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

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.....

yes i got spark.thanks pat

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

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

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!

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.

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?

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