No power to #4 fuel injector!

[warredon]

This is for a 1991 K1. I thought for sure I had a clogged fuel injector because I had recently replaced all of my hoses, fuel filter, and several other things under the tank. I found that #4 still would not spray after cleaning the injectors and replacing the O rings. I hooked an analog meter to the #4 connector and found no signal at all, but checked the signal on #3 and it reads fine.

Does anyone have any ideas of some sort of probable cause? I have no idea which pins on the Motronic go to #4 or even if they do. Is there a diagram somewhere that shows where each one of the Motronic pins go? Is it possible for the Motronic itself to go bad on just one cylinder? Thanks!

[RICHO2006]

Hello

I have an '85 K 100 and I am under the impression that all the injectors fire at the same time. If that is the case with your bike then the problem could be where the wire from #4 joins the harness.


Richo

[warredon]

Hello

I have an '85 K 100 and I am under the impression that all the injectors fire at the same time. If that is the case with your bike then the problem could be where the wire from #4 joins the harness.


Richo

Yep, I just found a wiring diagram and that is what it shows. I don't know why I didn't realize that to start with. That is something that I should have known. I'm looking into it now. Thanks!!

[BuddingGeezer]

The 85 K100 used the Bosch L Jetronic fuel injection system. The L Jetronic pulses all 4 injectors at the same time twice per engine cycle.

Bmw uses similar systems on their motorcycles and cars. Early Bosch Motronic systems such as the 4.1 and 1.5 pulsed all injectors at the same time. The later 2.5 pulses the injectors sequentially once per engine cycle.

I can't answer your question, I'm sure someone can and will. My point is don't assume that your Motronic operates the injectors like the L Jetronic.

Ralph Sims

[warredon]

Thanks Rico and Ralph! I found a broken wire under the rubber boot at the connector where it connects to the injector. I probably did it myself when I was working in that area replacing fuel hoses and throttle body mounts etc. It wouldn't be the first thing that I've screwed up while trying to fix something else. It was easily fixed but it had me puzzled for a while. I think I'll go for a ride tomorrow, they're predicting 72º. Thanks again!

[mrich12000]

Have a nice ride .It's getting better up here as well.:thumb

[moondog]

Call me a dummy and send me back to school but how can the Motronics pulse all injectors at the same time? Wouldn't a cylinder be on an exhaust or compression stroke? What am I missing?

[BuddingGeezer]

Call me a dummy and send me back to school but how can the Motronics pulse all injectors at the same time? Wouldn't a cylinder be on an exhaust or compression stroke? What am I missing?

I don't know if the Motronics on the K1100 pulses all injectors at the same time. The Bosch L Jetronic on the K75s and K100 2Vs does.

I don't think you missed anything. That may be why they flood the plugs easily. It also maybe why a K1200GT with 130 HP gets as good or better gas mileage as a K100 with 90HP. It is a waste of fuel. It also may be why I have never seen a picture of a 2V K bike with blued headers.

Also with 4 plugs and 2 coils, each plug wastes a spark twice in the engine cycle.

Ralph Sims

[roy]

Even though the injectors are firing, the fuel won't get into the cylinder unless the intake valve is open. So yes this could contribute to flooding issue but unless the fuel settles out of the air mix it should all burn. Probably not nearly as efficient as the injector firing only while the intake valve is open and air is flowing into the cylinder.

Every twin or four cylinder bike I have owned has always had at least two cylinders firing from each coil.

Roy

[moondog]

Well DUH:scratch ......talk about forgetting my basic knowledge of engines. Well that does seem to be a waste of fuel. But I suppose it could contribute a little cooling. Weird. Learn something new every day:thumb

[cjack]

I don't know if the Motronics on the K1100 pulses all injectors at the same time. The Bosch L Jetronic on the K75s and K100 2Vs does.

I don't think you missed anything. That may be why they flood the plugs easily. It also maybe why a K1200GT with 130 HP gets as good or better gas mileage as a K100 with 90HP. It is a waste of fuel. It also may be why I have never seen a picture of a 2V K bike with blued headers.

Also with 4 plugs and 2 coils, each plug wastes a spark twice in the engine cycle.

Ralph Sims

As far as I know all the injectors fire at the same time on all the BMWs thru about 2004. The wiring diagrams for the 1200 bikes and the latest F models, all the injectors are wired separately...which would allow them to be timed separately. That would allow more precise fuel charge to meet emissions and perhaps to maximize HP.
When they are timed together, the fuel charge is smaller for each injection appropriately so that the full charge is the addition of them. I don't think there is any fuel wasted.