Cheap gauge with BEP3.0 only shows between 1-2k RPM? K1100 (SOLVED)

[Kevin1100]

Hello,

I've been riding for a few months now and am very happy with how my aftermarket gauge works (I'll try to attach photos) except for the tacho. It doesn't NOT work at all, because at idle it will show around 900 rpm when hot and when I pull the choke it will go up to 2k rpm. However when riding it never goes above 2k and it rises very slowly from 1k to 2k when revving/accelerating. I have seen videos of guys who have the same gauge and also with the BEP3.0 unit I have where the tacho does work, but they don't mention how they got it to work. That's on a k100 too by the way, not sure if the tacho signal is different to a k1100. I have verified that the tacho signal itself is not faulty by installing the OEM gauge, and with that the tacho does work as it should. Any ideas?

[Laitch]

Brick tachometer signals need help for translation into many aftermarket instruments. Your tachometer is one of them. The K1100 has the same tachometer setup as the rest of the lineup. Many owners have been successful getting them to operate. This thread from the K-100 forum explains what often is needed.

[Laitch]

Here's additional testimony, Kevin. Skunky seems adept at adaptation when it comes to customizing, and rbm has been educated in the ways of electrons.

[Kevin1100]

Hey Laitch thanks for that. I've tried adding the capacitor and resistor + ground but couldn't get it to work earlier. The tach would not read any RPMs at all anymore. Figured maybe I had wrong parts. However I have now tried fiddling with the ground a bit (touching the bare wire end to other grounds) and the RPMs would dance around. The ground connection I used is good so either I have a bad solder from the RPM signal wire to the resistor which goes to ground or I do actually have bad parts. Whenever touching a battery ground the RPMs would dance around for around 3 seconds and then die off again, sometimes jumping back up a bit after a while but never stable. It seems like it still might be a case of bad parts though since the RPMs are not stable even with stable ground. Just to be sure I'm going to re-solder a ground wire with a new resistor in to make sure everything I did is at least correct.

[Kevin1100]

Jeez okay got some very erratic readings at first, RPM jumping around between 1-4k and then going dead etc. so my first thought was I messed up the connections somehow. Took it all apart, solders looked really nice but I thought what the hell, and redid it all. Again, solders looked nice and I verified a bit more with my multimeter but again, same result, no dice. I took the ground connection with resistor off to see if it worked with just the capacitor. 0 RPM. Then I took the capacitor out to see if the RPM signal wire actually still worked. It did, same as before: between 1-2k rpm at all times (even WOT). Okay, I added the resistor and ground back in without the capacitor to see if that worked. 0 RPM. So that fix did not work for me sadly. Good news is my solders are increasingly getting better so that's nice.

Then it struck me like lightning. These gauges have a setting for amount of cylinders, either 2 or 4. I thought I remembered having tried setting it to 2 cylinders before but then suddenly I remembered that I didn't do that because I thought it would mess with my speed signal, which is dead accurate so I didn't want to do that. I have now set the cylinder amount to 2 and when revving it a bit the gauge does seem to respond a lot better. Tomorrow I will give it a ride to see if it works and if the speedo still reads correctly. My working theory now is that because we run on a wasted spark system meaning we run on 2 coils to power 4 cylinders, maybe the gauge wants to read it like a 2 cylinder because ignition lead #1 should fire twice for every 4 cylinder firings.

Sometimes you just gotta take a step back and try the simplest stuff first I guess. I'll update tomorrow if this works or not because if it does, that would mean that this gauge with the BEP 3.0 would actually work properly without any custom wiring which is pretty nice for a €20 gauge. If it doesn't work, I'll probably just take my loss and accept it as it is since I've been riding it for months without a working tacho anyway so I guess I'm already kinda used to it.

[Kevin1100]

Welp, it's one of those times where I'm gonna have to admit my own stupidity. It does seem to work relatively well now that I have set the amount of cylinders to 2 in the gauge settings. I'm not sure how accurate it is but yesterday in 2nd gear with WOT I ended up riding 115 km/h and the gauge showed about 7800 RPM. I think the max I've gone in 2nd gear is around 130-135 km/h so if that's the rev limit of 8700 that would seem correct.

I thought about deleting this post since the point is kind of obsolete but I guess maybe I could help out others with the same problems by leaving it up.

To people with a K1100 (I have the late 1999 model with ABS2), the same cheap Amazon/China/Ebay gauge and the BEP3.0: before doing anything else, try playing with the settings first. My speedo is actually also surprisingly accurate. I have the following settings:

• Wheel circumference: 2060 (got this off someone else in a Youtube video).
• Amount of magnets: 6 (I have none fitted, the SPD output on the BEP3.0 works fine).
• Fuel gauge resistance: 2 (the only choices are 2 and 3. I have tried both and neither really works well. With a full tank it says it's about 85% full, and from half empty to completely empty it always just shows about 40%. It's no problem for me since I just keep an eye on my odometer and fill up after about 150 km to be sure. You can also keep your OEM fuel gauge somewhere if you'd like).
• Cylinders: 2 (as I mentioned above, I think this works because we have 2 coils. I believe the RPM signal comes from ignition lead #1 which also fires when cylinder #4 fires because of the wasted spark system. As far as the gauge is concerned it gets 2 signals per full engine rotation which is why I think this works and setting it to 4 cylinders doesn't).

I know these gauges are widely sold by different brands and some have slightly different options/settings so check out what works for you. But the moral of this story is to just try out all the settings first to see if you can make it work that way. Definitely a lot easier and faster than messing around with the wiring like I did!

[Laitch]

I thought about deleting this post since the point is kind of obsolete but I guess maybe I could help out others with the same problems by leaving it up.

I'm glad you didn't delete it, Kevin.     Different explanations of successful installations with common modification products like this instrument are helpful even if they seem like repetition. One explanation may be understood by a reader when a different explanation wasn't. I've run into that during my own learning and that's why when I've done procedures, occasionally the Haynes, the Clymer and the BMW workshop manual have been open on the workbench at the same time.
 

I recommend that all members download and read the LE Jetronic Training Manual available in the Service Bulletin section of the Technical Directory. The manual explains how all the engine components operate and interact. It explains what Kevin was able to work out on his own; namely, the system reads two pulses for one 360º crankshaft rotation.