No spark on #1 at low revs

[naughtyG]

I'm experiencing no spark on cylinder #1 at low revs on my '86 - on idle that cylinder stays cold, when riding I can hear and feel it kick in at around 4500-5000rpm. :ummm:

I have thrown new plugs in, and I have replaced the coil. I've measured tension on the coil connector and both wires show 12V. I've connected the offending coil/HT leads/plugs to #3 coil wires to check and it sparks just fine, so I know these components are good.

All 3 other cylinders fire just fine. What could cause just #1 not to fire?

My guess is the TCI - anyone else?

 

[maleko89]

G, did you try a spark tester or remove the plug and ground to verify it wasn't firing?

 

[MaxMidnight]

Are you getting fuel to #1, i.e. is the plug wet?

 

[naughtyG]

I have removed the plug and grounded it, this is (and the fact the cylinder stays cold) how I know it isn't firing.
Also by connecting the #1 coil to the #2 coil wires and grounding the plug is sparks fine, so I know the plug / HT lead / coil combination is good.

Steve, I can smell petrol whenever it idles and my fuel consumption is atrocious, so I'm pretty sure fuel is coming through. Also the old plugs were all equally black.

So, TCI? I can't think of any other way only 1 out of 4 cylinders wouldn't fire, and then only at low revs!

 

[MaxMidnight]

Have you got power and continuity in the red/ white wire from the ignition unit and continuity on the orange (?) wire to the coil?

 

[tugla]

if you swap the #1 and 3 coil connection wires does cylinder 3 go cold at idle.

I'm thinking you could have issue with crb 1. if it runs good above 4500. when it idles and to the touch cyl is cold if you look down the carb is there fuel pouring down cylinder? maybe stuck float or need of shot gun. only reasons I say this was exactly what I had last week on mine and what it was. since u can smell fuel...

just a though.

 

[one2dmax]

I have indeed seen TCI's do this (and other weird shit).

 

[bishan]

..

 

[MaxMidnight]

Greetings and welcome to the site.

The yellow is correct for #3 coil (see attached PDF) - there isn't normally a blue wire.
There will be a Grey wire which takes the feed to the tacho spliced into it somewhere along the loom.

You will need to trace where the blue wire goes to find its function.

 

[bishan]

thank you for the diagram, Maxmidnight. it's very useful.

 

[bishan]

..

 

[naughtyG]

Have you got power and continuity in the red/ white wire from the ignition unit and continuity on the orange (?) wire to the coil?

Hey Steve,

I do indeed have power on both the wires feeding the coil - both measure just about 12V. What do you mean by continuity? Where would I test that?

I've now sourced another TCI, so when I get the time, I'll be swapping it over and hope it'll fix my problem!

 

[bishan]

..

 

[naughtyG]

my apology to jump into your thread, G, I hope you dont mind. I had the same issue, but mine is coil # 3.

No apology needed! I'm hoping the TCI swap will fix it here, but it'll be interesting to find out what your problem is too.

 

[PaulVmax]

G to test the wire continuity put your volt meter on the bell sign (volt meeter buzzes when circut is complete) put on volt meter wire on the coil side and the other volt meter wire on the other side (tci side) and see if it buzzes it will also give you OHM reading this should be very low like 0.02ohm no buzzing/ high ohm reading means bad wires i just done all my vboost system wires.

 

[naughtyG]

Thanks Paul that's what I understood. When I go to swap my TCI I will test all four coil feed cables and compare resistance.

 

[PaulVmax]

yes G

 

[PaulVmax]

do it before you replace you tci to make sure that it is that