Misfire at idle and low revs

dmad_dood · Postby **dmad_dood** » Sun Mar 24, 2013 9:09 am

I've started to notice a misfire at idle (900-950 rpm) and then when it slowly revs out it misfires a tad at 1900 rpm. Just trying to figure out what it could be? I pulled the plugs and they looked pretty good, no fouling or anything so im lead to believe it could be a dodgy ht coil/lead. Are the bp's known for any issues regarding misfires or anything.

Thanks,

Jono.

project.r.racing · Postby **project.r.racing** » Sun Mar 24, 2013 10:40 am

pretty common for old coils to cause misfires. also the solid section of the lead that goes between the camshafts also get pinholes with age and end up arcing to the head instead of the plug. check that also.

93_Clubman · Postby **93_Clubman** » Sun Mar 24, 2013 11:21 am

Borrow a known good set of sparkplug leads to test, & also check the ECU PCB for leaking capacitors etc.

dmad_dood · Postby **dmad_dood** » Sun Mar 24, 2013 12:34 pm

also the solid section of the lead that goes between the camshafts also get pinholes with age and end up arcing to the head instead of the plug

By the solid section are you refering to the section that goes into the distributor where the leads plug in

Thanks for the help, i hope its just the leads which isn't very big or costly to fix, i was going to do them eventually anyway. While im at it i might also do a grounding kit, it cant hurt.

Any suggestions on what leads to go for??

Cheers

project.r.racing · Postby **project.r.racing** » Sun Mar 24, 2013 4:56 pm

there is only 1 part of the leads that goes between the camshafts.

sailaholic · Postby **sailaholic** » Sun Mar 24, 2013 8:24 pm

The solid part is the part that goes down into the engine and connects to the spark plug.

No distributor on mx5. It didn't fit so they (mazda) used a Mitsubishi cam angle sensor off the Evo engine instead.

dmad_dood · Postby **dmad_dood** » Mon Mar 25, 2013 7:18 pm

Thanks for the help, it seems to be getting worse the more i drive the car thou.. is there anyway i can isolate the leads to see if there faulty or not?

Cheers.

93_Clubman · Postby **93_Clubman** » Tue Mar 26, 2013 9:08 am

Sparkplug leads can be checked for continuity using a multimeter, but even if they check out ok off car, they can still break down under load on car.

project.r.racing · Postby **project.r.racing** » Tue Mar 26, 2013 1:40 pm

while the car is running, pull the leads out and lay them flat against the engine cover. if the spark jump from the end where the spark plug goes, all good. if spark jumps from somewhere else, then the insullating material has degraded, as per my first post.

dmad_dood · Postby **dmad_dood** » Tue Mar 26, 2013 7:29 pm

project.r.racing wrote:while the car is running, pull the leads out and lay them flat against the engine cover. if the spark jump from the end where the spark plug goes, all good. if spark jumps from somewhere else, then the insullating material has degraded, as per my first post.

Are you saying pull the leads out with the plugs in the engine or pull them out with the plugs still attatched and resting on the head? Either way do you mean just cranking the engine over when checking cos the engine obviously cant run.

project.r.racing · Postby **project.r.racing** » Wed Mar 27, 2013 9:08 am

start the engine. allow to warm. pull just 1 lead one at a time. the engine continue will run. check lead. replace. move to next lead. repeat process.