Intermittent Misfire on All Cylinders

[oldfaithful]

The conformal coating can be very misleading. It's not evenly distributed and it has a tan brown color. It tends to make a component look burned when it isn't.

[oldfaithful]

You are welcome, I admire your resolve!

 

Do we see an oops 1/2 to the left the second nut up from the bottom?

 

Were you able to clearly show a miss on all 4 with a spark test at 1/8"?

For myself that would be a reason to point at the control box.

 

You're correct. There are two oops at that nut. They are merely anchor points for the heat shields though and shouldnt effect the circuit. My question, though rhetorical, is have they always been that way?

[Patch]

You're correct. There are two oops at that nut. They are merely anchor points for the heat shields though and shouldnt effect the circuit. My question, though rhetorical, is have they always been that way?

 

Well that I don't know but if you look at the marks I made on the pic you can see that the connector looks like it has been work on, and that no way it left the factory with that bad area we mentioned. 1 with an arrow

 

Anyways using some simple software I marked a couple of areas that should be checked. zoom about 200 times

 

Have you considered asking Puc for the one off his bike?

[Patch]

looks like I forgot to load the picture??

[videoarizona]

I think that is just the marking on the diode, a zener diode to show what end is what. Here is a link to wikipedia about them.

https://en.wikipedia.org/wiki/Zener_diode

 

Hope this helps.

 

Rick F.

 

Could be... Hard to tell.

That board is one of the cleanest I've seen from members posts. Solder joints look quite good for it's age. I agree that there are a few joints that need checking, but overall it's in decent shape.

Edited July 9, 2018 by videoarizona
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[oldfaithful]

Well I went ahead with the TCI "preventative maintenance". Replaced diodes and discolored resistors. I also removed & examined the ground at the coil bracket, since I was in the area and found it to be clean. Re-install and test to find...no change. The random spark miss on all cylinders is still there.

[videoarizona]

[sldunker]

Back to basics. Did you ever do the compression test? Are your plug wires wire and not carbon. I tried carbon wires on my 84 when I had it and it always ran funny. Like it had a miss. When I went back to wire the bike ran fine.

[frankd]

First off, it doesn't matter at all if your plug caps measure 5K or 10K. The value of this resistance only limits the current flow from the coil after the spark is struck. These caps are there to limit the ignition noise getting into the radio. Seeing as all 4 cylinders are miss firing, a bad coil or low compression on one cylinder couldn't cause the missing in the other 3 cylinders. It has to be something common to all 4 and it still sounds to me that it's the ignition system. Does somebody with a 84-89 Venture live near you and might be talked into trying his TCI in your bike? That would answer a lot of questions. You mentioned you were going to get an Ignitech----I do have one of Dingy's later files. I got it in 09/15 and he said it was the latest. If you want it send me a private message with your regular Email address in it and I will send it to you.

 

Frank

[Patch]

First off, it doesn't matter at all if your plug caps measure 5K or 10K. The value of this resistance only limits the current flow from the coil after the spark is struck. These caps are there to limit the ignition noise getting into the radio. Seeing as all 4 cylinders are miss firing, a bad coil or low compression on one cylinder couldn't cause the missing in the other 3 cylinders. It has to be something common to all 4 and it still sounds to me that it's the ignition system. Does somebody with a 84-89 Venture live near you and might be talked into trying his TCI in your bike? That would answer a lot of questions. You mentioned you were going to get an Ignitech----I do have one of Dingy's later files. I got it in 09/15 and he said it was the latest. If you want it send me a private message with your regular Email address in it and I will send it to you.

 

Frank

 

Yes it has to be ignition. If it is all 4 then its TCI or harness to and or from the control box.

[oldfaithful]

Yes it has to be ignition. If it is all 4 then its TCI or harness to and or from the control box.

 

That has been my train of thought lately too.

 

However, just to eliminate other variables...I picked the cylinder that I thought might be considered the "worst" of the 4 and replaced the coil with an extra from my inventory. The coil I pulled out measured within spec at room temp (both primary & secondary resistance), and so did the replacement. The original coil looked good with no cracks or visual defects, while my extra has some cracking along the top of the plastic casing. (I tried to seal it up with RTV prior to installation.)

 

Start her up and the miss is reduced, still there, but not as frequent. What are the odds that all 4 coils are breaking down at the same time?

 

I'm not yet convinced that this is the culprit. I have an Ignitech unit arriving next week and will let you all know how it goes. If the ignition module doesn't do the trick, I'm thinking of upgrading to COPs next.

 

Additional notes:

All connectors have gotten treated with dielectric grease before being reconnected.

Miss has been present at startup (cold) and when hot.

[Patch]

That has been my train of thought lately too.

 

However, just to eliminate other variables...I picked the cylinder that I thought might be considered the "worst" of the 4 and replaced the coil with an extra from my inventory. The coil I pulled out measured within spec at room temp (both primary & secondary resistance), and so did the replacement. The original coil looked good with no cracks or visual defects, while my extra has some cracking along the top of the plastic casing. (I tried to seal it up with RTV prior to installation.)

 

Start her up and the miss is reduced, still there, but not as frequent. What are the odds that all 4 coils are breaking down at the same time?

 

I'm not yet convinced that this is the culprit. I have an Ignitech unit arriving next week and will let you all know how it goes. If the ignition module doesn't do the trick, I'm thinking of upgrading to COPs next.

 

Additional notes:

All connectors have gotten treated with dielectric grease before being reconnected.

Miss has been present at startup (cold) and when hot.

 

I experimented with an injection system some years on a German unit. I had a sequential ignition firing sequence, the Bosh coils are very expensive and had a proven track record.

Those coils deceive when measured, (2 coils per cylinder) but I was convinced that they had reached max duty _even though they fired.

 

The coils proved to be the answer.

 

The moral here is, it's not about chances they all drop dead at the same time rather, how well/fast they charge and discharge and more about duty cycles then ohms readings.

 

If you believe the above then you can relate this to my mention on that 1 pickup coil as well.

[oldfaithful]

I promised an update, so here it is. I've received the Ignitech unit and installed it. I like this product. It fired right up and seems to have no dead spots...but the miss at idle is still there. I left the TCI unit in place as a backup, in case I ever have problems with the new unit. That leaves 2 possible sources, as I figure it: the pickup coils or the ignition coils.

 

I've got an 86 MKII that has been an occasional donor. A pickup coil swap might soon be under way.

 

 

 

I'll also be tweaking the program in the Ignitech unit because it doesn't seem to match the Yamaha manual's timing diagram at all. Mine is setup for use with the original MAP sensor.

Does anyone have an Ignitech program that better matches the advance curve in the manual? Even if it's from a different year that won't be plug-n-play, I'd appreciate the chance to see a working advance curve that looks more like the Yamaha design.

[Patch]

So I have zip experience with Ignitech units but, I can say that it is best to first get the ignition system in order before you trying any adjustments.

 

The opportunity to tune advance is interesting, but my experience would be to tune within the ranges that best suit your typical riding. Too much early piston pressure can do a lot of damage. In any case the speed of which the ignition will work is crucial to the end tuning results.

 

Again a gap test would serve you well.

[oldfaithful]

Time for another update:

 

Before swapping the pickup coils, I opted for the easier ignition coil swap. My backup ignition coils from my parts bike were found to have several cracks, so they were not used. I've purchased used COP coil sticks from a Honda CBR and installed them. The Ignitech unit works just fine with the COP coils, but I installed a section of spark plug wire between a COP and the spark plug...only to find that the miss is still present at idle.

 

The pickup coil will be pulled from the donor bike next.

[Patch]

Wouldn't life be easier with a money tree in every ones back yard;)

 

So opted for stick coils.. Are they 1.5 ohm? Lets us know next time..