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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 7 Series / 8 Series > 7 Series - E23 / E32 (1977 - 1994)

7 Series - E23 / E32 (1977 - 1994)

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  #1  
Old 02-18-2013, 01:49 PM
jgmathieu jgmathieu is offline
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Location: Santa Cruz, CA
 
Join Date: Feb 2013
Posts: 4
Mein Auto: 1994 740il
Smile Check engine light on '94 740il

1. Car was running rough & check engine light would come on.
2. I replaced both O2 sensors and same problems appeared.
3. Mechanic said engine running rich & suggested Air Mass Sensor replacement which I did.
4. Car would run OK but in the morning, on start up, would run rough and check engine light would come on. I tried Techron additive and problems still exists.
5. Will change all spark plugs this week.
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Questions:
Should I get a torque wrench for installing the plugs?
Mechanic said that rich/lean readouts are coming from Bank 1 (driver's side of engine).
Would reversing the O2 sensors pinpoint the problem could be with the sensor itself?
Any other suggestions?
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  #2  
Old 02-24-2013, 04:34 PM
jgmathieu jgmathieu is offline
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Location: Santa Cruz, CA
 
Join Date: Feb 2013
Posts: 4
Mein Auto: 1994 740il
Angry 1994 740il running better, but....

I finally changed all the plugs and the car is running smoother but on the right side of the engine, there was quite a bit of oil that probably leaked in from the valve covers. I think the oil was causing the car to run rough and that I was getting suction from the oil cap while the car was running. I don't think that is right so maybe a crankcase ventilator sensor ???
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  #3  
Old 02-24-2013, 08:07 PM
TerryY's Avatar
TerryY TerryY is offline
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Location: Woodland Washington
 
Join Date: Jul 2003
Posts: 670
Mein Auto: BMW '95 840
The V 8 runs with the crankcase under vacuum. If air is leaking in it will cause a rough idle. If enough air leaks in it will cause a check engine light at idle.

The Nicasil problems main symptoms were a rough idle and the check engine light that appeared when the engine went to idle at traffic lights.
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Woodland Washington
'95 840Ci
'98 740i
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  #4  
Old 02-24-2013, 08:56 PM
jgmathieu jgmathieu is offline
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Location: Santa Cruz, CA
 
Join Date: Feb 2013
Posts: 4
Mein Auto: 1994 740il
check light still on

Thanks, Terry. I really think that is the problem now. Can I do this job myself ? (Replace the crankshaft ventilation sensor)
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  #5  
Old 02-25-2013, 07:17 PM
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TerryY TerryY is offline
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Location: Woodland Washington
 
Join Date: Jul 2003
Posts: 670
Mein Auto: BMW '95 840
The "PCV" valve on the back of the intake can be replaced in place but it isn't what I would call fun. I believe it is officially called a "non return valve"
The torx screws are easy to round out and being button heads on my old '94 they are impossible to remove if you strip them.
Before you get too excited about all that coming pain check and see if the two rubber plugs are still in place and not rotted out on the back of it.
If you decide you must replace it then consider buying a full set of intake manifold gaskets including the one between the throttle body and intake manifold and the four between the intake manifold and the engine. Then you can just take the intake manifold off and do the back screws in a much friendlier environment. More work to get to it but much less pain to do it.

Before you start tearing big stuff apart though, take out the farthest back spark plug on the passenger side. If it is oily/black /sooty then take out the front spark plug on that side too and swap them. put the coils back on and start the engine. If the idle is now smooth then it may be time to do a leak down test on the motor. If the idle is still rough or it smokes on cold start then the non return valve is one of the list of probable causes.
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Woodland Washington
'95 840Ci
'98 740i
'00 Range Rover Vitesse
www.wuffer.net
www.8coupe.com
www.8er.org
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air mass meter, o2 sensor, running rich, spark plug


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