Non-firing cylinder
clairetoo - 25/10/12 at 04:14 PM
After all the faffing about with my V6 Mx5 , which has got me nowhere ( 
) , I seem to tracked down the basic problem - one cylinder isnt firing
.
I have changed everything - injector , wiring , plug , swapped the plug leads , and just done a leak-down test .
It was the same as the next cylinder - just over 10% - with no audible leaks from the throttle body , exhaust or breather .
So - what the fudge is going on ? Pulling a plug lead off any other cylinder causes the engine to nearly stop , but has no effect on that cylinder ,
which also pops flame from the throttle body when revved .
Any suggestions welcome !
Jon Ison - 25/10/12 at 04:22 PM
Got a spark ?
The next thing I would look at is can you see the injector down the inlet tract ? If so is it injecting, in my experience its usually lack of fuel
rather than lack of spark on fuel injected cars cuasing this problem.
clairetoo - 25/10/12 at 04:29 PM
I have a spark , and on removal from the engine the plug from the offending cylinder is wet - so I have spark , fuel and compression .
I just checked my TDC mark , and its spot-on - checked the timing with a timing/advance light and its spot-on .
rb968 - 25/10/12 at 04:37 PM
Weird one Claire. Spark and wet plug?
Have you got a spare coilpack to try? In case its broken down on that one lead?
Sorry only thing I can think of on top of what you have tried.
Rich
clairetoo - 25/10/12 at 04:42 PM
I have tried swapping the two leads on that part of the coil , and nothing changed - I've spent two days off and on swapping and changing stuff ,
to no effect
jollygreengiant - 25/10/12 at 04:56 PM
Are the valves on that cylinder opening properly, First garage I worked in one mechanic had a V8 Yank with a misfire on 1 cylinder. He changed the
distributor, serviced the carb, removed the head and over-hauled them, changed the coil, changed the leads, did the heads again. Then one day he was
running the engine with the rocker covers off and noticed one of the valve rockers was barely moving. Turned out one of the cam lodes almost made a
perfect bearing cos' it had worn round(ish).
Just a thought.
DIY Si - 25/10/12 at 05:07 PM
Could it over-fuelling that one cylinder? An injector sticking open would cause roughly what you're seeing.
clairetoo - 25/10/12 at 05:34 PM
quote:
Originally posted by DIY Si
Could it over-fuelling that one cylinder? An injector sticking open would cause roughly what you're seeing.
I've now tried four different injectors in that cylinder !
ashg - 25/10/12 at 05:56 PM
you say you have spark. is that when you pull the ht lead off? have you actually checked that the spark plug is working? hows the finger getting
on?
DIY Si - 25/10/12 at 05:56 PM
Ummmm.......
clairetoo - 25/10/12 at 06:01 PM
quote:
Originally posted by ashg
you say you have spark. is that when you pull the ht lead off? have you actually checked that the spark plug is working? hows the finger getting
on?
I've gone through a complete set of plugs from a spare engine , tried the old trick of heating the plug before fitting - I have a good spark at
the plug , but nothing once its in the engine .
Edit to add - the fingers are still sore , two of them dont bend at all
[Edited on 25/10/12 by clairetoo]
on_eighty_runner - 25/10/12 at 06:05 PM
assuming spark plug is ok, (swap with one from another cylinder)
The inlet valve make be stuck open . You mentioned flames in its inlet tract,
No other route for flames unless timing on that individual cylinder is miles out. (spark during induction stroke)
clairetoo - 25/10/12 at 06:15 PM
quote:
Originally posted by on_eighty_runner
assuming spark plug is ok, (swap with one from another cylinder)
The inlet valve make be stuck open . You mentioned flames in its inlet tract,
No other route for flames unless timing on that individual cylinder is miles out. (spark during induction stroke)
Thing is - the leak-down test showed no problems . I've been pulling and swapping plugs all day.........and surely a timing issue would effect
all the cylinders , not just one ?
[Edited on 25/10/12 by clairetoo]
Nickp - 25/10/12 at 06:22 PM
Has it got hydraulic lifters? Faulty one keeping a valve open maybe? You've done a leak down test, but have you done a compression test?
[Edited on 25/10/12 by Nickp]
clairetoo - 25/10/12 at 06:29 PM
quote:
Originally posted by Nickp
Has it got hydraulic lifters? Faulty one keeping a valve open maybe? You've done a leak down test, but have you done a compression test?
[Edited on 25/10/12 by Nickp]
Could that happen - it does have hydraulic followers , could they `pump up' when running , but leak out when stopped ?
One `test' I have done is simply to place the palm of my hand on the top of the throttle body , it sucks my hand hard to the `body , but doesnt
slow the engine at all .
Nickp - 25/10/12 at 06:35 PM
quote:
Originally posted by clairetoo
quote:
Originally posted by Nickp
Has it got hydraulic lifters? Faulty one keeping a valve open maybe? You've done a leak down test, but have you done a compression test?
[Edited on 25/10/12 by Nickp]
Could that happen - it does have hydraulic followers , could they `pump up' when running , but leak out when stopped ?
One `test' I have done is simply to place the palm of my hand on the top of the throttle body , it sucks my hand hard to the `body , but doesnt
slow the engine at all .
It is possible. Does it spit back against your hand when you do that test? Mind those pinkies 
sebastiaan - 25/10/12 at 06:38 PM
Blocked exhaust primary maybe?
We're running out of options here.... Maybe it's voodoo? 
britishtrident - 25/10/12 at 07:09 PM
Just because you get a spark testing with the plug out doesn't mean there is a spark under compression, the voltage required to jump the
spark plug gap is much higher under compression. At these high voltages the insulation of the coil pack or distributor cap as to be in top class
order or the spark will jump to earth.
clairetoo - 25/10/12 at 07:10 PM
quote:
Originally posted by Nickp
quote:
Originally posted by clairetoo
quote:
Originally posted by Nickp
Has it got hydraulic lifters? Faulty one keeping a valve open maybe? You've done a leak down test, but have you done a compression test?
[Edited on 25/10/12 by Nickp]
Could that happen - it does have hydraulic followers , could they `pump up' when running , but leak out when stopped ?
One `test' I have done is simply to place the palm of my hand on the top of the throttle body , it sucks my hand hard to the `body , but doesnt
slow the engine at all .
It is possible. Does it spit back against your hand when you do that test? Mind those pinkies
Nope , no spitting at all (at tickover)
I am being careful - I'm using the other hand for testing stuff
Nickp - 25/10/12 at 07:12 PM
A colourtune kit might help you see what's happening spark wise.
rusty nuts - 25/10/12 at 07:24 PM
As Jolly green giant has already suggested check that the valves are opening, I wouldn't be suprised if the exhaust valve isn't opening
which would give you compression but not allow the cylinder to fire properly causing spitting back through the throttle body and a wet plug. I've
had similar symptoms a few times, a couple of times it was due to worn(read non existent )cam lobes and another was due to a tappet adjuster coming
loose
adithorp - 25/10/12 at 07:48 PM
quote:
Originally posted by rusty nuts
As Jolly green giant has already suggested check that the valves are opening, I wouldn't be suprised if the exhaust valve isn't opening
which would give you compression but not allow the cylinder to fire properly causing spitting back through the throttle body and a wet plug. I've
had similar symptoms a few times, a couple of times it was due to worn(read non existent )cam lobes and another was due to a tappet adjuster coming
loose
Agreed. Seen it years ago on a RangeRover that had 2 exhaust cam lobes worn down to nothing. had compression, spark and fuel but wouldn't fire on
those 2 cylinders.
clairetoo - 25/10/12 at 07:59 PM
Thanks for the suggestions guys - looks like tomorrows job is to pull the cam cover off that bank , and have a good look .
I do have plenty of spares - the Fury engine just happens to have dead rings and a broken cam belt
ashg - 25/10/12 at 11:53 PM
Not having much luck at the moment are you.
MikeRJ - 25/10/12 at 11:59 PM
An air leak on the inlet manifold/throttle body is a possibility. That would account for both the flame spitting activities and not running at idle,
as well as not affecting a leak down test.
[Edited on 25/10/12 by MikeRJ]
clairetoo - 26/10/12 at 06:38 AM
quote:
Originally posted by ashg
Not having much luck at the moment are you.
Thats putting it mildly.......if I didnt have bad luck , I wouldnt have any luck at all
clairetoo - 26/10/12 at 06:41 AM
quote:
Originally posted by MikeRJ
An air leak on the inlet manifold/throttle body is a possibility. That would account for both the flame spitting activities and not running at idle,
as well as not affecting a leak down test.
[Edited on 25/10/12 by MikeRJ]
I thought that - but removing and sealing the bodies made no difference , I even swapped the whole setup and nothing changed
BaileyPerformance - 26/10/12 at 08:50 AM
Hi Claire,
Please list the compression of each cylinder.
I would guess all cylinders should be at least 150PSI? (check each cylinder with the throttle open, unplug megasquirt)
MikeRJ - 26/10/12 at 08:55 AM
quote:
Originally posted by clairetoo
quote:
Originally posted by MikeRJ
An air leak on the inlet manifold/throttle body is a possibility. That would account for both the flame spitting activities and not running at idle,
as well as not affecting a leak down test.
[Edited on 25/10/12 by MikeRJ]
I thought that - but removing and sealing the bodies made no difference , I even swapped the whole setup and nothing changed
You are running individual throttle bodies on this right? Are you certain the butterfly on this cylinder is well synchronised and sealing correctly -
if it was too far open compared to the others the same symptoms would be seen. A vacuum measurement downstream of the butterfly with the engine
running would rule this out (if not already done).
clairetoo - 26/10/12 at 08:55 AM
quote:
Originally posted by BaileyPerformance
Hi Claire,
Please list the compression of each cylinder.
I would guess all cylinders should be at least 150PSI? (check each cylinder with the throttle open, unplug megasquirt)
I'd love to do that - but I dont have a compression tester
BaileyPerformance - 26/10/12 at 09:00 AM
Me again!
Ment to ask what do you mean by leak down test? we have a snap-on device that applies air pressure to a cylinder (from a workshop compressor) and its
supposed to identify poor sealing valves and rings - the thing is next to useless! (this device is labeled "leak tester"
We always found a basic compression test to be more useful at identifying engine problems, an old trick is to squirt some engine oil down the
offending cylinder and re-test - if the compression comes back up you know is the bottom end, if not its the top end.
You said your other car has an engine problem? What caused that?
BaileyPerformance - 26/10/12 at 09:06 AM
quote:
Originally posted by clairetoo
quote:
Originally posted by BaileyPerformance
Hi Claire,
Please list the compression of each cylinder.
I would guess all cylinders should be at least 150PSI? (check each cylinder with the throttle open, unplug megasquirt)
I'd love to do that - but I dont have a compression tester
Oh!
You need to buy one! ebay!!
We see loads of poor running customers cars here - normally the owner has replaced everything assuming its engine electronics but never do the basic
checks! For example we had an Escort Zetec in awhile ago, the thing ran rough and would not idle what cold, so the owner replaced the idle valve (£50
from Ford!!!!) No effect.
I did a compression test... one cylinder had 70PSI on it, rest over 150. Engine scrap. Always check the basics first.
BaileyPerformance - 26/10/12 at 09:12 AM
This is what you need....
http://www.ebay.co.uk/itm/PETROL-ENGINE-CYLINDER-AUTOMOTIVE-COMPRESSION-DUAL-TESTER-TOOL-KIT-/300723181279?pt=UK_Diagnostic_Tools_Equipment&hash=i
tem46047f96df
clairetoo - 26/10/12 at 09:28 AM
A leak down will tell you far more than a basic compression test - you can have acceptable compression with poorly sealing valves .
The leak test tells you straight away where the problem is - leaking valves can be heard through the throttle body , exhaust valves can be heard at
the tail pipe......and dead rings will blow out the oil filler .
clairetoo - 26/10/12 at 09:33 AM
quote:
Originally posted by BaileyPerformance
You said your other car has an engine problem? What caused that?
Too much abuse It was getting a bit smokey , then a lot smokey........and the final straw was last time I went to start it (just to move it on the
drive) the cambelt snapped !
I do have several spare engines , so if its a major mechanical issue I can just chuck another one in 
BaileyPerformance - 26/10/12 at 09:38 AM
quote:
Originally posted by clairetoo
A leak down will tell you far more than a basic compression test - you can have acceptable compression with poorly sealing valves .
The leak test tells you straight away where the problem is - leaking valves can be heard through the throttle body , exhaust valves can be heard at
the tail pipe......and dead rings will blow out the oil filler .
If you had "acceptable compression" it would be running on all cylinders as you have replaced/swapped everything else.
Leak down test is a waste of time in your case, all you need to do is perform a basic compression test, trust me, buy a basic compression tester then
you can prove if the engine is OK or not.
What happened to your other engine? Why did that die?
BaileyPerformance - 26/10/12 at 09:41 AM
Sorry,
Just learnt to read!
You said your other engine started to smoke.... And cambelt failed.
The engine with the miss, have you had it on the road?
What AFRs to you aim for cruse and full throttle?
clairetoo - 26/10/12 at 09:49 AM
This is the engine in my Mx5 - I got it through the MOT , but thats all its done so far.........
I run about 15/15.5 at cruise - and aim for 13.5 on full noise (but not too bothered about full throttle , its not often used ) Thats in the Fury -
its already too damn fast , and easily capable of over 150 mph 
BaileyPerformance - 26/10/12 at 10:18 AM
quote:
Originally posted by clairetoo
This is the engine in my Mx5 - I got it through the MOT , but thats all its done so far.........
I run about 15/15.5 at cruise - and aim for 13.5 on full noise (but not too bothered about full throttle , its not often used ) Thats in the Fury -
its already too damn fast , and easily capable of over 150 mph
That may explain why its dead, never go any leaner than 12.5AFR full throttle, going lean at cruise is OK but if your overall AFR is 15, you could
have a cylinder at 16 due to unequal airflow (you can never get throttles 100% balanced)
For example a totally stock 1600/1800 MX5 (i know you have changed the engine, but the same applies) runs 12.0AFR full throttle and 14.7AFR cruise.
These engines are strong, i have never heard of one blowing up, running alittle richer at full throttle makes engines live longer if you plan to
thrash it. If the manufacturer decided to map them rich it was for good reason.
They also run a slightly retarded (from idea) total timing, again this is to make it live longer if you thrash it. I cant remember the exact number
but 32deg would be enough for max power, 36deg cruise.
The only way i would run 13.5AFR full throttle was if i had knock detection, your engine may have suffered det but you wouldn't be able to hear
it in a car of that type.
Normally if an engine has not been modified, is set up correctly and kept cool you can hold it full throttle red line for as long as you like without
damaging it. ( i know you said you dont use full throttle very often, but det will damage and engine in seconds)
clairetoo - 26/10/12 at 12:09 PM
I'm just going to the bottom of the garden ............ to swear A LOT (and maybe even shoot myself.....)
I had tries swapping the plug leads around at the coil - after all , if one side of a paired coil works , the other will as well ? It had no effect
.
So today . I took the coil off my Fury ............ and now it runs properly Just been for a spin around the block , and its proper
......................... at last
Thanks to all for the suggestions - at least I can say for sure now that everything is good , so time for a bit of mapping
Nickp - 26/10/12 at 12:12 PM
HURRAH!!
rb968 - 26/10/12 at 12:19 PM
quote:
Originally posted by rb968
Weird one Claire. Spark and wet plug?
Have you got a spare coilpack to try? In case its broken down on that one lead?
Sorry only thing I can think of on top of what you have tried.
Rich
Cough, cough........
Can I claim credit then?
Glad you got it sorted.
Rich
clairetoo - 26/10/12 at 12:22 PM
quote:
Originally posted by rb968
quote:
Originally posted by rb968
Weird one Claire. Spark and wet plug?
Have you got a spare coilpack to try? In case its broken down on that one lead?
Sorry only thing I can think of on top of what you have tried.
Rich
Cough, cough........
Can I claim credit then?
Glad you got it sorted.
Rich
yep - you are now allowed to be smug for the rest of the day
Thing is - each section of the coil runs two cylinders - and only one wouldnt fire (at all) , I had swapped the two leads over , to no effect , so I
had almost ruled out the coil