I'll restart this thread here because I'm chasing info on why it doesnt go..

I have a 1994 K1100LT sidecar. I got it as a non-runner. Yesterday I drove down and picked it up, a 1100km round trip. Pissed down with rain all the way down and all the way back but thats by the way.

The previous owned said it got progressively harder to start over a couple of months, then wouldnt go at all. He tells me he replaced the fuel pump and filter and some hoses, then gave up. Old pump, filter and other bits are in the top box so I believe him.

About all I noted this morning is that the fuel pump isnt running and is obviously the reason it doesnt go. Now I'm looking for reasons the fuel pump doesnt work. I expect there are some cutouts to check - neutral, clutch, sidestand etc. Tank connector. Fuses. Any other suggestions?

Does the pump run for 1.5 seconds when the key is turned on. If it does then the problem isn't the pump if not the problem is the pump or connections.
I have come across a hall sensor plate that was flooded with oil that caused a problem that was much the same.

RicK G wrote:Does the pump run for 1.5 seconds when the key is turned on. If it does then the problem isn't the pump if not the problem is the pump or connections.
I have come across a hall sensor plate that was flooded with oil that caused a problem that was much the same.

No the pump doesnt run at all so its likely connections. The starter motor turns over ok and all the rest of the electrics work.

Start with the connector of the tank/fuelpump. That's the easy one.
Try to clean the contacts, and bend the females a bit inside.

Next is the fuelpump relay, in the relaybox, swap it with the horn relay.

Side stand is high on the list. Been there. Just to clarify although you need either neutral light on [neutral on itself is not enough, must have the light on] or clutch in to start, you also need the side stand. Also, side stand cut out stops the pump priming so if pump is not priming, start there.

Fuel pump relay can go faulty too, I think the horn relay can be changed over.

Fuses can look good but can also still be faulty so a change of fuses is a good idea.

I have been victim of diy pump jobs by 2 previous keepers on my last 2 Ks that I bought. The reinstall not done correctly and the pick up not placed correctly meaning its not actually getting fuel despite the tank being half full- fuel starvation.

A little more progress of the one step forward two back variety. I located the tank connector. There are 4 wires, green, brown and a couple of others (Fuel & Temp gauges). I worked out that the green and brown run the pump. With the ignition on. the bike side (male) of the connector gives me 12v on the green and white and about 7.5 on the other, zero on the brown. Brown is earthed. So, I rigged up a positive connection to the green and an earth to the brown on the tank side (female) with the connector disconnected. The pump went for about the required 15 sec then stopped. I tried cranking it but the bike didnt go.

Now for the odd bit - I bared the green wires either side of the connector to check the voltage. With the connector disconnected I get ~12v on the male side. With the connector connected this drops to 0.25v and is the same on the tank side. This seems a bit strange to me. Should this happen??

Hi Phil, do you have the K1100LT wiring diagrams? If not I still have my manuals with the K1100 diagrams and can copy and forward to you.

What year is your bike?

Cheers

Gaz wrote:Hi Phil, do you have the K1100LT wiring diagrams? If not I still have my manuals with the K1100 diagrams and can copy and forward to you.

What year is your bike?

Cheers

Hi Gaz - I have a manual on a stick that came with the bike. I assume it has wiring diagrams but havent checked, so thanks but I think I'll be right. The bike is a 1994 ex the UK (Imported as a sidecar outfit)

Rockman wrote:A little more progress of the one step forward two back variety. I located the tank connector. There are 4 wires, green, brown and a couple of others (Fuel & Temp gauges). I worked out that the green and brown run the pump. With the ignition on. the bike side (male) of the connector gives me 12v on the green and white and about 7.5 on the other, zero on the brown. Brown is earthed. So, I rigged up a positive connection to the green and an earth to the brown on the tank side (female) with the connector disconnected. The pump went for about the required 15 sec then stopped. I tried cranking it but the bike didnt go.

Now for the odd bit - I bared the green wires either side of the connector to check the voltage. With the connector disconnected I get ~12v on the male side. With the connector connected this drops to 0.25v and is the same on the tank side. This seems a bit strange to me. Should this happen??

dropping voltage whilst under load , ?

i would go back to the fuel pump relay and measure there  as you are getting the voltage drop either side of the connector 

or just put in a new relay and measure again

dont forget the corroded fuse holders issue , may just need a little cleaning and a new fuse in there  (one with clean blades etc )

A voltage drop like that is classic of a bad connector, possibly a broken wire, bad relay contacts.

RicK G wrote:A voltage drop like that is classic of a bad connector, possibly a broken wire, bad relay contacts.

It'll be the weekend before I can get back to it. I'll need to remove some of the tupperware to get into it properly.

Edit - I found 1/2 hr and swapped the pump and horn relays. The pump now runs for the required ~15 sec but with a horrible graunching noise, and the bike doesnt run of course. It could just be vibration against the side of the tank, but I think I should pull everything out of the tank and check whats going on. I'll also pull an injector or 2 to see if they are working, and check if there is spark.

yeah, new pump by the sound of it 

an injector clean would also be a good move , after changing the hoses 

good luck

Yesterday I pulled one of the plugs out - no spark, so there is another issue to investigate. I also noticed that the plug was dead dry, so probably the injectors arent going either. Both could be related.

Hall sensors would be a good place to start looking. They control the spark and injection timing.

RicK G wrote:Hall sensors would be a good place to start looking. They control the spark and injection timing.

G'day Rick, how do I go about testing the sensors?

Incidentally, I did pull the cover off on your suggestion that the housing might be full of oil, but it was dry.

RicK G wrote:https://www.kforum-tech.com/electrical/Hall_sensors/Hall_sensors.htm

Thanks.

I'm waiting for a HE sensor plate to show up - I have 2 coming, so one at least should be here in a few days if I am lucky.

The new HE sensor didnt fix the problem so it was back to the beginning.

I progressively disconnected every connection I could find, cleaned it with Deoxit then reconnected. Then suddenly I had spark. So I put the tank back on and it started instantly and ran like it had never stopped. No smoke, smooth idle, all the good K1100 things.

The only problem I've now got is that when I put on the rear brake the engine stops. The brake light still works. I'm guessing there is another connection behind the RHS footpeg plate that is being pulled by the brake pedal or something.

Check that the wire from the brake lever to the bulb monitor unit (grey/green) is loose, and hasn't been pinched when the footpeg plate was mounted, which could result in a dead short when you apply the foot brake. Or it could be the switch. Or check the green/black wire too.

I found it - a wire had been blanked off with tape and was dangling free. It was being jammed by the foot pedal. Easy fix.


I did a short run up the back lane (about 300m) and it cut out when revved a bit, but could be restarted and would idle ok. Symptoms look like either a blocked fuel filter or bad pump to me. I disconnected the fuel line to the injector rail and run the pump. About 30 secs to fill a baked bean can doesnt seem nearly enough. I'll investigate the filter first, then the pump.

I seem to recall that fuel pump flow is rated at something like 33 liters/hour or about a half liter/minute.  Depending on the size of your bean can the test seems to sound like your pump is okay.  Still, I would check/replace the filter and the hose connections in the tank.

My OEM pump does 2.16 Lt/min Chinese copy does 3.9 Lt/min.
Regards Martin.

Well mine would be doing about a litre a minute at best. I have a new filter and a spare pump so when I get a chance I'll get to it.

The fuel pump spec in the BMW service manual says the pump flow is 45 liters/hour.  I guess my memory isn't what I thought it was.

so 750 ml/minute, although Martin's number says 2160 ml/minute. I'll change the filter first, then measure mine accurately.

When you look in the tank with the fuel pump running, it's pretty easy to see that the excess flow returning from the rail to the tank is nowhere near 2 liters/minute with the OEM pump.

There was a recent thread about an overfueling problem that measured two litres a minute, I thought there's no way my brick dribbles that much so I measured it. Turned out to be two litres a minute. Remember this is the excess fuel we're measuring so you have enough volume. But we don't know if the pressure is high enough, that maybe wants to be measured, if the replaced parts don't fix it.

Like Point seven five says, you want point seven five a minute, so that seems to be OK.

If you slowly squeeze, but not fully, the return hose near the tank, and that improves the situation, that could point to low fuel pressure. With something soft or blunt of course, maybe like say circlip pliers.

I changed both the fuel pump and filter. One thing I did notice is that the new filter is much easier to blow through than the old one, although the old one was wet and the new dry which might partially explain it. Pumps fuel, but maybe less than the other pump.

Anyway, that may not be the problem - I have lost spark again. I tried a different HES in the hope that was the problem, but no difference. Now I am a bit flummoxed as to what is going on. The only thing I can add is that as soon as I got spark previously it ran well.

I remade/checked most of the connections without effect.

I checked the wires that were being shorted by the brake pedal. Incidentally these are Brown-Blue & Brown on the bike side of a connector and Green-Red and Green-Yellow on the other side. The GrRd and GrY are joined. Not sure what these do except that the starter wont run with them disconnected. Located near the fuel pump connection on the RHS at the back of the tank.

Could it be my Motronics unit is stuffed. There doesnt appear to be any way of testing these other than replacement. Anyone got a spare I could borrow?

I think the side stand switch is fed by a brown and brown/blue wire. The wires might be pulled apart from over stretching.

Maybe the side stand switch was bypassed by joining the two wires together, cause you got a sidecar.

daveyson wrote:I think the side stand switch is fed by a brown and brown/blue wire. The wires might be pulled apart from over stretching.

Maybe the side stand switch was bypassed by joining the two wires together, cause you got a sidecar.

Most likely that is the case. I'll leave them joined. Cheers, Phil

Maybe unwrap it to see that they are still joined well, maybe even solder it, that might be the cause of your problem.

daveyson wrote:Maybe unwrap it to see that they are still joined well, maybe even solder it, that might be the cause of your problem.

They are already soldered, but there is a fair excess of wiring so I'll cut it back to the minimum and resolder. Be neater anyway.

Or even the wire itself might be damaged when it was getting squished.

What year model is it Phil I have an ECU for both year models.
The green /Yellow red/yellow is for the sidestand and a brown /blue is the engine air temp sensor with a blue/brown is the fuel pump relay eth to the motronic.

This talk of side stand switch and loss of spark has me wondering; does the side stand switch inhibit the spark on the K11 like it does on my 16valve K100RS?

daveyson wrote:Or even the wire itself might be damaged when it was getting squished.

This might be the case. I cut and rejoined the wires this morning and now I have spark. When I get time I'll put everything back and see if it goes. Hopeful.

The weirdness continues. With the sidestand(?) wires joined I have spark and the starter motor works, but the fuel pump doesnt. Disconnect the wires and the fuel pump goes but the starter motor doesnt.

Another thing - possibly related. I understood that the fuel pump and horn relays were different from the others, but all mine are the same - like this.  With the ignition turned on what should I get at each of the terminals for the fuel pump?

Like mentioned, I think you say your brick is a '94 model, but the side stand wire colours hints it might be a '93 model. Is it a '93 model? It's almost as if you're using a changeover relay in the wrong place.

daveyson wrote:Like mentioned, I think you say your brick is a '94 model, but the side stand wire colours hints it might be a '93 model. Is it a '93 model?

94 is correct. The sidestand wiring is in fact brown/blue and brown as per the screen shot below (down the bottom). Connects through to the motronic relay. The wiring diagram snip is the engine one for a 94 K1100LT.

I am inclined to leave these wires connected as that is what it appears they should be, and concentrate on why the fuel pump doesnt go. I suspect the previous owner has swapped relays in and out without realising that there are two different types.

I don't see a green/red wire on the drawings, I'll spose it's red/green.

The red/green and green/yellow wires are joined, I'm thinking they shouldn't be. Those colours are at the fuel pump relay.

Probably a photo of the connection you mentioned would help, but I'm not familiar with k1100s

Here's the wiring of the 1993; https://mega.nz/file/zvQnjaCa#Zqx8CTGUb9cAUqIGYx51s4tIjTV_qEH2j9-DMUL9pTE

This is the 1994; https://mega.nz/file/GjYFHYxZ#CIekMEnDXaSxJ6anv-wvJY0lq_lF_DPKkF3CGBHBnMY

PDF to download

The green/red and green/yellow are irrelevant as they plug into the brown/blue and brown of the sidestand switch wiring and originally would have had the actual sidestand switch on the end of them. Disconnect these and the starter doesnt work for one.

What I am getting is intermittent ignition spark, intermittent fuel pump and intermittent injectors. The thing linking all of these is the motronics unit so that is my next thing to check.

The starter won't go with the side stand wires disconnected. That would make the computer think that the side stand is down. That might be normal that the computer won't allow the starter to turn while the side stand is down, as a safety feature.

Do the green striped wires disappear into the wiring loom, or can you follow them to where the side stand was disconnected? Edit: If they're into the loom, maybe they are relevant.

Edit: I see we've had our wires crossed on occasion due to the different colour codes between the coloured diagrams and the Clymer ones that I was using.

daveyson wrote:The starter won't go with the side stand wires disconnected. That would make the computer think that the side stand is down. That might be normal that the computer won't allow the starter to turn while the side stand is down, as a safety feature.

Do the green striped wires disappear into the wiring loom, or can you follow them to where the side stand was disconnected?

Yes that is what I thought, hence they need to be connected. The green striped wired were just a dangling loose one end and connected to the br/b and b wires of the sidestand circuit thorough the right sized connector and were originally joined when I got the bike. This connects to the motronics relay and from there back to the starter relay, and motronics.

Rick has spare ECU's so I'll try to borrow one and see what diffence that makes. Its the later one btw.

Today I was moving the ECU around (not secured in place) and tried the starter - and it ran, for a while. When I moved the ECU a little it stopped, so I moved it back where it was and it went again, for a few minutes. I gave it a rev and it stopped and wouldnt restart.

This has me wondering if I have a damaged or pinched wire in the ECU plug or further back. I'm reluctant to slit the wiring and plug open but it might be the only way. The actual connectors in the plug look ok. Any comments?

Keep playing around with it. I'm a bit susso of the motronic relay. You might feel or hear it cut out at the same time as the failure, or wiggle the green/black wire from the relay to the motronic. Or keep hunting for the cause.

Dismantling the connector is easy enough - just make sure you don't miss the screw on the 'nose'.

Dai wrote:Dismantling the connector is easy enough - just make sure you don't miss the screw on the 'nose'.

Ah, it comes apart. Good to know.

All up and running again. All I need to do now is tidy up the sidecar wiring and give it an oil & filter change and its ready for a rego inspection.

Here's what I found;

The intermittent starting and stopping problem was an earth lead that had been left off the battery by the PO. It would earth out on the frame from time to time and the bike would go until it was moved.  It wasnt easy to spot as it was hidden under a sidecar mount. Connect this to the battery and it would start and run well FOR A WHILE, then it would stop, but would restart when it had cooled down. Classic HE sensor failure. Luckily I had a new sensor on order from Motobins and even better it showed up today. Fitted it and all is well in the universe.

So now I have 2 u/s HE sensor plates. I'll put new sensors on these and put them away as spares.

Many thanks to all who contributed to the fault finding.