light load misfire

Postby **NitroDann** » Sat Aug 11, 2012 5:59 pm

What air fuel ratio?

Dann

gslender · Postby **gslender** » Sat Aug 11, 2012 6:03 pm

Dwell set correctly? Spark gap enough? Afr too lean? Is it AE decel or truly a misfire? Have seen AE decel look like misfire. Turn it off by setting to 100%

G

manga_blue · Postby **manga_blue** » Sun Aug 12, 2012 12:34 pm

ozi_milhouse wrote:Its hard to judge because of the misfire. Before the misfire its at about 13.5 but because of the miss it spikes lean then goes back to about 13.5. if i hold the throttle just right i can instigate multiple misses and make it sound like a rotor or boxer engine. has me stumped.

If there was a miss caused by no spark then wouldn't that show up as a momentary rich condition instead as raw fuel went down the exhaust?

manga_blue · Postby **manga_blue** » Sun Aug 12, 2012 12:49 pm

Dunno, worth researching, but if you're right then both an ignition miss and a transient lean mixture problem would show as a lean O2 result?

plohl · Postby **plohl** » Sun Aug 12, 2012 9:56 pm

a missfire will show lean as the lambda sensor does not detect unburnt fuel. I have seen this in my car a billion times lately :roll:

Postby **NitroDann** » Sun Aug 12, 2012 10:02 pm

Oxygen sensors sense oxygen.

Any missfire of any variety shows lean.

Dann

manga_blue · Postby **manga_blue** » Mon Aug 13, 2012 1:50 am

You live and learn.

I asked the question in the first place because your problem sounded as much like a rolling lean mixture miss as an ignition miss.

Postby **NitroDann** » Mon Aug 13, 2012 2:03 am

I agree, which is why I asked air fuel ratio as a first question.

Its hard to diagnose past these basics from behind the innanet.

Dann

jerrah · Postby **jerrah** » Sat Aug 18, 2012 7:50 am

Unplug the tips and see if it stops. My mysterious miss was caused by noise from my coil pack upsetting my tips signal. This triggered random accel enrich and decel which presented as a miss.

bruce · Postby **bruce** » Mon Aug 20, 2012 3:04 pm

Could it be something mechanical - burnt valve?

plohl · Postby **plohl** » Mon Aug 20, 2012 4:29 pm

dirty injectors? maybe???

bruce · Postby **bruce** » Mon Aug 20, 2012 4:46 pm

Dirty fuel, dirty fuel filter?

I want to say 'spark plug leads', but you've changed them.

bruce · Postby **bruce** » Mon Aug 20, 2012 5:36 pm

Faulty ECU? I doubt any electrical noise would affect it as it is inside a tin box (to avoid noise).

toppertee · Postby **toppertee** » Mon Aug 20, 2012 5:47 pm

I had a bit of a miss at around 2-3 rpm. GSlender had a look on sunday. TPS had a dirty signal.
Switched to full MAP all good. Have you tried running yours on 100% MAP?