91 K75 no turn over/ "putting" - K-Bikes.com - Excellence in Motion
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post #1 of 7 (permalink) Old Jul 6th, 2009, 10:40 pm Thread Starter
Join Date: Sep 2008
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91 K75 no turn over/ "putting"

I have a 91' k75 with ~19k miles. I am the third owner to this bike; previous owner had no concept or care for maintenance. Rode for about 2 years without any noteworthy issues. Bike been out of commission since summer '08. Before posting, I went through all the posts in the forum in hopes of finding a solution. Alas, no dice. There was a former post about a issue that is no longer occurring but the bike is still not running right.

First issue: started bike, "cannon-blast" single backfire, then constant thick blue/white smoke from exhaust; bike would idle and did not lose power; good compression on all cylinders upon testing

Resolution: new plugs, cleaned injectors, cleaned fuel rail, replaced O-ring seals on injectors, replaced outer valve cover gasket (slight leak); smoke went away, but idle remained rough; believed fuel had leaked due to deposits in injectors which pooled then ignited causing the huge backfire

Current Issue: Bike will not remain running or idle properly under normal conditions; only way to get bike to idle is to manipulate vane/flap in airflow meter to middle of range and only then with choke or throttle open to some degree; more throttle = die, less throttle = die

What it does: starter whirs, sputtering trying to turn over, occasional larger sputter, no turn over, just revving

With assistance at meter: starter whirs, hard start to idle once vane is in an agreeable position, rough idle which ends when vane is released or pushed to max or too little/much throttle

Fuel refreshed
Fuel filter replaced (was bad)
Fuel treated with LucasOil fuel treatment
Fuel injectors cleaned (some deposits but none have reappeared)
Fuel rail cleaned
Fuel tank inspected (sparkling)
Compression Test (all cylinders good)
Fuses checked
New battery
New injector O-rings
Battery ground sanded/cleaned
TPS disconnected (no change)
Airflow meter disconnected (will idle very rough, but does idle)
Airflow meter opened and wheel adjusted for testing (worse or no change)
Two earwigs removed from inside FICU
Bunch of listening, figuring, unhooking, etc

Bad airflow meter
Bad soul (ICU/ECU/*CU)
Bad injectors

Critical Note: Manipulating the airflow meter has the same effect whether installed in the airbox or free wheeling outside the box.

I'm thinking either airflow meter ($800 new - $50>$200 used) or injectors ($130 new each - $75>$100 refurb Ford injectors). At the price of the parts, I would prefer not to be tossing them at the bike for diagnostics. Raked my brain and good auto mechanic's brain for any light towards the root cause. I can't blame any of the suspects as too many variables are at play.

Assistance would be most appreciated. I'd post a YouTube video for diagnosing sounds if it will help.

Last edited by Vey; Jul 6th, 2009 at 10:43 pm. Reason: critical info
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post #2 of 7 (permalink) Old Jul 6th, 2009, 11:33 pm Thread Starter
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Plugs are black and fuel soaked. No oil on the plugs; just fuel. The throttle behavior seems to indicate it is running rich along with the plugs being coated.

Additionally, idle sputter starts off stronger briefly when first starting after sitting then settles into a weak sputter. Continues as such no matter how many consecutive attempts at turning over.
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post #3 of 7 (permalink) Old Jul 7th, 2009, 11:02 am
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Location: , , UK
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I don't have your bike - does it have a diagnostics socket? With most parts of an efi system costing $$'s and you might get it wrong, I'd rather spend 1/2 hour less $'s at the dealers with diagnostics first if that's possible.

We can all guess at this part or that part, but only computer diagnostics stands a chance of looking at the whole system and comparing yours with what it knows to be a good bike. The TPS is usually a very critical component in an efi system and is often crucial to set the idle and main running engine maps so I don't understand why you disconnected it and it didn't do anything, rather I'd have thought it wasn't doing anything and that's what I'd have looked at first. The later bikes also initialised the ECU mapping with the TPS set correctly against its stop, so if you have somehow run the bike and the ECU has a load of duff data from a non-existent TPS . I'd see if the ECU needs to be left off battery 1/2 an hour, all parts connected and then re-try an ECU reset if there is one to re-learn the setup.

This is always the problem when you have one bike and one fault in a complex system - not having the luxury to swap known good parts over - then there's the 'double fault' scenario as well. I'd look at boneyards for parts anyway once I had a good idea what might be the problem.

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Last edited by voxmagna; Jul 7th, 2009 at 11:11 am.
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post #4 of 7 (permalink) Old Jul 22nd, 2009, 6:45 pm Thread Starter
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I spoke with the dealer and he stated that diagnostics on my bike via the scan tool would not be beneficial as the data is very limited which they would get. I did unplug separately the only two control units I could find on there (FICU & ICU) for atleast 30 minutes with no change in the issue. I have acquired a Haynes manual on my bike to move forward.
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post #5 of 7 (permalink) Old Jul 22nd, 2009, 9:30 pm Thread Starter
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Tried adjustments on the TPS and Airflow meter for idle mixture - no change. Its still responding to the airflow meter vane movement only.
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post #6 of 7 (permalink) Old Jul 24th, 2009, 2:30 am
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Take a look at this site, IBMWR K-Bike Tech Pages and see what they have there. The folks on that site have been riding BMW's since before there were dirt roads. They will have a great knowledgebase to support the early 90's k-bikes, and may have what you're looking for...or very close to it. 3/4 of the way down is the Fuel/Ignition section.

Had a K75RT 6 years ago, had to be one of the smoothest riding bikes out there. But, that was 6 years ago, and I never had a fueling/ignition issue.

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post #7 of 7 (permalink) Old Aug 15th, 2009, 9:22 am
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Location: Algonquin, IL, USA
Posts: 41
Did you figure it out?

First I would check for spark with an inductive timing light You say it idles so as you give it gas does it loose spark? Could be weak coils?
Then I would check the air snorkles and throtle body.Spray with carb cleaner all over while running, see if idle changes, if it does you have an air leak.
Then I would then pull the fuel rail with the injectors still hooked up to the rail put them in a 5gal bucket (still hooked up to the tank. turn the motor over (try to start) watch the spray from the fuel injectors,Should be a nice spray all the same.

I am assuming you did already disconect and re-connect the electrical connections for the fuel computer under the seat and the ICM/ECM under the tank. If none of that works time to get out the ohms / volt meter and start testing.
Too bad your not close I have spares of all the electrical parts I use for testing.

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