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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: acyclicsalmon on October 05, 2021, 12:33:03 AM
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Greetings from the perpetually lovely California Bay Area, I come to the finest k-brick forum in the land to interrogate some of the brightest german bike wizards to assist in helping me determine what next steps I should undertake to get my bike running.
[About the bike]
- verified 1986 K100RS
- 28k miles
- Very well maintained, always garaged and all that jazz
- My favorite money pit ('88 Honda Nt650 is a close second, cursed electrical gremlins)
What I'm dealing with, in details
Here is a video illustrating the problem: https://youtu.be/aWsNbFavYVc
[let me paint a picture here] -- On Wednesday I finally took my k100 for its first proper ride in about 1.5 months (She's been recovering from a mild fender bender that destroyed my exhaust, which has since been replaced). I went out for a short ride, perhaps 15 minutes, to grab a pint with the miss. She linked up with friends, I went for a longer ride on the highway to ring out the bike. I filled up with a full tank of premium, and got about 5 miles on the highway before my power cut, bucking me forward, before quickly recovering to about 50% power, which was just enough to allow me to get off the highway. I rode her gently at about 30 mph, before the same bucking sensation further limited my speed to about 15-20 mph. From that point on, I was able to slowly make my way home at about 15-20 mph, with my tach struggling to go past 2-2.5k. I could get to 2.5k only with the gentlest of increase, anything sharper and she'd knock back to 1.5k before eventually getting back to 2k rpm.
[here's what I've checked so far]
My immediate thoughts were 1) overheating, and 2) the throttle position switch, which I had learned kills fuel during deceleration until 2k. Below is what I've done since the incident:
- Removed the TPS switch cord. Let the bike cool, and went on a ride the next day. The bike rode for maybe 10 minutes without issue before the same thing happened again.
- Checked to ensure the coolant levels are good and that the thermometer functions. Coolant is fresh (<2k miles), and thermometer was pulled and functioning perfectly (popped open instantly at 80*C, as expected)
- Pulled the spark plugs (while bike was hot). They were black and sooty and the spark plug holes weeped oil. Even though this sounds suspect, I checked the spark plugs literally 2 days prior and they were perfect, meaning perfectly grey and clean. My strong hypothesis is the 10 mile drive home after the incident caused them to foul and this is not the primary cause of what we're seeing
- Checked the fuel tank -- gas was clear and clean
[here's other things I've taken care of earlier this summer, just to provide further color ]
- Replaced the fuel filter with an OEM unit, fuel pump rubber housing, fuel pump filter + bracket, internal tank fuel line (500 miles ago)
- Replaced the fuel line to the throttle rail (about 2k miles ago)
- Replaced the air filter and inspected the MAF sensor -- all clean and all good AFAIK (3k miles ago)
- Fresh synthetic oil + oil filter (3k miles ago, though at time of incident my oil was a hair low (slightly before the top part of the circle on the eyeglass)
- Replaced some random rubbers (like the z-tube crank breather hose) and got a fresh odysee battery (3k miles ago)
- Treated the fuel tank plug with some Deoxit
With all the above checks, my intuition is that the Hall Sensor has gone kaput, but I'm cautious pulling it being aware that she may not live to exit my garage spot. I'm also electrically challenged, so the LED test described so well on this site leaves me somewhat terrified. Does all the above indicate to you that this is likely a Hall Sensor problem? I have a local guy selling one for $120, which seems as good as it gets
I should also leave as an addendum, I did accidentally ride my K100 for about 300 miles last year with 0 coolant. The coolant drain plug dropped somewhere between my coolant change in Seattle and Bend, Oregon, when my bike shut down due to overheating (oops). My thinking is that the heat could have accelerated the hall effect sensor's doom, but I don't want to make any assumptions since the last 4k miles have been without incident.
Bike Photos
I've included some bike photos, since its always easier to help a patient when you can see who you're working with. I will say, I checked out 4 different K100's before landing on this one, she was hands down the cleanest and had the longest and most full maintenance record. I will keep this bike alive, even if she ends up in the hands of our Bay Area's 150$/hr specialty BMW mechanics...
[see next post for photos]
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(http://www.motobrick.com/gallery/3/7500-300921003457.jpeg)
(http://www.motobrick.com/gallery/3/7500-300921004311.jpeg)
(http://www.motobrick.com/gallery/3/7500-300921003557.jpeg)
(http://www.motobrick.com/gallery/3/7500-300921003526.jpeg)
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I'm guessing that all 4 plugs where black and sooty?
I'd suggest you check your water temperature sensor and associated wiring as it does affect the fuel/air mixture.
Verify your air flow meter is not jammed/sticking.
Re the oil level, the ideal level is dead center of the glass. The ring around the glass defines the maximum and minimum levels.
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Typical HES failure symptom is that the bike just dies suddenly and completely when it heats up and then restarts fine when cooled down.
Crappy running when the bike heats up can be caused by coils going bad.
See page 21 here:
https://bmwmotorcycletech.info/K100%20troubleshooting%20Starting.pdf
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A long shot but a quick check. If the problem disappears after lifting the fuel cap, the tank vent might be partially blocked, probably worse after filling. The fuel filter might be partially blocked from swelling if it's drawn some condensation from the fuel.
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I am thinking the engine temperature sender or the coils. Both are known weak points, especially the early model coils.
The sender(or it's wiring) can cause the mixture to get way too rich to run properly. It will cause all 4 plugs to be fouled. On the other hand, a weak coil will cause misfiring, especially at wider throttle openings, and will only affect the 2 cylinders it fires. Testing with an ohmmeter doesn't always spot the problem. Some coil problems only surface when they get hot. Do your coils have black or orange insulators where the plug wires connect? Early models had black and the later ones were orange.
Also, Scott is correct about the oil level. Ideally, it should be on the dot in the middle of the circle. A high level may make the plugs dirty, especially if you park on the side stand for long periods.
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My strong hypothesis is the 10 mile drive home after the incident caused them to foul and this is not the primary cause of what we're seeing
The "incident" caused, and continued, the fouling.
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Do your coils have black or orange insulators where the plug wires connect? Early models had black and the later ones were orange.
Also, Scott is correct about the oil level. Ideally, it should be on the dot in the middle of the circle. A high level may make the plugs dirty, especially if you park on the side stand for long periods.
The top and bottom of the sight glass ring are the same as MAX and MIN on a car oil dipstick. Any level inside the red circle is fine. Be sure to check the sight glass with bike on level ground on the center stand with engine cold or been sitting for a couple of minutes.
I always top off to about here:
(https://i.imgur.com/HBl8Xuv.jpg)
Early and late coils also have slightly different terminal locations.
(https://i.imgur.com/hG1x2og.jpg)
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Wow ! thank you to everyone who contributed to helping me diagnose this problem. Really a one of a kind community here. I've lurked for over a year but this is my first time actively posting, glad to do so. Some responses below:
- The youtube link was included, I hope others were able to see it. If not, here is the link again, but I left a space in the middle in case its the auto video load thats breaking it: https://www.youtube .com/watch?v=aWsNbFavYVc
- I'll bust out my ohm meter to check the coils, I've never peeled the cover back so its my first time seeing them. I'll report which type of coil I have as well.
- good to know about oil, i swear i had someone tell me you should always be at top of red circle. Currently I'm at exactly the yellow line, maybe a hair above.
- I absolutely could see the temperature sender being a problem, I do seem to remember the fan coming on in a strange fashion recently, where it never full ran, just seemed to speed up and slow down in an oscillating fashion. I chalked it up to simply lower bay area temperatures.....
- I will try the fuel tank vent suggestion next time this happens
Thank you again, this community is absolutely wonderful and a trove of information that I hope is preserved for years to come.
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Fun updates! Was able to peel back the coil covers for the first time, dang they look cool. I couldn't find my multimeter so I didn't test them, but they did look pretty darn clean and in good shape. The connectors and plugs were all clean and I hit them with a touch of deoxit just in case.
(http://www.motobrick.com/gallery/3/7500-051021224258-3869318.jpeg)
While seeking out the temperature sensor unit (which I now see is a pain to pull), I noticed an uncovered nipple, as well as a hose with a check valve on it coming from what looked like the tank. I assume that hose should probably connect to this nipple, but wanted to double check.
Can someone enlighten me to what the hose and nipple are for? I assume thats the tank vent line, but why would it connect to the engine? I tried digging through my Clymer's manual but it was hard to find what I couldn't identify.
(http://www.motobrick.com/gallery/3/7500-051021224301-38772.jpeg)
On a final note, I think I'm going to go ahead and buy a new temperature sensor unit anyway -- I forgot to mention a pretty big point earlier, namely that my bike has the worst fuel economy I've heard of on a brick, something to the tune of 20-24mpg..... Given that I dont see any hose leaks, this seems like a likely very likely culprit, and the new sensor is only about 25 bucks. Though this ultimately seems unlikely to be the root cause of my current issue. Thoughts appreciated, and thank you once again.
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The nipple at the front middle of the engine is supposed to hook up to the tank vent pipe up under the right rear corner of the tank. It's there to meet CA emissions standards because ten molecules of gas escaping into the air will destroy the planet. Find a plastic or rubber cap to put over it and forget about it.
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The idea was fumes would vent into the crankcase, be drawn through the z-hose along with blow-by gases from combustion, and be recycled into the fuel/air mixture to be burned off in combustion. There were problems with this. The attached document explains the situation.
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At 24mpg the problem is an incredibly over rich mixture. I just had a friend who cooked the temperature sender on his boat's diesel when the engine overheated. I suspect you have done the same to yours.
You can check the temperature sensor by measuring the resistance between pins #10 and #13 on the big ECU plug. Should be about 2.5K ohms at 70F and about 250-300 ohms when the engine is warmed up. Not only can the sensor be bad, but there can be corrosion on the connector that makes the ECU think the engine is cold.
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Thanks Gyphon, that certainty inspires confidence that this is the issue.
I went ahead and pulled the injectors as well, courtesy of this telling thread on BMWMOA: https://forums.bmwmoa.org/showthread.php?48214-Power-loss-91-K75/page3 [Similar symptoms, guy changed near everything but the injectors are what finally did it]
I'll be sending those over to Mr. Injector. His 2 week lead time works quite well in my situation, as I'll be crossing the pond to both London and Frankfurt for the next 2 weeks anyway.
I also ordered a new temperature sender unit. Will post a response to this thread in probably 3 weeks at this rate.
Thank you all very much for the help, its greatly appreciated.
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I'll be sending those over to Mr. Injector. His 2 week lead time . . .
Two weeks!? Dang. When I started with him many moons ago the turnaround was one or two days. He must be busy. I guess that's what happens when you do a great job for a reasonable price. Go figger.
Here's some info on reinstalling the FIs:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/fis/fis.htm
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I had a similar issue with my 1984 K100 when I lived in London and it would randomly cut onto 2 coils and lose power. Turned out to be corroded connectors and a bad coil in the end. Good luck sorting yours out and keep us posted on the outcome.
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Just got my injectors serviced. Only 5-10% flow loss across injectors so the problem is definitely not in the injectors. Will install next week in addition to the temp gauge and report back on the fix.
Will likely look at coils next.
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Wanted to give this crew an update:
- I received my injectors back from Mr. Injector. He did a fantastic job and the experience was quick and painless. Like I mentioned, there was little flow loss so the benefit was mostly in cleaning them up and installing new o-rings. I oiled them up and in they went
- I replaced the spark plugs with D8EA's (the D7's were not in stock) and properly gapped them as per the Haynes
- I installed the new coolant temp sensor, did a coolant flush, and cleaned up the coolant inlets
At this point I'm feeling eager and keen so I crank her. One burp then nada. Hold the throttle open all the way and keep cranking. Nothing still. One or two more oily burps later, she's dead from 1-2 minutes of total cranking (I know this is not good but I was anxious to see life)
During one of the cranks I didn't hear my fuel pump come on, so cue panic that I fried a relay or fused something shut from the amperage.
- Deoxit everything I haven't hit before (under tank ecu), major frame ground points, fuel tank plug, relays, etc. etc
- Swap horn + fuel pump relay (Does everyone else have 2 orange relays and a black one in their control box?) The black one had different pins than the others but thats what I swapped
- Checked plugs, looking good and wet from gasoline
- Pulled injectors, they're squirting perfectly
- Tested plugs, they're firing nice and blue and perfectly uniform (also shocked myself)
- charged battery overnight
Still couldn't get her to fire, so I resorted to starter fluid in the airbox. That was the ticket. She smoked and billowed and barely held an idle, but after 2 minutes of coughing and sputtering she idled first only on choke, then after 5 minutes just on idle. Still not 100% satisfied, but this could have been simply what was needed to get the cobwebs out.
Ill test to ensure the temp sensor is doing proper readings on the ECU (as well as the other tests in the diagnosis guide) and take her for a ride probably on wednesday.
Thanks for everyone's help on this, hope to share more good news soon.
As for the intermittent issue of not revving past 2000
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Bad fuel pressure regulator? (FPR)
Is there fuel in the vacuum hose from the throttle bodies to to FPR?
Do you have a fuel pressure gauge for testing?
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Swap horn + fuel pump relay (Does everyone else have 2 orange relays and a black one in their control box?) The black one had different pins than the others but thats what I swapped
- Some bikes have 2 orange relays, some have two light blue relays (same relay though, just different color)
- The right colored relay is the horn relay, the middle colored relay is the load shed relay
- The fuel system relay is the one on the left. It is different because it has five pins. Two of them are 87 pins that output to
1 - Fuel injectors and L-Jetronic fuel computer
2 - Fuse 6 to temp sensor relay and fuel pump
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Maybe I've misunderstood but from your first post it seems that you replaced the muffler which was damaged after a drop. Maybe the replaced muffler is blocked, or became blocked. That could limit the revs. It might have a bit of a hissing sound. If it revs good with the muffler removed, that would be it. A blocked air filter, or inlet, could do the same.
Be sure the relays are back in their right places.
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Non OEM fuel hoses can kink over, especially the supply line where it goes into the tank. Also check the return line
and the in tank lines.
Regards Martin.
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Cheers crew, always appreciate the help. All tubes look great and are unkinked, and I went on a test ride earlier today. Besides starting rough, rode wonderfully. However, the bike is absolutely running rich right now. Sparks right up with the fuel pump fuse removed but quickly floods.
I will check the fuel pressure, I dont have a pressure tester, but I will try and source. Sparks right up with the fuel pump fuse removed, then quickly floods and has a hard time starting again afterwards.
Any other ideas why the bike might be running rich at start-up (and probably beyond?) I feel like there was a rattle from the fuel pump around 3k RPM, so will probably check internals though most of those are new.
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Two quick checks.
With the fuel cap assembly removed, you should see fuel returning to the tank. If fuel isn't returning, the pressure regulator is prevented from working, and the fuel pressure will be about double what it should be.
With a screwdriver to the injectors you should hear a ticking noise, meaning they are turning on and off as they should. If not ticking, they might be permanently on, also causing overfueling.
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I will check the fuel pressure, I dont have a pressure tester, but I will try and source. Sparks right up with the fuel pump fuse removed, then quickly floods and has a hard time starting again afterwards.
Any other ideas why the bike might be running rich at start-up (and probably beyond?)
First, eliminate the idea about the defective fuel pressure regulator. Many of the major auto parts suppliers will loan such tools to people who provide a deposit with a credit card then will refund the entire deposit on return. The tool is loaned without charge. It's use is explained in the troubleshooting guide on site.
Secondly, I read a couple of references from you to a "temp sender" or "temperature sender unit" and that you would check for "proper readings" on the "ECU." Are you referring to the fuel injection control unit and the coolant temperature sensor, and if you are, what were the readings?
Another critical fuel mixture component is the air flow meter and the air temperature sensor mounted in the roof of its intake. Did you check to be sure that the meter's air vane is rotating and rebounding smoothly? Have you inspected the air temperature sensor for fouling. Have you cleaned the meter's electrical connector and verified that it is tight?
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WTF. Guess it's my own damn fault. I bought the wrong temp sensor. I bought the temp sensor for the 16v bike instead of the 8v. I'm getting 7.5k-ohms at 23*C. Some posts suggest they're interchangeable, but I think the proof is in the pudding here.
This seems a likely culprit as I'm getting majorly rich running conditions at start, and even once I get a steady idle, if I hit the ignition button she dies immediately.
I didn't check the fuel pressure yet, but thats on the to-do list as soon as I can get to a tool shop for a rental. When I look in the tank I can see fuel returning to the tank so it looks good from a visual inspection.
I had the air vane inspected by a shop about 3000 miles ago, they said it was in excellent condition so I'm not looking into that just yet.
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Good evening Brickers,-
The Problem:
I recently acquired a new coolant temperature sensor for my bike. I measure the resistance at the sensor itself, I get 2500ohms at 20*C. Right on cue!
I plug in the sensor to its harness, then measure the resistance at the EFI connector (pin 10 + ground) -- I get 7000ohms at the same temperature. Uh oh! Certainly explains why I'm flooding my engine non-stop.
the Obvious solution:
Both ends of the connector have been liberally treated with deoxit, blown out, dried, clean as a whistle and inspected. This bike is in pretty damn good condition -- almost no rust or corrosion anywhere (Thank you california!). Still 7000ohms resistance.
Frame ground points (connecting to harness) have received the same treatment -- liberal cleaning + deoxit.
New solutions?
With the obvious completed (and completed well, I think), what should I be thinking next? Is there a way to easily test the added resistance in the harness cable? Are there easy ways to replace the coolant temp harness, or figure out where its coming from?
Am I just being dumb?
Thank you again for your help through my trials, I hope to get this bike on the road soon.
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As I typed this out, I thought about it pretty logically: If I wanted to measure if theres resistance in the EFI harness, I should measure the resistance of the harness itself. DUH!
I measured the resistance of different parts of the wire:
- Frame ground <---> EFI harness ground pin: Almost 0 resistance (my multimeter shows some resistance, but its pretty old and analog. I get the same resistance when I touch both tips of the multimeter together, so assuming its zero resistance)
- Coolant sensor ground <-----> frame ground: ~6000 ohms. The culprit!
- Coolant sensor ground <------> EFI harness ground pin: ~6000 ohms
Looks like I have a proper starting point here! I'm considering at this point a few options:
Before I proceed, can somebody confirm my intuition here that I most certainly shouldn't be seeing resistance in the above places?
- Buying a new coolant sensor female connector (any suggestions on brand / make?)
- Wiring the above ground director to frame, bypassing any extra resistance that other parts of the harness might be contributing (only assuming the above doesn't fix the problem)
- Buying a brand new harness (looks to be about $70 for a good condition model)
Any advice? More deoxit isn't cutting it....
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What is the resistance between the following:
coolant sensor ground and the coolant riser(where the sensor screws in)
coolant riser and the engine block
engine block to the frame.
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I'm thinking you might need to go back and make sure you're reading the right pin. Have you tried reading the resistance between the contact on the Temperature sensor connector and the big ECU connector?
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What do you mean by coolant sensor ground? There is no ground wire to the coolant sensor. The temp sensor has two wires, neither one of them is ground. One wire "sends" resistance to the E terminal of temp relay. The other "sends" resistance to Pin 10 of the L-Jetronic. Both wires are colored Violet/Green. You can see the two resistance units in the temp sensor at the top of TMG's first image. The ground line in that diagram could be misinterpreted as a wire but it is not. The only ground for the temp sensor is the threads where it screws into the side of the coolant exit pipe.
To test the wiring there should be zero or negligible resistance between:
a - one of the temp sensor connector terminals and the E terminal of the temp relay
b - one of the temp sensor connector terminals and Pin 10 of the L-Jetronic
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I highlighted the two temp sensor wires in green in this diagram:
https://i.imgur.com/avTHk6z.jpg
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Wow, thank you Frankenduck!!! I suppose it was naive of me to assume that one of the coolant sensor pins was a ground, of course the frame to sensor connection itself would function as a ground.....
You're an absolute legend, and thank you for hopping in to help right my path.
Regarding the measurements specified:
- temp sensor connector terminal and pin 10 -- negligible / zero resistance
- temp sensor connector terminal and E terminal of temp relay -- Will check tonight when im back from work
Thank you Scott and Gryphon as well, some comments below to you both:
- Gryphon, my original measurements were between the temp sensor connector and big ECU connector under the seat
- Scott_ I'll take a look at those measurements later tonight as well.
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Okay! Have some measurements to report:
- Temp sensor connector to E terminal of temp relay -- negligible / zero resistance
- coolant sensor ground and the coolant riser(where the sensor screws in) -- negligible / zero resistance
- coolant riser and the engine block -- negligible / zero resistance
- engine block to the frame -- negligible / zero resistance
Here's the interesting one, unclear from my searching if its a problem or not:
- Pin E to Pin 31 (ground) on the temperature relay: About 6000ohms
It certainly appears that the extra resistance between pins 10 and 13 on the icu is coming from the temperature relay. I even bridged pins E and Pin 31, with the temperature sensor in place, to demonstrate to myself that the extra resistance was from the temp sender relay unit.
Feels good I suppose, but upon disassembly and tracing the solder joints (as well as a magnifying glass inspection of solder lines and jiggle test on pins), I don't see any issues.
Can anybody confirm if I should be seeing resistance from Pin E to Pin 31 (ground) on the temperature relay?
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pins 10 and 13 on the icu
Nitpicking: The L-Jetronic is an ECU, not ICU. The ICU is up at front of the frame.
I tested five temp relays and all have about 4500 ohms between E and 31. Not sure if this matters though. Maybe rbm knows. He knows electron chasing better than I do.
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Okay, you have a good ground from the temperature sender to the frame, and hopefully to the battery.
You also have good continuity from the temperature sender's connector to pin 10 on the ECU connector.
And finally, you have a new temperature sender.
So, what is the resistance from pin 10 on the ECU connector to ground?
Since you have confirmed all the connections and wires are good, you should be seeing 2500 ohms. If so, the problem is somewhere else.
Have you checked the resistance between pin 13(ground) on the ECU connector and ground on the battery?
The temperature relay is a red herring. It has nothing to do with the driveability of the bike. All it does is turn on the fan and the high temperature idiot light.
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... I tested five temp relays and all have about 4500 ohms between E and 31. Not sure if this matters though. Maybe rbm knows. He knows electron chasing better than I do.
There might well be resistance between Pin E and Pin 31 on the temperature relay. Pin E is an input to an electronic circuit. The electrons emitted by your tester trying to flow between the two probes will encounter resistance in the circuitry combined with the resistance of the temp sensor element (because it is in parallel). How much resistance I can't say because it depends on the path those electrons will take as they move through the electronic components. That's probably why you and acyclicsalmon see different values.
That particular measurement (Pin E to Pin 31 is invalid and doesn't tell you anything unless you disconnect the temp relay to eliminate the input circuitry and measure from the disconnected plug.
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I literally took the morning off because this frustrates me so much.... thank you to everyone who has helped up so far, but I'm going to have to put a pause on this work as I head out of town for thanksgiving holidays tonight. I also ordered a new multimeter because I'm frustrated that worst case scenario my shit analog multimeter might be contributing to my confusion.
Did some measurements this morning:
- pin 10 on ECU connector to ground: I have continuity across all ground points I could identify, so when the temp sensor is plugged in the resistance is 2.5k + some mysterious amount of extra resistance that I cannot pinpoint)
- pin 13 on ECU to battery ground: zero resistance (makes sense, they're both ground)
- Temp sensor pin to pin 10 on ECU: zero resistance (makes sense, one of the wires goes from temp sensor to pin 10)
- Temp sensor grounding point (on coolant riser) to pin 13 on ECU: zero resistance (makes sense, its ground to ground)
- Temp relay ground pin to battery ground: zero resistance (makes sense, both grounds)
Given that I have continuity from the temp sensor pin to pin 10, and continuity from the temp sensor grounding area to pin 13 on the ECU, i absolutely have no clue why I would have all this extra resistance when I measure the temp sensor resistance from ECU pin 13 to ECU pin 10. It literally seems to be defying electrical common sense.
Thank you again for the advice, this bike has been nothing but frustration for me.
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Realizing I have an even more obvious answer on my hands -- so if you followed the last thread I started, I had what I thought was a failed temp sensor. I accidentally ordered a 4v motronic replacement, got pissed and chucked it in the bin, then ordered a replacement 2v temp sensor off eBay (confirmed this time!!)
As I test the replacement 2v temp sensor, I'm not seeing any continuity or resistance between either temp sensor pin and the metal chassis of the temp sensor. This screams to me You were sent another 4v sensor, fool!.
Fool me once.....fool me twice.....
I pulled the 4v sensor out of the bin, lo and behold, no continuity between the pin and metal chassis of temp sensor either. I pull my old sensor out of the garbage and boo-yah, it has continuity between pin and housing.
Here's where it gets dicey.
I had a weird problem in my old thread where after a good warm up (like 15 minutes), my bike would cough and hiccup, then refuse to ride over 2500 RPM and 20 mph. I pulled the temp sensor, and the resistance between both SPADES was damn high, like 5-7k ohms. Problem solved, right?
Well now that I'm looking at the OEM temp sensor again, the resistance between sensor spade and housing is actually within spec....2.5k-ohms. So maybe this whole snafu around the temp sensor was completely misplaced and I didn't need to deal with ANY of this.
Back to the drawing board....
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Maybe not. Make doubly sure that the stand pipe threads into which you screw the temp sensor are clean and showing bare metal so that there is good electrical contact between the body of the temp sensor and the stand pipe.
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Maybe not. Make doubly sure that the stand pipe threads into which you screw the temp sensor are clean and showing bare metal so that there is good electrical contact between the body of the temp sensor and the stand pipe.
There's a lot of bare metal to bare metal contact in those threads so I doubt that's the issue. Easy to test though by putting a multimeter probe on the nut part of the sensor to make sure that it's well grounded.
(https://shop.maxbmw.com/fiche/NotesParts/61311459197_1_B.jpg)
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From your reply #37:
"pin 10 on ECU connector to ground: I have continuity across all ground points I could identify, so when the temp sensor is plugged in the resistance is 2.5k + some mysterious amount of extra resistance that I cannot pinpoint)"
How much of this mysterious resistance is being added?
You claim to have zero ohms between the Temperature sender connector and ECU pin 10 as well as a good ground to the case of the sender.
If you are reading additional resistance when you put it all together the problem is probably that your temperature sender connector is not making good contact with the pins on the temperature sender. It's the only place where additional resistance could come from.
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Just completed a few tasks on the bike tonight, seems to have brought it back to life. Had a nice 30 minute ride around the city tonight with no issue, and in fact, never heard the bike purr so well. Still unclear if I’ve solved the original issue fully. Here’s what I did tonight:
- Installed the new (correct) coolant sensor. For those following, i thought my initial issue was a broken coolant temp sensor. Turned out 1) I was measuring it incorrectly [It actually worked fine], 2) I ordered the wrong replacement temp sensor at first
- Did a timing advance on the hall sensor. Super easy and solid results, I do recommend it as an easy mod for better low-end torque + smoothness.
- Filled it with fresh distilled water + coolant
Beyond the things I did tonight, my other maintenance work included:
- De-oxiting every major connection
- cleaning all the frame grounds
- having the injectors serviced by mr injector
- checking the coils
- installing new spark plugs, properly gapped and all
- checking the temp relays
- battery new and fully charged
- testing the thermostat in the radiator
- sealing off the CA compliance engine vent
- inspecting the air filter + air vane
- somewhat new fuel filter + fuel pump basket
I’ll update this thread if anything new happens or it breaks again, but for now I’m done worrying. She lives again (fingers crossed)-
Actually on second thought I may as well check and see whats causing this rattle at 3.5k revs.....
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Nice job! These beasts are hard to kill. Yours should run nicely for a long time now.
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When it stalls again, check resistance at the coils if you hadn't already. If ok, disassemble the ignition switch and clean its contacts.