Problem with the Nr.8 cylinder on a3.5 V8

[pat71]

hi Technocrats my name is pat if got a county 3.5 V8 with a problem. The cylinder nr. 8 does not fire!:confused: Went to a mechanic to get the gas system tuned wen we noticed it. but after a while it ran again. We checked the spark, set the dwel , ect.I drove home and it was all good. But 1 Day later the nr. 8 cylinder did not run.:confused:Compression test did schow wery lo pressure 100 P.S.I .not very happy:mad: This hapend all after traveling for 8 months from NSW up to cape york,savana hyw,arnhem land,gibb river road,pilbra douwn to perth.Currently in Peth.Would anybody have a idea what the problem could be.thankful for any suggestion.

[Sprint]

do you have spark on that cylinder? if no it'll be a dead plug or plug lead, LPG is excellent for finding ignition system faults.....

[pat71]

yes i got spark.thanks pat

[Sprint]

try swapping the plug and lead with one from another cylinder...... it could be that the plug and/or lead have partially failed, but it isnt showing untill its expected to work.....

pressure and the gas make it a LOT more difficult for a spark to occur, think of it as the equivalent of opening up the spark plug gap

[Blknight.aus]

Time for a leak down test and a spark check on that pot. leave the existing plug in place and run the engine with a test plug in place on the end of the lead

[snowbound]

what difference will a faulty spark plug make to the cylinder pressure? Surely we are talking valves or maybe head gasket, though I suspect the latter would throw up other symptoms. Just my thoughts, I know there are some pretty cluey techs on here!

[Blknight.aus]

for my line its just a check. if the single cylinder is run cold from no spark therefore no firing of the fuel that goes in can wash the oil from the walls and the problem of low pressure is possabley shot rings.

That'll be born out by the leakdown test.

[pat71]

Thanks Guys solved the problem with new sparkplugs, running fine.will recondition the engine sooner or later if money alows it.would a 0.7 sparkpluge gap help to ignite gas?

[justinc]

If you have electronic ignition, (which you should have with LPG) then a .8 to .9mm gap will be better, otherwise .75 is adequate, just.
100Psi is on the edge of needing some attention. Check the cam first though, as if the lobes are worn off the comp readings will also be low and doing any other jobs to an engine in need of a cam is a waste of $$$.


JC

[Blknight.aus]

seconded Ive found that LPG likes a bigger gap on a hotter plug.

for older cars with a single coil via a dizzy type arangement you can get a coil with an "overwound" secondary that throws a meaner spark. but its a double edged sword, if you have any hassle with supply voltage, points or condensor it'll let you know in no time.

[bee utey]

[QUOTE=Blknight.aus;1146994]seconded Ive found that LPG likes a bigger gap on a hotter plug.

Funny that, I use a colder plug with a smaller gap. Otherwise all my theories of LPG running over 30 years would be wrong. LPG is a slow burning fuel so creates more waste heat, that also explains why a few extra degrees advance works.
I use Bosch WR7DC plugs with 0.8mm gap, in NGK that would BP6 etc.

[3.9County]

Im running NGK 6ES's on my County and she runs pretty well on both gas and petrol.


Does anyone know what would the main cause of drying up piston dampner oil in my Strombergs? The oil level decreases pretty rapidly..

[djam1]

Im running NGK 6ES's on my County and she runs pretty well on both gas and petrol.


Does anyone know what would the main cause of drying up piston dampner oil in my Strombergs? The oil level decreases pretty rapidly..

They have a small O ring that perishes this will cause the oil to leak away quickly.
I got a kit from SUMidel in Sydney not particularly easy to replace but it can be done.