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Finally got around to replacing my one iffy Ref sensor. Damn! No more funky idle issues. Feels like 10 hp. Why do the little things take so long?

That's probably the cause of the idle and driveability problems a lot of us are having. My reference sensor was replaced about 800 miles and 2 weeks before I bought the car, but I don't know if it was new or not. I'm assuming it was since the only other things on that invoice were oil change and fuel line and the parts alone were $182.

Do you know the part number for a 533?

Thanks.

Finally got around to replacing my one iffy Ref sensor. Damn! No more funky idle issues. Feels like 10 hp. Why do the little things take so long?

The one on the bell housing or another one?

Ok, help educate a newbie.

Who/what/where/when/why is the ref sensor?

My 88 535is rough idles sometimes, usually when cold. I don't have any drivability issues, most of my problems are cosmetic. But under the hood, it's a damn good thing I've got a Bentley. Give me a unix box, apache, and perl and I'm good to go. Give me a wrench, and you might just have to draw me a map to the nut/bolt. I'm not an idiot, just learning.

From what I understand (correct me if I am wrong) shouldn't the speed sensor cause the idle issues. The reference sensor is the TDC sensor, correct? So, if the refernce sensor is not getting a signal ... no start or run. And, if the speed sensor is not getting a signal / correct signal ... drivability issues.

Josh,

Having a clean signal from the reference sensor is every bit as important as the speed sensor, especially at idle. The Motronic ECU shifts the timing to make fine adjustments to the idle speed. The ICV sets the base idle, and is mainly responsible for dealing with maintaining idle speed when things like the A/C cycle and load the engine.

All this is explained in the books regarding Bosch FI and Engine Management by Probst, and the similar tome written by Aird Forbes. I highly recommend both of these author's informative books on the Bosch FI/Engine Management Systems, of course you shouldn't buy these until after you've purchased a Bentley.

You Do Have A Bentley, Dont You ??

HTH

Rich

Of course I have the Bentley :-) ... I do realize the importance of both. The car will not run without signal from the reference sensor but may be able to run without signal from the speed sensor, right ???

The reference sensor reads the one pin on the flywheel for crankshaft position and speed sensor reads flywheel teeth ... right ???

So, my assumption was that the speed sensor would more than likely cause idle issues and reference would be more of a cause for a dead car. Of course, with intermittent signaling this can get weird.

Am I correct in this, Rich. Thanks for the input.

Josh,

The engine will run if the speed sensor dies, but not well.

The engine will not run if the reference sensor fails.

However here's why the reference sensor being good is important. There are probably failure mods of the sensor which allow the sensor to output a signal of appropriate amplitude for the ECU to recognize it. Now what would you think would happen if the ECU some some sort of odd signal from the reference sensor that the ECU interpreted as two impulses, or maybe delayed due to some odd failure mode.

Because the Motronic Engine Management System shifts timing to adjust the idle speed, it's extremely important that the reference sensor be outputting the correct signals. In addition, think about how ignition timing affects engine performance.

Because the sensors are electronic devices, they can fail in ways that you cannot detect unless you have an oscilloscope to view the actual output pulse waveforms. If the sensors fail in a way that creates a defective input signal the ECU, no telling what sort of interesting things the ECU might do. Basically like all things handled by computers, "Garbage In / Garbage Out" .

Rich




[Edit by Rich Euro M5 on [TIME]1110390499[/TIME]]

Great Explanation .... Thanks a ton Rich

Rich,

That was lucid, cogent and very interesting. Thank you.

Tom

Thanks Rich. That definitely helps.

OK, to be accurate, it was probably the speed sensor I replaced (the one that rides near the flywheel teeth). I tend to refer to them generically as "ref sensor" because it's the same part (on my car).



[Edit by Velocewest on [TIME]1110404196[/TIME]]

[QUOTE="Jim in CO - 533i"]Do you know the part number for a 533?

Thanks.[/QUOTE]

The Bosch one from EAS is F6010-12760, $53.85, free shipping.

https://www.europeanautomotive.com/index-exec/

Found the box -- Bosch number 0 261 210 002



[Edit by Velocewest on [TIME]1110421901[/TIME]]

I've been battling a wonky fast-idle miss for a few months now. Replaced practically everything trying to chase it down. A buddy even checked out the output from the (new) speed/reference sensors on his oscilloscope....

The speed sensor gave a nice and uniform output for all the teeth. No apparent issues there.

The reference sensor appeared to have an anomaly in that the signal went DOWN a bit before rising. Does anyone recognize this as a specific problem? The timing seems to bounce around, which would be consistent with the ECU having difficulty getting a good reading. Maybe this explains my fast-idle miss?? Swapping in the old sensor and adjusting the air gap did not help/change anthing.

I inspected the flywheel reference sensor "pin" and it's not a pin at all, but a hunk of metal several times thicker than an individual flywheel starter tooth. Sound right?? Sensor signal should RISE first and not go down, just like the signals from the speed sensor. Grounding issue?? Flywheel issue??

Love to hear from someone who has seen the waveform of the reference sensor on an oscilloscope...

BK

[QUOTE="greg.epps"]Ok, help educate a newbie.

Who/what/where/when/why is the ref sensor?

My 88 535is rough idles sometimes, usually when cold. I don't have any drivability issues, most of my problems are cosmetic. But under the hood, it's a damn good thing I've got a Bentley. Give me a unix box, apache, and perl and I'm good to go. Give me a wrench, and you might just have to draw me a map to the nut/bolt. I'm not an idiot, just learning.[/QUOTE]
You sound exactly like me! You using linux too? Suhweet. Now where's the coolant tank? One thing that learning unix taught me though, dedication. I am going to learn how to work on my beemer, and that's that.

[QUOTE="Jordan528e"]You sound exactly like me! You using linux too? Suhweet. Now where's the coolant tank? One thing that learning unix taught me though, dedication. I am going to learn how to work on my beemer, and that's that.[/QUOTE]

No, I'm using Solaris 8 mostly, a little HPUX, and a little, old time AT&T Unix RTR. Actually never touched Linux. I've learned most of it by the seat of my pants and reading books (O'Reily, Unix in a Nutshell and the Perl Black Book). So now I'm learning my bimmer the same way, the seat of my pants and books (Bentley manual).



[Edit by greg.epps on [TIME]1110458123[/TIME]]