Misfire on boost

lmrdave · #1 24-08-2007, 07:36

Ok, I'm a little rusty on Silvia fault finding, got a little misfire on boost, but it doesn't happen all the time, any pointers where I need to start looking?

I'm guessing electrical as it's intermittant, but I ain't sure!

PukkaSilvia · #2 24-08-2007, 18:30

replace your spark plugs.Buy bcpr7es plugs and set them at 0.9mm

Im pretty sure that is your problem

mr_turbo · #3 24-08-2007, 19:03

y set them to 0.9? ive jst orderd bcpr7es-11 as i wanted a colder plug have i ordered the rong plugs? the standard gap is 11mm isnt it?

s13eater · #4 24-08-2007, 19:19

probley be a stronger spark on boost, not as though many people run enough boost to blow the spark out.

lmrdave · #5 24-08-2007, 20:56

Cheers guys, I'll bag some up tomorrow.

Think I've got a coolant problem too, it's hard to get to the bottom of the rad but I reckon it's only the top getting hot. Temp guage is fine and heater chucks out hot air. Bottom hose on rad is luke warm but not hot.

Tried to bleed it just running it with the rad cap off and making sure it was topped up, didn't seem to be getting any air out it though.

Any bleeding tips?

Might take it for a run tonight but I don't want to cook the poor old girl!

s13eater · #6 24-08-2007, 21:07

is the thermostwat working ok, if it is and you leave the rad cap off for long enough whilst ticking over then it should get the air out ok, is the water look like its moving when its up to its right temp ? if not the thermoostat ain't working, if it is, then no idea mate.

PukkaSilvia · #7 24-08-2007, 23:40

Quote:

Originally Posted by mr_turbo

y set them to 0.9? ive jst orderd bcpr7es-11 as i wanted a colder plug have i ordered the rong plugs? the standard gap is 11mm isnt it?

Well 0.9 seems to be a good medium. If you are running standard boost levels and the plugs are new and your igntion system is in good condition you probably would be ok on 1.1mm.

The bigger the gap the more voltage the spark needs to jump.

Also the more cylinder pressure/boost there is the more voltage the spark requires to jump the the tips

I said 0.9 is a good medium as the larger the gap is the best combustion you get. and vice versa,

Towards the top end of things people tend to go for iridium plugs,you may of seen them. These have thinner tips which require less voltage than standard plugs, so you should be able to run a larger gap and get better combustion. But in the average s12 owners world iridium plugs are a little ott for the outcome

Hope that all makes sence.

lmrdave · #8 24-08-2007, 23:42

Off to flush the rad out tomorrow I think, but Ill pick up a thermostat just incase.

lmrdave · #9 25-08-2007, 22:36

Good call guys, plugs sorted misfire, broke two HT leads getting the buggers off though.

Got quoted £75 for a set of HT leads of I just had a look around the garage and found some pinto ones that fitted, popped into the motorfacters and had a word with a guy I know in there, theyare actually £12.95+ VAT the chap on the phone quoted the FJ20 ones.

Both rad pipes where hot once I got down to the garage so it looks like I was worrying about nothing.

PukkaSilvia · #10 26-08-2007, 01:23

Excellent.