Ok ive fitted mondeo coils on a BMW k100 8v 1986

All seems quite happy apart from the Tacho reading at idle equals 2500rpm. Normally at 80mph its 5000rpm but now it reads 10500rpm.

I believe there it a potentiometer in the lunch that allows for some adjustment. Is it man enough for this sort of adjustment?

I’ll follow up with some more specifics FYI. Mrs is shouting at me :-)

Funny that it's about double what it should be, as if it gets a signal from both coils, when it should only be one. Was she also yelling at you when you connected the wiring up? How have you wired them up?

Can you give some more details about the coils? It's good to know about alternatives that work.

Sorry just re read that. Is there a potentiometer in the lunchbox that is the dials? For adjustment of tacho?

4x D7EA plugs
1x 12807 coil pack
1x focus electrical plug : asin: B0B7GMVJDH
Pin 1 = Cyc 2&3
Pin 2 = ignition live
Pin 3 = Cyc 1&4
(No Earth)
4x M4 coupler HT leads with resistors
Cyc1 - 370mm long - 4.75 kohm
Cyc2 - 340mm - 4.90 k
Cyc3 - 270mm - 5.40 k
Cyc4 - 170mm - 4.65 k
1x bespoke bracket
Various spade connectors to temporarily link focus plug to oem harness.

Coil primary -
0.6 between live and signal.
1.2 from signal to signal.

Coil secondary -
Forgot to test - 1 & 4 m4 coil plugs
17kohm- 1 & 4 plug boot
7.85kohm - 2 & 3 m4 coil plug
18kohm - 2 & 3 plug boots

Once I’ve tidied up I’ll pop a photo up. I’d didnt want to hack the harness up until it proved itself so it is untidy at the moment and bracket needs some tweaks but appears to function fine I was going to run a tank of fuel through it and see if it suggests anything concerning then re check resistances and plugs. It’s done 60miles so far .

Tacho is a mild irritation, the original earths are now spare, I was going to terminate these properly under the hope that it might cure the tacho issue (wishful thinking) other wise I was going to open the clocks up but I have limited time at the moment. It also crossed my mind putting a resistor and diode in the tachometer feed but was hoping for some input from a spark friend or here before I try this.

The mrs is happily oblivious to my tinkering, she is wondering why I have been walking around with some silicone sheeting wrapped around my left hand calf though. Oh HT leads have 90 deg ends at both coil pack and spark.

Just couple of snaps whilst I was cutting the HT leads to length.
I’m updating the bracket to include a place to mount my ignition switch. If it works I can supply a 3d file to anyone who’ is interested will need to be printed for a glass filled oil and fuel resistant substrate. There is part of me tempted to mount it so the signal plug is pointing up. Not particularly nice pointing out the way.

There is an adjustment for the tachometer (rev counter). I fitted a k75 tacho to a k100 and noticed it was not correct and was able to correct it by adjusting it. If you open the lunch box you will see it at the top.

I just tried it on the bench, with the rev counter showing 6000 I was only able to bring it down to 5000. I also put a diode in series with the input but no change i.e. 6000 input still showed 6000.

So not man enough for a Mondeo man.

Great that will buy me some time. I don’t want any mechanical limit in the box to start causing me problems at the moment during motorway driving it its hitting 10.5k rpm I don’t really want it to go any further just in case there is a stop mechanism behind.
Did you mean diode or resistor you tried? I’m assuming a resistor would be helpful but I was only thinking about popping a diode inline just to prevent any electrical trickery going back to the coils I would not expect the diode to adjust the signal in anyway. Unless I’m missing something, very possible.

I used a diode, a resistor will only reduce the output of the coils. You need some way to half the frequency of the coil output.

Ok gotcha! So are u are saying it is more the fact that it is a combined coil pack that is doubling the out put /frequency rather than the resistance. I was thinking the tacho would be working on a current or voltage value and that is why a potentiometer is integrated in the clocks already and is able to adjust it ?

I've deliberately ignored posting a reply cause this is over my head. In the meantime how many Volt's do you read at the wire to the tacho? I can't see where you have connected this wire to the coils. And the other wires.

ddunks wrote:The mrs is happily oblivious to my tinkering,  she is wondering why I have been walking around with some silicone sheeting wrapped around my left hand calf though.

Me too.

200miles done and all behaved fairly well, actually potentially too well. I was starting to notice some mild clutch slipping and it crossed my mind the ignition was working so efficiently I needed to adjust my clutch a touch (wishful thinking?). 1 dy later the clutch has gone bang :-( I think the old banger needs retired for a while. If I need to do a clutch I should probably do a full sweep of the jobs on the to do list and get her set up for another 100k. FYI I put an uprated oil resistant clutch in from MOTORWORKS 51k ago, I had kinda of expected abit more out of it. Any opinions on what you should expect from a clutch?

Did the oil pressure light come on when the clutch went bang?

You also have a thread at the moment about an output shaft rivet that popped off. Are you sure that the clutch has gone bang, or have the rivets gone pop?

Yes it went with a clunk pulling out of a t junction. It did cross my mind but no, oil light didnt come on. Gears are still engaging comfortably and the bike can still just about creep along at very low revs /5mph but probably wouldnt go up a hill. It drastically slips. I did some extreme adjustments of the clutch and this either totally disengaged the clutch or made no significant difference. Welcome to anyone’s 2 cents but assume it is the clutch.

I think I'd be looking at the output shaft. If you need to go in for the clutch, you may as well pull the intermediate housing too and change it.

Yeah, I think it is time to do a long list of stuff, seals and replace old rubbers plus exhaust studs but the output shaft will be the first push before trying to slowly assess and reassemble, may even paint the frame. It’s been run through quite a lot scottish winters relentlessly and I’m not much of a spit and polisher.

One thing that may not be in your toolbox but you will need to get the intermediate housing off - a T30 Torx bit. BMW use just allen (caphead) bolts everywhere else but the intermediate housing is a mixture of 8mm capheads and T30 Torx. Go figure. I think they had a hopper full of T30s to get rid of - or maybe Gunther just orded the wrong bolts, so the production line put them where they can't been seen Be aware that two of the litte b*st*rds are hdden away in dark corners.

Also, be prepared to hit them with an impact driver. I've had two housings come off really easily and the third took so much abuse from an impact driver and a 3lb hammer that I thought I was going to break the housing. If you chew up the heads of the Torx (mine weren't, quite) you can hammer a 6mm Allen bit into them. Any damaged ones, replace with capheads.

Actually, if any single Torx gets damaged, I'd replace them all with capheads. BTDT.

Just going back a bit, it might be worth measuring the Voltage at the wire to the tacho. I'm thinking if it's too high, your idea of a resistor might be right after all. There was a case where the Voltage being too low affected the tacho.

Actually it's a dynamic signal, so maybe just try a resistor, or see if the coil wires can be separated.