No 4 not firing.

[BJ]

Bike running like shit again.
Just had my injectors cleaned and while apart I pulled and tested tested all the leads, caps coils etc.
All tests within spec.
All plugs brand new, but No 4 cylinder plug is wet but not firing. Pipe is cold as.
Does get a little warm after a few minutes but at that stage the others are untouchable.
I changed the plug, same result.
Shims are in spec.
Assuming there is nothing wrong with fuel delivery what is the likely cause of no firing?
Can a coil delivering to two cylinders breakdown on one and not the other?
Due to age of bike I am tempted to buy a new set of coils, leads and caps.
Are there any sensors that would affect just 1 cylinder??
Thaks

[steve porter]

Can you swap the leads around temporarily maybe 1 with 4 to see if you get the same cylinder not firing? 

[grog]

Mate, you must hate that bike. Can you borrow a HEI tester, just do each lead to check spark. If same coil is ok on one cylinder and not other can only be lead or end cap.

[Irish in Oz]

Wet your hands a run your fingers up and down the lead and cap, best done at night with lights out in shed.

[grog]

Irish, might be better with lights on, ambulance will find him easier.

[Irish in Oz]

I just remembered Catty had a similar problem on No.4 recently, he did same as you injector clean etc. he borrowed my vacuum gauge and was reading high on that cylinder, turned out to be throttle body sticking closed. I've messaged him to get more details about plug readings.

[froudy]

Unscrew the plug cap from the lead on No.4. Trim 5mm off the lead and screw the cap back on. Sometimes it can do the trick

[Irish in Oz]

Catty messaged me back, he had same problem wet plug, and some popping from it trying to fire.

[BJ]

Can you swap the leads around temporarily maybe 1 with 4 to see if you get the same cylinder not firing?

I'll try this in the am

[BJ]

Unscrew the plug cap from the lead on No.4. Trim 5mm off the lead and screw the cap back on. Sometimes it can do the trick

Has been done!

[BJ]

I just remembered Catty had a similar problem on No.4 recently, he did same as you injector clean etc. he borrowed my vacuum gauge and was reading high on that cylinder, turned out to be throttle body sticking closed. I've messaged him to get more details about plug readings.

I'll throw the vac gauges on tomorrow and see where they are sitting.
Guess there could some change since injectors have been cleaned.

[BJ]

So, leads one and four will fire cylinder 1 but neither will fire cylinder 4.
Switched plugs between 1 and 4. Same result.
Conclusion, not electrical.
Put the Carbtune vac gauges on and cylinder 4 was at the top limit and stayed there for a few turns before it started to come down
Cylinder 1 fair bit low and 2 & 3 hovering around the middle.
Wound down cyl 4 and up on 1.
Was amazed at two things.
A - the vac gauges were sooo easy to adjust which would have to be from the extra clean injectors.
B - bike runs like a charm.
I recall that the guy who cleaned my injectors said one was way dirty and I think he had it in the sonic cleaner for five hours.
My advice - If you clean injectors then vac the throttle bodies as part of reinstalling

My bike has been running like shit for about three years so I'm hoping this will be the solution.

Other part of the story.
About 18 mths maybe more, the bike was in the Stealership and they said they cleaned the injectors.
I had to use an impact driver with hammer to release the two screws that hold the fuel rail. Those little f#@$kers were tight.
The screw heads were unmarked and there is no way they had been out before. The bastards.
I replaced them with stainless bolts so can use a ring spanner to loosen.

[KiwiCol]

That's great to get a result.   

@Irish in Oz
Thanks Jeff for a good steer,  we will all look for this as a solution from here on, not just leads or plugs etc.

[froudy]

@BJ
Glad you got it sorted

[grog]

BJ, well done.