K75 Flooding

[NMPete]

Hi -  Well, I’m still stuck. I finally got my 1988 K75 C (16K miles) started (replaced the injectors) but it is still flooding after a difficult start.
If I unplug the fuel pump it will start and idle until it runs out of fuel.  If I plug in the fuel pump, it immediately floods, but will start with full open throttle.  It jumps to 5K RPM and has a lot of exhaust smoke. If I let it warm up (at 5K) and rev it to 6K, it revs up quickly and easily to 7.5K sounding normal (good). If I drop below 5K it immediately stalls (floods out because the plugs are soaking wet with gas). I did a lot of reading in the Forum and found one person with a similar problem, but there was no solution.

I have been trying to resolve this for several weeks with no luck.
Here is what has been done:
- New fuel injectors
- Used ECU (has exactly the same response as the original)
- Installed a used cleaned and tested water temp sender
- New spark plugs that have strong spark at starter cranking and at 7K
- Tested the air flow meter, air temp sensor and fuel pressure (36 PSI static and 34 PSI steady at 6K-7K  RPM) per the wonderful Troubleshooting Guide
I have no BMW mechanic in less than 200 miles and they only like newer bikes.

So, after repeated testing and changes, I can’t get it to run like normal. I have a feeling this is a good bike mechanically and want to get it running correctly. If you know anyone that can help, please let me know.

Any suggestions?

Many thanks
Pete
New Mexico, USA

[frankenduck]

What new fuel injectors did you install?

[daveson]

I had a problem which I think matches your symptoms. The injectors are supposed to be getting constant power and a pulsing earth. If they're getting constant power and constant earth, the injectors will remain on instead of pulsing on and off, causing flooding.

Using a screwdriver like a stethoscope against the injectors, you should be able to hear the injectors ticking while cranking. If they're not ticking, that's a problem.

[NMPete]

I bought new injectors form Euro Electrics in Denver CO.  I also had the  original injectors cleaned at InjectorRX in Houston TX.  They did a great job for good price.  Tried both sets - always the same flooding.

I'll try the screwdriver trick.
Thanks

[stokester]

I'm not sure of the exact symptoms of a failed fuel pressure regulator but did you check the pressure to the fuel rail?


I agree that checking the injector signal would be next on my list.

[NMPete]

I did try the "screwdriver trick" and yes, I could hear each of the fuel injectors clicking regularly with starter running and the fuel pump disconnected (sounded like Norton valve tappets!).

The fuel pressure regulator seems to be working correctly; 36 PSI at idle and 34 PSI at 7000 RPM.

Any idea of a different sensor that would cause flooding?

Thanks

[The Mighty Gryphon]

On the end of the throttle bodies is a module called the throttle position switch (TPS) with two micro switches that sense the position of the throttle butterflies.  Have you tried unplugging the module?

If the components in the system are working properly, then the problem may be in the engine control wiring harness.  You may have worn insulation allowing a short circuit to ground or a broken wire.  Have you checked the signal values from the engine sensors at the big connector at the ECU?

[NMPete]

Yes, I tried with the TPS unplugged - no change.  I did the Ohm and 12V tests on the ECU plug as described in the Troubleshooting Guide.  Everything seemed O.K. per the expected values. 

The water temp sensor is good, but not sure if connection is good.  Is there a way to test it?

Thanks
Pete

[The Mighty Gryphon]

Pins 10 and 13 of the big ECU connector are connected to the engine temperature sensor.  2500 ohms at room temperature and about 250 at operating temperature.

[Laitch]

The fuel injection timing is primarily based on engine speed. The Hall Effect Sensor (HES) supplies the engine speed signal. The engine speed signal is the basis for cold starting and running with inputs from the air temperature signal, intake air volume signal, coolant temperature signal and the throttle position signal. The HES hasn't been checked. If the HES is sending a signal indicating an engine is running at high revs when in fact it isn’t, it’ll be flooding until it is actually running at high revs, which seems to be what is being described here.

The ignition control unit outputs the engine starting speed at pin#8. Its output should be checked. An extract from the troubleshooting guide is below. They are measured as AC values not DC.


The HES hasn't been checked. If the HES is sending a signal indicating an engine is running at high revs when in fact it isn’t, it’ll be flooding until it is actually running at high revs, which seems to be what is being described here.

[daveson]

Did you use Teflon tape on the temperature sensor?

[frankenduck]

The HES hasn't been checked. If the HES is sending a signal indicating an engine is running at high revs when in fact it isn’t, it’ll be flooding until it is actually running at high revs, which seems to be what is being described here.

The HES sensors only send a signal when the hole in the rotor cup passes by them.

[daveson]

Yeah, if the sensors are working properly, but they might not be. At say 4,000 rpm it's working at rapid speed, but if it gets lazy it might take one second or more to turn off, then it probably won't be turning off or on.

[Laitch]

The HES sensors only send a signal when the hole in the rotor cup passes by them.

Firsly, it's dangerous to put self-portraits in your posts on the Web. You should remove that before somebody on the Dark Web misuses it and takes advantage of you.
 

Secondly, I understand from your bio that you know all that you do from making more mistakes working on Bricks than almost anybody. I haven't gone that route. All I can claim is that I don't know what short circuits, crossed wires and etc. within the HES wiring harness can do, and also that we're discussing a K75—not a K100—the rotor of which has two windows yet is designed to send three signals.

If Pete will check the output at ICU pin #8, that could reveal something. Certainly if, as he claims, everything he already has checked is perfect, the failing of perfection is quite an anomaly.

[NMPete]

Hi - Sorry for the delay; my internet was our for 1/2 a day.

I did test the water temp sensor at ECU #10 - got 2250 Ohms.  Also, tested sensor housing to ground - 0 Ohms (cleaned male and female threads and no teflon tape).

Tried to test the HES at pin #8 of the plug; got 10.8VAC when I push the starter button.  All I have is a cheaper VOM from ACE Hardware and not sure I can measure mVAC with this.  Of course the starter is not working with the HES unplugged.  To test this with the starter running (or the bike running) I guess I would have to strip the correct wire a little? 

PS:  I looked at the Hall sensors, look clean and no oil or overheated wires, etc. 

[daveson]

The coils should be receiving a pulsing earth signal at pin one, from the hall sensors. Not sure about the location of pin one on a K75, but here is the test on a K100, with an LED test light, clamped to battery positive.

https://youtube.com/shorts/5VrtFtr07-4?si=XDsprvcOJm3lh-Yx

[Laitch]

I guess I would have to strip the correct wire a little? 
I looked at the Hall sensors, look clean and no oil or overheated wires, etc.

Don't be stripping wires. Don't base electronic component function capability by the looks of its wiring. The process of elimination will get you back to the HES and ICU if necessary.

[frankenduck]

Firsly, it's dangerous to put self-portraits in your posts on the Web. You should remove that before somebody on the Dark Web misuses it and takes advantage of you.
 

Secondly, I understand from your bio that you know all that you do from making more mistakes working on Bricks than almost anybody. I haven't gone that route. All I can claim is that I don't know what short circuits, crossed wires and etc. within the HES wiring harness can do, and also that we're discussing a K75—not a K100—the rotor of which has two windows yet is designed to send three signals.

If Pete will check the output at ICU pin #8, that could reveal something. Certainly if, as he claims, everything he already has checked is perfect, the failing of perfection is quite an anomaly.

Yes, 3 and 4 cylinder HES are slightly different but the rotor cup will never spin six times as fast as it should which is what you imply. Also, if the HES could (which it can't) send out six times as many pulses as it should than the ICU would fire the plugs six times per revolution. Good luck with that.

As I stated: UNPOSSIBLE.

[Laitch]

Yes, 3 and 4 cylinder HES are slightly different but the rotor cup will never spin six times as fast as it should which is what you imply.

You're inferring that. I'm not implying that. I discussed the difference because you weren't making it clear in your illustration. I'm stating the ICU output and the HES input need to be investigated when feasible. In this case, they'll probably considered if other areas of exploration are cleared.

[daveson]

[quote ...fuel pressure (36 PSI static and 34 PSI steady at 6K-7K  RPM) per the wonderful Troubleshooting Guide...
[/quote]

I'm wondering if we can be confident about the fuel pressure gauge, seems strange that the pressure drops at higher revs.

It floods and dies when the tank is connected. I'm thinking about the possibility that the return valve in the tank is blocked, causing flooding, this has been an issue with a few threads. If you extend the fuel return line into the tank through the opening for the filler cap instead of the return valve, that might solve the flooding problem. If it does, the return valve is probably blocked with rust and crap, then just carefully clean it out. Another test would be to direct the return hose into a fuel container instead of it being connected to the return valve under the tank.

It's on the cards if it's been in storage for say a few years.

[NMPete]

Hi -  I didn't know there is a return valve in the tank.  The pressure regulator seems to be working O.K.  My fuel pressure gauge is new and I think it is good, but it could be off some.  I will test it again.

I will try the return line into the filler opening.

Thanks
Pete

[Laitch]

. . . the possibility that the return valve in the tank is blocked, causing flooding, this has been an issue with a few threads. If you extend the fuel return line into the tank through the opening for the filler cap instead of the return valve, that might solve the flooding problem.

If Pete's fuel tank is its original, it doesn't have a return valve; it has a standpipe within the tank. That change was made in 1986, according to Largiader at Virgina Motorrad. Models eventually had the standpipe's outlet empty at the ceiling of the fuel tank just above the vapor evacuation chamber. This was done so fuel wouldn't spill from the return hose port when the hose was detached.

[daveson]

Yep that rings a bell, funny though since you'd think the valve would prevent that anyway. Maybe it's blocked anyway, or maybe the hose or the pressure regulator itself.

It seems that everything is good, but something must be wrong to cause flooding. One easy check would be to remove the filler cap assembly and look to see if fuel is returning to the tank while cranking (it might be easy to see without removing the assembly) If there's no fuel return, that's a definite problem which would result in higher fuel pressure, causing flooding. There's something strange about the pressure being lower at revs than at idle.

Pete, where was the pressure gauge attached?

[NMPete]

Great questions - The gas tank is not original; it is a little bit later but the same fit, etc.  The filler cap is removed. With the pump on (starter button and when running at 5K +) there is fuel returning from a series of metal tubes along the top of the inside of the tank from the return hose outside.  I have tested the "inlet" pressure (hose from the tank) and the "return" hose  - both show 36 PSI.

I will do a pressure test again next week and monitor it at different RPM ranges  and let you know.

Thanks
Pete

[Laitch]

I have tested the "inlet" pressure (hose from the tank) and the "return" hose  - both show 36 PSI.

Agree with daveson. Return pressure shouldn't be that high; it should be a trickle to light stream. Your gauge is faulty or maybe the fuel pressure regulator is faulty.