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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 09-13-2012, 06:51 AM
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ztom ztom is offline
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Location: Thousand Oaks CA
 
Join Date: Sep 2007
Posts: 844
Mein Auto: 1997 528i
Misfiring under load - KNOCK SENSOR!

I did a lot to track this down, discussion on this thread..
http://www.bimmerfest.com/forums/sho...ire+under+load

..but today it is solved - I disconnected the knock sensor and the stumble/misfire at freeway speeds under load (like going uphill) is gone. I've ordered a new knock sensor but driving around I don't detect any issue for now with the sensor disconnected.

I think for any e39 over 150K mi, I recommend at least to disconnect the sensor to see if some power is restored in the 3-4K rpm range. This problem started maybe 10-20K miles ago, at first at 3500 rpm and then most recently it happened under less load and at lower revs down to around 2800rpm.

Here's my story, may help others:

>Did easy misfire DIY first - swapped coils between cylinders and put in new plugs, and checked old plugs for signs of misfire.

>Changed the bank 2 pre-cat O2 sensor because I could see dynamically on the code reader it was lazy

>Swapped in a spare CPS and vanos solenoid, no change. Note in doing this it's easier if you take off the oil filter cap to get more room.

>Pulled the fuel rail and swapped out the FPR and injectors with another 528i, no change. Also cleaned the injectors in ultrasonic with 70% alcohol/water.

>Swapped in spare MAF

>Then I realized I could check the STFT trims in real time. I could see that I was not having a lean condition (as happens if MAF dirty or non-metered air getting in via any intake boot crack), rather STFT's were fine even under load. I did notice that when it stumbled the timing advance would drop from +30 degrees (typical at frwy speeds) in quick drops to say 27 degrees. I attributed this to knocking, but now I realize it was the knock sensor sending a false signal. Appears that under load the ECU is interpreting a bad knock sensor signal as a knock.

>Then disconnected a lot of things all at the same time - MAF, Vanos, both pre-cat O2's. Problem persisted.

>Finally, with everything connected again, I disconnected only the knock sensor. The plug is under the intake manifold next to cylinder 4. I did not need to remove the intake. Rather took off the bolts to the PS fluid reservoir, removed the oil filter cap, removed the +12V bolt on the intake and pushed the 12V socket down below the intake. In this way I could reach under the intake and pull off the knock sensor connector. Driving around, I'm still expecting to see a CEL for missing knock sensor, but I drove once so far for about 20min under various loads/speeds, no CEL yet.

One of the replies earlier suggested I replace the knock sensor. Whoever that was, thank you.

Last edited by ztom; 09-13-2012 at 06:54 AM.
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  #2  
Old 09-17-2012, 10:53 PM
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ztom ztom is offline
I gotta have more cowbell
Location: Thousand Oaks CA
 
Join Date: Sep 2007
Posts: 844
Mein Auto: 1997 528i
Update..
..I replaced the knock sensor & it solved the stumble. During the time I had disconnected it I only got a cel once, strange. The car definitely when into limp mode, poor acceleration from no timing advance. I didn't need to remove the intake manifold to replace sensor. Now I see how much power I lost from a knock sensor degrading. A degraded knock sensor quietly robs performance.

..with this much power it's clear my cats are ok, not plugged.
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  #3  
Old 09-18-2012, 06:46 PM
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16valex 16valex is offline
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Thanks for the update.
Didn't know a knock sensor can be that critical to engine performance, learn something new every day
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  #4  
Old 09-18-2012, 06:56 PM
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bluebee bluebee is offline
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Location: San Jose, California
 
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Mein Auto: 02 BMW 525i M54 auto 130K
I'd have to check, but I don't think the knock sensor is listed in the misfire thread:
- How to diagnose a BMW E39 engine misfire (1)

OK. I couldn't help myself. I'm compulsive that way. The knock sensors aren't mentioned even once in that entire thread.

I'll have to add a reference to here so that others benefit.
__________________
Each repair should invariably add to our knowledge base by the process of inexorable incrementalism.
Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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  #5  
Old 09-22-2012, 09:35 PM
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ztom ztom is offline
I gotta have more cowbell
Location: Thousand Oaks CA
 
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I also posted here
http://www.bimmerfest.com/forums/sho...ght=under+load

I now cleaned the icv & throttle body. Found the icv bracket was bent so icv not fully seated in the intake, but the misfire continued. I checked the tps & resistance variation when turned was ok, 0.9 to 5 kohms. Watched the stft & o2s in real time & ok, fast switching & no lean condition.

I now think the issue is a cracked head (which I already knew) & oil or radiator fluid leaking into cyl 3, because that plug is wet & showed damaged ceramic from detonation. With new plugs it seems to not misfire, so I think over time the plug gets coated & spark gets poor. Right now the car runs great, idle also very smooth, & good acceleration. I know I need to change the head, done that before.

Last edited by ztom; 09-22-2012 at 09:39 PM.
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  #6  
Old 09-23-2012, 10:26 PM
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bluebee bluebee is offline
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Location: San Jose, California
 
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K
Quote:
Originally Posted by ztom View Post
I know I need to change the head, done that before.
Yuck. Good luck. I can't imagine doing that myself.

Dunno if these can help:
- Summary advice to provide users who suspect a major engine repair due to overheating (1) (2) (3) (4) & how to test an engine for a blown head gasket, cracked heads, a warped block, stripped head bolt threads, cam seizures, contaminated bearings, coolant hydrolock, or piston, ring, or valve damage (1) (2) & what are the major factors in deciding whether to rebuild the engine, replace the engine, or sell the car (1) & a DIY for replacing the I6 M54 head gasket (1) (2) & replacing the V8 M62TU head gasket (1) & why these engines are so prone to heat-related damage in the first place (1) & welding the crack between cylinder #3 and the water jacket on the exhaust side (1) & what engine swaps are most recommended (1) (2) (3) & where to obtain a new or rebuilt head (1) replacement short block or long block (1) (2) & how to lift & remove the engine (1)
__________________
Each repair should invariably add to our knowledge base by the process of inexorable incrementalism.
Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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  #7  
Old 09-26-2012, 08:36 PM
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ztom ztom is offline
I gotta have more cowbell
Location: Thousand Oaks CA
 
Join Date: Sep 2007
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Mein Auto: 1997 528i
Update - driven 200 mi so far & gone up hills @ frwy speeds, no misfire, so I do think misfire under load was bad plug & made worse by old knock sensor.
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  #8  
Old 10-14-2012, 09:04 AM
yoman793 yoman793 is offline
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Location: NOLA
 
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Mein Auto: e39 530i
gonna be swapping out my knock sensor ASAP. posted on that other thread that this is the same thing that has been happening to me. I tried several other things attempting to find the problem. I'm hoping its just the knock sensor and not a cracked head...

and your saying you didnt have to remove anything to get to the sensor? did you come at it from underneath the car some how? or just wiggle your way behind the intake manifold?
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  #9  
Old 10-14-2012, 10:28 AM
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ztom ztom is offline
I gotta have more cowbell
Location: Thousand Oaks CA
 
Join Date: Sep 2007
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Mein Auto: 1997 528i
Only from top. Of the two places bolted, the front one easy, the rear a little harder but not difficult. Unbolt ps res. & remove oil filter cap. Don't replace the knock if new plugs eliminate the knock. I think in my case I have cyl 4 plug getting damaged from too much heat. But I do think the knock replace helped. I do wonder if the knock "microphone" degrades.
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  #10  
Old 10-14-2012, 10:36 PM
yoman793 yoman793 is offline
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ah ok. i took a look at it today and see what you did. i think i can get at it easy enough. im gonna order that part on monday and give it a go. new plugs did help the car but did nothing for the hesitation problem. same old ****... i did notice a bit of oil in cyl #1 plug well though which was disconcerting.... that plug came out just by loosening it with my hand, so im hoping/praying it just wiggled itself loose.
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  #11  
Old 10-15-2012, 05:03 AM
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16valex 16valex is offline
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Quote:
Originally Posted by yoman793 View Post
ah ok. i took a look at it today and see what you did. i think i can get at it easy enough. im gonna order that part on monday and give it a go. new plugs did help the car but did nothing for the hesitation problem. same old ****... i did notice a bit of oil in cyl #1 plug well though which was disconcerting.... that plug came out just by loosening it with my hand, so im hoping/praying it just wiggled itself loose.
I would hold on replacing your knock sensor.
Your hesitation is probably cause by clogged or leaked CCV system, if you have not recently replaced it's time to do so, (hint oil in plugs)

And if the CCV doesn't help, the next thing for you is to replace the VANOS seals ( known issue)
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  #12  
Old 05-04-2013, 09:43 PM
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ztom ztom is offline
I gotta have more cowbell
Location: Thousand Oaks CA
 
Join Date: Sep 2007
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Mein Auto: 1997 528i
Many miles later, need to post an update - the stumble was a cracked head. Replaced & now ok. My issue was very specific - a stumble under load at freeway speed.
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