'86 K100 Refuses to accelerate above 2500 RPM after warming up

[acyclicsalmon]

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.

[acyclicsalmon]

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.

[acyclicsalmon]

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....

[Scott_]

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.

[The Mighty Gryphon]

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? 

[frankenduck]

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

[frankenduck]

I highlighted the two temp sensor wires in green in this diagram:

https://i.imgur.com/avTHk6z.jpg

[acyclicsalmon]

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.

[acyclicsalmon]

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?

[frankenduck]

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.

[The Mighty Gryphon]

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. 

[rbm]

...  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.

[acyclicsalmon]

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.

[acyclicsalmon]

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....

[rbm]

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.

[frankenduck]

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.

[The Mighty Gryphon]

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.

[acyclicsalmon]

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.....

[The Mighty Gryphon]

Nice job!  These beasts are hard to kill.  Yours should run nicely for a long time now.

[Laitch]

When it stalls again, check resistance at the coils if you hadn't already. If ok, disassemble the ignition switch and clean its contacts.