My problem is back. Poor idle and missing at low RPM (low power).

Originally I thought I had a bad spark plug. Swapped them out one by one until it ran better when I replaced one of the plugs. I think it was #2.

Then the problem came back.

So I decided perhaps I have a clogged injector. I ran a half bottle of BMW Group Fuel System Cleaner through it over 500 miles or so. That seemed to help.

Then the problem came back.

Now I am back to my original idea of having a bad coil.

The spark plug wires look old. The insulation shows wear from rubbing, especially near where the wires pass through the cylinder head "hole" in front of my left toe.

New non-BMW wires are $100 or so from my dealer.

What I was wondering is if anyone knows if the ends unscrew (like some of the older BMW automobile wires do). That way I could pick up some high quality new spark plug wire and make my own wires using the old ends and boots...and save a few dollars.

Any comments?

Thanks!

Hi Scottie,
If you want to replace the leads try http://www.motoelekt.com they have K bike leads and attractive price. They gave me excellent service too. If you know a garage with one of the Sun diagnostic machines or similar you can go down and clip the diagnostic on all four cylinders and you will see the voltage and pattern for each cylinder. That will show you instantly if you have low output on a coil. Which should cause misfiring on two cylinders at the same time given each coil fires two pots.
Regards,
K-BIKE

Poor idling?????

What that could be?

This week, my brother had a similar problem with its K100. It was a bad connection on the ignition computer.
A month ago, I had a problem too and it was a bad battery. Don't forget, the alternator kicks in around 1,500 rpm and the idle is between 850 and 1000rpm. Try to hook your car battery to the bike and see how it runs (disconnect it from the car first).
Another thing is the CO setting in the airflow meter. Are your spark plugs having a nice light brown color?
Yes, one of the wires could be bad, but before spending the money, I would check these things first.

Hi Scottie,
One thought is an air leak from the rubber hose from the airbox into the engine crankcase is reported to give a rough idle. Next thought what about air leaks around the throttle bodies and the balancing rubber caps they perish and leak. Check with butane or propane to see if the gas is sucked in causing the engine to run differently when the gas is sucked through the leak.
Regards,
K-BIKE

Ah, thanks guys.

I was suffering my way to work this morning, trying to nurse the throttle at lights to keep her running.

I kept wondering..."What could be causing this problem?"

A thought crossed my mine - bad connection between hall sensor and ignition computer. Or faulty ignition computer?

Who knows?

I will remove the tank tonight and clean and inspect the connectors at the ignition computer.

Next step: start buying new parts.

I guess I will start with new wires.

Then new hall sensor.

Then a single ignition coil to swap out with the installed ones.

If you have any ideas, let me know!

(Perhaps it could be a faulty fuel pressure regulator, but then i would think it would give a puff of black smoke at idle from being flooded)????.

Oh, forgot to mention. I have replaced the crankcase breather hose a few months ago with a new one.

Hi Scottie, could it be something simple (and cheap!) like a bad tank of fuel as it seems to go for quite a while after being "fixed"?

Blocked fuel filter or pump strainer?

Regards,

Phil

phil_mars wrote:Hi Scottie, could it be something simple (and cheap!) like a bad tank of fuel as it seems to go for quite a while after being "fixed"?
Blocked fuel filter or pump strainer?
Phil

The fuel pump delivers a constant flow and pressure to the fuel rail. I believe that if the fuel supply was at fault, the engine would most likely run fine on idle but would be starving fuel at higher rpm.

If your bike is running fine on idle when cold and starts to be a problem when warm, I would test the Hall sensor with a hair dryer.
Start the bike cold and see if the idle is correct. If yes, shut off the bike and start to heat the Hall sensors with a hair dryer. When they are warm, restart the bike and see if it makes a difference.

How warm should it be???
I don't know the answer, but you could find it by opening the cover of the sensors when you come back from a run (or after having the bike running on the stand for 5 minutes). Sneak in the kitchen. Your wife must have a meat thermometer . Borrow it for 5 minutes to probe the temperature. Don't forget to clean the grease/oil/gas before you put it back in the kitchen. :joker:

Runs fine above idle. Checked my battery last night. Hooked up a 10amp battery charger to see if perhaps poor voltage could be causing the issue. Still would not idle well with the battery charger connected.

Tested the fuel pressure today. 36 psi at idle. However here is something curious. The fuel pressure does NOT change if I appply 15 inches of vacuum to the fuel pressure regulator vacuum hose. Shouldnit it REDUCE the fuel pressure if vacuum is applied?

Scottie,

36 psi is dead on the BMW specs and I don't think you should be worried about the fuel pressure.
Having worked as an hydraulic technician for few years, I understand the way that a pressure regulator valve works, but I still cannot understand the relation between the vacuum hose and the fuel pressure.
In a straight hydraulic pressure valve, the pressure side of the valve will try to overcome the resistance of a spring. If it does, the valve will dump the excess pressure to the tank.
anyways, the pressure is OK and I would try to investigate about the ignition or maybe an air leak.
Is the problem occurs only when the engine is warm or do you experience it when it's cold too?

Bert

Hi Scottie I realised we had discussed the fuel question when I re-read your earlier thread.

Might be worth checking the ignition switch contacts and maybe an alternator issue which is a similar idea to Bert's with the dud battery as increasing voltage/ current can overcome poor electrical connections.

My theory with high voltage problems is they seems to get worse under load and of course there is always the case with bikes of this age that it may not be the same problem just a similar one. Perhaps having the injectors professionally cleaned or replaced (about $90 for a set on EBay)??

Once again just throwing ideas around.

Regards,

Phil

Hi Scottie,
Have you checked for a vacuum leak the runs badly at low RPM but OK at higher revs points amongst other things to vacuum leaks.
Regards,
K-BIKE

I think I may have it licked this time. Although my leads were measured at 5k ohms and did not show any sparks "leaking out" when viewed in the nightime, I went ahead and replaced the leads. Instead of paying BMW for new leads, I made some up using some caps from a BMW M10 motor (which uses the same connectors on the coil/rotor cap) and small spark plug caps from a mid-80's yahama. Both wire ends have the screw on connector which drives a threaded bolt into the core of the wire. I used high performance solid core copper wire. Don't know if these will read 5k ohms, but I figure that was probably for radio supression anyway.

Result: bike is running fine except for the occassional sputter off idle when the engine is thoroughly warm. Might be running a little lean. I will richen it out with the idle screw and see what happens.

Again, the bike runs awesome above 2500 RPM. Go figure?!?!?!?!

Hi Scottie, wish I had seen this thread earlier, only just learning the nack of watching them. I had exactly same problem on my last RT. The same reasoning and thoughts as noted here by all members. Then the same cure, and problem totally solved, except I forked out for BMW HT leads. Price... best not mentioned here... Obvious answer really, and I only wish I had thought of making my own like you. Cheers Boris the Bike

OK guys I'm back. Eventually the bike started running like CRAP again!?! oh why oh why?

Do you want to know the whole story. It is a saga let me tell you. My dad came out to visit me and I wanted to take him on a trip to Big Sur, one of the most beautiful places in the world to ride. Two other friends joined us. My dad and I set off to meet up with them in Santa Cruz. Me on my 1982 Yamaha Seca 650 (lovely bike - had it for over 20 years now) and my dad on the K100RT. Well by the time we got to the coast, the K100RT was running poorly and eventually it wouldn't run at all.

My friend stepped up and lent my dad his MP3 250 to ride for the day. What a savior. All went well until the ride home. We decided to take 101N back since we were running low on time and had to meet my wife's family for dinner. My dad and I were running about 60 mph in the right lane, me behind him, when a big gust of wind blew him about four feet over into the car next to him. I was aghast. He struggled with it for a split second trying to regain, but his left handlebar dragged the car as he slowed down, turning his bars right. He went down instantly on his left. I screamed in my helmet and locked up my own brakes, my only thoughts being to attempt to stop the traffic behind me, 5 lanes of rush hour-California style freeway traffic so my dad wouldn't get run over. He was wearing my leathers so I knew he'd survive going down, but I really thought he would killed by the traffic behind us.

I laid my bike down on its left in a giant powerslide and ran up to my dad. Somehow all five lanes of traffic had managed to come to a stop behind us. There were cars in all manner of places, some in between the lanes, but no wrecks. It was a miracle. Now to check on my dad. He was conscious. A lady was taking his pulse. Thank goodness - she's a nurse. She checked his vitals while another biker called 911. My dad was ok, albeit with a badly broken left arm. Needless to say, he's alive and well today to tell about it. Just came out of his 2nd operation to pin his arm today. Three cheers to my dad. They say a cat has nine lives. My dad must have used up a handful by now, too.

He even made friends with the ambulance crew. They came to visit him. "Man you are a great guy," they said. "Most bikers really get angry when we have to cut away their leathers. You didn't mind a bit."

To which I responded, "That's because they were MY LEATHERS!"

Anyway, now I've got three bikes down scattered over about 100 miles. Nothing to do but call my wife and settle in for an earful. Make that two earfuls and a reserve for many further earfulls yet to come.

After about a week, I've got most of the bikes gathered up. I've got a very big bill to pay to fix up my friend's MP3. And I still have that gosh darn friggin' punch-me-in-the-head problem with my darn K100!!!!!

Fast forward about amonth to this week. I pull the ignition apart on the K100 again. I source a replacement set of coils and measure them out. Here's the key in case you want to avoid this adventure I've been on:

Bad K100 coils will measure 0 ohms across the two high volt ports, 4a and 4b.

Good K100 coils wll measure 10k ohms across 4a and 4b.

Coils swapped, bike runs fine now.

However I still have some sort of very light misfire at freeway speeds which you can definitely feel after the bike is really warmed up now which I do attribute to old HT leads. (I put the stock ones back on.)

When I get my life back in order, pay for my friends bike repairs and have a spare $100 I'll pick up some new leads and hope that fixes this once and for all.

hi,

What a story, seeing a dear one go down like that is a real nightmare, good to know that your father is recuperating, must be a serious injury to require pins. Hope you will ride together soon.

Any one else had experience with sudden side winds, is it realy a big issue? I have never experienced it myself except for big trucks running in illigal speeds PASS me.

ATB
Roy

Oh Scottie,
I do so hope that your Dad, ( sounds a cool dude), heals quickly and that you get out there together to the Big Sur again on the bikes! You know the maxim, "fall off a horse, get back on asap". Must have been a hell of a gust of wind to shunt him across a whole lane and cause the accicdent, still I am led to belive everything in the USA is bigger. A coil gone dud. Sounds right to me. Electrics are such a on/off, pain to find and fix. Best wishes to your 'Dad' from London, oh yes ear plugs and or selective hearing can solve a lot of trouble, that and a bunch of flowers! Cheers Boris the Bike .

Hi Guys, I am back with good news. I have been enjoying my K100RT so much that I forgot to write to update you guys that I had fixed my bike. A pair of coils from a friend's parts bike and I am back to running like new again.

As it turns out, both of my coils were bad. I didn't notice this because I was comparing my resistance measurements against the other coil. What a strange coincidence that both coils went out at the same time?????

I am very happy to have the bike running perfectly again.

Oh, and my dad is doing better each day. He'll be back on two wheels again before next summer.

Re new wires, I bought some from Germany on the fleabay.de site for 50 Euros for the full set. Just wait and see; they'll come by once in a while. Otherwise there are offers for new leads on the british BMW site, but no doubt you should be able to resource or make them cheaper yourself at a lower price.