Hi All

I've been having a problem with a mis-fire while running on gas for the last
couple of months. I have gradually changed all of the ignition components,
plugs, coil pack, leads etc. and still have the misfire. It seems to run
quite smoothly on petrol but misses on gas, more so at the lower revs under
load than at the higher revs.
So I decided to do a compression test today. (had to buy a new compression
tester as I couldn't find the old gunsons one from ages ago)
cyl #1 - 12 bar
cyl #2 - 11.5 bar
cyl #3 - 11 bar
cyl #4 - 7 bar
hmmm looks like a problem with no 4. I put some oil in the bore and no4 went
straight up to 13 bar which suggests rings, although I may have put more oil
in than the teaspoon that Haynes recommends, could some of it found it's way
on to the valve seats ?. Is lpg more prone to ring problems, I hadn't heard
that. Any suggestions or thoughts.

It looks like I either need to dig deep into my pockets or spend many hours
in the garage pulling the engine to bits.

Steve

W reg passat 1.8 20v with Necam system.

On Fri, 20 Jan 2006 18:36:44 -0000, "stevet"
wrote:

Hi All

I've been having a problem with a mis-fire while running on gas for the last
couple of months. I have gradually changed all of the ignition components,
plugs, coil pack, leads etc. and still have the misfire. It seems to run
quite smoothly on petrol but misses on gas, more so at the lower revs under
load than at the higher revs.
So I decided to do a compression test today. (had to buy a new compression
tester as I couldn't find the old gunsons one from ages ago)
cyl #1 - 12 bar
cyl #2 - 11.5 bar
cyl #3 - 11 bar
cyl #4 - 7 bar
hmmm looks like a problem with no 4. I put some oil in the bore and no4 went
straight up to 13 bar which suggests rings, although I may have put more oil
in than the teaspoon that Haynes recommends, could some of it found it's way
on to the valve seats ?. Is lpg more prone to ring problems, I hadn't heard
that. Any suggestions or thoughts.



In my experience of a lifetime of working on old knackered engines,
anything that could show 100 psi (7 bar) on a compression tester was a
working engine with more life in it yet. Of course it depends upon
what sort of engine you have, and I would guess that yours may have
quite a high compression ratio.

But before you go any further, did you do the test on a fully warmed
up engine, with the throttle wide open? The results may not be
meaningful if not.



--

TSH

For email, replace 'SpamOnlyToHere' with my initials

LPG info. page: www.tshargrave.co.uk
Now with added Biodiesel

Hi Stewart

the engine was warm - give or take 15 to 20 mins after I got home from work
and got the tools out etc. Yes the throttle was wide open. Haynes lists the
compression ratio as 10.3 to 1.
What I can't quite work out is, why does it run so well on petrol and
misfire on gas. I've had the car about 2 years and it has gradualy got worse
over the last few months. I did wonder if the gas injectors can get clogged
or if the vapouriser pressure is out of adjustment. The system doesn't have
individually controlled injectors but a central regulator thing with some
sort of stepper motor and 4 pipes that dissapear to underneath the inlet
tracts

thanks for you help

Steve


"Stewart Hargrave" wrote in message
...
On Fri, 20 Jan 2006 18:36:44 -0000, "stevet"
wrote:

Hi All

I've been having a problem with a mis-fire while running on gas for the
last
couple of months. I have gradually changed all of the ignition components,
plugs, coil pack, leads etc. and still have the misfire. It seems to run
quite smoothly on petrol but misses on gas, more so at the lower revs
under
load than at the higher revs.
So I decided to do a compression test today. (had to buy a new compression
tester as I couldn't find the old gunsons one from ages ago)
cyl #1 - 12 bar
cyl #2 - 11.5 bar
cyl #3 - 11 bar
cyl #4 - 7 bar
hmmm looks like a problem with no 4. I put some oil in the bore and no4
went
straight up to 13 bar which suggests rings, although I may have put more
oil
in than the teaspoon that Haynes recommends, could some of it found it's
way
on to the valve seats ?. Is lpg more prone to ring problems, I hadn't
heard
that. Any suggestions or thoughts.



In my experience of a lifetime of working on old knackered engines,
anything that could show 100 psi (7 bar) on a compression tester was a
working engine with more life in it yet. Of course it depends upon
what sort of engine you have, and I would guess that yours may have
quite a high compression ratio.

But before you go any further, did you do the test on a fully warmed
up engine, with the throttle wide open? The results may not be
meaningful if not.



--

TSH

For email, replace 'SpamOnlyToHere' with my initials

LPG info. page: www.tshargrave.co.uk
Now with added Biodiesel