jy951

Like some past posts this forum from others, who have MAFs, AFM chips, and Piggy-back combos, I was also getting a "popping" sound from my exhaust during part throttle transition (to accel after a decel, and from idle to accel at times).

When I first installed the mods, I was getting the "popping" during decel too, but I was able to tune that out via MAFterburner. So, since I was able to do that in MAFterburner, I figured that I could tune out the part throttle "exhaust popping" too.

Well, that proved to be elusive until this weekend, when I designed a steeper slope from idle to part throttle fueling in my MAfterburner tune. As a result, my AFR decreased from 11.6 - 11.7 to 11.3 - 11.4 during part throttle transition, and the "exhaust popping" became almost non-existent, it was like driving a stock 951 again. I made several runs to confirm that I had significantly reduced this nuisance. I did not figure that an AFR of 11.6 - 11.7 would be too hot (for my 951) during part throttle transition. In the process, I'm sure that I also improved my timing too.

Reducing the "exhaust popping" during part throttle transition to almost non-existent (makes a very very very small pop now, u have to listen for it) is music to my ears. Since I accidently stumbled on this, I have not completely tested the new MAfterburner tune, since I've fattened it during part throttle transition. I need to check my AFR under boost, and make the necessary adjustments, to keep the AFR in the 11.9 - 12.2 range under boost. I happened to be testing my Kokeln chip for a totally different purpose when I stumbled upon this discovery.

Rogue_Ant

Interesting! Just wondering how your improved your ign timing too?


Rogue

jy951

No proof - just a hunch. I was under the impression that smoother (closer to stock) performance was the result of better AFRs and timing.

Since my new MAFterburner curve has yielded better part throttle performance, I just assumed that I might be getter better timing nbrs, as result of the improved MAFterburner curve. Like I said, I just stumbled upon this discovery, I don't know if it's my new overall design (increased slope/drop from idle to part-throttle area of the curve - about a 60 deg slope from hot to rich) of my MAFterburner curve, or the increased spacing (from an avg of 4 to about 8) between voltage values.

All I know, is that the KoKeln chip exhibits "exhaust popping", at part throttle transition, if the AFR is 11.5 or greater. By lowering the overall AFR at part throttle transition to 11.3 - 11.4, the exhaust popping is SIGNIFICANTLY reduced, to almost to nothing. Immediately afterwards - I switched from the KoKeln to a MAX Power (customized for my set-up) DME chip and the "exhaust popping" re-surfaced, using the SAME MAFterburner curve. So, I suspect that programming plays a SIGNIFICANT role here.

The MAX chip appeared to be hotter at idle (than the KoKeln chip - 15.1 vs. 14.4) on the same MAFterburner curve, under the SAME operating conditions. At part throttle, BOTH chips registered 11.3 - 11.4, but the (generic) KoKeln chip DID NOT exhibit "exhaust popping" and the MAX chip did. Is the programming for ignition timing (both hit the injectors pretty hard - some fairly loud ticking from opening & closing) the difference between these two AFM chips????

I know others in this forum have experienced (from reading quite a few posts)this "exhaust popping" issue, and I just wanted to share my discovery. It doesn't mean that it will work in other 951s, or in the SAME 951 (mine), if the chips are different (noted above), it just happened to work for me using Kokeln AFM chip. Note, the KLR chip during both runs was MAX chip.