1986 635CSI Starting & Dying Issues

[Dreameraver]

I've researched this to the point my head hurts

Auto Trans, 120k miles, owned for 2 months

Symptoms:

1. I can drive it for a week or two, starting it 20 times without fail. Then it just won't start. I try it 4 or 5 more times, sometimes it will start right up again, sometimes I sit for 10 minutes, try it again 2 or 3 times, and it starts.
2. Driving fine, it randomly just dies. It did this twice on me. Both times I pull over, turn the ignition off, turn it back on, and it starts. I haven't driven it since.

Replaced the crankshaft sensor (and ICV because it was bad... separate issue). From the research I've done there are supposed to be reference sensors on the bell housing. I took it to my local import shop I've done business with for a long time.... he's scratching his head because he can't find a cam sensor, and there are two ports on the bell housing, but no sensors. This, from my reading on this site, would be the first place to check for connection, failure (bad ohm reading).

[DesktopDave]

Sounds like two different issues.

The no-start can be a very frustrating issue to troubleshoot. Off the top of my head, common causes are an intermittent ignition switch, they have a tendency to wear out internally. Automatics can also have troubles with the shifter, an iffy inhibit switch can kill the motor. Another problem with the starter is the 'start' signal wire (small black/yellow wire) will get loose or fall off the starter lug.

Secondly, you might have yourself an upgraded car there. A lot of hobbyists have upgraded these cars from Motronic 1.0 (speed & position sensors on the bellhousing) to Motronic 1.3 (crank position sensor on the vibration damper, cam sensor on the #6 plug wire). If so, the transmission will still have the sensor holes, but no sensors installed.

[Dreameraver]

Sounds like two different issues.

The no-start can be a very frustrating issue to troubleshoot. Off the top of my head, common causes are an intermittent ignition switch, they have a tendency to wear out internally. Automatics can also have troubles with the shifter, an iffy inhibit switch can kill the motor. Another problem with the starter is the 'start' signal wire (small black/yellow wire) will get loose or fall off the starter lug.

Secondly, you might have yourself an upgraded car there. A lot of hobbyists have upgraded these cars from Motronic 1.0 (speed & position sensors on the bellhousing) to Motronic 1.3 (crank position sensor on the vibration damper, cam sensor on the #6 plug wire). If so, the transmission will still have the sensor holes, but no sensors installed.

That's the best news I've heard in a week, kind of. Where in the Motrnoic can I find the model #, or is there a physical I can check to tell the difference.

So if there's no sensor wires being due to an upgraded Motronic, and the crankshaft position sensor was just replaced, is the only other thing to do besides checking / replacing the start signal wire on the starter and ignition switch to replace the ECM? I know that was a big jump - trying to get to an end.

[carsnplanes]

I think DD is assuming when you say it won't start, that it won't even crank over. I this the case? or is it that you can crank it, starter motor spinning, but it just doesn't catch or run. Which is it?
Even if it cranks bust doesn't start, I second the ignition switch as the start position may supply the needed signal to the starter but the 2nd position or "Run" position signal is absent sometimes. That can cause the engine to just shut off.
I also agree if the two flywheel sensors are missing, then you should look for the fwd crank pulley CPS connected to the #6 plug wire to confirm

[Dreameraver]

I think DD is assuming when you say it won't start, that it won't even crank over. I this the case? ...

Good eye - Yes, always has plenty of crank

Even if it cranks bust doesn't start, I second the ignition switch as the start position may supply the needed signal to the starter but the 2nd position or "Run" position signal is absent sometimes. That can cause the engine to just shut off.

I presume you are not talking about the cylinder, but just the switch itself.

I also agree if the two flywheel sensors are missing, then you should look for the fwd crank pulley CPS connected to the #6 plug wire to confirm

Yes- the CPS @ #6 is there and replaced. The confusion I had, until the help received here, was the BMW mechanic I talked to never mentioned the upgrade to Motronic 1.3 - I told him I replaced the CPS, and was scratching my head looking for a Cam sensor, and he said to look for the reference sensors which, with the clarification here, I now realize are replaced by the on-board diagnostics within the 1.3.

I will replace the ignition switch. and dig into the Motronics 3.1 to see if I can figure out what the failure is.

Thanks so much to all who helped.

[Dreameraver]

OK - I've done some preliminary research. Part of the problem is conflicting data, which always makes it hard.

According to this article - http://theiconicbmw.com/about-me/tec...oubleshooting/ ...........

"The final versions of the E24 (’88-’89) ran the M30B35 “World” motor with an updated version of Bosch hardware: Motronic M1.3."

According to Wikipedia, "Motronic 1.1 was superseded in 1988 by the Motronic 1.3 system"

I can't figure out how to tell if mine is the M30B35 or the M30B34. Pretty sure it's the 35, has the Motronic 1.3 from the factory. How can I tell the difference?

Vin - WBAEC8419K3269207 if this helps.

BTW - probably the best forum I have ever been a part of.

[DesktopDave]

Don't listen to that jerk, he has no idea what he's talking about.




Just kidding, that's my blog.



Update: I added a post below with your full decoded VIN. You have an '89 with Motronic 1.3. I've left my original post here just for informational purposes.

The M30 has many very similar versions with easily interchangeable parts. The 6-er never ran 1.1 as far as I know.

To make it more confusing, the 1.1 and 1.3 are nearly identical. The 1.3 computer can even be plugged into the 1.1 harness. However, the only cars that got that were the '88-only 325 (E30) and 528e (E28), so called "SuperEta" cars. There are other even more exotic systems on the ///M cars and other exotica, but those cars really sit in a weirdly different & arcane world.

To determine what you've actually got in your car, I'd start with the engine. The easiest way is to look at the cylinder head/cam box cover. If it has a BMW roundel, that's the older B34 cover. If it has "BMW" spelled out in block letters, it's the B35 cover. The intake manifold likewise is slightly different. A B34 will have "3.2/3.4" on the side of the plenum. The B35 is simply labeled "3.5".

There are many other subtle differences. The B32 & B34 Motronic 1.0 wiring harness is in a thick vinyl tube, running alongside the fuel rail, with individually wired plugs to each injector including the cold-start injector under the plenum. The B35/Motronic 1.3 has a nifty plastic conduit above the manifold, clipped onto the injectors, next to the fuel rail. It has no cold-start injector at all.

The computers are different too. The earlier 1.0 cars have a DME (ECU) typically ending with -059. That DME connector plug only has two rows of pins. The later 1.3 typically ends with -179, and the DME connector plug has three rows of pins.

[DesktopDave]

I just ran that VIN, you definitely have a late model E24 with Motronic 1.3. Your car was built March 31, 1989.

If you like trivia...I know I do...your car was built very near the end of production. There were only 1064 E24 chassis built that year, I believe only 583 were US-market 635CSiA (automatics). According to RealOEM, E24 production ended in April '89; you have one of the very last E24! From the bit of research I've done, the final car was VIN 9289...so...most likely your car (9207) is one of the final 100. BMW does play games with VINs at times, it might be fun to contact BMW Group Classic to see if they could shed some light on your car's provenance.

Here's a few good resources with production numbers:
http://www.e-24.ru/eng/theory/tech/number/
https://bigcoupe.com/phpBB3/viewtopic.php?f=24&t=28408

There are only a few working BMW VIN decoders out there at any given time. They are hit-and-miss when it comes to working 100% of the time. I've been using bimmer.work recently, here's their decode for your car:

WBAEC8419K3269207
Type 5384
Model 635 Csi
Market USA
Development Code E24
Chassis Coupe
Steering left
Doors 2
Engine M30
Displacement 3.50 l
Power 0 kW
Drivetrain Rear-Wheel Drive
Transmission automatic
Color Bronzit-beige - 139
Upholstery - 0268 (black nappa leather?)
Manufacturer BMW AG
Production Plant Born, Netherlands (VDL Nedcar) (that's wrong, this should be Dingolfing instead)
Production Date 1989-03-31


216 Servotronic Servotronic
240 Leather Steering Wheel Lederlenkrad
290 Lt/aly Wheels Star Spoke 44 Lm Raeder/sternspeiche 44
441 Smokers Package Raucherpaket
459 Seat Adjustm., Electr. W. Memory Sitzverstellung, Elektr.mit Memory
533 Air Conditioning For Rear Fond-klimatisierung
925 Shipping Protection Package Versandschutzpaket

[Dreameraver]

DD - THANK YOU! That's a world of information that I will store.

I'm one of those guys who love provenance. I preserved my most cherished American Muscle before I sold it all. Now I got bit by the Euro-Bug and loving it. The 635 was a bucket list car for me. I rode in one back in '85 or '86 and became enamored with the 6 Series ever since. I probably looked at 25 or more over the years but never fount "The One", until I stumbled upon it a few months ago. I knew it was the one for me, so I bought it without even driving it... just started it up, let it idle, and stood there while it was running and talked to the owner for 45 minutes. Just the condition of the car and it idling 'fairly' smooth was enough for me. At the price it was a no-brainer. Now I'm dumping a ton of time into researching it, figuring out its idiosyncrasies, and paying the toll as I go down the journey. Finding the solutions to the different problems has been a joy. I can't wait until the day I can drive it down the road with full confidence. Once I'm there the next step is to see how I can increase the performance / hsp, and begin to do the little things that will keep it original and spruce it up. I have a long ways to go but it will be a pleasure trip.

I will let you all know how this issue turns out / resolves before I post the next thread to figure out a couple of other things.

THANKS TO ALL! Steve

[Dreameraver]

From here: https://www.spectrapremium.com/en/aftermarket/north-america/camshaft-and-crankshaft-position-sensors#:~:text=The%20crankshaft%20position%20sens or%20monitors,RPM%20and%20relative%20engine%20spee d.&text=The%20camshaft%20position%20sensor%20is,in jector%20and%20coil%20firing%20sequence.

"The crankshaft position sensor monitors as a multifunctional sensor used to set ignition timing, detect engine RPM and relative engine speed. This sensor negates the need for manual distributor timing."

"The camshaft position sensor is used to determine which cylinder is firing to synchronize the fuel injector and coil firing sequence."

So my car has only a crankshaft position sensor, no reference sensors, no camshaft sensor. What takes the place of the camshaft sensor? Is it handled electronically by the ECU?

[carsnplanes]

Yes, everything for managing fuel, timing and spark in the Motronic 1.3 is programmed in the ECU and calculated using the front CPS, AFM, ECU temp sensor and O2 sensors.

[Kenneth1948]

One of my cars is an '84 733, it had about 120k at the time this problem occurred.
Like yours, my problem was intermittent, sometimes it would start and run for a few days then die or wouldn't start after a short run.
I replaced the fuel pump with a new Bosch pump, in-tank pump seemed to be working OK.
Then after a 2 - hour run up the interstate it died, fortunately at an exit. I ended up having to tow it home.
After much trouble-shooting here was the cause and fix for my problem:
My car had been owned by one family and not used continuously, it had been parked for months at different times.
The fuel tank had rust in it and particles of rust got into the fuel pump and would stop the pump intermittently.
Like yours, sometimes it would start, other times not. Or run for a while then stall.
The successful fix was to remove the fuel tank, scour it out with some phosphoric acid (I actually put some old lug nuts in the tank and agitated them with the acid solution - quite a work out!) cleaned and dried thoroughly, installed tank with new pump and filter, fresh gas and away it went. That problem was solved and never occurred again.
It may be possible to rig up a fuel pressure gauge that you can see while driving to diagnose this problem. But I can't think of a way to do that safely.
Good luck, John Kenneth

[Dreameraver]

Yes, everything for managing fuel, timing and spark in the Motronic 1.3 is programmed in the ECU and calculated using the front CPS, AFM, ECU temp sensor and O2 sensors.

Thank you

[Dreameraver]

One of my cars is an '84 733, it had about 120k at the time this problem occurred.
Like yours, my problem was intermittent, sometimes it would start and run for a few days then die or wouldn't start after a short run.
I replaced the fuel pump with a new Bosch pump, in-tank pump seemed to be working OK.
Then after a 2 - hour run up the interstate it died, fortunately at an exit. I ended up having to tow it home.
After much trouble-shooting here was the cause and fix for my problem:
My car had been owned by one family and not used continuously, it had been parked for months at different times.
The fuel tank had rust in it and particles of rust got into the fuel pump and would stop the pump intermittently.
Like yours, sometimes it would start, other times not. Or run for a while then stall.
The successful fix was to remove the fuel tank, scour it out with some phosphoric acid (I actually put some old lug nuts in the tank and agitated them with the acid solution - quite a work out!) cleaned and dried thoroughly, installed tank with new pump and filter, fresh gas and away it went. That problem was solved and never occurred again.
It may be possible to rig up a fuel pressure gauge that you can see while driving to diagnose this problem. But I can't think of a way to do that safely.
Good luck, John Kenneth

Great input / insight

I bought this from an older man who just liked cars. Mostly Mercedes. He has a mechanic who takes care of all his cars. This car, the BMW, was I think somewhat of an aberration for this guy because he is pretty much a Merc only guy.

He owned the car for about 5 years I think, and had not been driven much at all. I think he just cleaned it up and put it on the road for sale. Enter me....

I don't really do much mechanical any more, and I never did a ton of it personally, but I try to understand it as best I can and have conversations with my mechanic friends to try to get to solutions of problems. This one has been interesting.Here are th e4 min initial issues..... I've barely driven it in the 2+months I've owned it, and it's been at the mechanic's shop for about 3 weeks....

1. Tried to get it smogged (CA) and failed 4 tries on the evap test- still have to take it ack and try again.
2. Throttle would get stuck @ 2000RPM regularly - think I figured that one out because of the plastic clips on the throttle line that has the little metal "Barrels" clipped in - one of the two didn't have enough tension, the barrel would come lose and get stuck. (This is in case future readers might have that issue where this solution would help them.)
3. Hunting for idle.
4. The intermittent dying / not starting issue

I've replaced the Idle Control Valve - it was bad, but didn't improve anything. Also replaced gas cap (1 link in Evap, had cracked gasket) - but the test machine uses it's own cap, so that doesn't affect the outcome.)
I have new vac lines, rotor and cap, wires and plugs

I will do all of this and look at doing the fuel tank, possibly an evap filter, fuel filter, etc.

[Kenneth1948]

I scanned through the previous posts here and I certainly respect the knowledge and experience behind them.
I know my fix here sounds simple, almost too simple but I went through months of agony trying to figure it out. Changed out the ECU and many other parts. Your problem may well be something different but your symptoms are quite similar so I posted it anyway. The fuel pumps are quite susceptible to contamination like rust and remember, it's on the upstream side of the fuel filter
I had a fling with some old Volvos before I fell for an old 6er. The inside of the tank on the 164 looked like something off the Titanic. It would stall when the strainer inside the tank got clogged up but if you shut it off and the lack of fuel pressure would allow some fuel to flow again and you could re-start and drive a few more miles. I bought a 244 cheap with a similar problem. I applied the same fix described above for the BMW and it ran fine until my daughter totaled it.

If this is your problem, monitoring fuel pressure while driving would be a good way to diagnose it. I wouldn't recommend running a high pressure fuel hose and gauge inside the car. Anyone tried mounting a gauge temporarily so you can view it through the windshield?
I will try to find some time in the next day or so and see what I can come up with. Good luck, John Kenneth

[OBwan]

I had an 88 635 Auto twenty years ago that had similar issues. Sometimes it would start right up and be fine and others it would not start at all or quit going down the road. I tried relays sensors to no avail. Then Steve Haygood recommended changing a module under the dash and it stopped. I want to say it is the cruise control module. Under the dash left side of the steering wheel. He said if it wont start and you could jump the wires going into the module, it would bypass the module and if it started that was it. Sorry I can't remember what it was but it must be common enough for him to throw out there.

[Kenneth1948]

I'm not sure about a cruise control module but there is a security module under there that is supposed to prevent the car starting if the ignition is "jumped" in the case of theft. This was one of the items I looked at when trouble shooting my problem. It's a black rectangular box clipped under the dash near the steering column and can be by-passed fairly easily. It should be well documented on this and some of the BMW boards as to which wires to disconnect and which wires to connect.

[Dreameraver]

I'm not sure about a cruise control module but there is a security module under there that is supposed to prevent the car starting if the ignition is "jumped" in the case of theft. This was one of the items I looked at when trouble shooting my problem. It's a black rectangular box clipped under the dash near the steering column and can be by-passed fairly easily. It should be well documented on this and some of the BMW boards as to which wires to disconnect and which wires to connect.

OK - Now I'm thinking........................... the previous owner put in an electronic key lock and it has a matching FOB for it. I'm wondering...................How do I search the forum for this security module?

[1986series6]

A remote aftermarket key lock will not be wired into the ignition circuit.
If it's an alarm or remote start, that probably would be wired into the ignition.