A few weeks ago, I replaced the seals on the VANOS unit on my E39. Replacing the seals is supposed to restore low-end power and response, increase fuel economy, and help the car idle better. I can’t say I have noticed any dramatic improvement in how the car runs since doing the job. Granted, my seals were only partially worn, but in the 500 miles I’ve driven in the past few weeks, the only noticeable change has been a slightly smoother idle when cold.

However, a few days ago I came across a discussion on a forum that alerted me to another possible issue that might affect the performance of the VANOS unit, hindering it from functioning as it should even after a rebuild. The VANOS unit is actuated by two solenoids, each with an electrical connection. One problem with electrical connections, particularly under the bonnet, is that they get dirty. Dirt and grime finds their way between the contacts, impeding the flow of the current. This can easily be sorted by cleaning the connections with some contact cleaner.


But the forum discussion suggested that in addition to dirt, there might be too much of a gap in the contacts (where the arrow below is pointing to), meaning they don’t grab the receiving pins as tightly as they should. Obviously this too would impede the flow of the current – think about the way a lightbulb flickers if it is not securely fixed in its base. On his own car, the forum poster resolved this by taking a pick to the female end of the connection and crimping the contacts more tightly. In his case, this simple step meant all hesitation and loss of power disappeared.


I investigated the connections on my car today, and though they were not particularly dirty, I cleaned them anyway. Further, while I couldn’t tell if they were especially loose, I crimped the contacts a bit more tightly and reconnected them. I did the same for the connections to the mass airflow sensor and DISA valve (a unit affixed to the intake manifold that adjusts the length of the runners).

The poster on the forum reported significant improvements after 30 miles of driving, so I went out to see if I would notice the same results. After a 40-mile drive, again, I can’t say I noticed the same types of gains that he reported. What I did notice, however, was a marked increase in fuel economy. Since doing the seals, I’ve observed a bit of a drop on the average fuel mileage reading on the on-board computer. I haven’t thought too much of this up to now – it’s been quite cold, and I’ve been driving a little differently to evaluate low-end power gains. However, driving in my normal fashion today, I saw a gain on the average reading on the on-board computer of nearly 2mpg.

It is too early to declare any kind of definitive results, and this is something that will be need to be evaluated over the long-term. But at this point it does seem plausible that simply attending to some of these electrical connections could very well have positive results.

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