Why Does This Happen?
Modern BMW engines now feature direct injection,which offers advantages in fuel consumption efficiency as compared to conventional port fuel injection. The N54, N55 engine of the 335i, 135i, and 535i are all direct injection; this means in particular that the fuel is injected directly into the combustion chamber of each cylinder and not in the intake tract. As a consequence, fuel is no longer sprayed before the intake valve. While gasoline engines are proving to need more maintenance, the diesel engine (M57) found in the 335D and the X5 Diesel have also shown that they need this service performed as well.
One of the major benefits of port injection is that the fuel keeps the intake valves clean. With direct injection the intake valves are only in contact with air and and blow by gases from the crankcase breathing system. On turbocharged cars the oil in the intake tract will be higher due to increased blow by compared to a naturally aspirated engine. This will accelerate carbon build up on the intake valves. The carbon build up process is gradual and overtime it will affect the efficiency of the motor and cause a rough idle and power loss. If left unattended the Service Engine Soon light will eventually appear. Direct injection has many benefits, but unfortunately carbon build up is an inevitable repercussion.
What Can Be Done?
In order to avoid removing the cylinder head for cleaning, a system has been devised to clean the intake valves on the car. During the walnut blasting service each intake tract is cleaned separately, as in order to avoid for the cleaning fluid to enter the combustion chamber the valves must be closed, only one cylinder has closed valves at any given time.
We utilize a media blasting tool designed specifically for this application by BMW. This blasting tool is using compressed air to inject fine walnut shell granules into the intake tract while simultaneously removing them along with the carbon build up. The walnut media hits the intake valves and port area at high speed removing the carbon build up without damaging the aluminum of the cylinder head or the intake valve. The advantages of this method are obvious: cylinder head removal isn’t necessary, and the working time per cylinder is fairly short, just a few minutes each.
When Should I Have This Service Done?
We typically recommend this service be done every 50k miles. There are other instances when this should be done because it is more economical in combination with other jobs we commonly do on the N54 and N55 engines.
To get access to the intake ports the intake manifold has to be removed. Some other common problems with these engines are starter failures and oil filter housing gaskets leaking. Both of these jobs require the intake manifold to be removed. The oil filter housing gasket commonly develops a leak around 60k to 90k miles, so if you find your gasket is leaking we suggest the carbon blasting be done at the same time. Oil filter housing gasket leaks are common on BMW N54 and N55 engines and is 3.6 labor hours when done exclusively.
Similarly these engines also have starter issues and commonly fail at 50k to 85k miles. If your starter fails we highly suggest doing your walnut blasting service at the same time and potentially preemptively changing out the oil filter housing gasket as well. Done separately these repairs/services can total 11 hours of labor. Most shops will advertise cheap walnut blasts but won’t offer to preemptively address other failure points that may occur for you in the near future. We highly recommend taking care of all three of these potential problems in one shot, this is how we save you money in the long run.
If your direct injection car is having problems due to dirty intake ports, a problematic starter, or a leaking oil filter housing gasket please give us a call. As always we will perform a free diagnosis and inspection your car and suggest the most economical service and repair solution for your BMW.