Have a bit of a pickle..

About a month ago started, we started having problems with my partners VFR. It would just stop, quite randomly and then refuse to start. Engine would turn, but wouldn't start. After a while it would then deside that it was OK again and run, quite happily.

So we get it back to the workshop and its in a running mood again, and there it is happly idling for about 5 minutes. Then suddenly without reason or hesitation it stops, as if you had turned it off.

So although I didn;t suspect it, I thought I best check fueling. As I thought, fine, no issues, plenty of fuel gettign to carbs. So I check sparks..... Aha, no spark fine so it must be a dirty contacts etc etc, so I systematically clean every and all electrical connections despite all looking quite sound. Still no spark, Kill swith works fine, ignition is fine fuses fine. Coil tests OK, HT and LT sides, I have good earths and a desent 12.5 volts. So after ruling out obvious we start getting to the slightly abnormal.

So I replace the ECU, and still I have the same issue, so I look at the tech manual and do some tests I have voltage where it should be, and so I bypass all of the switches wires etc etc and give the ECU a direct 12v, still nothing. I just dont seem to be getting any signal to tell it to fire, IE pulse coils. Yet the pulse coil test resistance is within spec, but I dont have a peak voltage tester to make sure that their doing their jobs as sugested in the tech manual. Running a normal meter accross the pulse coils on AC voltage I get 1.2 and 0.9 v, which is well below the 1.8v minimum peak value specified in the tech specs, but it might be changing too fast for a digital multimeter to pick it up.

So this is the next part to replace. But Im owing to the fact it is a sealed non moving part not exposed to the elements and permamently submersed in a bath of oil, it does seem unlickely that they have both symaltaneously broken, yet im left with little alternative.

I just wanted your 2 cents before I go spend some more cash on these parts!

Thanks,

Jody

Thats an interesting one!

I had a similar problem many years ago with a phantom misfire, it turned out the be that there was an break in one of the wires in the loom that sometimes made contact and sometimes didn't.

Took a few weeks and many new parts before I decided to test all the wires continuities with a friend moving the loom which revealed an intermittent short.

Bloody nightmare.

Pulse coils are a bit awkard to change but it'll rule them out one way or the other if you do change them. It just seems odd to me that sometimes it works, sometimes it doesn't, which reminded me of my phantom problem, usually if somethings died it stays dead.

I forgot to add in that ever since Ive had it in the workshop, it point blank refuses to start so I think it can now be classed as officially dead. At least for the time being.

As for the intermittent connection, it is possible but unlikely Owing to the fact that I rewired it 2 ago. The back end is heavily modified and lowered (looks nothign like a VFR any more) and because of this work a lot of the electrical components have been relocated to save on space, but 2 days ago with all of this going on I decided to shift the components again as some were getting damp (mainly the ecu) so the regulator is now at the front of the bike, fuse box is down where the thermostat is along with the clutch diode and flasher relay and ive moved the ECU to behind the battery tray so that wires to the rear end are minimal. But, my point is that whilst doing this work, ive have checked continuity of all wires that have been spliced and rejoined before I taped the loom back up.

But, there could indeed be something ive missed so I will probably check it again for sake of completeness!

Jody

So, despite replacing the pulse coils, I still have no spark...

So ive gone back to basics, checked and rechecked EVERYTHING and found nothing abnormal, even adding an earth or two for good measure.

So, if anybody has any ideas on how to get the damn thing working, Im open to sugestions. I don;t care how stupid it may sound, its most likely somthing completely stupid that ive overlooked, but for the life of me I can't work out what it could be.

The only component in the ignition circuit that I havn't replaced, are the coils/plugs, but both of the coils check out within specifications and are identical to each other and as for the plugs, there virtually brand new with less than 2000 miles on them, so I woudl be exctremely dissapointed if all 4 have gone in such a short space of time, besides when it was running it wasn't misfiring and would run extremely well.

Damn I hate electrical faults......

I think my next aquisition would be a peak voltage tester so that I can perform some of the tests in the spec manual, but at the price they are and the lack of use I can see the device getting, it almost seems a bit of a waste of time.

Whilst I ponder this purchace, I need ideas from you guys, even stupid stuff, that I may have missed. More often than not, we overcomplicate problems and the simplist of answers is probably the case!

Jody

Hiya, i'm guessing you've got a multimeter, so i'd say make sure there is power geting to the ecu when its plugged in incase theres a high resistance joint somewere, I'd take the plugs out aswell so you dont flood it with all the cranking over your doing and it'll give the starter an easier time. other than that keep measuring continuity between sensors and ecu, and maybe measure things from the ecu conectors just incase theres a break in the loom. Keep going its bound to be something daft it always is, and it'll be the last thing you'll check as well!!!!
Hope you crack it soon
Cheers
Ian

Firstly, take off every connector and spray them with wd-40 / contact cleaner and re-assemble.

My other idea would be to replace the whole loom...

http://cgi.ebay.co.uk/Honda-vfr400-nc30 ... 240%3A1318" onclick="window.open(this.href);return false;

It's only at £10.00 too.

Indeed I do have a multimeter, the most irritating thing about it is the fact that I didn't get the model above the one I bought some time ago as it offerd a peak voltage function. Never mind, we make these silly yet irritating little fo-pars... Regardless, the fact that the model up was undesirably more expensive with a whole host of functions that I would never use was the clintching factor in my decision.... yet.... "What will I need a peak voltage tester for", springs to mind from that decision.....

Replacing the loom is a sound decision, with a slight snag. My current wiring loom is so... erm... well non standard its rediculous to even think about just how long it would take me to cut, splice and solder a new loom together. The fact that 100% of the components from the thermostat backwards have either been moved or removed makes me shudder at the thought of doing it again. Not being a brag, im pretty certain that my soldering techinques and abilities with wires/components would have me beleive that the loom is pretty A-Ok, and through my travels upon trying to solve this little issue, I have checked and rechecked continuity, circuit paths and polarity of all wires that have been cut. Now many woudl argue that there is a distinct possibility that there could be a high resistance joint and/or break in any one of the 50+ wires Ive moved. But, on stripping the bike down I decided to relocate even more of my components for ease of access (most of which have now ended up under the thermostat housing), so once again ive torn the loom down to the last wire and moved them, whilst in the process checking any and all exsisting joints/connectors etc etc.

But, for the sake of completeness, I will probably buy a second loom so that I can plug it in to the bike to see if by some jolly cock up I have made a rather interesting mistake. At least then I would be certain.

The stupid thing is, according to the tech manual, all of my sensors check out within specification as far as can be measured and all points back to the ecu not processing the signals correctly. Yet, the chances of having three duff ECUs is in the rather astronomocal region. But then again If all other likely possibilities have been exhausted, no matter how obsurd the remaining one must be, it must be correct.... Which is why i swear ive missed something... just what on earth is it.

Simple checks made:

12.8v at battery (on a side note, the batter is only 3ah instead of original 6ah to save on space, but has performed without fault for the last year)
12.7v measured at ECU Black/white wire and at both coils
Regulator/Rectifier is from a.... who knows, it was just in a box I found ina breakers yard. Works well though.
3 Different ECUs
New pulse Coils
Coils check out within specification in the tech manual (each coil measures 3 ohms primary (spec is 2.5-3.5) and 23.5k secondary (spec is 14-24k))
Pulse coils measure 0.5k each (spec is 0.45-0.55k)

Jody

Tis a strange one!

Have you not got a known working ECU? Or a bike nearby to test your ECU's in?

That 2nd hand loom ideas a good one.. :) Have you tried a bigger battery just to isolate that? I tend to steal the 95ah, 850cca battery from the car when im in the process of needing some serious cranking over to save the poor bike battery.

While some might say it's dangerous having that extra juice just make sure you don't have any shorts before using a bigger battery as the extra juice it can supply would torch the loom!

Apart from that.. good luck :)

If your handy at the wiring, could you make up a engine run loom just to try it, it maybe easier than buying and swaping the whole thing?
Oh yeah remember that if you've got both plugcaps off you need to put plugs in both of them to get a spark.
Cheers
Ian

Im currently in the process of creating my new small loom that just runs the ignition circuit, but i have a small query.

So do you think that omitting the tacho wire and speedo wire woudl cause any problems for testing purposes. Im aware that by not having the speedo wire connected it starts to misfire above about 5k rpm but apart from that the bike would run fine and start fine yes? And also, the ECU probably doesn't require the tacho wire connected, correct?

Jody