3-Series (E21, E30)Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.
Newbie, please help 1987 325e (M20) engine not firing
Folks, this is a 1987 325e with 285K Miles on it. About a week ago, the car quit while driving through a 25MPH zone (fortunately). Immediately looked under the hood and found that the wires from the Altitude Sensor or the Manifold Absolute Pressure (MAP) Sensor got extremely hot and melted the insulation and SHORTED out the whole engine wiring harness. Signs of hot wires were also evident on the wires coming out of the AIR FLOW METER. The MAP sensor was obviously damaged.
I replaced the whole engine wiring harness. Tried to start the car with no luck. The engine cranks smoothly but will not fire. I was told that the car will start WITHOUT the MAP Sensor in place and this is only needed in high altitude areas? Others indicate that this sensor must be connected in order to run the engine. I haven’t purchased the sensor yet.
All fuses = OK. Battery checks = good. Gas tank = FULL (filled the night before!)
Did NOT check all the relays though.
Here are my questions:
1) Is there a troubleshooting guide for the AIR FLOW METER? (measuring resistance maybe or voltage levels) to determine if it is needs to be replaced along with the MAP sensor?
2) Is there a troubleshooting guide for the MAP sensor?
3) Is it possible to run the engine WITHOUT the MAP sensor?
4) Can anybody guess the extent of the damage caused by this wiring harness meltdown?
Any takers on this one before I invest in un-needed parts? Any recommendations? Or any other tests I need to perform? I’m kind of running out of ideas here.
Thanks for all your help…and looking forward to your thoughts and ideas…
Ok, so it cranks...do you have a saprk at the plugs if you do are the plugs wet...getting fuel? the car will run without a MAF but only if its running, you can unplug it and it will keep running but if you turn off and try a re-start it will not start.
__________________ VELVET BLUE UK INDIVIDUAL , IM THE LAST UNITED WE STAND DIVIDED WE FALL
I stepped in a plate of Pasta the other day - now I have to worry about my Carbonara footprint!
I have a 1987 325e m20 2.7L and mine is doing the same thing as we speak.. If yours is like mine there are two sensors locatred at the driver's side bell housing. The two sensors are the same. One is the speed sensor (closest to the front of the car) and the other is the crankshaft sensor/reference sensor/pulse generator. That particular sensor has different names. I guess they changed them throughout the years. The Bentley manual calls it the reference sensor and if you go to RealOEM.com Online BMW Parts Catalog put in your last 7 digits of your vin. Then navigate to Engine and then Ignition System and you will see the sensor which they call it the Pulse generator. Look at mune RealOEM.com * Diagram Selection
Right now, I am trying to pull it out and it BROKE!!! UGH. The other part is still in the hole and I don't know how to get it out. So be careful when you pull it out. The one you want to pull out is the one closest to the rear. But be carefull.
Hope this helps!
Thank you very much for the insight. I will definately check them out tomorrow. I got a loaner car from my cousin as I have been troubleshooting it rather slowly. I don't have the Bentley repair manual, but curious why two identical sensors? the digram you emailed only shows one sensor with bracket for 2 sensors. The car has two (side by side) with one has a lighter color connector. I havent traced them. Do you recall which connector goes to which sensor?
Would you please do me a big favor... when you receive yours please measure the resistance between the terminals on the connector and report that. Like between (1 & 2) and (1 & 3) and between (2 & 3) if this is a three terminals (using a standard digital multimeter or analog). I wanted to compare with my sensors and figure out if one is bad or both.
Also did your car have any symptoms before failing to start? Mine was kind of hesitating to start before the wiring harness all shorted out. I had to crank it several times before she would start. But once it started, there were no hesitation with running or engine RPM or power. Only at the start. The wiring from those sensors were not melted like the ones from the Altitude sensor and the Air Flow meter. This is not to say that they are not bad or worn out.
Please also let me know if you get yours to run after you install the sensors.
I really appreciate your feedback...thanks a lot!
I got the part in but the crankshaft sensor broke off while I was trying to get it out and now the other half of the sensor is stuck in the hole. I have been trying to get it out but it will not budge at all. So I drill a hole in it and still won't budge. I am afraid that I have to remove the bell housing in order to tap the sensor out, which I don't have clearance for and I don't want to tow the car to a shop just so they can tap the stupis sensor out. That would cost hundreds of diollars just to get out a sensor???
I don't know. Maybe I just might part out the car and get another BMW....
Man, what a bummer! have you tried to soak it with WD40 and let it sit overnight and double soak it again. I would even use a carb cleaner and clean it up to losen the gunk.
I'm in the same boat like you are. I was planning on working on the car this weekend and perhaps order the sensor. I just don't know if it is this sensor or something else? If I replace this sensor and car does not crank, I'm not going to waist any more money or (more importantly) time on it. I found a couple nice BMW here locally that I might get.
Do you remember which connector goes to which sensor? (I think they are color coded and the lighter connector goes towards the rear of the car).
Did you check the resistance on the terminals for the new sensor? I appreciate that so I can check mine this week end.
IF you look under the throttle body, the connector on the left closest to the radiator should be black, whcih is the speed sensor and the one on the right, which is grey is the crankshaft position sensor. They are both the same sensor but sense different things.
The lighter color one (grey) does go toward the rear of the car in a 15 degree anggle, which is the crankshaft sensor. And if the sensor is bad then you will not get a spark, not even fronm the ignition coil. What you can do is take out the crankshaft sensor, take out the speed sensor next to it, which s the black coded one, disconnect both, connect the speed sensor to the crankshaft connector under the throttle body, and slide in the sensor into the hole closest to the rear. Try to start the car. The car should start without the speed sensor. So, if the car starts using the speed sensor as the crankshaft sensor then you will know it is a bad crankshaft sensor.
I hope I made sense. Remember, the speed and crankshaft sensors are the exact same. Borrow the speed sensor and see if the car starts...
I didn't test the sensor because I don't have the equipment to test it.
That will keep me a little busy and give me something to look forward to this week end.
You are making excellent sense and I did give you a well-earned rating (recommendations) based on the info you provided.
Will let you know...
Thanks.. I hope it works. I just hope you don't snap the old sensor like I did. Hopefully with a little side by side twist both sensors will break free and slide right off.
When I get home I am going to tap the broken sensor into the bellhousing and go from there.. Wish me luck!
Remember, take the black connector sensor (Speed sensor) and connect it to the grey connector (Crankshaft sensor connector) and don't forget to put back the Speed Sensor to its original place and buy a new sensor from the place I mentioned above..
Good luck this weekend and don't be afraid to ask fro help,. I am always on...
I was wishing good luck and success since last week and was hoping to hear the good news. I am relying on your sucess to get mine to fire. Anyways, good luck to you again this weekend...
Do you agree with this: If the two sensors are identical and they measure, record and sense rotation of the CAM position and speed why can't I swap the connectos on the harness WITHOUT physically swapping the sensors? This theory will only work if the signal sensed from both sensors is the same. However, I have a feeling that they sense different RPM speeds (due to internal mechanical shafts, etc) and therefore send different signal levels to the engine unit. I have to look at them from underneath the car. I also have an oscilloscope that I will connect to the stupid sensor and see what I get while I'm cranking the car. later...
You can't swap at the connectors because one meaures speed and the other measures the crank revolutions. If you swap at the connectors you still will not be able to tell if the sensor is bad. The only way to do that is by removing the crankshaft sensor and replacing it with the speed sensor to see if the car will turn over. You are testing to see if you get spark by using the speed sensor. Lift the car at the driver's side with a jack as high as it can go and you will be able to reach the two sensors adn you won't have a problem unbolting the allen bolts. Just be careful when taking off the sensors so you don't break them like I did. It should take you about a half of an hour to disassemble.
To get to the sensor connectors you will have to take out the Air Flow sensor and aifr filter and intake hose that connects to the throttle body.
The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.
AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.