Persistant single cylinder problem

[tig5]

I've finally got my bike back together and a new R/R installed. Unfortunately my rear cylinder gremlin lives on.

Charged battery. Attached a new multimeter. 12.9vdc with key off.
With engine running, volts increase and sit between 13.5 and 13.8v, from idle through rev range.

Bike idles and runs nicely for 10-15 minutes then the rear cylinder begins to cut out. Particularly problematic at low revs, bike refuses to idle. If the throttle is wound open the rear cylinder will occasionally kick in but it takes a while to get home! During this time the bike becomes more difficult to start (starter seems to spin more slowly) and I have also noticed that the digital gauges sometimes reset while start button is pressed. This usually only happens when the gauge is disconnected then reconnected to the battery which suggests to me that voltage is very low. I haven't retested voltage after the rear cylinder has started cutting out.

The tach needle on the digital gauge bounces around quite erratically, this symptom persists regardless of engine performance. I've tried using resistors which didn't work. I'm not sure if this problem is related but I have read that low voltage can influence tach performance.

Rev limiter wire is clipped and taped.
Problem persists with different TCIs.
New R/R has 3 white wires and 1 red and 1 green. Red and green are wired directly to battery.

I've replaced the fuse box. This bike has some creative wiring solutions compliments of the PO and I'm wondering if it could be a wiring problem. Positive battery lead is looking pretty corroded.

I replaced the stator with a spare taken from an engine that was described as "running". The old stator was giving me ridiculously low VAC readings which turned out to be a faulty multimeter.
Since my tach isn't working I haven't measured VAC from stator accurately. Valyes ranged from between 30-70 (from memory) VAC when I plugged the multimeter in to the current stator white wires and rolled through the rev range.

The original R/R had 7 wires total from memory, the new one has 5. The wires that the old R/R originally connected to are unattended. Someone mentioned these were related to lights and signals? Lights and signals seem to work ok at the moment, at least while engine is running properly. The old R/R connecter block at this junction may have been suspect throughout this problem. At this point R/R is wired directly to battery.

In a big nutshell, bike seems to be losing voltage somewhere.
Electrex fault finding chart suggests charging system is not to blame.

I'm getting a bit stumped...

On a positive note the bike looks a lot better.
I will go back through the Electrex Chart again in the next day or 2 to double check figures.

In the meantime any thoughts would be AWESOME!

[QBS]

The tach gets its' input from a gray wire that comes off the spark coil wiring.  If you haven't already done so, inspect and clean all spark coil related connections and the ground that is related to the spark coil wiring.

[tig5]

Thanks QBS, I've inspected this coil, cleaned connections and even tried jumping to tach with a new wire. No improvement.

[Re-Vision]

Assuming the problem is electrical, try replacing right side coil and High-Voltage plug wire and spark plug to rear cylinder. If the Y/B Rev Limiter wire is disconnected at tach, disconnect or cut at TCI also in case it's shorting to ground somewhere.     BDC

[Rikugun]

Assuming the problem is electrical, try replacing right side coil and High-Voltage plug wire and spark plug to rear cylinder.

Rather than replace you could also swap the coils left to right and see if the problem moves to the front cylinder indicating a bad coil. If the problem persists with the rear cylinder the problem may be in the rear pickup coil. Pickup coils don't seem to be particularly problematic on V's but you can't rule it out. The 4 pin connector (is it clean BTW?) at the TCI holds these B,R, and W wires. Using an R scale capable of +/- 110 ohms check them with the bike at room temperature. If the values are equal and within spec, ride the bike until the rear cylinder drops out, pull over and test them again. Any difference? Resistance may increase slightly on both but a significant difference between the two is problematic.

Also unlikely but not impossible is every TCI you've tried is faulty.  ???

Remind me again how you deduce the rear cylinder is cutting out? Spark tester? Y pipe temp?

There are some clues given that can be made to fit a particular diagnosis but don't rule out the possibility there are multiple problems within the arena of "electrical" or even simultaneous fuel and electrical fault.

Bike idles and runs nicely for 10-15 minutes then the rear cylinder begins to cut out.

Is this from cold where it starts and runs on choke but as the engine warms and choke is removed the problem arises indicating fueling?  Or, is this a typical failing electrical component symptom whereby the component comes to operating temp and breaks down?

Charged battery. Attached a new multimeter. 12.9vdc with key off.
With engine running, volts increase and sit between 13.5 and 13.8v, from idle through rev range.

Depending on the charger used, 12.9 fresh off the charger seems a little low. Nominally 13.5 sounds a bit low while running through the rev range. I'd expect nominally 14.5 right above idle and beyond. Not that this is necessarily contributing to your immediate problem but of some concern to me.

The abandoned wires from your OEM R/R should not be a problem provided they are not shorted. On my US '82 the yellow from the OEM R/R does nothing and the brown senses system voltage. Apparently your new R/R does not use a sensing wire. Are there any wires from the new R/R not in use? Is the R/R one of the inexpensive E-Bay Chinese units that seem to very prevalent now?

Does the tach sense from the rear coil and have you tried disconnecting it?

[tig5]

Thanks for the thoughts guys. I will switch the coils over tomorrow and give it a try. So far I've been diagnosing by a lack of spark and a cool cylinder.

I'm not familiar with the difference in coils and pick-up coils. Coils are bolted to the frame at the end of the spark plug leads, where are pick-up coils? I don't have much experience in that dept.

I can't remember which coil the tach reads from but I'll disconnect. New R/R has all 5 wires in use, 2 to the battery and the 3 white to the stator. New R/R is a cheap one.

I'm wondering if the problem could be a short somewhere? There really is some suspicious wiring in places but not so much around the charging system.

[Jimustanguitar]

The pickup coils are inside the engine case. The pickup coils are essentially a crank position sensor that tells the ignition box when to fire the ignition coils...

The tack would read from the pickup coils, they're the "source" of the spark timing.

[tig5]

Thanks for that.

I was under the impression the tach got it's signal from the ignition coil rather than the PU coil? Mine is wired that way anyway. I have no idea where the PU coil is inside the cases but I'll do some research. It's not part of the stator unit is it?

I just found another electrex sheet which looks quite useful.

http://www.electrexworld.co.uk/pdfs/Troubleshooting-3P-PMG-&-RR.pdf

I'm not sure if the values etc are bike specific or if I could work through this sheet and use it as a guide?

[Re-Vision]

The tach does get its signal from the right (rear) coil through the gray wire. When tach limits are exceeded it puts a ground on Y/B wire running from tach to TCI Unit.
The pick-up coils are located inside the case near stator, if one of them fails it will cause the same condition as the tach limit circuitry does (one of the cylinders will quit firing).
Something else you might try, when rear cylinder is not firing, try wiggling connectors and harness in an attempt to get rear to fire. In particular the connectors associated with rear coil (right side) and four wire connector from pick-up coils to TCI unit       BDC

[tig5]

Thanks.

When I replaced the stator I replaced the whole side cover so I imagine that included the PU coils. This replacement didn't improve situation.

I'll have another look at the HT coils and give things a wiggle. Would a problem in this area account for a drop in voltage? That link I posted looks very useful but I'm not sure if the figures/values/measurements stated are relevant?

[Rikugun]

I was under the impression the tach got it's signal from the ignition coil rather than the PU coil? Mine is wired that way anyway.   Then try disconnecting to your digital tach and see if conditions improve I have no idea where the PU coil is inside the cases but I'll do some research. It's not part of the stator unit is it? If you replaced the stator with the cover then yes, you changed the PU coils too. These are also called pulse coils and are attached to the inside of the stator cover separate from the stator itself.

I just found another electrex sheet which looks quite useful.

http://www.electrexworld.co.uk/pdfs/Troubleshooting-3P-PMG-&-RR.pdf

I'm not sure if the values etc are bike specific or if I could work through this sheet and use it as a guide?
  I think the tests are valid and practical within reason. I don't think you can't use the brake light as a "control" as outlined in Step 1 however flicking the key switch on/off will do the same. The low limit for charge rate (13.6) stated in Step 3 although acceptable is generally higher with MOSFET and OEM Vision R/R's. I can't comment on Step 4. Step 8 basically tricks you into connecting the R/R  directly to the battery which I think you've already done. Hopefully with heavy wire and maybe even a 30 A fuse on the red wire? I like that loads are used to further validate what might otherwise be inconclusive results in these tests.

[Re-Vision]

Tig

Would a problem in this area account for a drop in voltage?

Anything that puts a load (shorts)on the battery and/or charging system will try to pull the voltage lower. Voltage changes are more noticeable when charging circuits are not operating.     BDC

[tig5]

I appreciate the thoughts, I'll get stuck into it tomorrow and report back

[Jimustanguitar]

I was under the impression the tach got it's signal from the ignition coil rather than the PU coil? Mine is wired that way anyway.

So the tach reads from the high voltage output of the secondary winding of the ignition coil?! or it connects to the low voltage input side of the coil and this connection just physically takes place at the ignition coil?

I'm pretty sure the tach is reading the pulses that trigger the spark and not the spark itself... I guess they go through the CDI box first though, so it doesn't technically come STRAIGHT from the pickup coils like I said...

[QBS]

The latter.  TCI (Transistor Controlled Ignition) box is controlled by the crankshaft position sensors, and replaces the points in what is basically an ignition points and spark coil system.  Like ignition points, the TCI sends timed bursts of 12vdc  to both spark coils.  One of the coils (not sure which one), sends its signal on to the tach via the tachs' grey wire that branches off of the coils' low voltage harness.  This is how the tach is gets its' RPM data.

[Rikugun]

Short of waiting til spring to remove my gas tank and look...  Can someone confirm gray is the rear cylinder circuit color?  :-\

[Re-Vision]

I can.    BDC

[Rikugun]

Thank You  :)

[tig5]

I charged my battery again and it showed 13.4v off the charger.
With the key (and light) on it dropped to 12.9v.
With the engine running I was getting a slow increase up to 13.9v or 14.1 if I turned the lights off. From what I gather, that's reasonably acceptable?
I swapped the coils over and check the contacts and ground and fired it up. Went for a 15 minute ride with occasional stops to check the charging voltage. Everything seemed ok. If I kill the engine the voltage at battery slowly drops to about 13.2v.
My ride wasn't long enough to say that switching/cleaning the coils solved the problem but I'll take it for another run tomorrow.
My tach is still bouncing all over the place. The right coil has 2 wires including the grey. Am I correct that one wire provides the current, the grey provides the signal for the tach, and the frame provides the earth? The left coil also has 2 wires and the third black wire that grounds between the coil and the frame. I couldn't quite get my head around the differences between left and right.
I have the stock gauge cluster lying around and I'm thinking I might try and hook it up to test whether it also bounces or not. I remember seeing a photo in another post which identified which points on the unit connected with which wires. I'm only looking for +ve, -ve and tach. I'll have a hunt for the photo, if anyone remembers which post it was on a link would be appreciated.

[Jimustanguitar]

The left and right coils are identical, they just fire at different times so it's important to wire the right one to the right plug wire. They do get their ground connection through the mounting studs. If you ever take them off again, it's a good idea to remove the paint from around those holes so that you can make an even better connection. Some have also reported that the coil housings can crack and stop working well after that. If they're off again, a visual inspection is in order.

Not familiar with which wire colors do what. Hopefully somebody else can chime in on that one.