R1150RT 2nd Load Relay for Twin Spark

[roger 04 rt]

The early twin-spark R1150RTs connect all three ignition coils (2 stick coils for the primary plugs and one conventional coil for both secondary plugs) to the battery, directly through the contacts of the key switch. Later R1150RTs added a "2nd Load Relay", which connects the stick coils directly to the battery through a relay. Why did they do this?

 

From reports, the measured resistance of the secondary coil is less than 2 ohms. My measurement of the stick coils shows a primary resistance of less than 1 ohm. That means that the saturation current (maximum current flow) through each stick coil is 12 amps (24 amps total) and for the lower-plug coil is 6 amps--those current levels are only achieved momentarily, for a few thousandths of a second. At saturation current, the total momentary current is 30 amps. The parallel resistance of all three coils is about 0.4 ohms.

 

I measured the contact resistance of the key switch on my twin-spark at about 200 milli-ohms, or 0.2 ohms. Do the electrical engineering math on this and knowing that it takes time for an inductive coil to charge and reach saturation current, if the battery voltage was 12V and when all three coils reach saturation, the voltage at the top of the coils will be 8V and it will be 8 volts for anything connected to the key.

 

What is connected to the key circuit:

 

--two stick coils

--the lower plug coil

--Fuse 1

--Load Relief, Fuel pump, & Motronic Relay control coils

--Kill Switch

--Tachometer

--other relays and indicators

 

Looking at the list there isn't anything that is going to be too seriously upset by the voltage spikes. But during the initial moment of cranking, when the coils are momentarily left on for maximum dwell and the starter has dropped the battery voltage to 9-10 volts, the voltage dips, at the key switch could reach 6 volts. Far from ideal.

 

When some engineer at BMW realized that adding the stick coils had increased the current 5X through the key switch, and that some starting and running problems could be traced to it, they decided to reengineer the wiring harness and add a "2nd Load Relay" and then route the stick coils through that relay, directly to the battery. I don't know why they didn't also route the lower plug coil at the same time.

 

My plan is to build a wiring harness and relay (done), switched by the key, that connects all three ignition coil directly to the battery. The next step is to find connection point X9450 where the 5 green wires for the above list of connects come together.

[roger 04 rt]

If anyone knows where all the green wires come together it would be a big help.

 

[legarem]

Hi Roger

 

My 2003 is a twin spark and I never had any problem when I start my bike. It always start ultra easily even at spring after a long winter.

 

p.s My bike is still pinging at 13.8 AFR but less than 13.5 AFR.

[roger 04 rt]

Sorry to hear you've still got the pinging. I get none at any AFR.

[roger 04 rt]

The key to this project was finding the place where the green wire from the Key (which is switched +12V) connects to the three ignition coils and the other 8 wires that are powered when the key is switched on. Thanks to MFOL the photo below which helped me find the "connector point" and Dirtrider for several workmanship tips.

 

Looking at the photo below there are two groups of connection points. One group is exposed in the photo and you can see the bundle of green wires. The other is in a black tape stub in the photo, circled in red.

 

The project to add the 2nd Load relay has a few parts, none complicate, total cost for the relay and wire about $15:

 

--find the bundle of green wires, remove the three wires for the ignition coils (find them by using an ohmmeter after the green wire connection is opened). And group those three wires into a new bundle. Then connect the control coil from a new relay (from euromotoelectric $6) to the original bundle of now 9 green wires. The original bundle is switched +12V.

 

--ground the other side of the relay control coil to battery negative

 

--connect one relay switch contact to the battery +12V

 

--connect the other switch contact to the new group of three green wires going to the ignition coils.

 

--take all the new wires, bundle them up and zip tie them along the left side of the frame, adjacent to the main wiring harness.

 

--the new relay was located on top of the airbox next to the battery.

 

One of the hard parts of the job after you've found the green wire connection point is removing the copper barrel that is compressed around them to create the connection. It's tough and hard to remove. I ended up filing one side off.

 

Status

The relay and new wire harness has been built and laid in place, waiting for me to connect it to the two groups of green wires, then tape everything over and tie wrapping the new harness to the old. Should be another hour tomorrow morning

 

I'm working patiently because this involves the 12 primary switched power wires for the motorcycle. More tomorrow.

 

[roger 04 rt]

It wouldn't be like BMW to add a relay part way through a model run, in this case after shipping a bunch of twin-spark R1150s. But they did, so there must have been a problem without it--but that's getting ahead of the story.

 

The install of the 2nd Load relay was completed late yesterday and took about 2 hours. To recap I disconnected all 3 ignition coils from the key-switched, green wire where they got their +12V, and connected all of them to a key-switched 40A relay, which in turn is connected directly to the battery. This creates a much lower resistance connection, which allows all three coils to charge more fully.

 

Since there were 12 Green wires at the original X9450 connection point, I did a lot of checking to make sure they were all reconnected properly in the new design.

 

Then I charged the battery, reset the Motronic and started it up. The first start after a reset can be sluggish but that was not the case. It fired right up and seemed to be idling smoother, which I ignored initially, believing that I had a case of "confirmation bias" (getting the effect I was looking for).

 

This morning I buttoned everything up (noticing a crack in the right side plastic that I've got to fix now, darn) and started the bike for the second time. This time for sure I can say it started easier and idled more smoothly, from the moment after it caught.

 

Went out for a test ride, and after getting a couple bars on the RID I pulled over and dropped the Fast Idle Lever to the off position. Normally if I do this before 4 bars, the idle is a touch rough and slightly low. Not so today. At two bars on the RID it idled as least as well as fully warmed up before. Once the RID was up to 6 bars the idle speed was 50-100 RPM higher than the last time I rode.

 

Over the course of the next hour-plus I rode a wide range of speeds and loads. Wide-throttle high-RPM acceleration is more responsive as is low-RPM torque. Riding in 6th gear at 45 mph and up was good, noticeably better than usual even taking into account the richer mixture on my bike.

 

When I pulled into the garage after the hour, the smoothness of idle was, no doubt about it, the best it's ever been. Overall, pulling all three coils off the key and onto their own relay has made a noticeable difference. Tomorrow I plan to log a cold start and ride to see if there is a measurable difference with the GS-911.

 

To my initial question, "Why did BMW add this relay?", it seems to me that with three ignition coils on the key switch, the coils were being undercharged before they were fired. And the improvement now is most noticeable at start, idle and high engine load.

[Twinsig]

Nice work!

 

 

[roger 04 rt]

For anyone interested in trying this modification, below is a rough schematic which may be clearer than the written description. The added wiring and relay are highlighted in yellow.

 

All of the original wires going into connection point X9450 are Green.

 

[JamesW]

Good morning Roger and nice work indeed. My '04 R1150RT has the 2nd load relief relay (bad nomenclature) but the secondary plug coil apparently still sees 12V through the ignition switch. I can't help but wonder if your new coil power system might result in cleaner secondary plug operation? Even after going two heat ranges hotter on the secondary plugs the plugs still are nowhere near as clean as the primary plugs.

[mneblett]

Good morning Roger and nice work indeed. My '04 R1150RT has the 2nd load relief relay (bad nomenclature) but the secondary plug coil apparently still sees 12V through the ignition switch. I can't help but wonder if your new coil power system might result in cleaner secondary plug operation? Even after going two heat ranges hotter on the secondary plugs the plugs still are nowhere near as clean as the primary plugs.

I haven't looked on my '04 yet -- where would I find the 2nd load relief relay if my bike has it?

[roger 04 rt]

I haven't looked on my '04 yet -- where would I find the 2nd load relief relay if my bike has it?

I believe it is to the left of the Coding Plug in that row.

[JamesW]

Would be pretty easy to wire the secondary coil directly to the factory installed 2nd load relief relay but I wonder if the factory relay would carry the load of all 3 coils? I like to think there was some good reason why the secondary coil wasn't included in the factory mod.

[dirtrider]

Afternoon Mark

 

[roger 04 rt]

This morning's start was the same as yesterday. Quick and steady from the first seconds. One bar on the RID and it idles w/o any fast idle lever.

 

 

Would be pretty easy to wire the secondary coil directly to the factory installed 2nd load relief relay but I wonder if the factory relay would carry the load of all 3 coils? I like to think there was some good reason why the secondary coil wasn't included in the factory mod.

 

Jim, Good question. I'm not sure there was a good reason. Got this question too.

 

Nice, thoughtful approach and neat solution.

 

Question: Were you having a problem which led you to this project?

 

Suggestion: Now that all coils are powered through the same relay, a failure of that relay will kill the bike. The factory arrangement is more fault tolerant and (I'm guessing) that is the reason it is the way it is.

 

Thanks.

 

I didn't have a serious problem recently. However, because I have hundreds of data logs from my bike and others that've been accumulated over the last 4 years while I experimented with lambda-shifting (LC-1 & AF-XIED). Because of that I see small changes in performance (e.g. how many seconds to start, AFR post start). A month ago I noticed some post-cold-start AFR shift that was fixed by new lower plugs. A couple years ago, I found that chronic undercharging of my PC 680 battery with a Battery Tender JR. led to very hard starting, first cold start of the day.

 

So I didn't have a problem but had this background of issues plus the knowledge that BMW made this change silently in the middle of the model run. And I couldn't shake the belief that it was an important improvement. When my starter needed a new $4 part and I had to spend $20 minimum to get it I had my motivation.

 

I didn't think of the redundancy issue of splitting the coils between key are relay but I do carry spares and jumper wires with me. It's hard to know if BMW wanted to add redundancy or if they reasoned that the common coil was proven on all prior Oilheads so no need to bother changing it. I don't care for the idea of several amp current pulses flowing through the key switch, leading to voltage spikes on the switched side. My key switch has 200 milli-ohms of resistance, I'm curious what a new switch is like.

[JamesW]

Hi again Roger, Before I make a mistake..if I read my schematic correctly it looks like the 2nd load relief relay was an add on in that the coils are still connected to +12V through the ignition switch and the relay contacts simply add another 12 volt path directly to or from the battery. So, if this circuit provided by the relay is in addition to the non-relay wiring then the secondary plug coil is also effectively connected to the battery through the 2nd relay. In other words there may not be any benefit to connecting the secondary plug coil directly to the 2nd load relief relay contacts as it already is in effect connected. Hope this makes sense.

[dirtrider]

Hi again Roger, Before I make a mistake..if I read my schematic correctly it looks like the 2nd load relief relay was an add on in that the coils are still connected to +12V through the ignition switch and the relay contacts simply add another 12 volt path directly to or from the battery. So, if this circuit provided by the relay is in addition to the non-relay wiring then the secondary plug coil is also effectively connected to the battery through the 2nd relay. In other words there may not be any benefit to connecting the secondary plug coil directly to the 2nd load relief relay contacts as it already is in effect connected. Hope this makes sense.

 

Afternoon James

 

If you are looking at the official BMW wire schematic then the ign circuit into the 2nd load relief relay is separate than the 12v B+ (red wire) into the 2nd load relief relay.

 

The ign circuit ONLY triggers the relay, no operational power is drawn from that circuit.

 

The stock under-tank-coil is powered ONLY from the ign circuit (green wire).

 

If you look closely you will see that on the 2nd load relay bikes the ign circuit (green wire) goes to only the 2nd load relay pull-in coil & to the under tank coil .

 

[roger 04 rt]

+1 to DR's answer.

[mneblett]

Afternoon Mark

 

Thanks, D.R. -- your catalog of photos is amazing.

[mneblett]

I just checked, and realized I didn't mention I have an RT-P. There are two relays in that portion of the box:

 

 

I'll check the next time the bike is apart, but I'd wager that one of them is the 2nd load relief relay.

[dirtrider]

Afternoon Mark

 

Look inside the cover of the fuse box, there might be a fuse/relay map inside the cover.

 

I have something on those RT-P relays somewhere but not sure where I have that info as it is in the old paper format.

[JamesW]

Hi D.R., I am most likely not looking at an official (BMW) circuit diagram. I don't remember where I got the diagram but it's one I downloaded maybe 4 years ago. Have regretted not buying the factory manual in '04.

[Boomer343]

Decided to do this mod while I have everything apart putting in my cruise control. I'm going to power the cruise control through this circuit as well.

 

Wanted to mention that in the green wire bundle there are two different wire gauges and you only need to test the larger gauge wires to find the ones for the coils.

[Boomer343]

Thought I better update on the wire bundle... there are three gauges of wire but only the largest need to be checked.

 

Also as a tip ... since a large crimp is needed I used a piece of copper tubing left over from plumbing a water line to our fridge.

If you use a small zip tie to hold the wire bundle it makes it easier to handle. I just cut the original crimp off rather than mess with it.

 

I used this product to wrap the bundle back up

http://www.amazon.com/Gardner-HTP-1010-Purpose-Silicone-Self-sealing/dp/B00004WLKT

[roger 04 rt]

Boomer, Thanks for the tips. How hard is it to remove that silicone tape you recommended?

[Boomer343]

Roger I have used a blade to remove it carefully but it does like to stick especially to itself. Lasts a lot longer than the usual tape wrap. I'll be checking this am to see how well it has adhered to the existing wrap.

 

I used a couple of zip ties to keep the whole bundle together for wrapping and then used the tape in 4 to 6 inch pieces. I also used the tape to make a sheath for the cruise control wires coming off the touch pad.

[Boomer343]

Just an update. I finally got the old girl fired up tonight and found that it is a good idea to put a fuse into the fuse holder for the new hot wire to the relay for this circuit to work. That was the one deviation from Roger's diagram that I did. Having seen the aftermath of car stereo systems wired in with no fuses I like to have them in place.

 

So .... was it worth the effort..... absolutely. There is no doubt my bike started quicker and went into a smooth idle. I am also using the axfied and have put new coils and spark plugs in previously. No other tune up procedures have been done by me.

 

Compared to when I purchased the bike, it had the original coils still working and new standard plugs, the addition of the axfied and now this mod has made a world of difference. The new iridium plugs and new coils made a very small change, nothing like this.