Discussion:
Misfire under load
(too old to reply)
Peter
2005-12-13 08:08:23 UTC
Permalink
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.

Peter
Reggy
2005-12-13 12:54:11 UTC
Permalink
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
Peter
swap the plug and pack for another , lpg is much more demanding sprk
wise . if the miss moves to the other cylinder you have an answer .
Peter
2005-12-13 17:01:27 UTC
Permalink
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each
cyl, and plugs have been changed couple of months ago. It idles smoothly
so I'd tend to exclude any vacuum leaks. Misfires only when running on
LPG (single point closed loop), petrol runs just fine. When it misfires
Check Engine flashes (and computer sets P0302 - misfire in cyl #2), and
vibration can be felt in steering wheel.
swap the plug and pack for another , lpg is much more demanding sprk wise
. if the miss moves to the other cylinder you have an answer .
i did that, we'll see. Spark plugs were both looking good, with light
(almost white) tan everywhere except for the spark area (which was black)
Austin Shackles
2005-12-13 14:01:45 UTC
Permalink
On or around Tue, 13 Dec 2005 10:08:23 +0200, "Peter"
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
iffy coil pack or lead or even an iffy new plug.

did it do this before the plug change?
--
Austin Shackles. www.ddol-las.net my opinions are just that
"You praise the firm restraint with which they write -_
I'm with you there, of course: They use the snaffle and the bit
alright, but where's the bloody horse? - Roy Campbell (1902-1957)
Peter
2005-12-13 17:02:46 UTC
Permalink
Post by Austin Shackles
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
iffy coil pack or lead or even an iffy new plug.
did it do this before the plug change?
It did that before very occasionally. I wrote it off to a vacuum leak, and
eventually ended up replacing intake manifold gasket (very rough idle), and
things were running smoothly after that

Peter
Austin Shackles
2005-12-13 14:03:02 UTC
Permalink
On or around Tue, 13 Dec 2005 10:08:23 +0200, "Peter"
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
'nother possibility is that the tuning of the gas side is not quite correct
and this shows up a weakness in the ignition when under load.
--
Austin Shackles. www.ddol-las.net my opinions are just that
"Ask yourself whether you are happy, and you cease to be so."
John Stuart Mill (1806 - 1873)
Peter
2005-12-13 17:03:57 UTC
Permalink
Post by Austin Shackles
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
'nother possibility is that the tuning of the gas side is not quite correct
and this shows up a weakness in the ignition when under load.
It has occured to me as well. It's BRC Just Light, and it's supposed to be
self-adapting. Even if it was faulty, why only one cylinder is misfiring?

Drained heavy ends just in case.

Peter
Austin Shackles
2005-12-13 20:22:24 UTC
Permalink
On or around Tue, 13 Dec 2005 19:03:57 +0200, "Peter"
Post by Peter
Post by Austin Shackles
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
'nother possibility is that the tuning of the gas side is not quite correct
and this shows up a weakness in the ignition when under load.
It has occured to me as well. It's BRC Just Light, and it's supposed to be
self-adapting. Even if it was faulty, why only one cylinder is misfiring?
Drained heavy ends just in case.
that was a long shot. Ignition weakness is most likely - might just be that
a marginal tune is showing up the ignition problem.

but the ignition gets my vote, to start with. see what happens with
swapping plugs etc.
--
Austin Shackles. www.ddol-las.net my opinions are just that
"Remember that to change your mind and follow him who sets you right
is to be none the less free than you were before."
Marcus Aurelius Antoninus (121-180), from Meditations, VIII.16
Peter
2005-12-14 16:25:30 UTC
Permalink
Post by Austin Shackles
Post by Peter
Post by Austin Shackles
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
'nother possibility is that the tuning of the gas side is not quite correct
and this shows up a weakness in the ignition when under load.
It has occured to me as well. It's BRC Just Light, and it's supposed to be
self-adapting. Even if it was faulty, why only one cylinder is misfiring?
Drained heavy ends just in case.
that was a long shot. Ignition weakness is most likely - might just be that
a marginal tune is showing up the ignition problem.
but the ignition gets my vote, to start with. see what happens with
swapping plugs etc.
Looks like it's NOT ignition trouble. Swapped coil packs & plugs, misfire
stays at cyl #2. It gets worse - engine won't produce power unless rpms go
above 3-4K. In fact after I revved it good on the highway it seems to do
better. I strongly suspect vaporiser - it seems unable to produce enough
propane at 2-3k rpms, and needs some heavy sucking action from the engine.
Blockage of some sort? Probably will have to take it to the installer...
petrol side still runs just fine.

Peter
Austin Shackles
2005-12-14 20:12:47 UTC
Permalink
On or around Wed, 14 Dec 2005 18:25:30 +0200, "Peter"
Post by Peter
Post by Austin Shackles
Post by Peter
Post by Austin Shackles
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
'nother possibility is that the tuning of the gas side is not quite correct
and this shows up a weakness in the ignition when under load.
It has occured to me as well. It's BRC Just Light, and it's supposed to be
self-adapting. Even if it was faulty, why only one cylinder is misfiring?
Drained heavy ends just in case.
that was a long shot. Ignition weakness is most likely - might just be that
a marginal tune is showing up the ignition problem.
but the ignition gets my vote, to start with. see what happens with
swapping plugs etc.
Looks like it's NOT ignition trouble. Swapped coil packs & plugs, misfire
stays at cyl #2. It gets worse - engine won't produce power unless rpms go
above 3-4K. In fact after I revved it good on the highway it seems to do
better. I strongly suspect vaporiser - it seems unable to produce enough
propane at 2-3k rpms, and needs some heavy sucking action from the engine.
Blockage of some sort? Probably will have to take it to the installer...
petrol side still runs just fine.
I asusme it was OK before?

Could be a blockage, could be diaphragm leaking.
--
Austin Shackles. www.ddol-las.net my opinions are just that
"'Tis a mad world, my masters" John Taylor (1580-1633) Western Voyage, 1
Reggy
2005-12-15 10:28:58 UTC
Permalink
Post by Austin Shackles
On or around Wed, 14 Dec 2005 18:25:30 +0200, "Peter"
Post by Peter
Post by Austin Shackles
Post by Peter
Post by Austin Shackles
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration can be
felt in steering wheel.
'nother possibility is that the tuning of the gas side is not quite correct
and this shows up a weakness in the ignition when under load.
It has occured to me as well. It's BRC Just Light, and it's supposed to be
self-adapting. Even if it was faulty, why only one cylinder is misfiring?
Drained heavy ends just in case.
that was a long shot. Ignition weakness is most likely - might just be that
a marginal tune is showing up the ignition problem.
but the ignition gets my vote, to start with. see what happens with
swapping plugs etc.
Looks like it's NOT ignition trouble. Swapped coil packs & plugs, misfire
stays at cyl #2. It gets worse - engine won't produce power unless rpms go
above 3-4K. In fact after I revved it good on the highway it seems to do
better. I strongly suspect vaporiser - it seems unable to produce enough
propane at 2-3k rpms, and needs some heavy sucking action from the engine.
Blockage of some sort? Probably will have to take it to the installer...
petrol side still runs just fine.
I asusme it was OK before?
Could be a blockage, could be diaphragm leaking.
http://www.prelube.com/articals.html
not directly applicable but there is some good fault-finding . I would
run the compression just to eliminate valves
Peter
2005-12-15 11:27:50 UTC
Permalink
Post by Reggy
Post by Austin Shackles
Post by Peter
Post by Austin Shackles
Post by Peter
Post by Austin Shackles
Post by Peter
What could possibly cause misfire in one cylinder only when running under
load, rpm range 2-3K? It's V6 engine with separate coil pack for each cyl,
and plugs have been changed couple of months ago. It idles smoothly so I'd
tend to exclude any vacuum leaks. Misfires only when running on LPG (single
point closed loop), petrol runs just fine. When it misfires Check Engine
flashes (and computer sets P0302 - misfire in cyl #2), and vibration
can
be
felt in steering wheel.
'nother possibility is that the tuning of the gas side is not quite correct
and this shows up a weakness in the ignition when under load.
It has occured to me as well. It's BRC Just Light, and it's supposed to be
self-adapting. Even if it was faulty, why only one cylinder is misfiring?
Drained heavy ends just in case.
that was a long shot. Ignition weakness is most likely - might just be that
a marginal tune is showing up the ignition problem.
but the ignition gets my vote, to start with. see what happens with
swapping plugs etc.
Looks like it's NOT ignition trouble. Swapped coil packs & plugs, misfire
stays at cyl #2. It gets worse - engine won't produce power unless rpms
go above 3-4K. In fact after I revved it good on the highway it seems to
do better. I strongly suspect vaporiser - it seems unable to produce
enough propane at 2-3k rpms, and needs some heavy sucking action from the
engine. Blockage of some sort? Probably will have to take it to the
installer... petrol side still runs just fine.
I asusme it was OK before?
Could be a blockage, could be diaphragm leaking.
http://www.prelube.com/articals.html
not directly applicable but there is some good fault-finding . I would
run the compression just to eliminate valves
Actually... http://www.prelube.com/articals.html#miss sounds like a
plausible explanation. I've had miss on cyl #2 before, but then it was due
to faulty intake manifold gasket (leaking right next to #2). Every now and
then the miss would appear under heavy acceleration on LPG and cold engine.
This was so rare that didn't bother me...

Peter

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