Intermittent issue

[Shirty]

Hi,

Haven't posted for sometime, as my 1988 K75 is generally very reliable.

However I seem to have an intermittent issue.

Some weeks ago I rode into work as usual, without any problems & no warning signs, but when I went to go home it refused to start. The engine turned over fine, with a nice fat spark from the plugs & fuel was definitely getting through. In fact the plugs were absolutely wringing wet, & clouds of fuel vapour were continuously ejected from the plug holes when I turned the engine over without the plugs in & no throttle in an attempt to get rid of the excess fuel.
When I got the bike home, the first thing I did was to clean off the earth terminal from the battery to the engine, which seemed to fix it as the bike started up without any problem.

The bike has continued to run as normal for the next couple of months, until I went to go home last Friday. Again the same problem as before, turns over, great spark, very strong smell of petrol etc. Ah ha! I know what worked last time, so I cleaned off the earth terminal fully expecting it to subsequently burst back into life, but alas no, it still wouldn't start.

I'm beginning to wonder if the problem may be with the fuel injection system causing it to over fuel & flood, with the amount of fuel on the plugs, & the strong smell.

I've yet to recover the bike home, but thought I'd start asking if anyone has any thoughts as to where to start looking?

Here's hoping.

Cheers  -  Craig

[alexis291]

Hi Craig, I don't expect it will make you feel any better but I had a very similar problem on my k1100rs a few weeks ago. When I went to start it, the engine turned over fine at normal speed but there was not a peep out of it. When I took the plugs out they were wet and the spark was good. I put it all back together and it fired right away. I did think it had started on three cylinders and discovered that one header pipe was colder than the others at idle but there is no noticeable loss of performance when riding (I have posted about this recently). I checked valve clearances and compression pressures and all were good. I used the bike for a couple of weeks without problem and have now sent the injectors away to be checked. It's an odd problem because it was all or nothing - the bike went from being fine and in daily use to not even attempting to start, then back to ok without me doing anything. I'll be surprised if injector servicing makes any difference apart from possibly evening up the exhaust temps. If I do find anything, I'll post it. Alex.


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[Shirty]

Thanks for replying, hope you get yours sorted.

Cheers

[Martin]

Clean the temperature sensor connector with DeoxIT, this should cure the problem. A dirty connection will cause the ECU to over fuel the engine. It could also be a faulty temperature sensor but as the problem is intermittent it is more likely than not the connection. I also smear dielectric or heavy silicone grease around the connection. I believe doing this will help keep out air and moisture which leads to corrosion in the connector. However some inmates believe greasing can lead to insulating the connections.
Regards Martin.

[alexis291]

Thanks Martin. Water or air sensor?


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[Inge K.]

Also check that it's good connection between the sensor housing and the water stub/engine.

[Martin]

Water temperature sensor, it is a known problem. You need to keep connections clean to avoid problems. If you remove the actual sensor, just clean the threads do not use sealant or thread tape. Use of either will effect the sensors ability to gain a good earth which it relies on in order to function.
Regards Martin.

[alexis291]

Water temperature sensor, it is a known problem. You need to keep connections clean to avoid problems. If you remove the actual sensor, just clean the threads do not use sealant or thread tape. Use of either will effect the sensors ability to gain a good earth which it relies on in order to function.
Regards Martin.

Thanks, I'll give that a go while the bike's in bits.
Hope that helps Craig too !


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[Inge K.]

Thanks, I'll give that a go while the bike's in bits.

Be aware that the sensor on the 4V models isn't grounded through the housing.
(my first reply was meant for the OP).

[Shirty]

Thanks Martin & Inge, I'll certainly be giving them a good clean up when I get the bike home.

Cheers  -  Craig

[Shirty]

Quick update.

Finally managed to get the bike recovered home today, & spent a few hours pulling & cleaning all the electrical connections, including the temp sensor, what a pain that is to get to! The contacts on the temp sensor didn't actually look too bad, but cleaned them anyway. Managed to get it back together before it got too dark. Sadly though it still dosen't start. It did sound like it tried to fire on the first revolution, but then just turned over leaving the smell of petrol.

Maybe the sensor is faulty after all  :musicboohoo:

Cheers

[Martin]

You can test the sensor. All you need is a thermometer and a multimeter, remove the sensor and check the values with a multimeter while raising the temperature of the water. New sensor if needed can be obtained from http://www.euromotoelectrics.com/ or a cheap one from Aliexpress https://www.aliexpress.com/item/High-Quality-Engine-Coolant-Temperature-Temp-Sensor-For-BMW-Motorcycles-K-100-K-75-K75-K100/32680512124.html?. I have heard of unsubstantiated reports of failures of the Chinese ones, your call.
Regards Martin.

K100 Temp Sensor Values.jpg (38.1 kB . 768x464 - viewed 318 times)

[Shirty]

Thanks again Martin, I'll take it out tomorrow & test as you suggest.

Will look at oem, probably from Motorworks or Motobins here in the UK.

Cheers. :2thumbup:

[Martin]

Shirty I have just ordered one for testing purposes from Aliexpress $10.92 US there is another from the same company $15.77 US . The only differences appear to be the colour and the seal. They quote a 35 day delivery. I've had the connector fail twice, it needed cleaning properly with DeoxIT, I also smear heavy silicone grease around the connector in the belief that it will keep the moisture and air out that can lead to corrosion and a bad connection. There are some that believe that by using the grease you can be causing electrical connection problems. I am already running a Chinese fuel pump, rear master cylinder and a Chinese $100 Au motorcycle GPS. Only problems I have encountered so far are with the GPS whose power supply failed and was replaced by a Jaycar one the I had lying around. I tried to contact the GPS supplier three times with no answer. When it does get here I will test it and post the results.
Regards Martin.

[Shirty]

The result of the testing:

In cold water, approx 10 deg C, around 6500 ohms, & in boiling water, around 1100 ohms.

The figures are quite a bit higher than they should be according to the chart, so it looks like the sensor is duff.

Cheers

[Shirty]

Just a quick update, all now appears good!  :yippee:

The replacement sensor arrived & was fitted over the weekend, now the bike starts & runs again!

Thanks for the help.

 :riding:

[Martin]

 :2thumbup: Still waiting for my Chinese one.
Regards Martin.

[Shirty]

I ended getting a secondhand one from Motorworks.

Cheers  - 
craig

[The Mighty Gryphon]

That's great news!