K75 difficult to start, runs extremely rich

[bast1472]

Unfortunately I'm back again with what appears to be another electrical gremlin, and hopefully nothing worse.

Toward the end of last year's riding season I took my K75 out for one final ride before putting it in winter storage. I noticed the battery was very weak during startup, and made a mental note of replacing it soon. I rode one of my usual scenic routes but got stuck in an unexpected traffic jam. Making matters worse, my temperature warning light came on as I was inching through the gridlock. Every time the light came on, I'd shut off the bike and walk it for a bit. Eventually I was able to escape onto a side street and get enough airflow to keep the temp light off until I made it home. A few weeks later I installed a new battery but the bike would not start. Now that the weather is improving, I'm able to do some more investigating. I can get the bike to run (like crap) if I give it some throttle, but it occasionally backfires and blows a ton of black smoke that reeks of gasoline. If I let off the throttle it dies, and I don't run it like this for long because I'm sure it's wreaking havoc on the plugs.

Based on these symptoms and other posts I've been reading, it sounds like the coolant temp sensor is bad. However, I replaced it with a new OEM Bosch unit which didn't solve my issue. I checked the temp sensor wiring inside the sheathing and from what I can see, it looks new and undamaged, but I'm beginning to suspect it might be a wiring issue rather than the sensor itself.  I also swapped in fresh plugs, new Bosch injectors, verified spark and fuel pressure, and checked that the air filter and airbox look clean. I have a spare computer that I hooked up, which had the same result.

Last season I replaced the Hall Effect sensor, so I don't think that's the issue (also those symptoms were distinctly different). I'm really hoping I didn't incur any engine damage from the brief moments it was running with the temperature light on, and the fact that it will fire up and run (albeit rich) gives me hope that's not the case. The overheating was a shock because I'd flushed the coolant and bled the system within the last year, and I've never had any cooling problems before, even in hot weather with lots of clutching. I'm thinking of acquiring a replacement sub-wiring harness but at this point I'm just throwing parts at it. Hoping to get your thoughts and recommendations on how to proceed given the details above. Thanks in advance!

[caveman]

may want to check the air vane in air intake box?

[Laitch]

The overheating was a shock because I'd flushed the coolant and bled the system within the last year, and I've never had any cooling problems before, even in hot weather with lots of clutching.

I was shocked to see a gun barrel in my face because I only had five dollars in my wallet and I had never been robbed before. 

∆. Follow caveman's suggestion. The vane should swing without sticking.

1. Grasp the fuel injection control unit plug by its left end. If you can swing it outward to the right without moving its latch, it has been partially disconnected and likely the source of your difficulties
 
⊛. A Brick engine can handle the interval of overheating you've described; stay calm.

⚧. Use a slender dowel to rotate the fan's blade assembly. If it doesn't rotate easily, there's part of your overheating problem. You    probably should check to determine if the Hall effect sensor assembly you installed has loosened and rotated out of alignment.

B. Tell us from where you purchased the temp sensor and give us its part number.

♋︎. With the engine cold and the ignition switch set to Off, set your multimeter to Ω and use its leads to connect socket 10 and socket 13 of the fuel injection control unit plug. Tell us the resistance. 2.5K Ω would be good but the range ok if a bit higher.



✿. Don't throw parts at it. Test for function.

[stokester]

✿. Don't throw parts at it. Test for function.

Yes, take it one step at a time for a diagnosis and keep a running log on what you find.  We're not dealing with a CAN bus and there is good advice here to ensure you don't spend any money unnecessarily.

[bast1472]

Thanks all for the tips. I still need to check out the vane and HES but here's what I was able to check today:

1. The fuel injection control unit plug is tight and doesn't swing loose without releasing the metal latch.

2. The radiator fan rotates freely.

3. The temp sensor is from Euro MotoElectrics, Bosch part # TEMPSENS-K197O (https://www.euromotoelectrics.com/TEMPSENS-K197OE-p/tempsens-k197oe.htm). Prior to this one I had been running an EnDuraLast temp sensor from the same retailer, part #TEMPSENS-K197.

4. My multimeter shows 3380 ohms across sockets 13 and 10.

This week I'll check that the Hall Effect Sensor has not moved, and dig into the airbox to see if the vane is stuck. By the way, I replaced I replaced the HES two seasons ago with an EnDuraLast K049EDL from EME.com. Before replacing it, I was having another starting issue where the bike would only run (like crap) with the computer unplugged.

[frankenduck]

What fuel injectors did you install?

The fan should spin up if you put 12V to the A2 pin of the temp relay socket. (Pin layout is printed on the temp relay.)

As noted, the temp light coming on isn't a big deal. Similar to a car, after the warning comes on, when it gets even hotter the radiator cap will blow (and get your left foot all wet) before there's any engine damage.

[bast1472]

The latest fuel injectors I installed are these EnDuraLast ones from EME: https://www.euromotoelectrics.com/product-p/finj450edl.htm

Good to know about the radiator cap and the fan test, I'll verify that it still functions. Thanks.

[frankenduck]

I meant right foot, not left, for radiator cap blow.

The power wire to the fan at A2 is violet yellow.

Do you know the Bosch part number of the fuel injectors? It shows on the side. It's probably impossible to see with them installed though.

Here's an example of a stock K75 injector:

[Laitch]

Do you know the Bosch part number of the fuel injectors?

According to the EME link bast supplied, the Bosch part number is the same as you indicated in photo.

[frankenduck]

According to the EME link bast supplied, the Bosch part number is the same as you indicated in photo.

The same page says that the original 210 FI is discontinued. The only way to know is to inspect what one has in hand.

[The Mighty Gryphon]

My multimeter shows 3380 ohms across sockets 13 and 10.

That reading sounds like the sensor's normal resistance of ~2400ohms added to the resistance of ~1000ohms in the ground connection.  That looks like a very cold engine to the Jetronic causing it to make a very rich mixture after the engine warms up.  My suspicion is that there may be a bad electrical connection between the temperature sender and the stub and/or between the stub and the engine block. 

What is puzzling is that you are reading a thousand ohms between the connector pin #13 and the engine block.  That should be close to zero, and could be causing a bunch of other weirdness in the operation of the engine.

Last, have you checked the zero on your meter??? 

[Laitch]

The same page says that the original 210 FI is discontinued. The only way to know is to inspect what one has in hand.

That goes for just about everything bought online.  The idea attempting to be conveyed in the text is likely to be that the injector is a replacement for 210 with the same characteristics as 210—somewhat on the line of EME replacement fuel sender, the oem version also discontinued. The only way to know first hand beyond inspection of the injector is to test the flow rate, impedance and other submagical stuff.

[frankenduck]

That goes for just about everything bought online.  The idea attempting to be conveyed in the text is likely to be that the injector is a replacement for 210 with the same characteristics as 210—somewhat on the line of EME replacement fuel sender, the oem version also discontinued. The only way to know first hand beyond inspection of the injector is to test the flow rate, impedance and other submagical stuff.

The best way to know the specs for a given fuel injector is to know the manufacturer part number that is printed on it and check the data sheet for that product. There is nothing magical nor even "submagical" about it. What does the word submgical even mean?

[Laitch]

What does the word submgical even mean?

Below magical

[Past-my-Prime]

Below magical

Sometimes things work and even the engineers don't know exactly why. It may or may not be magical. It could also be substituting for magical. That's how I interpreted it!