Welcome to Tech Talk, where our resident BMW tech Nick Owen answers all your pressing BMW technical questions, frustrations, and issues. Have a question for Nick? Email him at techtalk@roundel.org. Let’s get into it.
E31 Issues
We have two BMWs, a 2004 330Cic and the 1993 850Ci. I have a 1993 850Ci that will not start. Batteries good, on maintainer. The fuel pumps will not fire up with the turning of the key, we have jumped them at the relays, they pump, and the car runs. Not good, but it runs. The tach does not work, check engine light flashes, EML light off.
The engine runs on all 12 cylinders but is sluggish on acceleration and will not idle. Checked the immobilizer, removed the fuse, and the engine ran when the fuel pumps were jumped as before. it seemed to run and accelerated smoother, but that was the extent of any effect, same with tach and check engine light.
Checked the two fusible links in the trunk, they are good.
Any comments or suggestions greatly appreciated.
John Smolich
Elk Grove, CA
This is a tough one. I have suggestions and questions, but I would really need to have a schematic for this vehicle handy to be more helpful. I will say that—based off what you are telling me—if you are bypassing the relay and you are able to get the car to at least start and run then you probably have either a bad relay or a bad command module of that relay. But this is me guessing. The E31 is a unique model to BMW, especially the V-12, but I have heard of issues this one will exhibit and from what I gather it is usually frustrating and expensive. In all honesty I am not that versed in the E31 chassis. It is truly tough to say what this issue could be without professional assistance and resources.
Hi Nick,
One last update. The problem ended up being the upper crankshaft sensor on bank one; replaced it and the car ran great.
Problem on way home, the heater core or connecting plastic piper gave out, back to shop on tow truck. Bunches of fun. Thank you for your interest and help.
John Smolich
Grading Fuel Grades
I’m lucky enough to own three BMWs: a 2022 840i Coupe, 2022 X5 40i, and 2019 Z4 30i. None of them ever driven very aggressively. Two of the three are daily drivers. Wondering about any issues using regular gas vs premium. I am strictly using Shell regular and do not seem to see or hear any issues.
Any thoughts or guidance?
Patrick Ongena
Dallas, TX
When it comes to premium vs regular, we must take some things into account. Brand is a factor, the better quality of fuel, the better it is for the engine in the longer run. But the most important part is octane level. BMWs require a minimum of 91 octane to “operate as designed.” This is mainly due to compression ratio. BMWs tend to have a high compression ratio which equates to good engine response and pickup when accelerating. Any time the vehicle is accelerating, the engine computer is managing knock or pre-ignition (engine ping). It is doing this based on demand (throttle input) and changing fuel/ignition timing/air delivery to build the necessary power to accelerate, based on how much demand you are asking. Lower octane will ping more and therefore make the engine computer work more to compensate. The problem here is that the knock is still happening, even if you do not feel or hear it. But when knock occurs due to low octane, it is much harder for the engine computer to catch and manage.
Now, can you run a lower octane? Technically, yes. The engine computer can adjust as needed to make the car run. But it will have reduced power. You may not feel it but it is reduced. MPG might suffer, never did a study on it. But the car will run and you can go about your drive. However, I cannot advise on long-term damage. My training and experience as a 20+ year BMW tech has insinuated that it is not good. But the only time octane level came into the diagnostic process was after the customer brought the vehicle in for a drivability concern. Mainly rough running and hesitation on acceleration.
My final $.02 on the matter is do it at your own risk but the vehicle is recommended to have min 91 octane for a reason.
Recall Thoughts
What is your take on the latest recall from BMW? Just received yesterday that two of my cars (840 Coupe and Z4) are in recall for possible fires caused by water getting in to starter motors. The advice from BMW is leave your car(s) outside as the “remedy is unavailable.” My service advisor in Dallas told me they do not have any replacement parts in stock.
Since neither of these two cars are rarely, if ever out in the rain, I guess I just lay low till “remedy is available.”
Curious about BMWCCA thoughts.
Thanks
Patrick Ongena
Recalls happen all the time. The severity of the recall varies but for the most part they are precautionary measures for something unique to the vehicle. When it comes to parts, “remedy unavailable” means that the updated part has not been released by BMW. Usually due to supply so that when the recall gets issued, there are enough replacement parts available to satisfy the first wave of cars coming in for recall. Once the part gets released, you will either get a letter in the mail or the dealership will contact you.
