13/08/2005
Ah, the Mercedes E220 CDI – a truly popular and reliable workhorse on UK roads. However, like many diesel engines, it can sometimes fall victim to a rather unpleasant issue affectionately (or perhaps not so affectionately) known as 'Black Death'. This isn't some mythical curse, but a very real and concerning build-up of tar-like substance around the fuel injectors. If you've noticed a strange smell, rough running, or visible goo around your injectors, you're in the right place to understand what's happening and what needs to be done.
This guide will delve deep into the causes, symptoms, dangers, and most importantly, the solutions for this common Mercedes ailment. Understanding this problem is key to preventing minor leaks from escalating into major, engine-damaging repairs.
What Exactly Is 'Black Death'?
The term 'Black Death' refers to a sticky, hardened, tar-like substance that forms around the base of the fuel injectors in certain diesel engines, most notably Mercedes-Benz CDI units, including the E220. It's not actually 'tar' in the traditional sense, but rather a solidified mixture of combustion gases, soot, and oil that escapes past a faulty injector seal. When the copper washer (seal) at the base of the injector fails, hot, high-pressure combustion gases leak out. These gases then mix with oil vapour and carbon deposits, solidifying into an incredibly hard, impenetrable mass over time. This substance can completely encase the injector, making removal incredibly difficult and potentially damaging.
The Science Behind the Mess
Injectors are seated in precise bores within the cylinder head, sealed by a small copper washer at their base. This washer ensures a perfect seal, preventing combustion gases from escaping the combustion chamber. Over time, due to heat cycles, vibration, improper torque settings during previous installations, or simply age, these copper washers can degrade or deform. Once compromised, even a tiny leak allows hot, pressurised gases to escape. As these gases cool and mix with oil mist from the rocker cover (which often sits above the injectors) and carbon from the exhaust, they polymerise and harden, creating the infamous 'tar'.
Common Symptoms of Injector Leaks
Catching 'Black Death' early can save you a significant amount of hassle and expense. Keep an eye (and nose) out for these tell-tale signs:
- Strong Diesel Fume Smell: Often the first and most obvious symptom. You might smell diesel fumes inside the cabin, especially when the engine is running or when stationary. This is due to the escaping combustion gases and unburnt fuel vapour.
- Hissing or Chuffing Noise: A distinct puffing, hissing, or chuffing sound coming from the engine bay, particularly noticeable at idle. This is the sound of gases escaping past the failing seal.
- Visible Carbon Build-Up: Look around the base of the injectors. You might see a black, gooey, or hard, crusty substance forming. This is the 'tar' in its various stages of formation.
- Rough Running or Misfires: While less common in the early stages, a significant leak can affect combustion, leading to a rough idle, hesitation, or even misfires.
- Reduced Fuel Economy: Although not always directly attributable, inefficient combustion due to injector issues can subtly impact fuel consumption.
- Engine Warning Light: In some severe cases, the engine management system might detect issues leading to a dashboard warning light.
Why is 'Black Death' Such a Big Deal?
Ignoring this issue is a recipe for disaster. What starts as a simple, inexpensive seal replacement can quickly escalate into a nightmare scenario. Here's why it's so critical to address it promptly:
- Extremely Difficult Injector Removal: The hardened 'tar' literally glues the injector into its bore. Standard removal methods become useless, often requiring specialist tools like hydraulic pullers, or even drilling out the injector.
- Damage to Cylinder Head: Aggressive removal attempts can damage the injector bore in the cylinder head, potentially requiring costly machining or even a new cylinder head.
- Injector Damage: Injectors themselves are delicate and expensive components. The force required for removal can bend, break, or otherwise damage the injector, necessitating its replacement.
- Fire Hazard: Escaping diesel fumes and hot combustion gases in the engine bay present a genuine fire risk, especially if there's any fuel spray.
- Engine Performance Degradation: While the primary concern is mechanical damage, severe leaks can also lead to poor combustion, reduced power, and increased emissions.
- Blocked Oil Passages: In extreme cases, the build-up can spread and potentially block oil return passages or other critical areas, leading to further engine complications.
The Repair Process: A Challenging Task
Repairing 'Black Death' is not for the faint-hearted or inexperienced DIY enthusiast. It's often a labour-intensive and messy job that requires patience, specific tools, and a good understanding of engine mechanics. Here's a general overview:
1. Safety First
Always disconnect the battery and ensure the engine is completely cool before starting any work. Diesel fuel is flammable, and hot engine components can cause severe burns.
2. Access and Initial Cleaning
The engine cover and any obstructing components (like the air intake manifold) must be removed to gain access to the injectors. Then begins the arduous task of carefully scraping away the 'tar'. This can involve chisels, picks, and specialised chemical cleaners designed to dissolve carbon build-up. This step alone can take hours, depending on the severity of the build-up. Protecting surrounding components from debris is crucial.
3. Injector Removal
Once as much 'tar' as possible has been removed, the injector clamp bolt (which is typically a single-use stretch bolt) is loosened and removed. Then comes the moment of truth: attempting to extract the injector. If it's heavily seized, a slide hammer or a specialist hydraulic injector puller will be necessary. This stage is where injectors can often break if not handled correctly, turning a seal job into an injector replacement job.
4. Bore Cleaning and Inspection
After the injector is out, the injector bore in the cylinder head must be meticulously cleaned. This involves using a specialised wire brush (bore cleaner) attached to a drill to remove all traces of carbon and ensure the bore is perfectly smooth and clean. Any remaining debris can cause the new seal to fail prematurely. Inspect the bore for any damage or pitting.
5. New Seals and Bolts
Crucially, new copper washers (seals) and new injector clamp bolts (stretch bolts) must always be used. These bolts are designed for single use and stretch slightly when torqued correctly to provide the necessary clamping force. Reusing them can lead to immediate seal failure.
6. Reassembly and Torque Settings
The injector is carefully reinserted into the clean bore, ensuring the new copper washer is correctly seated. The new clamp bolt is then installed and torqued to the manufacturer's precise specification. This torque setting is critical; too loose and it will leak, too tight and it can deform the new seal or damage the injector. Always consult your vehicle's workshop manual for the exact torque setting for your specific E220 model.
7. Testing
Once everything is reassembled, start the engine and carefully inspect for any leaks or unusual noises. A smoke test can also be performed to confirm the integrity of the seals.
Comparison: DIY vs. Professional Repair
| Feature | DIY Repair | Professional Repair |
|---|---|---|
| Cost | Lower (parts only) | Higher (labour + parts) |
| Tools Required | Basic hand tools + specialist injector tools (puller, bore cleaner) | Workshop tools + specialist equipment |
| Skill Level | High (patience, mechanical knowledge, problem-solving) | High (experienced technician) |
| Time Required | Potentially days, especially if seized | Hours to a day, depending on severity |
| Risk of Damage | High (to injectors, cylinder head) | Lower (due to experience and proper tools) |
| Warranty | None | Often comes with a warranty on parts and labour |
Prevention is Better Than Cure
While 'Black Death' can be a daunting problem, there are steps you can take to minimise your risk:
- Regular Servicing: Adhere to your Mercedes' service schedule. A good mechanic might spot early signs during routine checks.
- Prompt Action on Symptoms: Don't ignore that faint diesel smell or slight hiss. Address it immediately.
- Professional Installation: If injectors ever need to be removed (e.g., for testing or replacement), ensure they are reinstalled by a competent professional using new seals and the correct torque settings. This is paramount.
- Quality Fuel: While not a direct cause, using good quality diesel can help keep your fuel system cleaner overall.
Frequently Asked Questions (FAQ)
Q: Can I just ignore the 'tar' around my injector?
A: Absolutely not! Ignoring 'Black Death' is one of the worst things you can do. It will only get worse, making the eventual repair far more difficult and expensive, potentially leading to significant engine damage or even a fire.
Q: How long does it take for 'Black Death' to form?
A: It can vary significantly. A small leak might take months or even years to build up a substantial amount of 'tar'. However, once it starts, the process accelerates as the leak worsens.
Q: Is it always expensive to fix?
A: If caught early, when only a seal needs replacing and the injector isn't seized, the cost is relatively low (parts are cheap, labour minimal). If the injector is heavily seized and requires specialist tools, or if the injector itself gets damaged during removal, the cost can escalate significantly, potentially running into hundreds or even thousands of pounds if a new injector or cylinder head repair is needed.
Q: Can I prevent it from happening again after repair?
A: Yes. The most crucial steps are ensuring the injector bore is perfectly clean, using new, genuine copper washers, and installing the injector with a new stretch bolt torqued precisely to the manufacturer's specification. Regular checks for leaks are also advisable.
Q: What if my injector is completely stuck?
A: If an injector is completely stuck, it will likely require specialist tools such as a hydraulic injector puller. In severe cases, where the injector simply won't budge, the cylinder head might need to be removed, or the injector carefully drilled out, a task best left to highly experienced professionals.
In conclusion, while the sight of 'tar' around your Mercedes E220's injectors can be alarming, understanding the 'Black Death' phenomenon is the first step towards a solution. Prompt action is key to preventing a minor issue from becoming a major headache. Whether you tackle it yourself or entrust it to a professional, ensure the job is done meticulously, paying close attention to clean bores, new seals, and precise torque settings. Your E220 will thank you for it by continuing to provide reliable service for years to come.
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