New-to-me 1992 735iL – the fun begins!

[shogun]

It fits your 735 M30. My list is not complete, otherwise it would be much longer, BOSCH 1197311027 = BMW 12311726022, PORSCHE 964 603 141 00, VW 034 903 803, BOSCH EL 14V-4C / HR10, MERCEDES-BENZ A 003 154 31 06,MB A 002 154 79 06, MB 003 154 31 06,MB 002 154 79 06,PORSCHE 964 603 141 00, VW 034 903 803 and more.
The Bosch alternators were used in many cars and the same voltage regulator is used, just under a different brand p/n, for your M30 engine the alternator is the same as on my M70 (not the compact version as on the E32 M60) and the slipring of the alternator is larger with 28mm on M30/M70, whereas the smaller size compact one on the M60 E32 and my E36 M3 has only 14/16mm and the voltage regulator is also then different to fit that slipring.

[Cactuar]

So much good information in the latest posts! Thanks guys.
You really gave me hope that this could be the right fix

Not a lot of spare time to look at the car lately but I did peek at the voltage regulator tonight.
I wanted to take it off but the upper screw is blocked by the oil filter canister.
It looks like I'd have to take out the alternator, or at least move it using the belt tensioner/bracket.

Maybe this week-end I can take a proper look and report back.
Also I need to get alligator cables for my voltmeter, I only have the short leads with the pointy bit at the end that came in the box.

[E32FAN]

Amazon.ca can help, of course. Delivered to your door for $10.

https://www.amazon.ca/eBoot-Groups-A...322773&sr=8-10

[Cactuar]

Alright I couldn't wait longer, I took the alternator and voltage regulator out. How is it looking to you guys?
The tips (brushes?) are longer than 5 mm but definitely shorter than a new regulator.

20200917_042002.jpg20200917_042639.jpgvoltageregulator1.jpgvoltageregulator2.jpg

[shogun]

Length seems to be o.k., I just measured a new Hella voltage regulator and the brushes are 11mm long (what is sticking out). But is one of the brushes shorter than the other or is it just the angle of the picture? Do you have a picture of the slipring where the brushes run on?
Here some pics of a 140A Bosch slipring, and he mentions that if the slipring has such deep groves as in pic 2, it has to be replaced http://www.e32-schrauber.de/bmw/s-lima.htm
the groves in the slipring should not exceed a depths of 1.5mm
bad one http://www.e32-schrauber.de/bmw/date...r/P1000507.jpg
new one installed http://www.e32-schrauber.de/bmw/date...r/P1000526.jpg

Repairing a Bosch, 120 A alternator http://www.3dzubehor.com/Rover/Boschrepair.html

[Cactuar]

Yes one tip is shorter than the other. Here is the inside where the regulator goes:

Attachment 678287

[CroughtonE32]

I'm not sure if your 92 il and my 90 i came with the same alternator. I just looked at my motor and my original OEM part I found it at Autohaus online. This is the picture they post and looks exactly like mine. The voltage regulator is an easy part to find and although Real OEM has it up well above $150.00, they don't cost that much any longer. If you just google "Voltage regulator for 1992 BMW 735il", you'll see them pop up for under 40 dollars US. Now that you've got it out, and those brushes are short on one side, you may have found your problem. If you have a problem finding the part, PM me and I'll send you mine. I might not need it for years. It's just sitting here. Also, I hope you saw that YouTube video i posted of the guy rebuilding one completely. Not so much for your specific repair here, but entertaining as hell.
Jeff

[E32FAN]

I think the defect is electronic, so you should replace the regulator.

[Cactuar]

Yep, I just placed an order for a new Bosch voltage regulator.
It took me forever to find one at a decent price in Canada. Napa wanted 100$ for it, yeah no.
Even RockAuto only had Chinese junk when searching for all the parts interchange numbers. No Chinese junk on my car.

Then I came across this part number: Bosch 30097. That's the internal Bosch number, and it can be found on RockAuto: https://www.rockauto.com/en/moreinfo...k=280020&jsn=3
Oddly enough RockAuto doesn't list any compatible parts.

66$ CAD shipped and taxed (50$ USD) is my kind of deal I should receive it next Thursday, then we'll know if it fixes my issue!
Thanks everyone for the help.

[CamE32]

You guys must have short memories *kidding*

Replacing the regulator a few weeks ago made no difference to the idle in my case, and the original one on the car was basically identical to the picture you shared @Cactuar

The only improvement I noticed was to the steadiness of the voltage reading - which must be good, I assume, but evidently not the root cause of the issue we're experiencing

I do hope your experience is different though!

[E32FAN]

You guys must have short memories *kidding*

Replacing the regulator a few weeks ago made no difference to the idle in my case, and the original one on the car was basically identical to the picture you shared @Cactuar

The only improvement I noticed was to the steadiness of the voltage reading - which must be good, I assume, but evidently not the root cause of the issue we're experiencing

I do hope your experience is different though!

Here on the forum, the only way we can assist other members is to think deeply on the reported symptoms, and suggest further tests to perform, and hopefully to theorize a new root cause of the core malady, and then test each theory. That's the nature of debugging.

Sadly, it is possible to replace one defective component with another defective component, and so conclude that that part is not the cause of the fault. I have done that with relays - swapping one bad relay for another bad relay, both having pitted contacts. Then I feel foolish when I realize what I have done.

We should not have short memories. Thankfully, some members here have VERY LONG memories. shogun

[CamE32]

Agreed on everything you said!

Trust me, I'd be ecstatic if Cactuar replaces his and it solves the rough idle - I'd even be relieved if it means I need to replace the whole alternator!!

[CroughtonE32]

I think when E32FAN came up with the fact that the interior lights were dimming at the exact same time the idle was dipping, he may have come across something. I can't wait to see if this little swap does the trick.

[Cactuar]

Oh yes Cam, your experience came to my mind immediately when I went looking for a voltage regulator.
What if it doesn't solve my issue and it's another 60-100$ spent?
But because the lights dim slightly every time the engine speed changes, I'm hopeful that it will fix my issue. As far as I know your interior lights were steady and didn't dim correct? I'm hoping my issue is different.

But yes it could very well be a red herring. Because of how difficult it is to find the root cause (not even my mechanic could find it) I'm ok with trying parts. The parts cannon is loaded and firing

[CamE32]

Oh yes Cam, your experience came to my mind immediately when I went looking for a voltage regulator.
What if it doesn't solve my issue and it's another 60-100$ spent?
But because the lights dim slightly every time the engine speed changes, I'm hopeful that it will fix my issue. As far as I know your interior lights were steady and didn't dim correct? I'm hoping my issue is different.

But yes it could very well be a red herring. Because of how difficult it is to find the root cause (not even my mechanic could find it) I'm ok with trying parts. The parts cannon is loaded and firing

I can confirm that my interior lights were not dimming (or at least not noticeably), but ever since I fixed that vacuum leak caused by the fuel tank vent valve hose, my idle problem is basically identical to yours (as in seemingly more predictable/steadily-imperfect). Also, LOL at the 'parts cannon'.


Update on my hunt: I started the car today after my oil pan fiasco and there was sadly no improvement to idle - I was thinking maybe the loose pan was causing a vacuum leak that would go undetected with a standard smoke test, but that doesn't appear to be the case.


Best of luck! Eagerly awaiting your results

[letank]

Yep the interior lights still dim a bit when the engine speed changes. It does it in idle and in reverse.

Battery voltage with the car off is 12.37 volts. During idle it's 14.2v, and I saw an increase to 14.5v or so when the engine speed changed but only sometimes.

BTW 12.37 v is really low, about 50% discharged... 100% is 12.56v. Try to charge the battery before cranking... and opening any door, opening the doors put the system on stand-by for 16minutes and draw some current. If the battery is weak it is not going to hold any charge when it is challenged by the awake signal!
The 7 series has this 140amp alternator which is going to put some drag on the engine when it is charging the battery reading of 12.37v, the alternator goes to full charge and dragging the rpm down at idle. Same when you have the AC on.

With the restricted travel, I leave the hood unlatched after the last drive... we do not drive too much lately, once a week or every other week, the small car or the motorcycle does the city duties... and yes our 1 year old battery drops to 12.45v after 1 week, so every 4 days I connect a slow charger to the engine bay posts.

Ideally you should not rely and an alternator to recharge a weak battery. I have a solar charger for the vehicle parked outside... it does a good job.

[E32FAN]

Our E32 cars have several feedback control systems (FCS):

1. DME regulates the Engine speed seeking to hold the idle setpoint

2. Voltage Regulator regulates the battery charge current seeking to hold the full-change battery voltage setpoint

3. IHKA regulates the two cabin temperatures seeking to hold the driver and passenger temperature setpoints

4. Cruise Control regulates the road speed seeking to hold the cruise setpoint

5. Radio regulates its FM frequency seeking to stay on-station

7. Active suspension seeks to hold the car level.

etc.

Every FCS system constantly compares its operation to its setpoint, and calculates an error that must be closed as best possible using its actuators.

For FCS 1, the DME commands the Idle Control Valve duty cycle to regulate engine intake air.

For FCS 2, the Alternator Voltage Regulator commands the field current to regulate the output voltage

It seems to me that Catuar's surging idle is evidence that FCS 2 is loading the engine via the alternator V-belt, and FCS 1 is responding to this changing mechanical load, striving to hold the engine speed setpoint.

The dimming of the interior lights shows that FCS 2 is moving off its setpoint. The varying idle speed shows that FCS1 is driven off its setpoint.

So, which is the cause, and which is the effect?

I may be wrong, but I think FCS 1 is responding to the FCS 2 changes. So FCS 2 is defective, oscillating, and it is causing the engine speed surging.

Just my thoughts. Please share your insights.

[Cactuar]

The voltage regulator was delivered today (gotta love how quick RockAuto is).

20200921_151315.jpg

Seeing how much longer the new brushes were got me excited for the install.

20200921_151143.jpg

Unfortunately when it was all said and done, I started the car and got the same hunting idle as before.

I was annoyed when I was done so I did not take the time to measure the output of the alternator.
Is there anythingI could measure that could give some clues?

The lights still dim as before btw.

[Cactuar]

FYI just checked the date code on the battery and it was made in September of 2014.

[letank]

The voltage regulator was delivered today (gotta love how quick RockAuto is).

Seeing how much longer the new brushes were got me excited for the install.

Unfortunately when it was all said and done, I started the car and got the same hunting idle as before.

I was annoyed when I was done so I did not take the time to measure the output of the alternator.
Is there anythingI could measure that could give some clues?

The lights still dim as before btw.

Bummer, so everything else is off.... AC, HVAC controls to null, Fan, radio... battery was fully charged at 12.65v before cranking?

You could have a parasitic or normal drain that is higher than what the battery/alternator can provide at idle...

If you increase the idle a tad to 800 what happen?

[Cactuar]

Everything else is off yep. The battery was charged to 12.35v yesterday (the car was off for a few days).
I charged it overnight and tried again this morning with the battery at 12.67v. Same result.

If I open the throttle slightly to engage the off-idle switch in the TPS the engine smooths out nicely and I can hear no variation in RPM.
However I can feel an occasional miss with my hand on the intake, and the engine shakes somewhat.
Bad ignition wires? Bad injectors?? The car drives well and pulls hard so it can't be those things right? And I already checked the wires and they were within spec.

[CroughtonE32]

So sorry this little fix did not take care of your idle and flickering interior lighting. I am curious though if the new brushes made any difference in the output of your Bosch alternator. If you remember what it was before the repair.
Jeff

[theBMWbeast]

I think my voltage is .02 volts off, maybe the x y and z plane aren’t coinciding at the exact right moments to perfect my idle...

Your battery charges, hold a steady charge? Alternator has no wild fluctuations?

Fuel, Air, Spark. Check fuel pressure, check for vacuum leaks (I remember potential intake gasket leaks?) check for ignition ( resistance through spark plug wires, coil readings, spark plugs gapped correctly, etc). I know you’ve done a lot of tests and checks, so I may be repeating myself once again. Check your TPS, does it click, measured values. AFM can be measured as well. Remove the dipstick, does the idle change. Same with oil cap. It should want to stall, if not potential vacuum leaks.

This is a 30 year old motor, with a design dating back 52 years now. It should be something simple. If you’re suspecting ECU problems (the only real dark art in this car), programa rebuilds units for ~200. Or you can open it up yourself and look at the condition of the solder joints. However my first line of attack would be vacuum, second sensors, third fueling. YMMV, Goodluck!

[Cactuar]

Thanks for the tips Mr. Beast. Tonight I started testing a few components.
All the grounds I could find are good (I get battery voltage).
Tried to check the voltage coming from the O2 sensor but could not complete the test, I was getting 20v+ and -10v at two different pin positions. The Bentley isn't clear about the pin assignment so I'll need to look into it more.
Will do more tests soon.

[E32FAN]

In June of 2018 your idle was steady (@ 7 minutes): https://www.youtube.com/watch?v=Ww4WUltnVkg

How about your CPS? It is on the "usual suspect" list.