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Hi everyone, I have a 1995 BMW e38 740i with the M60B40 engine and an automatic transmission. It has about 180,000 miles on the odometer. Long story short, three days ago the car was running perfect, no problems at all. Yesterday when I started the car to go to work, I immediately noticed something wrong – the idle was quite rough and the car lacked low-end power. However, since it was still in running condition and I really had to go, I drove it to my workplace and back home. On the drive back I noticed the car was running even worse. The idle was worse and power was lacking everywhere on the rev range.
This morning I started pocking around the engine bay, looking at the usually suspects, like MAF and air leaks around the intake boot, but I couldn’t find anything that was very much out of the ordinary. I started the car with the MAF disconnected and it was worse, so I guess was doing its job. I cleaned the intake boot and the air filter and I went for a drive to see how it is. It was fine for like 10sec and after that all hell broke loose… The idle was extremely rough, the car struggled to go above 25mph and upon stopping (like before a tight bend) it stalled a couple of times.
There are no ticking noises from the engine, aside from the entire thing shaking like crazy and a noticeable fuel smell outside of the car, particularly around the back side of it. The check engine light on my car is broken. I though the previous owner was messing with it, but it turned out to be simply a faulty light. I did not bother getting it fixed, because I figured it wasn’t that big of a deal. Anyway, I can’t see if the light is on, but my guess is hell yeah.
I am planning on checking the spark plugs and coils tomorrow morning. Still, other than that I don’t really have any idea what it could be. Any help would be much appreciated!!!
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Your best bet is to get your hands on something that can read codes for OBD1 BMWs. While working on that, a good place to start would be to check fuel pressure. Given your symptoms, it sounds like you may have a leaking fuel line, but I would avoid jumping to any conclusions before pulling the codes.
Given the low power, rough running and stink of fuel, it sounds like you aren’t firing on all cylinders. Could be a bad coil or plug.
You can try doing a Power Balance test. Be sure to check every cylinder, there might be more than one cylinder contributing to the problem.
When you say a fuel smell, do you mean a straight-up fuel smell as in a tank/line leak, or do you mean an unburned fuel smell from the exhaust?
The smells is of unburned fuel and it is quite strong, which had led me to believe it is a misfire or even several across more than one cylinder as it was suggested earlier.
Therefore, the last couple of days I started poking around the ignition system and I found out that the spark plug wells of cylinders 5 through 8 on bank 2 where filled with oil. The same was true for cylinders 3 and 4 of bank 1. So in fact the car was running on 2 cylinders instead of 8… I ordered a pair of new valve cover gaskets, a set of spark plugs and 8 new ignition coils and went to business. I just finished everything today, but couldn’t actually start the car, because my battery ran flat. I forgot to disconnect it, silly me… I have left it charging overnight.
I will get back with an update tomorrow. Hopefully the problem will be fixed.
Problem solved!
The rough idle and loss of power was definitely caused by the excessive oil in the spark plug wells. Taking the oil out, replacing the valve cover gaskets and plugs did the trick. The car is running silky smooth again.
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