Hi guys.

How can you spot ignition misses due to improper spark gap in a log?

 

I can't speak as an expert on spotting ignition misfires on a log, but I can say that you won't see knock as a result of the misses. You should, however, get slightly richer afr readings (i.e. a couple of 1/10ths)

However, it is VERY easy to see if you have misses due to too large of a spark plug gap by just changing the plugs: Pull your old ones, check their gap, and install new plugs gapped down between .022 and .020. I use NGK bpr7es.

 

Check the gap, if it is wrong fix it, if the misses go away ... you've spotted misses due to improper spark gap.

Yes cheeky I know but determining the [b]cause[/] of a miss will usually be a trial and error affair in my experience.

 

Misfires are actually seen as lean spikes in the logs/AFR meters since the fuel isn't actually burned.

 

to tell you the truth because i had this problem, i think in my logs my load was spiking down slightly.... like i would see a load of around 270 dropping gradually but somewhere in there i would see a slightly lower value and then increase to the previous gradual drop....

i dont know if its my imagination but thats what i have experienced...

Also and i recently dynoed the car after changing plugs, i asked the operator if misfires due to plugs would show on the dynograph... he said that we would see small spikes but nothing of this happened...

 

On evos under 400whp, I've rarely seen evos misfire due to spark plug gap. On big turbo evos, misfire is pretty common beginning just under 500whp and upward and gapping the plugs down does wonders to get rid of it.

 

yep...

thats my case... however the 1-step colder plugs that i had before had opened their gap since i installed them from 0.024 to the amazing 0.028 thus misfiring to death, especially 3rd and 4th gear... one thing i noted also is that the load couldn't see a high figure no matter what...

It is pretty crazy to have a 3065 turbo and not being able to pass 260-270 load values...

 

The load will do funny things when it drops spark, you can feel it break up more than anything. I havent seen many misfires equate to knock but it could technically happen. AFR's get erratic, most of this looks like it has been covered, but the main thing is driver feel and not the log.

 

Okay! Thanks for the input all.

 

i would have to disagree on misfires accure only on 400whp evo's. I'm currently running right around 350whp with my stock evo 8 turbo , but because i am spiking at 26psi. My plugs were gapped at .026 and popped at 22-23 psi , then gapped to .024 and popped at 24-25 psi. now gapped at .020/.021 no longer popping at 26psi.

 

The easiest way is to log your front O2...a misfire will be a very sharp downward spike.

If you log a wideband, it should correlate with a sharp upward (lean spike) and may oscillate a bit.


Eric

 

Along with lean spikes, you will definately feel it too, car will accelerate normally but with brief breaks (like 0.25 sec) in between.