Ok, guys sorry for beating a dead horse as I am sure you have answered this question many times but here we go again:

I recently did some modifications to my PCM tune by using Catstuner and it worked great, but I think I am still running a little too rich. I was wondering if the datamaster program will record enough to get a generic idea of the AFR as I don't wanna spend all the money for a separate wide band O2? If I record a session and post it up or email it to someone will you be able to tell where my prob lies? Here is some generic info on my motor setup:

95 LT-1 OBDI
383 Eagle Stroker kit
Not sure on compression but I think it is 10.5 or 11:1
Cam is comp cams 276-HR-14 xtreme energy
and 44 fpsi w/30# SVO Injectors

Let me know what I need to do and if datamaster will give me the info I need?

 

Are you talking WOT or at idle/cruise speeds? If at idle/cruise look at the LT Int which is the BLock Learn Multipliers (BLMs) for fueling..128 being perfect, anything higher is lean, anything lower is rich and you usually don't want them off of 128 by more than +-10 as they tend to get more inaccurrate the further off 128 they get.

WOT then you're shooting in the dark without a wb02, but can try to get the narrow band o2 mv around .900mv...seems like thats what mine used to be..but I've had a wb02 for so long I've forgetten so you may want to have someone else verify that before you go tuning for that.

 

Thanks and to answer your question, for right now I am not so worried about WOT as I can't do that too much now as I just put a new clutch in. If I make a run and record it driving around on datamaster can I send you the file to tell me what I might need to adjust if any?

 

Sure.
How familar are you with changing parms in Tunercat?
If there's is knock with knock counts, then some timing will need to be removed at the exact point where the knock first appears.
If its rich/lean with the LT Ints way off, then the MAF tables need to be changed....its not easy to describe how to change them...but I basically get all of the MAF readings from DataMaster where the LT Ints are way off...then from there compute a % that the MAF tables need to be rescaled.... IF you think of it this way..the MAF sensor output signal is frequency, Hz...not grams of air per sec... If you look at the MAF tables in Tunercats, you'll see the table entries are gmps related to specifc Hz.
Its these tables that are used to determine what the gmps reading is showing on DataMAster, and then from there fueling is determined by the gmps that is determined.

So for example, if DM shows a MAF reading of 100gmps and the LT Ints are sitting at 118, which mean you are rich, then you must scale the MAF table so that less fuel is commanded at the same Hz reading that equates to the 100gmps. Lets say the Hz for that is 1302.
So 118/128 = .92 therefore scale the MAF table reading of 100 by .92... 100 * .92 = 92..... so replace the 100gmps for that 1302Hz reading with 92gmps which will then lean out the fueling when the MAF senser is at that specific Hz.
Usually I just take an entire range within the MAF table and scale the entire range by .92 in this example...not the ENTIRE table, but say I had the same 118 LT Int reading for 80-120gmps...then I'd scale the MAF table with the range by .92 and then smooth out the transition end points so that the adjacent entries are not more than the next higher entry...that would really jack things up.

 

Thanks I'll give it a shot this weekend when I am messing with it again. I'll let you know.

 

Sorry, but one last question. I have read that if you run rich for a while it can faul up your O2 sensors. First TTS recommends cleaning them with Brake Fluid - is this safe or will it ruin the O2 sensor and second, how can you tell if one of your sensors is not working correctly? Will the voltage be something other than .450 on the Datamaster screen?

 

It can foul them up if the LT Int / BLMs are bottomed out, I think the lowest value can be 108...but I'll assure you once you are below 118 its not maintaining the correct AFR so my guess is too much driving with them below 115-118 is not good as my cars won't pass the sniffer emission test here if the BLMs are off that much but still within the "range" that the PCM can control fueling.
You can usually tell if they are weak if you get it up to oper temp and at idle, the O2 mv should be pretty active, if they are sticking on the same mv for more than a few seconds all the time, then its time to replace them. Also, if one sides LT Int/BLM is way off from the other side/banks O2 is another sign they may need changing.
Its a good rule of thumb that if they have more than 75k miles on them, they need changing, maybe 50k is more reasonable to always change them, at thats when the LT Int/BLMs have been maintained within 10% of 128 all the time.
I don't think DataMaster shows the O2 Cross-counts, but some scan tools for others cars do, and you just watch the O2 cross-counts at idle and they should cycle from 0-255 in less than 90 seconds...a cross-count is just the number of times the narrow band o2 crosses the perfect afr, lambda.