Air Flow Meter Video Here - 1987 K75s Won't Start Consistently

[BeemerNewbie]

Looking for some expert advice. I'm pretty familiar with mechanics and I've been chasing an electrical gremlin in a 1987 BMW K75s that had been sitting for 10+ years with about 45K miles. The symptom is it will start 1 out of 20...25...100 tries. Completely random. When it does start it runs solid. No spark to plugs.

The history of the repairs and trouble shooting to date:

Rebuilt the fuel delivery system. Pump, hoses, filters, etc replaced with OEM parts. All of it was degraded and corroded. Pump is working properly, fuel delivered to rails and FI spraying. Unknown what regulator PSI is, but presumably good since fuel delivery appears working, just no spark. Fresh fuel 91 octane, 1/2 tank.

Replaced starter relay with OEM. Old one disassembled after arched and starter stuck on as many owners have discovered with poor batter voltage.

Replaced temp sensor relay. Checked resistance referenced to numbers found herein, and seems to have gone bad.

Checked temp sensor, air flow meter, ground, etc signals to computer per http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/bike-wont-start1.htm and all of it was in spec.

Alternator was not charging battery so I pulled it and cleaned it up. Battery was also replaced with brand new Odyssey P925L. Alternator now charging correctly and battery holding proper charge during starting loads.

Fresh BMW grade oil. New filter.

New BMW plugs.

New OEM rubber for all intake parts. Everything rubber was worthless and needed replacement so no pin holes etc.

Cleaned ground contacts under tank and lubed up with dielectric.

Voltage at ignition switch is at least 12.5V between switch and top fuse when ignition turned on.

Pulled starter this evening and will replace brushes. Rest of hardware looks good and just needs a cleaning.

I think that covers most of the relevant stuff. So here are the symptoms:

With the new battery bike tries to start strong, but no spark. Voltage near 13V, ignition on - kill switch on voltage drops to around 12.75V which is within tolerance.

Prior to new battery (may still happen, but have not attempted more than a dozen starts on new battery), with ignition on, kill switch on the bike would try to kick over than occasionally back fire without me depressing run switch. Also noticed a small flutter in tach of about 100rpm. This was random but with enough start attempts would happen regularly.

When I attempt to start the load shed relay seems to be working properly as I notice the headlight dim each time the starter cranks over a revolution or so, but not sure if the relay is bad or not. I don't think that would prevent the bike from starting though and the voltage to starter is still at least 12.5V. Its as if the ignition computer won't let the bike spark for some unknown reason. I thought perhaps the temp sensor, but as stated earlier, the specs to the computer were good when I checked per the above link.

When the bike does start it seems to run fine. I've only ridden it around the neighborhood once in the 2.5 months I've managed to get it started maybe 6 times or so, but she sounds and response solidly. If I get it to start it will run, but when I shut it off and try a restart right away it just doesn't want to start again and I haven't seen any pattern to when it will decide to start for me again. Hot day, cold day, rainy day, dry day...

My only thoughts at this point are:

Ignition computer bad, but unlikely.
HES bad, but I'd see issues when its hot not cold and first attempting to starting.
Temp sensor actually bad despite the output I'm seeing to the computer.
TPS bad, but when I pull the TPS connection I still get same no start condition.
Coil bad, but very unlikely to see all three coils bad and no spark on all three plugs.


If cleaning up and replacing brushes on starter doesn't fix the issue, I'm out of ideas. So I welcome suggestions to any SMEs out there that think they can get this beast to run.

Thanks.



 

[Scott_]

Sounds like you may have a very similar issue as in this thread:
http://www.motobrick.com/index.php/topic,6894.0.html

[Bokobob]

Good explanation of what you are experiencing...I wish I could add something tangible, but can only offer my empathy and hope you sort it all out and have it back to top running condition pronto.

[K75RT Keith]

Mechanical failures of the electrical system are a pain.

I'm guessing you checked the connections for HT leads on the coils and that the plug boots are all the way on. 
Traced back the power wires from the coils for breaks, wear or damage. 
Checked the connections on the HES, pulled the plate and checked for damage to the wires on the sensors.
Pulled the start/stop switch and cleaned the contacts.
Checked the connection at the ignition computer, Disconnected and cleaned the connector with contact cleaner then reinstalled.
Replaced the fuses in the fuse block.

Load shed relay has no effect on starting.  Only bypasses lights and accessories.  If yours doesn't make the headlight go off, then it may need replacing.  BUT that wouldn't be the cause of your problem.  Only other thing I can think of is if it sat for that long, mice might have dined on some wiring.

 

[TimTyler]

... I notice the headlight dim each time the starter cranks over a revolution or so...

The headlight should turn completely off when starting.

[BeemerNewbie]

Made a few more diagnostic steps today to determine why no spark.

Checked signals from electronic ignition model which I had not done yet and found the following (see Bert's chart for reference pins/numbers):

Pin #1: 0.1 Ohms (OK)
Pin #2: 11.5V (LOW)
Pin #3 and #4: 0.6 Ohms (OK)
Pin #5: N/A
Pin #6: Fluctuates up to 10V, but no greater. (LOW)
Pin #7: 12.3V w/ ignition turned on (OK)
Pin #8: Reads about 3mV with ignition on. "OL" when starter engaged so was unable to get a reading. (NOT OK?)
Pin #9, 10, 12, 14: 0V w/ ignition on. Fluctuates around 0.5V and once or twice 1.2V when starter engaged. (NOT OK?)
Pin #11: 0.5V w/ ignition on. Can't get reading when starter engaged unless I use min/max function on MM with the AVG was between 0 and 1 (OK?)

With the out of spec results on pins 2, 6, 8 and 9 I'm leaning to a bad ignition module unless there's any better theories. I don't wanna drop more money in an ignition module only to find out it does not resolve the issue.

I did clean up the kill/starter switch and it made no difference.

HES look fine to the naked eye, but I may need to test it which I'm trying to avoid just out of annoyance. I'll be ordering some new brushes for the starter, but would be surprised if that fixed the issue. Wouldn't be the first time I've made the wrong assumption diagnosing this sort of stuff though.

Is it possible that the voltage delivered to the coils is just not high enough to excite the plugs? The impedance in the system somewhere in the ignition circuit just too great but on a full moon night will occasionally overcome the impedance and the bike will come alive? I wish I had a pile of spare parts to swap in, but that'd be too easy.

Can anyone refer to a cheap retailer with spare ignition modules and/or HES?

Thanks for the suggestions to date.

[BeemerNewbie]

Can anyone comment on the effect of a bad temp sensor? Will this prevent the coils from energizing, ie plugs sparking or will it prevent fuel delivery? Or both?

I'm debating on swapping out the engine temp sensor even though the output values to the EFI were within tolerance...or seemed to be according to Bert. 

Thanks.

[Scott_]

In your original post, you mentioned that the injectors were spraying fuel when the starter button is depressed, yes?
If so, that would lead me to believe that the FI computer is receiving signal from pin #8 of the Ign computer that the engine is turning.
As RBM mentioned in the other post on the same problem, in Berts chart-- volts~ is referring volts AC not DC as is normally assumed.
When your 3mv reading went to 'OL', you just need to increase the scale.

If your water temp sensor resistance measurements are within the range of the others listed on Berts page I don't imagine that your sensor would have any effect on your no spark situation. The temp sensor should only affect the fuel mixture.

[rbm]

10V on pin 6 while cranking does not bode well for your new starter relay.  You risk welding the contacts shut again.  And if the headlight only dims when cranking, there's problems with the load shed circuitry.  It's pointing to grounds, I think, probably brushes and commutator in the starter.Have you overhauled the starter (you mentioned getting new brushes and that the parts looked like they needed cleaning)?

[K75RT Keith]

FWIW Try the "I'm not a mechanic or engineer" reverse engine diagnostic system.

1.) Look at the wiring diagram and work backwards from the spark plugs.
2.) Starting at the spark plugs, check each piece in order back to the source. 

[BeemerNewbie]

As RBM mentioned in the other post on the same problem, in Berts chart-- volts~ is referring volts AC not DC as is normally assumed.
When your 3mv reading went to 'OL', you just need to increase the scale.

If your water temp sensor resistance measurements are within the range of the others listed on Berts page I don't imagine that your sensor would have any effect on your no spark situation. The temp sensor should only affect the fuel mixture.

Scott. I did notice the AC vs DC in Berts help guide. I'll see if I can finagle the MM to change the scale properly. The Flukes are suppose to adjust automatically though, but maybe I had a setting wrong.

In regards to the engine temp sensor, I read somewhere that if the resistance in the relay is too low it fools either the EFI or EIC into thinking the engine is too hot and wont start. Now if its the actual sensor gone bad I'm not sure what happens there. Is this not true. http://www.ibmwr.org/ktech/fan-diagnosis.shtml If we're talking the ambient air temp sensor than I would agree that it only effects the FAM.

10V on pin 6 while cranking does not bode well for your new starter relay.  You risk welding the contacts shut again.  And if the headlight only dims when cranking, there's problems with the load shed circuitry.  It's pointing to grounds, I think, probably brushes and commutator in the starter.Have you overhauled the starter (you mentioned getting new brushes and that the parts looked like they needed cleaning)?

Yeah I learned the low voltage vs starter relay issue with these Bosch's the hard way. When mine stuck and I pulled it apart the contacts were welded and one of them had dislodged and was rattling around in the case.

In regards to the load shed relay the headlight does go out every cycle of the engine rotation, but then back on momentarily until the next cycle if that makes any sense. Should it go out completely and stay off for the entire duration the starter button is depressed? If that's the case it is not working correctly.  There are no auxiliary add-ons to this bike. Its all stock. I did unplug the power to the headlight to reduce voltage drain during starting to rule out the load shed relay for a moment, but it had no effect. Still no spark or noticeable increase in voltages or cranking power.

I have not overhauled the starter yet. Ordered new brushes yesterday. When I pulled it and disassembled there was some carbon buildup but nothing terrible. The brushes were about .25 inches...which I think is something like 6mm and worn pretty evenly. I cleaned up the ground connections on the starter lead as well and resistance was something like 0.5 ohms so normal I think.

The next step is to build one of these LED testers for the HES that Bert suggested. If anyone has any tips on how to do this or where to get the parts (radio shack?) I'll put one together to help rule out the HES. If the HES proves good than its a used ignition module next.

Thanks for the suggestions and tips. The bike is being restored for my dad...he's of the right generation that rides these, although in fixing this for him I've come to appreciate the community these bikes have and the smooth engine (when its actually running for me) I especially like the cafe racers. In any case he is eager to test ride this once its up and running and I have new tires put on so he appreciates the expert feedback as do I.

[rbm]

Scott. I did notice the AC vs DC in Berts help guide. I'll see if I can finagle the MM to change the scale properly. The Flukes are suppose to adjust automatically though, but maybe I had a setting wrong.

If it's a Fluke Series 77/87/177 or the like, there is a button in the middle of the range select switch which, when repeated pushed, will preset the range.  You'll see the decimal point shift with each push.  As it moves to the right, the range increases.

In regards to the load shed relay the headlight does go out every cycle of the engine rotation, but then back on momentarily until the next cycle if that makes any sense. Should it go out completely and stay off for the entire duration the starter button is depressed?

It should remain out for the duration of the press.  Yours cycling indicates grounding problems through the starter.  Get that baby cleaned up and it should change the bike's behaviour.

If anyone has any tips on how to do this or where to get the parts (radio shack?) I'll put one together to help rule out the HES. If the HES proves good than its a used ignition module next.

There are plenty of electronics supply houses in Southern California.  One I've visited before on a trip to Irvine is Marvac Electronics.  They have outlets in Costa Mesa, Santa Barbara, and Sacramento.  you'll be looking for a standard Red LED and 440 ohm, 1/2 watt resistor. There are Radio Shacks around your area but they'll charge an arm and leg for this stuff.

[Elipten]

I think Radio Shack is gone.  All the ones in my area are now closed.

[BeemerNewbie]

My local BMW Motorcycle shop actually had some parts for the starter in stock so I didn't have to wait 2-3 weeks for them to arrive. I replaced the starter brushes and the starter is stronger, but still no joy with spark.

I went to Radio Shack and picked up some LEDs and resistors. Tested the HES per Berts instructions. I removed the HES plate from the engine block and placed a feeler gauge in the two sensors one at a time while switching the leads on the HES connector. The LED shut off as expected indicating a good HES.

After testing the HES, just for shits I attempted a start with no choke and it fired right up. Let it run for about 10 minutes. I noticed when I applied a quick snap of throttle off idle the engine wanted to die. I removed the TPS with the same urge to stall. When I shut her down and attempted a restart it did not start as usual.  Tried several times with no luck. Let her cool down and still no start. Pulled a plug and as expected no spark again.

I went back to the HES and checked all the connections and played around with the orientation of the HES plate to see if that somehow effected the timing or something, but still no spark. When it started up the first time the HES had been replaced in the exact position when it was removed. This thing is a finicky bitch.

I swapped the load sensor relay with the horn relay to see if the load sensor relay was bad (I know this wouldn't prevent spark, but mentioning as a side note), but still observed the same response from the headlight, ie shutting off then turning back on every cycle of the engine and not staying completely off during the full duration the starter button is depressed.

I also noticed when I attempted a restart and applied a little bit of throttle with no choke there was some "knocking" in the engine that may be normal or may not. Didn't sound great to me. Any thoughts on this? Not sure how this would effect spark, but thought I'd mention.

I ordered a used ignition module off ebay for cheap and should get that in a few days. The current one is probably good, but I'm out of ideas. I don't want to blow $150.00 on an HES only to find out it doesn't fix the problem either.

Any thoughts fella?

[rbm]

I'm perplexed as to why the motorcycle is so temperamental.  I don't believe the HES is the problem.  It MAY be vacuum leakage; when you replaced the rubber intake bushes, did you use silicone seal between the block and bushing?? 

I'm taking a stab in the dark.  Snapping the throttle open should have caused a corresponding change in the AFM allowing the inlet of more air, but possibly there is something wrong with that unit.  The wiper inside the unit may be malfunctioning (not registering on the variable resistive plate) or maybe the vane is sticking. 

A low cost check would be to extract and examine this unit for proper operation. For example, check the vane for free movement.  Open the top to check that the wiper is making proper contact with the resistive plate and possibly add the recommended wire to get better connection between the wiper arm and the corresponding connector pin.  There are Youtube videos detailing how to open, inspect and modify these units since they are common to many German cars of the same era.

[K75RT Keith]

The R1100 uses the same HES.  There is a thread with one of their members that made/makes replacement kits. 
Contact Tom Wade @ tom@wade.name     He sold kits for the R's and might still have the sensors and upgraded wires for sale.  He did about a year ago  at a better price than I found elsewhere.

[BeemerNewbie]

Gentleman the beast lives again! :clap:

As I mentioned in my previous post, I tested the HES and it was good. Purchased a cheap EIC off ebay, plugged it in and bingo. Starts every time now.

We're not done quite yet though....

The new issue I discovered last night when it actually started after fiddling with the HES is the throttle response hesitation. Any thoughts on what the "bogging down" of the throttle response could be attributed to?

I did pull the TPS when it was running and no difference and the TPS has the expected clicking so probably not TPS. I had to rebuild the fuel delivery system from tank down and have never checked fuel pressure. Interested in other possibilities though too.

Thanks for all the tips and suggestions on the electrical gremlin. Turns out the computers can go bad and I had the bad luck of being the 1 in a million it happened to.

[K75RT Keith]

I had a similar problem with mine and it turned out to be partially clogged injectors. Reading the thread again, can't tell if you had the injectors cleaned or replaced them.  Could also be a sticky MAF.