Anyone else having issues like this?

I sometimes have inconsistency between AFRs recorded on consecutive runs for the same map. It feels like the car is bogging down or hesitating. When I look at the AFR that I recorded I think that the mixture gets really lean spike in it about the same time as I felt the heistation. So it looks like there is not enough fuel getting in the chamber during those times.

But, the wierd thing is that the very next run might be smooth as silk. Any ideas?

Here are a couple of charts from consecutive runs I did last night.

-MD

 

Man... no love for my question....

 

Post a copy of the map. The lean spike is at 7300ish where the VDI opens...you need to watch that area. There is also a lean spike at 6250ish where the APV opens, and a bit at 5500ish where the VFAD opens if its in open loop.

Stumble could be the PCM pulling timing if it is lean enough to knock. The knock sensor is very sensitive.

 

After studying my baseline dyno data, I agree with those figures. Looking at some of the stock AFR's posted here, I am running leaner stock - hence the higher dyno number I tested on 2/26 and 3/11. So I need to pay particular attention to these areas also.

 

I'll work on getting the maps posted, but I'm not sure that would help anyone understand the crux of my question:

The AFR changes run-to-run DRAMATICALLY. Both of those AFR plots are with the CZ ON and the SAME MAP. I don't understand why there are such big differences with the same (seemingly) run parameters....

-MD

 

I know that you mentioned that map settings were the same between runs but were your driving conditions the same? I've seen similar behavior and there are several variables that can effect your A/F ratios. Such as when the calculated load changes when going either uphill (rich) or downhill (lean).

 

hmm.... I was under the impression that the ECU was running in open-loop mode when over 5k RPM and wide open throttle. If that's the case, shouldn't the system be unaffected by calculated load?

 

Open loop isn't quite as stationary as a lot of people want you to believe. The ECU appears to have separate maps for when you are in gears 1-4 and 5-6. It also acts like there are compensation values for calculated load, coolant temperature, ambient temperature...

 

I knew there were different ECU maps for all sorts of conditions, but thought that the open-loop mode was the saving grace for tuning with a piggyback. I guess you're saying that there are different open-loop maps, and that if the ECU isn't running the open-loop map that you tuned under, then you will get different results? I guess I'd better tune for a single redlight here in Albuquerque, and only race people at that particular light! :p

 

I thought I read somewhere that when the cat runs too hot, the ECU sends more gas in the mixture to cool it off meaning it is running a lot richer than normal.