BARELY tweaked S-AFC, now sputtering under full boost

[uberswede]

Long story short, got the car with a bunch of stuff on it already, put in my own boost gauge/controller, and wideband a/f gauge.

Once everything was monitored properly, noticed she was running rich; somewhere under 10:1, and would sputter a bit under high boost. So I started looking into how to tweak the S-AFC.

I played with the fuel curve a bit, and got the AFR to stay closer to 11, and she was running great.

I decided today to try to get a little closer to the 12:1 mark for the AFR, and BARELY tweaked the S-AFC. Not nearly as much as before. Immediately I noticed sputtering under high boost. So I started backing down a tiny bit at a time, until it got back to where the levels were before... and now it's still sputtering, with everything how it was earlier today, working fine.

UGHHHH. Spark plugs?

 

[Chaosweaver]

Yes, it could be the spark plugs. When you hit high boost does it feel like the transmission just dropped out of the bottom of the car or does it seem like it isn't firing correctly?

 

[PieEyedPiper]

Wait, 12:1 at WOT? If you're not running race fuel or E85 that is a pretty dangerous mixture right there. I'm not surprised you're having difficulties.

Not trying to scare you, but were you monitoring knock? You might want to perform a compression test, just to cross an annihilated cylinder off the list.
Unknown turbo? How much boost is "high boost"? What fuel mods do you have? I'm assuming you have upgraded injectors and fuel pump.

 

[JayRolla]

Agreed not a good idea to run that lean on pump gas. Our cars come with a stock afr around 9.5-9.8:1 so its normal to be under 10:1 since the wbo2 wont read any lower. I ran 10.9 at leanest with best results on pump gas.

 

[uberswede]

Chaosweaver :
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It just seems like it's not firing correctly... almost like one of the cylinders dropped out.


PieEyedPiper :
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I was told by a few people that high 12's is an optimal AFR, and was slowly working towards that number... but was only around maybe 11 at this point. Definitely noted. I already trust you guys on here more than anybody else I have talked to anywhere. I'll knock the numbers back down a tad as soon as possible.

The S-AFC, that was already on the car, is apparently monitoring knock. From what I've read around here already though, the S-AFC's don't properly monitor knock on 2g's? Is this true? If not, what should my numbers be looking like and when? I'll throw a compression test on the to-do list.

The "unknown turbo", after some research, looks like an eBay T70 knockoff. I bought the car with a handful of goodies already on it. High boost, at this point, is between 17-19 psi.

Fuel mods, as well, are unknown. There is a fuel pressure gauge, reading anywhere between 50-60 psi, so I can only guess there's at least an upgraded fuel pump. No FPR that I've found, and injectors MAY have been upgraded... they definitely seem to respond to the S-AFC, as I read as well that stock injectors only really move -5/+5 from something like an S-AFC.


JayRolla :
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Again, noted. I'll have to have a talk with who kept telling me an AFR in high 12's would be optimal. I only really started wanting to up the AFR once I first started monitoring it, it was well under 10, and sputtering a bit under boost closer to 19PSI.

If I stick to mid 10's for the air/fuel ratio, I should be ok in there, correct? Once everything else is tested and figured out?

 

[JayRolla]

Mid 12 afr's are ideal for natural aspirated cars and boosted cars running race gas or ethonal.

 

[Chaosweaver]

To be honest I wouldn't cross into the 12s in AFR, specially with a boosted car. I like to keep mine in the high 10s to mid 11s, good power at lower RPMs but you have to richen it up past 4500 to not risk blowing something.

What are your current SAFC settings?

 

[KKneipper]

To answer your question, instead of just repeating the same thing everyone else has said (which is all correct, by the way), you should check your spark plugs. If you were running too lean (even for just a couple blocks), you may have overheated a plug. Either that, or your spark wires may need to be replaced. I always like to start with the cheapest fix, so pick up some NGK G-power plugs and see if that fixes your problem.

 

[JayRolla]

Dont use G power ngk plugs. Run the BR7ES unprojected plugs. They are the best for boosted applications for up too 30psi and have been proven to lower knock just from being unprojected. There a little harder to find since they are for motorcycle and marine applications.

 

[KKneipper]

Those plugs may very well work. I have been running the G-powers for a few months now (had V-powers when I bought the car), and I noticed a huge improvement. Faster spool, and better response than the V-powers. If you want to go with the BR7ES plugs, you can probably have Checker order them for you.

 

[uberswede]

Chaosweaver : My S-AFC, if I recall correctly, is set to maybe -23 at lower RPM's (Hi-Throttle), and makes its way up to -29 or -30 by the time the boost kicks in, closer to 5000 rpm

I'm definitely considering new plugs, and checking a few other things... BUT... something else FAR more major has come up at this point... Please take a look at this thread.

http://www.dsmtuners.com/forums/new...nt-totally-crank-pulley-moving-out-could.html