Thread: V8 Breathing Heavily and Misfire on LPG

Sounds like a broken top compression ring. It could be replaced with the engine in situ providing nothing else was damaged. Head and sump off is quite quick. LPG does like its compression.

Or a broken head gasket leaking into the valley.... Easy way to check this without major work is to lift each rocker cover, then each rocker shaft and lift each push rod out 1 by 1.. There'll be a ring around 1 push rod level with the gasket if there is a compression leak.

G`day ,

sounds like it could be 2 things , cylinder 2 could hold the key to the breathing but may not .

Next time you do a compression test give #2 a squirt of oil and see how much if any the gauge rises above what it was without the extra oil . If it doesn`t alter it`s lower reading is not the rings but will be valve related .

If the engine oil goes black very quickly after a change this can be a sign of a fault with the rings .

Check that the flame traps , pipe work and connecting orifices are all clear , this can cause oil leaks and crankcase gasses will try to get out where ever is easiest .

What colour does the spark plug from #2 look like , if a ring fault it won`t look normal .

If the miss is as you suspect an electrical fault the plugs will all look similar in colour .

Leads will sometimes leak under load , at low revs when moving off for instance .

If you look under the bonnet , with the engine running at night with as little light as possible you may see some sparks .

The fact that you say it misses on LPG and not petrol is one reason why i think it may be 2 problems .

LPG requires a better spark or it will find fault in an ignition system where running on petrol can be ok .

I notice you don`t mention the rotor , they can cause a miss also .


I wouldn`t remove the push rods as suggested unless you take the inlet manifold off first or are prepared to do so .

Originally Posted by PLR

I wouldn`t remove the push rods as suggested unless you take the inlet manifold off first or are prepared to do so .

Just curious as to why you say that... The original engine in my 101 had exactly the symptoms described.. Down on one cylinder, and a misfire. No water in the oil, and heavy breathing. At higher RPM the miss would go. There were no obvious leaks around the heads externally. Before deciding to pull the engine out for a better temporary borrowed unit prior to the diesel conversion I did exactly as I described. Pulled the lids, loosened and lifted the rocker shafts.. At this point I found the scale and scum so knew the 'ex Disco' engine was tired. The push rods then fitted out easily. There's never been enough suction, and always too much scale to let the hydraulic followers be pulled out with a push rod. Sure enough there was a nice shiny ring around one of the rods which matched the head gasket line and happened to be from No 5. Out came the engine next day. It was knackered. For the half hour it will take to check this I think its worth while (after carrying out the checks you suggest).. as it looks like 'I love my Landy!' is fairly mechanically minded as he's already checking the logical things.

Originally Posted by PLR

G`day ,



I notice you don`t mention the rotor , they can cause a miss also .

and cracks in Dizzy caps, even some new aftermarket caps can do this also/

Originally Posted by PLR

G`day ,

sounds like it could be 2 things , cylinder 2 could hold the key to the breathing but may not .

Next time you do a compression test give #2 a squirt of oil and see how much if any the gauge rises above what it was without the extra oil . If it doesn`t alter it`s lower reading is not the rings but will be valve related .

If the engine oil goes black very quickly after a change this can be a sign of a fault with the rings .

Check that the flame traps , pipe work and connecting orifices are all clear , this can cause oil leaks and crankcase gasses will try to get out where ever is easiest .

What colour does the spark plug from #2 look like , if a ring fault it won`t look normal .

If the miss is as you suspect an electrical fault the plugs will all look similar in colour .

Leads will sometimes leak under load , at low revs when moving off for instance .

If you look under the bonnet , with the engine running at night with as little light as possible you may see some sparks .

The fact that you say it misses on LPG and not petrol is one reason why i think it may be 2 problems .

LPG requires a better spark or it will find fault in an ignition system where running on petrol can be ok .

I notice you don`t mention the rotor , they can cause a miss also .


I wouldn`t remove the push rods as suggested unless you take the inlet manifold off first or are prepared to do so .

Thank you for your suggestions PLR

When i did the compression test i did also measure the compression after squirting some oil into the cylinder. The reading did not change. HOWEVER, the motor was still a bit warm at the time, and I thought that the motor had to be cold to make this test meaningful. I haven't tried it again since.

I will check the colour of the spark plug. When i pulled the old spark plugs out they all had that nice tan colour though.

The oil stays nice and clean for a long while.

I did try an old (but working) dizzy cap and rotor, but forgot to mention them on my list (i should have just said i have tried everything apart from swapping the optronic light in the dizzy! Too worried about i'll break the chopper upon removal).

Edward

Originally Posted by Roverlord off road spares

and cracks in Dizzy caps, even some new aftermarket caps can do this also/

Thanks Roverlord. I too have had issues with aftermarket caps. My Lucas cap and Facet rotor have not given me any troubles.

Edward

I noticed you also said your coil was replaced, was it aftermarket ? we had a lot of trouble with aftermarket coils years ago so we only sell the lucas ones now . If you have another coil try a swap and see if the problem goes away.