Oneball
CCCUK Member
If that is the case then your problem is almost certainly in the electrical system. There are very few non electrical issues that test would show up (flooded plugs for example)
Recurrent misfiring problem
- Thread starter antijam
- Start date
antijam
CCCUK Member
I was much of your opinion. However, I've tested and swapped all the ignition parts separately. Everything is in spec and each item seems to be functioning correctly. The fact that all plugs fire satisfactorily outside the cylinder and my spark tester verifies an adequate voltage on all HT leads is leading me to think that the problem must lie elsewhere.
teamzr1
Supporting vendor
If the sparkplug gap is correct and your testing showed high voltages from coil than
it would have to be a makeup of the charge to the cylinder or dirty exhaust pulled back into the cylinders
Above points, I made and using a borescope to closely look at top of pistons and face of valves and seats
IF thinking there are misfires then be interesting to see the difference of AFR of B1 and B2 using
an AFR tester at muffler tips
it would have to be a makeup of the charge to the cylinder or dirty exhaust pulled back into the cylinders
Above points, I made and using a borescope to closely look at top of pistons and face of valves and seats
IF thinking there are misfires then be interesting to see the difference of AFR of B1 and B2 using
an AFR tester at muffler tips
Roscobbc
Moderator
Remember the old Colourtune sparkplugs?. With it's glass (rather than ceramic) insulator you would adjust your ideal mixture to a perfect burn and see the 'burn' through the glass insulator. Of course you would have to repeat for multi-carb/choke engines but it could be used to 'visualise' and establish it individual cylinders had potential issues.
teamzr1
Supporting vendor
Interesting, never heard of this test tool before
Some info
www.howacarworks.com
Sold in the UK
www.frost.co.uk
www.gunson.co.uk
Some info
Tuning the engine with a colortune plug
Although some experienced mechanics can tune a car's carburettor fairly well by ear, to do the job really accurately you need the help of special equipment.
Sold in the UK
Gunson Colortune Plug Kit (14mm)
Gunson Colortune Plug Kit (14mm) from Frost.co.uk - The Specialist of High Quality Tools & Equipment for the Classic Vehicle Restorer
www.frost.co.uk
Gunson G4074 Colortune Single Plug Kit 14mm
Gunson Colortune plug kit lets you tune 2
antijam
CCCUK Member
Yes indeed Rosco! - I didn't know they still made them? A rummage through my 'Tune-up' tool kit revealed this....
...a near pristine Colourtune kit! It has to be something of a museum piece - the last time I used it must be more than 40 years ago! It was very useful in setting up old SU's - you could adjust the mixture very easily with the engine running.
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Roscobbc
Moderator
I was going to add that were great for setting-up SU's or Strombergs - can't remember the viewing tube and mirror gizmo.....and yes its also more than 50 years ago used one. Shame we didn't start this conversation a few days earlier - had you not stripped the inlet off the engine you could have tried this on the 'iffy' cylinder.
Irrespective of that it would be interesting to try this of each cylinder in sequence to see how the air/fuel mixture is on each cylinder at idle........even when all is 100% there will be variations between cylinders.
teamzr1
Supporting vendor
If your borescope has a record video mode
Insert that AFR tool into 1 of the cylinders you think has misfire
Rig the borescope so it could record the tools color and go for a drive and check AFR under real-world conditions
and then replay the recording
This might also trap if there is any small cracks in a sparkplug arcing to ground
Insert that AFR tool into 1 of the cylinders you think has misfire
Rig the borescope so it could record the tools color and go for a drive and check AFR under real-world conditions
and then replay the recording
This might also trap if there is any small cracks in a sparkplug arcing to ground
antijam
CCCUK Member
Trouble is it only works if the plug is firing. Even then using the viewing tube and mirror could be tricky in tight places. I'm trying to imagine getting a sensible view of the plug in #7 of an sbc with headers !
antijam
CCCUK Member
I pulled all the plugs to do the compression test and noted which cylinder each came from. The only visible difference of those from the non-firing cylinders was that they were wet with fuel.
antijam
CCCUK Member
I'm preparing to re-install my intake manifold and I've noticed that both the old gaskets have heat crossover restrictors fitted. My new Fel-Pro gasket set comes with a restrictor for one side only and i'm wondering if this should actually be fitted and if so, in which side?
(Old gasket below with restrictor fitted - new one above, without.)
The engine is running a stock Quadrajet carb with divorced coil choke on a stock cast iron manifold. It's fitted with headers so has no heat riser valve. Obviously the choke will benefit from some heat transfer to come off - and stay off - as quickly as possible but the carb itself however could well do without any excess heat to avoid early vapourisation in hot weather. ( I've had a couple of occasions when the engine cut out in very hot weather and slow traffic. Restart was only possible after raising the hood and waiting twenty minutes or so. Certainly indicative of vapourisation or percolation.). Modern ethanol loaded fuel is even more volatile than petrol so any potential vapourisation problems are more likely nowadays. I believe the original Quadrajet mounting gasket was a composite affair designed to minimise heat transfer from the manifold but this is very hard to find these days and very expensive if you can, so I have only a standard thick gasket to mount my carb.
There appears to be a trade off between allowing enough heat through to actuate the choke properly but not so much that there may be fuel percolation problems in the carb....Web wisdom suggests that with my set-up the best compromise is having the crossover restrictor fiitted but only in the drivers side gasket, leaving the passenger side clear.
So, unless anyone can offer a better suggestion, that's what I'll try.
(Old gasket below with restrictor fitted - new one above, without.)
The engine is running a stock Quadrajet carb with divorced coil choke on a stock cast iron manifold. It's fitted with headers so has no heat riser valve. Obviously the choke will benefit from some heat transfer to come off - and stay off - as quickly as possible but the carb itself however could well do without any excess heat to avoid early vapourisation in hot weather. ( I've had a couple of occasions when the engine cut out in very hot weather and slow traffic. Restart was only possible after raising the hood and waiting twenty minutes or so. Certainly indicative of vapourisation or percolation.). Modern ethanol loaded fuel is even more volatile than petrol so any potential vapourisation problems are more likely nowadays. I believe the original Quadrajet mounting gasket was a composite affair designed to minimise heat transfer from the manifold but this is very hard to find these days and very expensive if you can, so I have only a standard thick gasket to mount my carb.
There appears to be a trade off between allowing enough heat through to actuate the choke properly but not so much that there may be fuel percolation problems in the carb.
...Web wisdom suggests that with my set-up the best compromise is having the crossover restrictor fiitted but only in the drivers side gasket, leaving the passenger side clear.So, unless anyone can offer a better suggestion, that's what I'll try.