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E28 (1982 - 1988)

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Old 06-07-2013, 07:54 PM
ckplays ckplays is offline
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Location: southern cali
Join Date: Jun 2013
Posts: 1
Mein Auto: 528e
O2 sensor causing problems

I've got a 1986 528e that's giving me problems. My friend and I just had the whole engine apart to change the head, #5 piston, and the broken timing belt that caused all the destruction. Now that it's all back together, the engine runs great... but only with the O2 sensor disconnected.
Here's a list of the things we've tried:

- Replaced O2 sensor with a BRAND NEW one. (No improvement)
- Cleaned and tested throttle position sensor (just two switches, not a potentiometer)
- Double and TRIPLE checked for vacuum leaks and I absolutely assure you all that there are NO VACUUM LEAKS!
- Ultrasonic cleaned and tested all fuel injectors (they are fine)
- New fuel filter
- No kinks or restrictions in fuel line
- Tested idle air bypass valve and checked adjustment (its fine)
- While motor was apart all valves were checked for leakage and rocker clearances set to .012" as specified.
- New spark plugs, wires, and cap. Has a healthy spark.
- Compression check shows all cylinders exceed the minimum spec 144psi (180-200)

Once again, the engine runs great with no O2 sensor. But with it connected the engine runs extremely lean and barely has enough power to move the car at low-mid rpms. It picks up a bit of power at 4000+ rpm, but not much.
I would just run it with the O2 off, but it needs to be smogged now and (although I do know a guy), I want to do it LEGALLY.

Any idea what is at fault?
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Old 06-07-2013, 10:33 PM
catso's Avatar
catso catso is offline
Location: Chicago
Join Date: Dec 2009
Posts: 3,112
Mein Auto: 2000 323i, 1988 528e
As a guess, I'd suspect the Air Flow Meter.
Don't be gormless; get some gorm!
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Old 03-03-2014, 04:25 PM
zackkcaz zackkcaz is offline
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Location: Ohio
Join Date: Feb 2009
Posts: 3
Mein Auto: 88 535i

What was the issue??

AFM? o2 sensor?
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