So i am new to tuning. I know just enough to be dangerous so be patient.

I was giving myself a little basemap street tune today and got my AFR's about where I want them for driving around. One thing that I noticed which I have no ideas about is that when I close the throttle while driving (shifting, coming into a turn) my AFR goes REALLY lean and I think i hear little misfires, or is this detonation?

help me a little and I can give more info. i dont know enough to give a really good description of the problem. thanks for any help.

 

When the throttle is closed above about 1100 RPM, you actually want to turn the injectors completely off. This feature is usually referred to as DFCO an acronym for deceleration fuel cut off. You didn't mention what system you are using so I don't know if it is capable or not. But it is a feature found on even the earliest Honda ECU's since they first implemented fuel injection. The engine doesn't stall because the transmission is rotating it.

W/out DFCO you were most likely going into a very low load region of your fuel table and firing either a tiny bit or a ridiculous amount of fuel. These regions are rarely tuned because you almost never see them unless you drive at very high elevation. Any fuel that gets sprayed will go into the exhaust unburned and ignite there. Or maybe they were lean misfires as you suspected. In either case, it's not a huge concern. There's really not much risk to your engine at very low loads.


If you are new to tuning then I can give you some very general pointers. Fuel requirements will increase until you reach your max torque RPM, then it will decrease. Rich mixtures burn faster so you need less timing advance. Lean requires more timing. As RPM's increase, timing needs to increase because there is less time to burn the mixture. As load increases, the mixture burns faster so timing should decrease. Low loads ie cruising in 5th you can safely run quite lean with lots of timing. (All of these taken together will seem to contradict each other, and that's why you should always rely on a dyno graph to lead you in the right direction.)

Don't fall into a trap believing that more timing advance and more fuel increases power. It simply isn't true, especially when you increase both at the same time which makes no sense. Nothing is true until it is dyno proven MEANING THAT YOUR CAR IS THE ONE ON THE DYNO. You can get your a/f ratios pretty close to where they should be just by following advice. But for timing you absolutely need a dyno. Run too much or too little and you will cause damage. And it's interesting that the more efficient your engine, the LESS timing it will require to make max power. And to top it all off, for the high load portion of your map, your goal isn't max power... you actually run a bit conservative to keep your engine safe. But you need to find your max power to know what amount of timing is safe.

 

hey, thanks for the advice. I have done all I can do when it comes to reading articles and buying books to get a basic grasp on tuning but when it comes down to actually doing it its a whole other story.

I'm using Neptune RTP in a P28 on my 01 prelude. Motor setup is Type S pistons, euroR manifold, ITR throttle body, mugen header, test pipe to a fart can exhaust. I used a P72 base map and made some tweeks, over all fuel trim increased and timing left alone. messing with my ECT corrections and gear based corrections. I haven't touched high cam yet. Fuel cut is set for 4% throttle I was just not sure if the little misfires were hurting something. I don't plan on touching the ignition tables until I find a dyno that will let me tune myself.

I am happy to post my NCL file and my datalogs if anyone wants to take a look at what I am doing.

 

It sounds like your fuel cut isn't working. Log the injector pulse widths and see whether they're turning off when they should.