Hi Guys,

Did a 4th gear pull today and noticed a AFR spike - just wanted to get your feedback/thoughts:

Now this is just a segment of the full log, however you can be assure that TPS=100 and has been 100 for a little while

Now the 11.4 AFR(bolded line) worries me, you will note that the IPW has NOT changed and also the LOAD and MAP is the same around that 11.4.

So either:
1) I am getting spark blowout??? Seems strange at 23psi and relatively low RPM.
2) Injector problem - But what??
3) LC1 playing up - unlikely since the rest of the log is pretty consistent.

Thoughts/Comments would be greatly appreciated!

Cheers
D.

 

From your comments I'm assuming your doing a top gear pull? LOL, anyways that is a fairly common spark misfire. High load coupled with the spark being set of during high cylinder pressures near TDC with only 3 deg of advance and I'll assume stock coils. I'm pretty impressed it didn't completely break up actually if you are on E85. That is quite a mild misfire, your lucky to catch it but I bet you couldn't even feel it in the car huh?

The cheap and easy fix is to go from 4 to 5 degrees on your map instead of 4 to 3 degrees. The higher the boost (IE load) and the closer you set the spark off to TDC (less ignition timing) the greater the chance of a misfire. Try to add 2 degrees of timing where I see the 3's (if its safe to do so on your car). If not, drop the boost half a pound.

 

4th gear - yeah.

93 oct (well 98RON), not E85...

Do you really think its spark breakup?

 

Look at the load, 250 load with only 3deg advance, pretty sure it is yes. The stock evo COP's suck quite bad.

 

I'd also expect some randomly occuring misfires at 4300 where you log cuts off. Still only 3 deg of timing and plenty o' load.

 

so what reduce my spark gap? to what? I know they are all set to 0.6mm atm...

wont more timing increase the chance of misfire? or is that irrelevant?

 

No, more timing will reduce chances of misfire.

 

I just fixed this exact same problem on my car literally minutes ago. 0.6mm = 0.0235 inches. I was gapped at .028 and was experiencing what I thought was spark blowout... regapped to ~0.023, and it went away. It is the depth of winter here (regularly -10* C and colder) and I attribute not noticing it during the summer due to the denser, cooler air of winter.

 

Tephra, be very careful if you try to regap the stock iridiums. You are _supposed_ to use a special tool but you can do it with needle nose pliers. I really doubt with that load you are misfiring on stock plugs unless they have a ton of miles. I would verify the gap is correct and/or try replacing them. Can you produce the problem, did this just happen in the 1 pull? if so it could just be a fluke.

 

Thanks Mike - yeah I know how sensitive they iridium's are

Doesn't always happen, but I have been fighting some weird AFR's for a long while...

Plugs are 24,000 kms old.

 

Is that just one log that did that or is it consistant? That's not much of a spike to worry about though, combustion isn't perfect every stroke.

 

im looking through some other logs now.

FYI - these are FIC1050's - not stockers.

understand combustion isn't perfect, but .4 AFR is quite a jump - and if its only 1 cylinder then that's even worse (since its averaged)

 

Dan - I just reread your second paragraph - Your not suggesting that my timing going from 4->3 is causing the problem?? but rather the low timing in the first place? (I am still not sure why lower timing results in higher chance of spark blowout??)

I think I get knock if I go from 3->5 degrees of timing. I know it *should* work, since I was running 4* earlier in the pull - but for some reason it will just knock.

edit - I just looked at the log and i am actually getting 1knocksum from the 4031RPM onwards (hence the drop)

 

I find timing to be the most inconsistent thing about evo motors. After peak torque every car seems to like its own blend of timing.

 

What was the airflow doing at that spot? Maybe thats the compressor's peak and the ecu just doesn't respond quick enough being a fraction of a sec.