Thread: Boost Spike
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Old 09-22-2013, 09:27 AM   #95
Seeking 9s on M6...
PMJ's Avatar
Drives: 2012 2SS/RS LS3 aka "BlackWidow"
Join Date: May 2012
Location: Houston, TX
Posts: 397
Originally Posted by ayousef View Post
so there is a boost spike and a lean spike that aren't tied together? I thought the lean spike was a result of the boost spike or vice versa, and that solving one would get rid of the other.

- Ill ask again, what is your fuel system made off, does it still use some kind of FPCM to control the pumps?

- There is a short duration between when the ECM commands the injectors to pulse and when the pulse occurs, do you have accurate injector data?

- Where is your wideband located at just to know if the problem is happening on both cylinder banks or one?

- One thing I noticed from the screenshot above is that MAF airflow and MAF Hz readings both drop, as in take a dive right at the boost spike, since its reading a lower MAF value it will command less fuel = lean out. I think you have to figure out why the MAF dives instead of going up. Is there something wrong with your MAF sensor?
Man, I thought I made peace w/my lean spike and now you bring up some good points.

I do not "think" the lean spike is causing the knock (but certainly could be contributing), because I have many samples of the lean spike w/out the boost spike and no knock. I now think the sudden transition of the bypass valve in the whipple & throttle position is causing a surge that causes detonation. The detonations causes sudden slow down, which causes the MAF (and MAP) to dive.

So to your questions/suggestions:
- Fuel system is a ZL1 pump w/ADM FPCM (I expected to have problems on the high end, but no problems at all up to ~850whp)

- I will try to disable transient fuel, but can you give me a little more description on why you think this might help?

- my wideband is only on the driver side bank, and now that you mention that, Pat G did notice w/the narrow band that the passenger side was richer than the driver side...the fuel supply line is on the passenger side...hmmmmm...

- the MAF is out of the equation at this point...yesterday I changed to SD tune...but it didn't address the lean spike i'm seeing, so I haven't concluded which way to go yet (I prefer the MAF based on I understand it better).

Next time I dyno, i'll hook the external wideband to both sides and see if there is a difference.

Mohamad, based on this latest info, let me know if disabling transient fuel still makes sense to you (and a little context of why).

thanks - I really appreciate all the advice and help!

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