1985 BMW K100 random miss

[johnny]

greetings...

i gotts nothing to do with nothing... ac is a whackhoe...

i asked a question and never gotts an answer...

does it miss while on the center stand when the engine is running...

j o

[warmas]

For your viewing pleasure.

https://drive.google.com/open?id=1bf2GFnnruHO4o-yDPXfhBsiN1wR7TF9H

[warmas]

I posted, finally, a video of my bike running.
Yes it does miss while on the center stand.

During the last two days I have made considerable progress due in no small measure to the aid I have received here.

Yesterday after taking a couple pictures of the bike, which the Management has displayed, I thought I had better disassemble the airbox/filter/airflow meter to verify they were installed correctly. I did'nt see anything wrong with them, but decided to see if I could obtain smooth engine operation by manipulation of the airflow meter while it was disconnected from the plenum. Moving the door in the airflow meter varied the engine operation from so rough it would barely run to smooth as silk, and from lean stumble to flooded rich. It was all good to know, now I know what it takes to allow the engine to operate smoothly. Just before dark I figured I should verify no intake leaks at intake manifold, sure enough a bit of starting fluid sprayed at their bases resulted in rpm increase.

Idle rpm then was around 1k.
You Tube showed how to relax the pressure on the airflow meter door to richen the mixture. Easily enough done, but due, I think, to the intake manifold leaks, I can't get the idle rpm below about 1.2k, unless I lean the mixture via the bypass screw, to drop the rpm, which causes rough engine operation at low power settings, and thus is a vicious circle. I think the cold start cam needs rigged to allow the throttle idle stop to bottom. Nevertheless, I have smoothed up the low power engine operation, which has improved the driveability immensely.

Yesterday I removed the injectors to see how they looked: orings were basically fine, a couple of the yellow nozzle pieces were cracked. I turned the orings upside down, as I had no spares, and reinstalled the injectors. No change noted in engine operation. Day before yesterday I balanced the intake manifold pressures of cylinders #2, 3, and 4 to cylinder #1. No real change in operation noted, but at least I know they are balanced.

Next task is to ensure intake runners are sealed leak-free to the head. Flexible rubber couplings at ends of throttle bodies look good, and seemed not to indicate leaks with starting fluid sprayed on them. I don't really want to remove the throttle body asssembly for fear of altering it's rigging. With the airbox and fuel rail removed there may be access to the socket head screws fastening the intake runners sufficient to determine whether they are loose.

At least now I know my ignition and fuel injection system is functioning. Bike did not want to start the morning. Disconnecting the coolant temp switch a bit allowed it to start right up. The CTS needs further investigation.

Bike has died a couple times for no apparent reason.  Dash lights out, headlight on.I thought initially the fuel pump was to blame, but now, after today's random stop, fiddling with the connector for the right hand controls seemed to restore power to the kill switch et.al.

It never ends.

[The Mighty Gryphon]

Just before dark I figured I should verify no intake leaks at intake manifold, sure enough a bit of starting fluid sprayed at their bases resulted in rpm increase.

Your throttle body bushings and/or injector o-rings leak.  Badly.  You need to focus on correcting that before you screw around with anything else.  If you mess with anything else right now you will only be making things worse.

Winter is here, so you might as well get it done.

[warmas]

The connections most prone to leak are those subject to the greatest pressure differential, which occurs downstream of the throttle plate. My careful application of starting fluid to the base of the intake runners showed an rpm increase, while careful application to other connections seem to indicate no leak. It seems to me if the fasteners for the runners can be tightened, within reason, a bit, and if then the leak disappears, I am good to go for a while. Rubber bits are perishable.

[The Mighty Gryphon]

The connections most prone to leak are those subject to the greatest pressure differential, which occurs downstream of the throttle plate. My careful application of starting fluid to the base of the intake runners showed an rpm increase, while careful application to other connections seem to indicate no leak. It seems to me if the fasteners for the runners can be tightened, within reason, a bit, and if then the leak disappears, I am good to go for a while. Rubber bits are perishable.

Close, but not exactly correct.  On your bike the air is measured at the MAF and the calculation for the mixture is made based on that measurement.  Unfortunately, there are a number of places between the MAF and the throttle bodies where unmeasured air can get in and lean out the mixture.  Every joint and connection is critical, not just those below the throttle bodies. 

You are probably correct in trying to tighten the hold down screws for the lower bushings.  I hope you are successful, but fear that either they're cracked, warped, or have bad o-rings under them and that tightening will be a temporary fix at best.

[johnny]

greetings...

does it miss while on the side stand when the engine is running...

j o

[warmas]

 Yes it did miss some while on the side stand. Curiously, the rpm increased a bit while on the side stand. Gravity opening the air flow meter door a bit?

A leak occurs across a difference in pressure. The difference in atmospheric  and  intake system pressure is greatest where the intake system pressure is the lowest, downstream of the throttle plate.  I am eager to learn how this statement is incorrect.

My experiment proved your point, i.e. that leaks contribute to unmetered intake air which cause rough engine operation.
Altering, as I have, the fuel map, richens the excess air enough to minimize rough operation, but, as you point out, does not solve the leak problem. The leak is only a problem at low power settings, at higher manifold pressures the leak diminishes in value. My bike now is eating a fuel/air mixture through a barn door spring adjusted one click weaker than, presumably, the factory setting. The change in idle quality is quite noticeable.

This bike comes factory-equipped with a powerful cockpit heater, and I plan to ride it all winter long.

[The Mighty Gryphon]

OMG!  Adjusting the MAF to fix a vacuum leak.  Who'd a thunk?

Brilliant!!!   :clap:

I'l need to add that to my repair techniques.  So much easier than screwing around with those throttle bodies!

[Laitch]

Yes it did miss some while on the side stand. Curiously, the rpm increased a bit while on the side stand. Gravity opening the air flow meter door a bit?

I doubt it. There is a lot of suction drawing air through that critter when the engine is running. A tilt in its angle shouldn't matter.

I wouldn't have tinkered with the air flow meter at all. The leaks in the air intake system need to be stopped. If all other fuel system, ignition system and electrical system elements have been checked then the throttle body balance should be redone according to widely accepted guidelines.

If you plan to ride all winter, be sure you read The Mighty Griphon's instructional posts here on bodywork repair. :giggles

[Laitch]

Adjusting the MAF to fix a vacuum leak.  Who'd a thunk?

Sometimes a guy needs to think outside the powerfully heated cockpit.

[The Mighty Gryphon]

If it still breaks up, you could wrap the throttle bodies with some Flex Seal tape.  That stuff even fixes boats!!!

[Laitch]

If it still breaks up, you could wrap the throttle bodies with some Flex Seal tape.  That stuff even fixes boats!!!

Now that's what I'm talking about! It comes in different colors, too!

[warmas]

My experiment with the airflow meter proved to me the rough engine operation at low power settings was due to lean fuel/air mixture, and subsequently I learned the cause and perhaps the fix thereof. I don't know everything, but do know to try the simpler fixes first. It seems often when I touch something, it breaks.

[warmas]

In spite of the communal suggestions, the rpm of the motor does increase noticeably when the bike is on the side stand.
I do not know why.
I think only the #4 cylinder intake runner has a slight leak.
I have experimented with tuning the three variables in the airflow meter and the ignition timing in my attempt at better gas mileage. The best I have found is a hair leaner on the wiper, one tooth leaner on the spring, and the idle mixture bypass at 3.5 turns open. Ignition advanced a couple mms. Bike starts easily, runs smoothly, plugs are dark tan to light brown.

Mileage varies, best so far just under 40mpg. With tall windshield and full fairing I may not get any better. K100 figures at fuelly.com place me near the median.

[The Mighty Gryphon]

Is it safe to assume that you still haven't installed the z hose from the block to the air box?

What happens when you remove the oil fill plug when the engine is idling?   

[warmas]

The crackcase vent to airbox is in place.

[warmas]

I do not know what happens when the oil fill plug is removed while the engine is idling.

[The Mighty Gryphon]

The crackcase vent to airbox is in place.

Good.  I hadn't seen that you replaced it. 

Does removing the filler plug change the idle?  Smoother, rougher, no change.

[warmas]

I will find out.

[Nine80seven]

How did it run at 4K rolling down the slab?  Feel anything?  Under load? 

[warmas]

I believe I have misspoken.
The crankcase vent attaches to the plenum, as distinguished from the airbox. The latter houses the L-Jetronic airflow meter.

I think removal of the crankcase oil filler plug creates a not-metered leak to the plenum. I doubt this leak adds more air to the engine. Rather, this leak provides an alternate path for the intake around, rather than through,  the airflow meter, perhaps altering its wiper displacement. My observation of my airflow meter operation as it now is tuned reveals nearly no wiper displacement at idle throttle, and small increases in wiper displacement at idle throttle cause no change in rpm: idle mixture is a hair rich which makes for a smooth idle. Engine runs smoothly enough, it seems, at all rpm, no load or on the road. No hesitation to accelerate.

Accordingly, I expect no change in idle engine operation as a result of removal of crankcase oil filler plug.
I also expect some change in engine operation at cruise rpm,  as I think a not-metered leak into the plenum gains in significance at greater airflow rate due to it's alteration of the wiper displacement. Bike on center-stand 4k rpm, observation reveals minute changes in wiper displacement cause noticeable changes in rpm. Bike at this load is tuned to rich edge of lean, lean edge of driveability. I think.

I can very easily be incorrect in my assumptions. Incorrect or not, to learn is the goal.

Another current project is troubleshooting the sole, 4l fuel level light wired to the instrument panel. 7l light is installed in instrument panel, but it's pin #8 is nonexistent in the instrument panel and the harness plug. 7l thermistor in sensor is missing, has been removed, 7l wiring in sensor is intact.
On the bench pin #7 to ground illuminates the 4l light. The sole thermistor in the fuel level sensor seems to function: resistance varies inversely with temperature, at 30F circuit is open, heat lamp on thermistor closes circuit, with continuity to  instrument panel harness plug #7.

I have made the 4l light blink while mounted to the bike. Problem may be, now, a simple loose connection.
A useful link: https://drive.google.com/file/d/1J5waA1gcBknatEtHhuTjmSl3Conag5ot/view?usp=sharing

[Laitch]

I expect no change in idle engine operation as a result of removal of crankcase oil filler plug.

That's simple enough to verify.

If there is no significant intake leakage, I expect the engine to stumble and perhaps stall when the oil filler plug is removed while the engine is running. If there is significant intake leakage, I expect the engine to keep idling.

On November 14 and 17 of 2018, you wrote that careful testing of the manifolds indicated leaks. You did not explain whether leakage was at the manifolds, the manifold bushings, or both. You seemed to indicate manifold #3 was a source of leakage and that you believed that tightening the clamps should correct that condition. You did not followup to explain whether the symptom of leakage had been resolved by means of tightening the clamps. A good strategy would be to disassemble intake assemblies for close inspection of the rubber components to find cracks that would allow air infiltration.

You indicated in a different thread that figures at fuelly.com placed the fuel usage of your moto in the middle of the usage range so things are looking up.

[warmas]

Thanks for the clue. I have checked and tightened, as best I can,  all the clamps and fasteners to the cylinder head.
I am not yet ready to reseal the intake system. It looks to be quite a job to take it all apart and reassemble with new rubber and clamps.

I suspect your expectation of engine stumble and perhaps stall as a result of oil-filler cap removal would be due to excessively lean mixture?

I now believe the intake leak is small, and exists only at the base of the #4 intake manifold, i.e. at the joint between the intake manifold and the cylinder head. It's significance is yet unknown.
All the intake air, except for a leak after the throttle, passes through the throttle body. Any leak before the throttle body does not alter the volume of air into the engine. A leak before the throttle body is, I think, either metered or notmetered by the airflow meter, according to it's position with respect to the airflow meter.

As regards your expectation of engine operation post-oil filler cap removal, I think such removal will not alter engine operation at all. I think oil-filler cap removal will have no effect on any post-throttle leak. The addition of a notmetered port to the plenum will not, as plenum and ambient pressures are nearly equal, alter engine operation noticeably at idle. At idle, at current tune, small airflow meter wiper displacements do not alter engine operation noticeably. At higher rpm a notmetered plenum leak becomes more significant. At 4k rpm on the center stand minute displacements of airflow meter wiper noticeably alter rpm.

Of course, I can be wrong.
Your thoughts?

[Laitch]

As regards your expectation of engine operation post-oil filler cap removal, I think such removal will not alter engine operation at all
Your thoughts?

Why don't you just go ahead and remove the filler plug while the engine is running? If nothing unexpected happens and the moto performs satisfactorily on the road, all's well.