Initial tune: Fuel trims whack

[big_d]

Alright, I bought my car with kind of a bad tune, so I decided to help it out. I bought a 90 Eprom and sent it to Steve to be socketed and chipped. The car currently runs a gm maf with maf-t gen2 (works just like an afc). I did a boost leak test to about 25lbs and fixed all the tiny leaks, and also set my fuel pressure to 38. I put the new ecu in and zeroed out my gen2 and started her up. I took it for a drive and it stumbles really bad (smells very rich). So Steve and I narrowed it down to my maf input (the person I bought it off of had it set to an LT maf when it really is an LS maf). Changed the input and it was still rich, so I left it for a while...Yesterday I have a bunch of free time to fine tune so I begin with my low trim. I got it to stay around 104% with the mainscale setting at -7 on my gen2. So I begin with my mid trim because it was slammed at 81.2%. I begin leaning it out, watching knock of course and it never seems to change(even though I was cruising for quite some time). I had to stop at a friend's house for like 5 minutes, and I come back out. I begin cruising and I happened to look at my trims and my low trim is at 81.2%!? I got pretty frustrated and left it go until I got to school. So that's where it sets. What could have caused my trim to change like that? I was kind of hoping to get my low and mid trims lined up before I install my wbo2 Friday to do some wot pulls, but this put a halt to that. Any help is appreciated. Thanks, Dustin

 

[the_mork]

I would suggest putting your wbo2 in and seeing where you really are, narrowband o2 sensors can't be trusted outside of a given air/fuel ratio meaning that they start to show large changes in ratios as very small voltage differences outside of their normal operating range.

 

[No_Skillz]

You should be adjusting LTFTs via the airflow sliders for the particular Hz that you are seeing. Set your global and deadtime settings to the recommended specs on the dsmlink manual and all fuel sliders zeroed. Only after you get your LTFTs to +/-5% via airflow sliders do you start messing around with the other stuff.

 

[big_d]

I don't have a narrowband, nor do I have DSMlink. Tuning with maft gen2. The mainscale takes percentage from all of the user tunes(low mid and high). It would be just as if I took -7 from low mid and high scales, if that makes sense. I am following the piggyback tuning guide, where it says to set up my low trim and move to middle trim. It just doesn't seem right that my trims would change like that.

 

[the_mork]

narrowband is the stock o2 sensor

 

[banishedmunk]

try setting your fuel pressure to 43.5 and make sure that when you do set it that the vacuum lne is off i had a problem with a friends car running extremely rich and come to fnd out the fuel pressure was at 35 psi withe the line off reset it and it fixed the extreme rich condition.

 

[big_d]

That's the thing, I understand it's running rich but why did my low trim do what it did. I just set my pressure between 37-38psi with the line off not very long ago. I guess I'll try setting it a bit higher, but that still doesn't really explain the trims. Any other thoughts? Thanks, Dustin

 

[Gstclipse69]

A 1g has base fuel pressure of 38.
A 2g has base fuel pressure of 43.
Leave the fp alone.

 

[big_d]

10-4. I don't know why my trims are doing that .