1987 K100RT. I’m trying to assess if the temperature sensor is working properly. In reading various threads, I believe I should expect about 2.4k ohm resistance between pins 10 and 13 at the FI module. Please verify if I should be testing the CONNECTOR or the MODULE. I would think it has to be the connector inasmuch as without the connector attached, the FI module is just a magic box buried beneath a bunch of wires without any connection to anything. Checking resistance between connector pins 10 and 13 I get a reading of 1.016k ohms at 61°F/16.7°C which seems far enough out of spec to warrant replacing the sensor. Thoughts?

Also, my reading led me to think pin 13 is a ground, but I get 1.01k ohms between pin 13 and frame ground (as measured from the connector, not the FI module). I am pretty diligent about keeping all grounds in good order, so I am wondering if the ground between the temperature sensor and the coolant pipe might be compromised. More thoughts?

Dave

Test is at the plug. Use any bare metal ground point for the test. The transmission battery ground bolt is handy if it's clean.

I would go back and make absolutely, beyond the shadow of a doubt, sure that I am checking the correct terminals on the cable connector.  You would not be the first to inadvertently put your meter on the wrong terminals. 

Yes, terminal #13 is ground.  You should see zero ohms to ground from that terminal.  If not, that could be the source of your problem and is the first thing you should troubleshoot. 

The fact that you are seeing pretty much the same resistance across the temperature sensor terminals(#10 & #13) is also concerning.  It says that the temperature sensor may be shorted out.  In any event, figure out what is going on between pin #13 and ground before chasing the temperature sensor.

The coolant temp sensor is grounded via the threads where it mounts.

The reason it has two wires is because it is a dual temp sensor. One wire goes to the L-Jetronic and the other wire goes to Pin E of the white temp/fan relay.

duck wrote:The coolant temp sensor is grounded via the threads where it mounts.

The reason it has two wires is because it is a dual temp sensor. One wire goes to the L-Jetronic and the other wire goes to Pin E of the white temp/fan relay.

Very important NOT to use ptfe tape on the threads. It grounds through the threads.

The reason it has two wires is because it is a dual temp sensor.

Does that apply to a 1989 K100RS?

Mine has only one temp indicator lamp.

If your bike is a 2 valve model it will have the dual sensor.  The later 4 valve K100RS has the single sensor, the fan is controlled by the Motronic unit where the 2 valve models have a temperature module that gets a signal from the second sensor.

Jordan53 wrote:

The reason it has two wires is because it is a dual temp sensor.

Does that apply to a 1989 K100RS?

Mine has only one temp indicator lamp.

The first post references pin 10 and 13 which means it's a 2V K bike.

One lead goes to the L-Jetronic control unit that controls the fueling based on coolant temp. (More fuel when cold.)

The other lead goes to the temp/fan relay which controls the radiator fan as well as the cluster's temp warning light.

More than you ever want to know about the temp system in K bikes:
https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/tempsensor/tempsensor.htm

Jordan53 wrote:

The reason it has two wires is because it is a dual temp sensor.

Does that apply to a 1989 K100RS?

Mine has only one temp indicator lamp.

All classic Bricks have only one temperature indicator lamp in the instrument cluster. A dual temperature sensor has dual purposes as duck explained. It helps to govern the fuel mixture and helps to govern engine temperature. When it fails to govern the fuel mixture, the engine variously runs, idles and starts poorly. When it fails to govern the engine temperature because it doesn't send a signal to the temperature sensing relay to start the fan, the instrument cluster temperature bulb is illuminated to warn the rider.

According to the serial number supplied at the bottom of your post and the photo you've posted of it, Jordan, your Brick is a 2-valve engine system just like the original poster's Brick and its sensor operates in the same way. Some models have an additional separate coolant temperature sensor mounted into their water pump cases that governs the operation of temperature dial gauge indicators mounted within their fairings. In models without coolant temperature dial gauges, a coolant drain plug is substituted for the gauge's temperature sensor in the water pump.

What may also help is replacing the aluminium crush washer under the sensor. I've had two sensors that appeared to be duff but in both cases the crush washer was badly corroded and upset the earthing.

Thanks Folks.
I see now the dual temp sensor is quite an unusual type.
It has one output that is binary - just on or off switching for the fan control and temperature alert lamp.
The other one is for the fuel injection and has a variable resistance output.

I once came across another type of dual temp sensor in a bus.
It had two switches with different set points. Neither were variable.
They controlled two banks of engine cooling fans, the second coming on at a higher temperature.

Point-Seven-five wrote:I would go back and make absolutely, beyond the shadow of a doubt, sure that I am checking the correct terminals on the cable connector.  You would not be the first to inadvertently put your meter on the wrong terminals. 

Yes, terminal #13 is ground.  You should see zero ohms to ground from that terminal.  If not, that could be the source of your problem and is the first thing you should troubleshoot. 

The fact that you are seeing pretty much the same resistance across the temperature sensor terminals(#10 & #13) is also concerning.  It says that the temperature sensor may be shorted out.  In any event, figure out what is going on between pin #13 and ground before chasing the temperature sensor.

You were spot on, I was reading the wrong everything…connector, pins, module. Surely someone will take my tools away from me and save me from myself! The temperature sensor appears to test fine (2.7k ohms at 67°F/19.3°C) and pin #13 to frame ground is zero. Also, the DVM probes I typically use were too blunt to make contact giving me an OL reading until I used smaller probes.

How is the bike running?  Are you trying to troubleshoot a problem?

Don't feel bad about what happened.  You wouldn't believe how many evenings I have spent staring at my bike and wondering what the heck is wrong, only to find the next day I was reading the wrong pin or relay or something equally dumb.  I'm sure I'm not the only one.

Gas mileage is around 36-38 mpg (and I drive like the old man I am). I thought temp sensor might be a problem (it doesn’t seem to be). Measured fuel pressure at 32 - a bit low. I bypassed the fuel filter to see if I may be dealing with a plugged filter but pressure was the same with and without the fuel filter. I ordered a fuel pump after visually inspecting the fuel regulator for leaks (vacuum or fuel). The air temperature sensor in the AFM was spot on at 2.5 ohms. There may be other issues with AFM but I don’t have any convenient way of measuring CO. No other issues with the bike but I will be taking it across the states again in June and prefer to not have problems.

36-38 miles per US gallon sounds about right. I get about 48 miles per UK gallon which means we are both getting about 0.3 miles per fluid ounce. That said, since we changed to E10 fuel here as standard (10% ethanol or other filler), I have noticed that I get about 10% less range on a tankful - about 200 mile range.

Paul: ya gunna have to feed it on superunleaded for a superbike Joking aside though; I wonder what the tradeoff would be between paying the extra for E5 and the mileage? I don't intend to find out: mine does get fed on E5 and damn the additional cost because of the possibility of having to spend lots further down the line to replaced E10-rotted rubber parts.

Dave: I doubt it's the pump giving you a slightly low feed. It's more likely to be the pressure regulator round behind the throttlebodies. It's something that has come up in passing in various threads on this forum - I recently had a similar low pressure problem and went to all the fuss of adding a variable pressure regulator and a gauge to LFB. The OEM regulator had been showing a smidgen below 30psi; the new kit is now running at exactly 36psi (2.5 bar) with no change of pump. Be warned; it's not a cheap solution but it's great if you're a mechanical fiddler! (I think Martin and Chris (SuziQ) did something similar too).

This topic: https://www.k100-forum.com/t18612-position-of-the-fpr

I have had lots of time to compare E5 and E10 in 5 of my K bikes since the E10 was in France years ago and I got stuck with using it over there many times. Without fail I can say the change from E5 to E10 resulted in a loss of 10% whether its my K1100LT [2 of them 96/97], K100RT 1984, K100RS 1983 or K100 Sprint 1984.

Dai wrote:Paul: ya gunna have to feed it on superunleaded for a superbike Joking aside though; I wonder what the tradeoff would be between paying the extra for E5 and the mileage? I don't intend to find out: mine does get fed on E5 and damn the additional cost because of the possibility of having to spend lots further down the line to replaced E10-rotted rubber parts.

 I’ve thought about that Dai…need to do the maths on the running cost of E5 or better versus E10.  Effect on performance and fuel system components all depends what the refiners dilute the gasoline with. If they use Fatty Acid Methyl Esters (FAME) then, unlike the cheerful stage group’s hopes, the system components certainly will not live for ever. Generally, a major change in composition will have an immediate but fairly short term effect - stuff in the system is dislodged and flushed through, which may cause blockages. Once settled on the new product, things tend to normalise. Some older rubber components are never happy though and their life (which is probably pretty aged on many of our K bikes) is likely to be shortened. 

Shortly after switching to E10 (Government enforced) I had a fuel pump failure. Very recently, I pulled the failed pump apart - it was badly corroded internally (rusted up) and the rotor was very stiff to turn. I suspect that was more to do with water in the fuel than refinery additives and diluents…possibly exacerbated by my habit of not leaving petrol standing in the tank for long periods of time to avoid the rubber goo syndrome.  Covid 19 has a lot to answer for.

The only effective solution is to ride, ride and ride some more.

I run hi test in my 85 k100rs{2v) get between 40-42 MPG. I also have been known to run her pretty hard at times so I guess I am doing ok.

I have had 5 bikes over a 10 year period with an accumulated 120,000+ miles mostly run on E10.  My 75's averaged a pretty consistant 45 around town and 38 to 42 when hauling ass on the slab with a full touring load.  The 4 valve 100's average 45 to 48 around town.

I ride like an old man most of the time.  I shift at 3500 to 4000rpm.  5th gear at anything over 55mph.  Easy on the throttle.  Except for when I am out west touring most of my riding is at altitudes between 200 and 2000 feet above sea level

At the end of the season I switch over to non-ethanol fuel.  I have seen a slight gain of mpg on non-ethanol of about 1-2mpg, but not enough to justify running it all the time.

One oddity I noticed in 2022 was that for a 8-9 month period all my vehicles, bikes and cars got a consistent unexplained 5-10% increase in mpg that I haven't seen again since then.

Point-Seven-five wrote:
One oddity I noticed in 2022 was that for a 8-9 month period all my vehicles, bikes and cars got a consistent unexplained 5-10% increase in mpg that I haven't seen again since then.

We’re at the mercy of the refineries - never know exactly what blend they make for us or what happens to it on the way to/at the service station. A glut of higher octane fuel and a lack of ethanol (or price hike in ethanol) could result in some richer blends reaching the pumps, masquerading as E10. Who’s going to know or complain about improved mpg? It wouldn’t be the first time that big industry have pulled a fast one on the generally trusting but mostly naive general public (e.g. VW exhaust emissions scandal). Putting premium blends in the wrong tank could have the same positive effect (for us rather than the environment) but I wouldn’t expect that to last for 8-9 months!

Jordan53 wrote:Thanks Folks.
I see now the dual temp sensor is quite an unusual type.
It has one output that is binary - just on or off switching for the fan control and temperature alert lamp.
The other one is for the fuel injection and has a variable resistance output.

I once came across another type of dual temp sensor in a bus.
It had two switches with different set points. Neither were variable.
They controlled two banks of engine cooling fans, the second coming on at a higher temperature.

No, both leads put out the same resistance. The even have the same wire color: violet/green.

The one to the temp relay could not be "binary" because the temp relay has three states:

1 - below  103 C - does nothing
2 - 103+ turns fan on
3 - 111+ warning light comes on

duck wrote:

Jordan53 wrote:It has one output that is binary - just on or off switching for the fan control and temperature alert lamp.
The other one is for the fuel injection and has a variable resistance output.

No, both leads put out the same resistance. The even have the same wire color: violet/green.

The one to the temp relay could not be "binary" because the temp relay has three states:

1 - below  103 C - does nothing
2 - 103+ turns fan on
3 - 111+ warning light comes on

Thanks duck.
This is stranger than I first thought.
At 33 years old, my K100 is the newest bike I own so multi-purpose components are a bit of a novelty to me.

Born Again Eccentric wrote:

Point-Seven-five wrote:
One oddity I noticed in 2022 was that for a 8-9 month period all my vehicles, bikes and cars got a consistent unexplained 5-10% increase in mpg that I haven't seen again since then.

We’re at the mercy of the refineries - never know exactly what blend they make for us or what happens to it on the way to/at the service station. A glut of higher octane fuel and a lack of ethanol (or price hike in ethanol) could result in some richer blends reaching the pumps, masquerading as E10. Who’s going to know or complain about improved mpg? It wouldn’t be the first time that big industry have pulled a fast one on the generally trusting but mostly naive general public (e.g. VW exhaust emissions scandal). Putting premium blends in the wrong tank could have the same positive effect (for us rather than the environment) but I wouldn’t expect that to last for 8-9 months!

Yes, BAE, I suspected a different blend from the refinery.  Possibly due to the reduced demand for motor fuel because of the Covid lockdowns and rising prices.  Because of my Asburger's induced OCD I have to calculate the efficiency of every drop of fuel I put in my vehicles.  Been doing it for going on 50 years now so I notice those things.