Richening Low Trim with MAFT?

[ViciousVendetta]

Just a quick question for the guys out there using a GM MAFT to tune. I recently got a pocket logger and have started trying to tune my setup. Ive done what I think according to the directions is richening the low fuel trim since its currently pegged at 139%, ive clicked the base dial to the right a few times but it still goes up to 139% each time after plenty of driving time for it to learn. So just to make sure im doing it right, what steps would I take to get my Low Fuel Trim down? The others are fine atm... Right now my Base is set at 5, aux 0 since I dont have n2o etc.

One other strange thing... It seems recently that pretty much every day when I go out and try to continue tuning, my logger is reading everything back at 100% then it takes a while for them to update, like the ECU isnt remembering the trims and gets somewhat reset. Is this normal if the car isnt ran for a few days between drive times? Or what would cause the ECU to forget the info like that? Logger is fine with new batteries...

Any info would rock, thanks guys!

 

[90blacktsiawd]

If you want to richen up the low fuel trim richen up the idle knob. Of course it is best to get your base set so that all your trims are around 100 and then fine tune from there.

I also use the pocketlogger software and have never had the same problem as you with the trims going back to 100. That only happens after the ecu gets reset for me. I dont know what to tell you on that one.

 

[Nautica985]

I have the MAFT and I cant get my low trim to move either. I have richend up the idle knob as far as it will let me and it still didn't change.

If your ecu keeps reseting, the capacitors in it are probably bad. Take out the ecu, remove the cover and see if the capacitors are leaking. They also have a fishy smell when they are going bad.

 

[v8s_are_slow]

This is probably a dumb question but how fast are you guys driving when monitoring the low trim? Really, just sit at idle when you tune it for low trim. About as soon as you start driving you're gonna be outta the low trim anyway so sitting at idle would be the best time to tune it. Also, don't even watch the "low trim" when adjusting it. Watch the "O2 trim" when adjusting that one cause while you may see the low trim sticking at 139%, the O2 trim will more than likely move. Get the O2 trim about where ya want it and the Low trim should soon follow. As you start driving it might move around a bit but you'll have it in the general area that you want it. Also, after adjusting it, O2 trims are pretty useless to be watching. It's also hard to use to adjust the mid and low using it but it can help. Just have to keep in mind that barely even touching the gas or letting off can change the results of the O2 trim readings dramatically.

And as far as the trims resetting, yeah, I'd think something's up with the ecu.

 

[jetdriven]

mine would idle really lean, 17.5:1 AFR and just off idle, (50-100 Hz) it was 12:1 pig rich. adding a whole lot of MAF compensation at 0 and 25 Hz while taking out some at 50 Hz fixed it. i also had to add a LOT of maf comp between 100-200 Hz.

 

[SiX_BoLt]

hey it seems that im having problems with my fuel trims as well. The thing is that they dont move around at all, just the o2 trim. No matter how much I lean it or richen, they all seem to stay at 100%. Any ideas? Bad ECU maybe? Also what is MAF compensation?

 

[jetdriven]

sounds like you might have a bad 02 heater. my car used to do that. when idling for more than a few mins the 02 would go to like .02 and stop responding, as it got cold. the ecu would keep raising the low trim to get the 02 back online. if i held it at 2000 rpm for a half a minute or so it would start cycling again and the low trim would move toward 100.

maf compensation is a set of tables in the ecu. they add or subtract from the maf signal internally in the ecu starting at 0 HZ and every 25 Hz until 400 Hz. then every 100 Hz to 1000 Hz, then every 200 Hz to 1600.

the ecu takes the Maftick (pulses per revolution, or Hz if you go 60 seconds) and adds or subtractsthe maf compensation value before using it in calculations. I had to change it a low in the low areas with the GM MAF. It doesnt emulate the 1G MAS very well below 300 Hz.

you change them with an EPROM burner and an EPROM ecu or just do a bunch of logging, determine the lean and rich spots on a nice closed-loop light throttle pull in 3rd gear from 25 Hz to 400 Hz and have Jeff from DSMchiips burn you a new chip.