Ever since dropping to the 2.87" pulley I have been getting this weird sudden leaning out of my afr at high rpm. It was pretty unnerving at first, but there were no signs the engine was actually running lean, and no hint of detonation. My last dyno showed signs of misfiring at high rpm, so after reading Mardigrasmax's post about the Kenne Bell Boost-A-Spark (ref:http://forums.maxima.org/showthread....ighlight=kenne), I installed one.

Here is a datalog of a run I did before installing the BAS, showing misfiring and resultant leaning out of the afr at about 6300 rpm (also note the slipping SC belt at about the same time):



After installing the BAS, and with the potentiometer set at 20 (and with a tighter SC belt):


After increasing the pot setting to 30:


The slight rise in afr in the last pic is most likely the result of fuel pressure starting to drop (ref:http://forums.maxima.org/showpost.ph...0&postcount=21)

 

Awesome, nice info!

 

that is great info. way to go stephen!

 

good info Stephen

 

Is it possible to chart RPM vs AFR, I'm having a bit of a time visualizing what's going on in that graph especially with the units showing as time and rpm. I think an RPM vs AFR graph would be very helpful.

 

Nice stephen, looks almost perfect. I got one of those too but they send me the wrong one the BAP instead of the BAS so I had to send it back but from the look of things I'm happy i decided to go this route. Thanks for the info.

 

awesome!!!!!!!!

great info

 

The afr starts in the upper 13's at 4000 rpm and drops to the mid-upper 11's, then shoots offscale lean when a cylinder misfires.

Some people think that misfiring would result in a rich condition because of raw gas in the exhaust. Misfiring results in a lot of unreacted O2 in the exhaust which is what the O2 sensor detects, hence the high afr. But that is a false reading since it doesn't reflect the actual afr in the combustion chamber during normal ignition.

 

VERY very nice investigating work Stephen...time to dyno another change(ATP cutout or e-cutout?) to see what difference that made.

Also, your VIAS switchover is still too high for the DEK...you can see the VE slope change point in your boost curve about 5200-5300rpm, I'd drop it to 4600rpm for the actual switch around 4700rpm or so.

 

what level of boost does misfiring or spark blowout usually become a problem? Around 14 psi?

 

Icey: Right now I have the 00NVI (Non-Variable Intake) that doesn't have the power valve, but when I put the 00VI back on I'll lower the switchover point.


Chris: I didn't start to see consistent misfiring or spark blowout till I dropped pulley size from 3" to 2.87". I was getting 11.5-12 psi with the 3" pulley and now I'm getting 14-14.5 psi. The afr starts to go lean (due to misfiring) at about 13 psi.

 

hmm, well once i get the cai setup done i will deff be hitting 13+ psi. Right now i am hitting 12-13psi. I guess i should look into getting this then. Thanks for the info Stephen

 

The 5th gen coils may be a tad stronger, but it is obvious that the maxima ignition system is not as strong as once believed. Any upgrade when boosted will prove to be a worthwhile investment.

 

Doh...why do you think the slope of the pressure is larger post 5200rpm then?

So you're giving up on the "00NVI" for good?

 

The first graph is with a functioning 00VI with rpm switch set at 5200 rpm. The other two are with the 00NVI.

Based on maf data I've been collecting, the meager gains I'm seeing at high rpm are not worth the more substantial losses at lower rpm. I still might try what you suggested and another variation or two, but not in the too near future.

 

Now I'm more confused...I don't see anything it in the first graph, but I see the transition in the 2nd between 12.0-12.1sec and in the 3rd between 16.8-16.9sec. Looks like the slope gets steeper from that point.

I don't think you should give up on that IM just yet...especially without trying a few more things.