I learned how to become a Common Rail diesel Expert!
MY12 Yeti SE 4WD Tdi is now healthy and smoke free. Fault finding was a journey of patience with some wrong turns and a few self inflicted mistakes. I'll contribute my rough notes in case anybody else has similar diesel engine problems:
1. Working on a 2l common rail diesel isn't easy. Removing parts can be difficult and expensive if things don't go to plan. Start by understanding the possible problems, causes, and plan to do checks and tests which avoid removing parts.
2. Smoke can be one of 3 kinds or a mixture: Black smoke = Excessive diesel or insufficient air, Blue smoke = Oil burn, white + blue smoke = oil + coolant water burn.
3. Smoke can have several causes. Severe black smoke (rolling coal) can be caused by faulty (open) fuel injector(s), low compression,loss of turbo boost pressure (insufficient air) or EGR problems may also affect air supply.
4. Oil burning blue smoke can come from bad piston rings, valve seals, excessive crank case pressure, bad turbo seals, faulty EGR operation, or blocked up and gunged EGR, pipes and inlet manifold. Also check the PCV.
5. Most of these possible causes are hard to prove, but doing the least invasive checks first will eliminate many possible causes.
6. Check 1: Run diagnostics and check there are no engine malfunction codes. If no, then smoke problems arise because the cause isn't measured and reported by diagnostics.
Check 2: Check for Excessive crank case pressure/blowback on idle by removing the oil cap and feeling with your hand. I actually measured my crank case pressure. You cannot do it at the dipstick because the tube is below the sump oil level. I used a spare V.W oil cap, drilled a centre hole for some pvc tube and connected it to a Monument Gas water gauge - but you can just use a long tube formed as a 'U' and put in some dyed water. I measured a partial vacuum of 3-4 inches WG on idle (Good).
Check 3: Do a compression test on each cylinder via the glowplug aperture (M10 x 1mm). N.B Most Chinese compression test tools are for petrol engines up to 300 psi and don't have the pressure or long reach adaptors required for diesels. I found a cheap 0-1000psi diesel comp. test set.
Check 4: Test each fuel injector connector with a multimeter: All 0.5 ohm = solenoid type = Good. All >200k ohm= piezo=Good.
Check 5: Injector leak off test. This requires plastic hoses connected to each fuel injector leak line. The amount of fuel leaking back is measured on idle for 30 seconds, then at about 2K rpm. There isn't an exact science, but the leak off volumes should be similar from each fuel injector and there should be some. The purpose of this simple test is to identify unusual fuel injector operation before trying to remove it. Warning: Bosch injectors code 03L/130/277J (0445 110 369 B004) are strange because the injector leak off connection is done with a nozzle and push fitting internal plastic retaining clip. Cheap Chinese test kits for Bosch injectors using external clips won't fit this type. They are also damn dangerous, because it's too easy for the plastic retainer to not engage and fill your engine bay with diesel!!
Check 6: Dynamic injector pressure test: Risky but some do it wearing gloves and safety glasses: Reverse the injector link to the common rail and tape the injector into a clear plastic tonic water bottle. Remove injector plugs to other 3 injectors to stop firing and have a second person crank whilst looking at the spray pattern. These injector nozzles have 4 outlets. You can only see them on the tip with a magifier or microscope.
Check 7: Eliminate the turbo as far as possible. Turbos passing oil causes blue smoke, particularly during acceleration. Remove a large clip on the turbo intercooler hose and check inside for any excessive oil pooling inside. The turbo is fed with high pressure oil which drains through gravity back to the sump. Check the turbo oil drain isn't blocked. The crank case back pressure (should be a vacuum!) is important because positive pressure prevents oil draining from the turbo and forces it past seals. Many good turbos are replaced when these are the real problems.It's more difficult to check turbo seal oil leaks on the exhaust side without removing the DPF and pipes - a horrendous job on the 4x4.
Even if these tests as much as you can do all look o.k, that is confirmation to look elsewhere.
7. I didn't do an injector leak test first (I should have). My test conclusions led me to fuel injectors. A diesel specialist will test 4 injectors for £80. If MY12 Yeti had done over 120k instead of 75k, I wouldn't have bothered testing the injectors, just go to a German firm that will supply a set of 4 re-conditioned and re-calibrated with test certificates. Another option I didn't do was buy a used injector for about £70, take a chance it was good and use it as a swap to check the others. After testing I was told injector 2 was so bad it shouldn't go back. But removing injector 2 gave me so much grief I could have damaged it? I was still uncertain and went ahead to buy a used injector with the same part codes from a Passat.
8. Removing a fuel injector from this CR engine: Easy is gently lift up with a flat screwdriver blade using the ABS rocker housing as a fulcrum point. That didn't work for me. Next option is a slide hammer. There are some Ebay injector removal kits using a slide hammer. The first type require the large nut holding the solenoid to be removed in the car. Frought because the solenoid pin, spring and spacer washer can jump out. Safest is the removal tool (Laser) that attaches to the side of the injector body using its fuel inlet nipple. The most important thing is impact must be absolutely vertical on the mounted centre line of the injector. I made a removal tool that clamps to the side with the fuel inlet nipple.
9. When injectors are removed you can check if their stem O rings are still in situ. Mine were burned away. This O rings prevents oil from inside the rocker casing falling down and welling close to the hot injector nozzle, it isn't the primary seal. There's an important copper sealing washer underneath each nozzle, this often drops back into the hole as the injector is removed. Remove the ABS rocker cover because you can then see lower down and inspect the PCV diaphragm.
10. In my case, some injectors had significant black gunge around their nozzles and copper washers were scored. The worst had a part of the surface blown away! The consequence of this is compression leaks inside the valve cover adding dieselto oil blow back and being fed into the exhaust. Remember I said check the compression leak readings for each cylinder! I replaced the copper nozzle washers and even lapped them smooth. I checked the cylinder head nozzle surfaces and gently cleaned them up a little with a 15mm flat cutter. The Chinese seat cutter set was flawed. Their smallest 15mm cutter head fits on a 17mm mandril which I had to turn down to 15mm.
11. Diesel Fuel injectors: I assumed they were piezo, I found no local or online firm that would recondition them. I should have measured them first with a multimeter. Mine were about 0.5 ohms each. Therefore they are solenoid type. A piezo injector will measure very high resistance. Bosch are very clever at making it difficult to do any servicing. The nozzles are coded and you can find parts, but the hex head they put on the nozzle won't fit any wrench. You can remove the insulated solenoid head with a large spanner, but small parts and a spring can leap out and get lost!!
12. Fuel injectors are coded: Before removing any fuel injector you should note the unique serial number code (7 digits) and its corresponding cylinder. If you have previously scanned the car, check the serial numbers and their position tie up. If they don't, somebody has been messing with injectors, replaced them or mixed them up! The 7 digit Bosch injector code incorporate a calibration value of tested fuel volume which the ECU stores. Using vcds and their 'Security access code' popup you enter the injector serial number. When this is done the ECU is supposed to learn and adapt to the new calibration. In practice, I think this means your engine will run smoothly without much diesel knocking? If you didn't recode an injector, I'm sure the engine would still run.
13. On the home straight I replaced the ABS rocker cover which I destroyed to get access to a stuck injector, fitted 4 injectors with new Viton O rings and copper sealing washers, fitted all the diesel pipework and got ready to purge the fuel lines using diagnostics. That done and after some prolonged cranking with a fully charged battery, the engine ran with NO SMOKE. It runs a lot smoother than it did before and I haven't had to replace a turbo, pistons, valves or piston rings.
CONCLUSION: Rolling coal black smoke was probably caused by poor injector nozzle sealing and a faulty injector.