Yes, that is what I meant to write.

This bike was running about 6mth ago. It started off the button but did not run smoothly. After checking a few things, I suspected flowmeter and pulled it out check it.  In doing so the large diam plastic tube from AFM to inlet manifold split.  The bike got put to one side because I did not have time.

Yesterday I tried to take another look but I forgot there was no AFM and the input was not linked up .

Surprisingly it did actually start, though ruff as guts and sounded like it was only firing on one cylinder.

Once I started checking around I found the missing AFM and got onto it. I fixed inlet pipe and put it all back together.

Now it won't start at all !  Not a pop !   Battery is good and gives a good fast turn over but not a sound from the motor. I checked sparks , a quick check in timing of cylinder #1 with a strobe, then pulled the injector ramp out to see if any were stuck. I span the motor to see the spray pattern and it FIRE UP !  , without the injectors.  It ran good and even for just under a second and then stalled. 

I concluded it must have been flooded and thought fine , it'll run now.

I put the injectors back in and ...... nothing.  Not a pop.

It seems that it may be spitting too much fuel and is flooding straight away.

Is it possible I've damgaged something by firing it up without the AFM connected?  Any other suggestions?

TIA.

Depending on what year and model Brick a faulty temperature sensor or connections can cause flooding. Are the spark plugs wet? The electrical connection at the sensor can be prone to corrosion. The thread on the sensor needs to be clean and free of thread tape or sealant   There is a procedure for testing the sensor on this site. 
Regards Martin.

Another, less likely, possibility, since it runs with the AFM disconnected, but not when connected, there could be something wrong with the AFM.

I'd think about disconnecting it again, maybe a few times, to see if that is a consistent pattern.

Thanks for the suggestions.

The bike was running almost normally with this AFM 6mo ago. It's been sat  on my floor since. I doubt the temperature thermistor stopped working or broke like that. Also the air temp will make a small adjustment to fuel flow but I doubt it's to the point of not getting a single fire from the engine.

I did swap in a different AFM and got the same result. Though I'm not sure of the state of that second one.

Just visually it seems to be throwing a lot of fuel. I've done visual inspections of injector spray before and from memory it was a lot less, though that just subjective recollection and could be spurious.

1. Yep might only be a small difference when working properly, but it might not be working properly, and way out of normal range, and considering also air volume. 
   

I spose it's still worth checking to see if it's consistently a go with the original AFM unplugged, and a no go when plugged in.

Was the fuel pulsing do you think, as it should be, or a constant stream? Another quick check, with the help of a screwdriver to an injector, you should hear it ticking, that would possibly confirm a pulsing supply of fuel.

Sure it's the usual injection squirts but it looks like twice the volume I recall seeing when last checking spray patterns. It's abit like it's running full bore petrol flow.

To be clear it was running like a pig without AFM and was hard to keep it going but at least it fired.

Beamer wrote:. . . it looks like twice the volume I recall seeing when last checking spray patterns. It's abit like it's running full bore petrol flow.

If the injectors were over-fueling the cylinders, the spark plugs would likely be damp with fuel when inspected after starting attempts. If they are, fuel pressure testing is an option.

Thanks.

Good suggestion.

Alas it's not that simple. Just tested the fuel pressure valve on an air line and it seems to blow off at about 2.7-2.8 bar ( aka atmospheres ) .  It seems the figure should be 36psi according to the "trouble shooting guide", though I doubt that is the BMW unit of choice so it is probably a rounded off conversion itself, 36/14= 2.6 atm.   The FPV seems fine.

I just swapped in the AFM from the K75 which ran fine yesterday and it did not change anything on the K100. A quick "poof" as soon as I turn the motor, then nothing. There's a good strong battery giving the motor a good spin but not a sound in terms of combustion.

Now , I've just swapped injectors between the two bikes. As I suspected there is exhorbitant flow on problematic machine, irrespective of which set of injectors are in. K75 works fine with the injectors which were in the K100 and my recollection of squirt volume was correct.

So I'm down to why is there excessive fuel flow on the K100 before it fires up?

To recap , fuel pressure good; flowmeter confirmed by swapping; injectors not stuck, confirmed by swapping.


What remains which could explain excessive fuel flow?  :?

Beamer wrote:What remains which could explain excessive fuel flow?  :?

Is excessive fuel flow the problem or is inadequate spark the problem?

I have said it is visually confirmed to be an excessive fuel flow.

Test the temperature sensor to eliminate it as a problem, mine has played up twice due to a flakey connection. Another brick had a bad connection under the tank. I got my bike to run on the two times that it failed by pulling the fuel pump fuse # 6 and cranking it over to dry it out. Once it fired up on the fuel left in the combustion chamber as it started to die as the fuel ran out I rammed the fuse back in . It was running rough and the throttle had to be manipulated to keep it running.
Regards Martin.

Excess fuel flow:

Dodgy temperature sensor reading 'cold'.
Incorrect temperature sensor.
Dodgy MAF reading 'full power'.
Diaphragm failed on fuel pressure regulator [FPR] meaning its all at 60psi and not 36psi.
Dodgy vacuum pipe from cylinder no 4 to the FPR. This can split inside the protective spring, again causing fuel pressure to rise to 60psi.
Faulty fuel injection control unit.

All of the above would result in all 4 injectors overfuelling equally.

Note that a ruptured diaphragm apparently can also allow fuel to be sucked via the vacuum pipes into the intake side.

Beamer wrote:I have said it is visually confirmed to be an excessive fuel flow.

You said it was visually confirmed to be an excessive flow based on a recollection. That doesn't amount to much data from this distance. Measure how much fuel is deposited into a bucket in one minute by one of those suckers, or spray them all into empty drywall bucket, measure that then pour it into a vehicle that can actually burn it. A 22-year old F250 would be my choice as a receptacle.

Nevertheless, Martin and Olaf have rolled out most of the alternatives and the troubleshooting guide has testing data for both the ignition control unit and the fuel injection control unit, either or both of which could be involved, too.

Yep, better to verify that the fuel is excessive, rather than rely on just a visual inspection. 

I think a faulty pressure regulator diaphragm would be the least likely of the above options. It's the regulator which provides the pressure, so if the diaphragm is split, the pressure would drop, not rise. If it was blocked (or the return valve in the tank was blocked) then the pressure would rise.

Thanks for all the suggestions but please read what I've already tested and eliminated.

laitch wrote:You said it was visually confirmed to be an excessive flow based on a recollection.

I also subsequently said I had swapped injectors with a running bike and I got excessive flow on the K100 with both sets of injectors.

me wrote:K75 works fine with the injectors which were in the K100 and my recollection of squirt volume was correct.

ie I am no longer going from memory, I have visually compared to quirt volume on a running bike. It's probably a factor of 5 or 10, I do not need a scientific volume check to confirm it is excessive flow on the faulty bike and I do not need to pull out the plugs to see whether it is flooded.

There is some insistence on checking the temperature sensor ( thermistor ) in the air flow meter, however, I have swapped the entire AFM with a running bike and it did not change the problem. It is not a faulty thermistor. 

Olaf:
Dodgy temperature sensor reading 'cold'.  [no, swapped ]
Incorrect temperature sensor.     [no, swapped ]
Dodgy MAF reading 'full power'.  [no, swapped ]
Diaphragm failed on fuel pressure regulator [FPR] meaning its all at 60psi and not 36psi.  [no, tested]
Dodgy vacuum pipe from cylinder no 4 to the FPR. This can split inside the protective spring, again causing fuel pressure to rise to 60psi. [Incorrect, pressure valve blows off 2.7 bar when off the bike, it require a depression to increase the fuel pressure, not reduce it.]
Faulty fuel injection control unit.

Yes, I have not yet checked the LE-Jetronic unit itself I'll do that today. I have a spare unit. I suppose there is also the possibility of a wiring fault between AFM and in LE-Jetronic controller.

laitch wrote:Nevertheless, Martin and Olaf have rolled out most of the alternatives and the troubleshooting guide has testing data for both the ignition control unit and the fuel injection control unit, either or both of which could be involved, too.

I don't see how the ignition control could lead to excessive fuel flow, in any case the bike started and revved up nicely from the flooded state with the injectors removed, until the fuel ran out. That was the starting point for this thread. Clearly the ignition side is pretty good.

I'll check the electronic controller itself today, though these are pretty robust, I'll be surprised if that is the problem. I also need to unplug the throttle switch unit, maybe its full throttle switch is stuck.

Thanks for the ideas.

It's not the air temp sensor it is the coolant temp sensor that will make it run very rich if it is faulty. A high reading like 2000 ohms will cause the ecu to think the engine is cold and needs a rich mixture. At running temp a reading as low as 50ohms is around about correct. The air temp sensor makes very minor corrections for air density.

Thanks Rick,  I thought we were talking about the thermistor in the AFM.   Looking back I see the graph Martin posted was labelled with "water temperature sensor" but he did not say that in his comment and I thought he referring to AFM, so I did not spend time on the detail of the graph.  I said air temp sensor was only a small adjustment and he did not correct me. I should have looked closer at the graph.

I'll check the connection to the coolant sensor later,  though the fuel flow is massively off, it's at least 5x what it should be.

Where abouts is the sensor on the block?

On the coolant outlet just in front of #1 injector TB It tests each pin to eth as there are two sensors in one. the other sensor is used to activate the fan and over temp protection but a temp gauge (if there is one) uses a separate sensor on the coolant pump.
The sensor has a copper washer and we have found that cleaning the oxide of the washer helps as copper oxide acts like a diode and can upset things.

LOL, The connector on the water temp sensor was not fully engaged !   It does not seem to have the usual positive retaining clip and a light tension on the wires pulls it off.  That probably happened when I took the AFM off to test it 6mo ago .

I'll have to look at the retaining mechanism.

Well that was quite a run around but at least I got to check a few things over.

Thanks for all the help.  Now I'm off to getting running a bit better overall.

daveyson wrote:Another, less likely, possibility, since it runs with the AFM disconnected, but not when connected, there could be something wrong with the AFM.

I'd think about disconnecting it again, maybe a few times, to see if that is a consistent pattern.

I thought they could not run if the AFM is disconnected?

I thought they could not run if the AFM is disconnected?

I would probably have bet money on that too before having accidentally tried it.

Like I said, it was as rough as guts and sounded like it was only firing on one cylinder, but it did start and if I played with the throttle, I could keep it running.

The thing is, this was also with the temp sensor disconnected which was causing it flood. 

Apparently the parameter space is quite large !

Beamer wrote:LOL, The connector on the water temp sensor was not fully engaged !   It does not seem to have the usual positive retaining clip and a light tension on the wires pulls it off.  That probably happened when I took the AFM off to test it 6mo ago .

I'll have to look at the retaining mechanism.

Well that was quite a run around but at least I got to check a few things over.

Thanks for all the help.  Now I'm off to getting running a bit better overall.

So you have it running, sort of, now? 

It was indeed the water temperature sensor?

Yes, that was the main problem. It was just the connector which had pulled off. It is the same connector as on injectors which I usually curse to being too hard to get off. This one has no retention at all. I guess the lugs are damaged.

It is now running "sort of" which is where I was last time I looked at it.  At least I've checked out a few things while chasing this down.

Can I assume that you checked the air filter when you were looking at the MAF?

How old is the fuel?  You might disconnect the fuel line from the tank to the injector rail and work the start button to pump a liter of fuel into a clean bottle.  Let it settle and see if there is any water in the system.

Are the valve clearances in spec?  While it's unlikely they could be causing a problem, it wouldn't hurt to check them as long as you have checked a lot of other things.

Last, how old are the spark plugs?  if NGK, do they have the terminal nuts?  Do you have the old style ignition coils(all black) or the newer type with the orange towers? You don't mention the vintage of your bike; early models had ignition coil issues that were corrected with an improved design around 1986.  Those older coils have caused a number of problems that were reported on this and other forums.

Is it possible that the wires for cylinders #3 and #4 are crossed?  It's easy to do because #4 is longer than #3.  That would make the engine run very poorly.  I know this because someone(I would never do anything dumb like that!) crossed them on my K100 when I was doing annual maintenance a few years back.

Because you seem to be getting enough fuel to start the engine and have it idle, I am beginning to suspect an intermittent spark problem, possible due to a weak coil or bad plug wires.  An often overlooked fact is that as the compression increases the voltage needed to create a spark also increases. 

At idle speed with the throttle closed, the engine doesn't demand much from the ignition system, but as the throttle is opened and more air comes into the cylinders, the pressure in the cylinders increases and more voltage is required to get a spark.  A weak or cracked coil or a bad plug wire may work at low speed, but will fail when the throttle is opened due to insulation failure allowing the current to leak to the metal of the frame or engine.

thanks for the list. Most of that was no relevant to this bike but I had bought some 2nd hand coils last time I was on this. ( Black ones , the bike is 1985 IIRC ) 

I swapped the coils and it's running a lot better. I'll take it out for a blast to get the cobwebs out of the AFM and do some low end tune ups like AFM bypass screw.  I think it's nearly a usable bike now.