.
At the power unit with a volume of 2.0, the valve cover is made of plastic, because of this, over time, oil begins to seep out from under it. Also, this motor does not like overheating, and if you do not keep track of the temperature of the engine, then in most cases the valve cover loses its geometry. Once every 60-80 thousand km, you have to change the eccentric shaft sensor. It is worth noting that if it malfunctions, the car will not start. Once every 100,000 km, the throttle valve needs to be replaced ( Valvetronic) - the electric motor is coked with oil. The rest of the gasoline engines are more reliable, but still, it is difficult to call them trouble-free. One of the most common ailments of gasoline engines is considered to be a small catalyst resource, which, even if refueled with high-quality fuel, is unlikely to last more than 70,000 km.
Quite often, the reason for visiting a service center is fuel injectors, which in our realities, on average, take care of only 80-100 thousand km. The first signal that there are problems with the injectors will be: poor acceleration dynamics, as well as blue smoke from the exhaust system. Chain timing on average, it serves 150,000 km, if you don’t notice in time that the chain has begun to stretch, everything can end very sadly ( the chain jumps and the valve piston bends). Over time, the vibration loosens the chain tensioner mounting bolt, as a result, oil smudges appear from under its seals. By a run of 100 thousand km, the variable valve timing clutch control solenoid is clogged with oil deposits. This immediately affects the dynamics, and it happens that the motor goes into emergency operation.
Diesel engines
The situation is no better with diesel engines. The most problematic is the 2.0 engine (177 hp), which, even with low mileage, can break the chain from the camshaft drive. If this trouble happens to the engine, you need to be ready to pay 800-900 USD. for restoration work price including original spare parts). The issue was resolved after 2008. Also, the disadvantages of this power unit include piezoelectric fuel injectors ( average resource 50-70 thousand km) that cannot be recovered.
Two-liter engine with 163 hp. equipped with a turbine from Mitsubishi, as a rule, its resource does not exceed 100-120 thousand km ( the axis collapses). Also, there may be problems with the turbine control unit ( change with turbine). The rest of the engines are more reliable, but suffer from oil leakage from under the exhaust manifold, which leads to damage to the intake flaps, and later on the engine. When using low-quality fuel, prematurely ( on a run of 50-80 thousand km) elements of the fuel system fail ( injectors, injection pump), as well as the EGR valve and particulate filter.
Transmission
It can be equipped with such gearboxes - six-speed mechanics and automatic transmission. If we talk about the reliability of the transmission, then with careful operation and timely maintenance, both boxes practically do not cause any problems. In rare cases, trouble with the automatic transmission is possible due to a malfunction in the control unit ( clutch stuck). In fairness, it is worth noting that the problem is not serious and is solved by diagnosing and removing the error. In mechanics, the weak point is the clutch. At medium loads, its resource is about 100,000 km, but if you use the car as a sports car, clutch replacement may be required after 30,000 km. Most BMW 3 series are rear-wheel drive, but there are also all-wheel drive versions in the secondary market. The most common problem of such cars is the short resource of the transfer case, which fails every 80-100 thousand kilometers. In most cases, for the further use of all-wheel drive, the transfer case has to be changed to a new one.
Features and disadvantages of used BMW 3 series suspension elements
Running BMW 3 Series combines acceptable comfort and a high level of handling. Most of the front suspension parts are made of aluminum, this solution can significantly reduce the weight of the car, but negatively affects the cost of running the chassis. If we talk about its reliability, then the three-ruble suspension will not disappoint in this component either. Many owners complain that after 50,000 km of run, when driving on poor road surfaces, extraneous noise appears from the suspension ( creak, knock). This feature is not a breakdown and is eliminated by lubricating silent blocks. Otherwise, if you do not take into account the struts and stabilizer bushings ( change every 30-40 thousand km), in the front axle, with careful operation, you won’t have to do anything up to 100-150 thousand km.
The rear suspension is also reliable. An exception can only be floating silent blocks, which very often fail at a run of 80,000 km. Rear tires are characterized by increased tread wear from the inside. This happens due to the fact that the wheels are installed by the house to increase stability. In the steering, most often the power steering pump delivers trouble ( have to be changed every 50-70 thousand km) and steering rack ( starts knocking on a run of 60-80 thousand km, replacement will cost 500 USD).
Salon
Traditionally, for most BMW models, there are no complaints about the “three-ruble note” interior, and this applies both to the quality of finishing materials and assembly. As for the reliability of the interior electrical equipment, here you should pay attention to the performance of the stove fan ( starts whistling over time). The problem is solved quite simply engine parts need to be lubricated), but to get to the fan you will have to disassemble the floor of the cabin. Also, there are complaints about the radio ( stops picking up radio stations). Raises questions and performance of the central lock ( stops responding to the remote control). To fix the problem, you will have to pay about 200 USD. ( replacement of the antenna in the trunk lid or wiring is required, the problem is relevant for station wagons). If, on the instrument panel, the indicator with a yellow steering wheel lights up, you must urgently contact the service. If this is not done, the steering wheel may jam at the most inopportune moment. In most cases, the disease is treated by flashing the control unit, but there are cases when the owners had to fork out to replace the electronic board.
Outcome:
In a used state, it has a number of rather serious shortcomings with power units, to eliminate which, in most cases, you will have to pay a tidy sum. However, if you are looking for a stylish and fast car that is a real pleasure to drive, then you will not find a better option in this price segment.
Advantages:
- Stylish design.
- High quality finishing materials.
- Excellent driving characteristics.
Flaws:
- High cost of repair and maintenance.
- Increased rear tire wear.
- Problematic power units.
