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Secondary Ignition - Hash on Burn Line
Secondary Ignition - Hash on Burn Line
What, if anything, is hash on the burn line indicative of?
The waveform below was taken with an HT capacitative pickup from the No 1 cylinder HT lead, shortly after startup on a cold engine. The other 3 cylinders only showed clean burn lines, and not all No 1 firing events showed the hash.
(Due to problems with the software/laptop, I wasn’t able to see if this type of event persisted as the engine warmed up; I suspect the hash reflects poor mixing of fuel/air in the cold cylinder.)
The engine is a 1.1L K Series Rover SPi.
The waveform below was taken with an HT capacitative pickup from the No 1 cylinder HT lead, shortly after startup on a cold engine. The other 3 cylinders only showed clean burn lines, and not all No 1 firing events showed the hash.
(Due to problems with the software/laptop, I wasn’t able to see if this type of event persisted as the engine warmed up; I suspect the hash reflects poor mixing of fuel/air in the cold cylinder.)
The engine is a 1.1L K Series Rover SPi.
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Steve Smith
- Pico Staff Member
- Posts: 1671
- Joined: Sun Aug 25, 2013 7:22 am
Re: Secondary Ignition - Hash on Burn Line
Hello Martin, I hope you are well and thank you for the post
The burn voltage does look exceptionally noisy and given this was a cold engine we have several possibilities to consider
Could I ask, did the vehicle misfire or run unstable during the initial cold start (perhaps uneven combustion more than misfire?)
If so, does this smooth out within a minute or so?
My line of thinking here is the condition of the air/fuel mixture during cold start
If we assume air intake and fuel delivery to be correct (a huge assumption I know but our other 3-cylinders are fine and this is an SPI) then my thoughts turn to oil or coolant ingress into the combustion chamber (This will soon clear)
Have you noted any oil or coolant consumption?
The other more sinister concern is reduced compression due to sticking or poorly seated valves as carbon deposits can form on the valve stems and ultimately intrude up into the valve guide (Oh the joys and wonder of the K-Series engine)
Before diving in, would it be possible to remove the spark plugs and compare them all for colour, carbon deposits and gap (Keep cylinder 1 plug clearly marked)
We may find clues as to the mechanical integrity of the cylinder
Once we have put the mechanical possibilities to bed, we can focus on air and fuel mixture, inspect for air leakage and fuel trim values when hot (via OBD)
Next, we can look at the integrity of the HT system, and my thoughts turn to not only the plug, lead and routing but also the rotor arm if this is a K-Series with the distributor cap located on the camshaft?
A visual inspection of the cap may reveal issues around the terminal for cylinder 1 HT lead. A test you can do to evaluate rotor arm gap (whilst removing the combustion chamber variables) is to disconnect the HT lead from spark plug number 1 and short directly to ground
Crank and start the engine to obtain the voltage required to jump the rotor arm gap, which you can then compare with others (From memory, this used to be 5 kV)
It would be great to see if your burn voltage has revealed a mechanical symptom described above, but if so, I would not dwell to much if the symptom clears when warm. We have to cut your engine some slack based on age, usage patterns and characteristics.
Often, if the vehicle covers very few miles, a prolonged drive will perform wonders for niggling mechanical issues. Whilst there could well be a scientific explanation and may theories as to why, I would be happy to accept any improvement as a result.
I have heard of such road tests being called “An Italian Decoke” to which I am sure there are many interpretations
I hope some of this helps and the laptop/software issue is resolved
Take care……..Steve
The burn voltage does look exceptionally noisy and given this was a cold engine we have several possibilities to consider
Could I ask, did the vehicle misfire or run unstable during the initial cold start (perhaps uneven combustion more than misfire?)
If so, does this smooth out within a minute or so?
My line of thinking here is the condition of the air/fuel mixture during cold start
If we assume air intake and fuel delivery to be correct (a huge assumption I know but our other 3-cylinders are fine and this is an SPI) then my thoughts turn to oil or coolant ingress into the combustion chamber (This will soon clear)
Have you noted any oil or coolant consumption?
The other more sinister concern is reduced compression due to sticking or poorly seated valves as carbon deposits can form on the valve stems and ultimately intrude up into the valve guide (Oh the joys and wonder of the K-Series engine)
Before diving in, would it be possible to remove the spark plugs and compare them all for colour, carbon deposits and gap (Keep cylinder 1 plug clearly marked)
We may find clues as to the mechanical integrity of the cylinder
Once we have put the mechanical possibilities to bed, we can focus on air and fuel mixture, inspect for air leakage and fuel trim values when hot (via OBD)
Next, we can look at the integrity of the HT system, and my thoughts turn to not only the plug, lead and routing but also the rotor arm if this is a K-Series with the distributor cap located on the camshaft?
A visual inspection of the cap may reveal issues around the terminal for cylinder 1 HT lead. A test you can do to evaluate rotor arm gap (whilst removing the combustion chamber variables) is to disconnect the HT lead from spark plug number 1 and short directly to ground
Crank and start the engine to obtain the voltage required to jump the rotor arm gap, which you can then compare with others (From memory, this used to be 5 kV)
It would be great to see if your burn voltage has revealed a mechanical symptom described above, but if so, I would not dwell to much if the symptom clears when warm. We have to cut your engine some slack based on age, usage patterns and characteristics.
Often, if the vehicle covers very few miles, a prolonged drive will perform wonders for niggling mechanical issues. Whilst there could well be a scientific explanation and may theories as to why, I would be happy to accept any improvement as a result.
I have heard of such road tests being called “An Italian Decoke” to which I am sure there are many interpretations
I hope some of this helps and the laptop/software issue is resolved
Take care……..Steve
Re: Secondary Ignition - Hash on Burn Line
Thank you, Steve, for such a comprehensive reply, and sorry for the delay: despite my preferences settings, I mustn’t have ticked the box in the topic to be notified of a reply in the topic.Steve Smith wrote: ↑Fri Aug 09, 2024 12:18 pmHello Martin, I hope you are well and thank you for the post
The burn voltage does look exceptionally noisy and given this was a cold engine we have several possibilities to consider
Could I ask, did the vehicle misfire or run unstable during the initial cold start (perhaps uneven combustion more than misfire?)
If so, does this smooth out within a minute or so?
My line of thinking here is the condition of the air/fuel mixture during cold start
If we assume air intake and fuel delivery to be correct (a huge assumption I know but our other 3-cylinders are fine and this is an SPI) then my thoughts turn to oil or coolant ingress into the combustion chamber (This will soon clear)
Have you noted any oil or coolant consumption?
The other more sinister concern is reduced compression due to sticking or poorly seated valves as carbon deposits can form on the valve stems and ultimately intrude up into the valve guide (Oh the joys and wonder of the K-Series engine)
Before diving in, would it be possible to remove the spark plugs and compare them all for colour, carbon deposits and gap (Keep cylinder 1 plug clearly marked)
We may find clues as to the mechanical integrity of the cylinder
Once we have put the mechanical possibilities to bed, we can focus on air and fuel mixture, inspect for air leakage and fuel trim values when hot (via OBD)
Next, we can look at the integrity of the HT system, and my thoughts turn to not only the plug, lead and routing but also the rotor arm if this is a K-Series with the distributor cap located on the camshaft?
A visual inspection of the cap may reveal issues around the terminal for cylinder 1 HT lead. A test you can do to evaluate rotor arm gap (whilst removing the combustion chamber variables) is to disconnect the HT lead from spark plug number 1 and short directly to ground
Crank and start the engine to obtain the voltage required to jump the rotor arm gap, which you can then compare with others (From memory, this used to be 5 kV)
It would be great to see if your burn voltage has revealed a mechanical symptom described above, but if so, I would not dwell to much if the symptom clears when warm. We have to cut your engine some slack based on age, usage patterns and characteristics.
Often, if the vehicle covers very few miles, a prolonged drive will perform wonders for niggling mechanical issues. Whilst there could well be a scientific explanation and may theories as to why, I would be happy to accept any improvement as a result.
I have heard of such road tests being called “An Italian Decoke” to which I am sure there are many interpretations
I hope some of this helps and the laptop/software issue is resolved
Take care……..Steve
I didn’t notice any misfire or rough running; it was the surprising, poor-emissions test that prompted me to delve deeper. And then I also noticed the occasional “missed exhaust beat” - a sticking valve.
But I feel certain you’ve hit the nail on the head with the sticking/poorly-seating exhaust valve. I’ve been wondering if, on the intake stroke, some exhaust gas is being drawn back into the No 1 cylinder through the valve face-seat interface and if that’s the cause of the hash? You once advised me not to draw conclusions over identifying the offending cylinder based on a pulse at the outlet of the exhaust because if the time of travel of the pulse.
I wonder if an accelerometer on the branches of the exhaust-manifold, or my adaptation of the NVH microphone in its magnetic case, might allow identification of the offending cylinder through the “loudest” event; that could be an interesting experiment, at least. (I might have to give thought to heat protection of the magnet/accelerometer.) It’d be good to extract the most info before the head comes off, including seeing what happens to the hash as the engine warms up; it appears as if it was indeed better on a hot engine, but I’d really want to repeat the trial and capture waveforms in one sitting as it warms up. (I have 11 months to the next MoT test, so, plenty of time to extract useful information.)
I did, indeed, carry out the tried-and-tested method of taking a shufti of the plugs, and all 4 looked the same - no different to anything I’d seen before. I’ll make a note to photograph the plugs in the future, as a group.
Using the Rover diagnostic software, I saw nothing obvious in the long-term fuel trim (LTFT), but I will keep my eye on this. (Previously, the LTFT improved ie became leaner on the refurbishment of the head.). Also, I always fill up with 20 litres of fuel. In the summer, it should get me 200 miles, in the winter 180 miles. So far, I haven’t noticed any difference, but I don’t clock up enough miles to be sure just yet, but I always monitor this key indicator. Too many shortish journeys - the very worst punishment one can inflict on an engine.
Before the captures, the car had a really good motorway run of over 100 miles (to pick up a second-hand OEM catalytic converter), so it really had opportunity to clear its throat, not quite an “Italian decoke” (https://frenchcarforum.co.uk/forum/view ... hp?t=21888), but well on the way.
I have one of those spark voltage testers:
A work in progress…….
Take care, Steve.
Martin