fuel trims causing a VERY lean condition.
A few months ago i posted about a weird stumbling issue i was having with the car. since i had gotten my VE's within 2% across the board(using LTFT's), i ruled it out as a lean condition and assumed it was an ignition problem.
well, now i know for sure that it's running lean as fuck regardless of what i do with the VE's. it goes even leaner when i plug in the MAF, to the point of being barely drivable from popping and stumbling.
i figured this out by manually commanding the AFR with the scan tool. when i set it richer than 11.5:1, the problem goes away and runs exactly like it should.... strong, no stink, no popping or stammering. it took me so long to figure out, because i had only associated bad exhaust fumes with a rich condition and blamed it on my previous exhaust leaks causing it to add fuel.
so i simply added 10% across my whole VE table(which i had previously tuned within 2% trim). it ran great for a minute until it started trimming about 10-15%, returning to the same popping and stammering shenanigans.
being a fairly inexperienced tuner, a few possibilities come to mind:
1. my injectors are a different size than advertized, causing my IFR calculations to be WAAAY off... but wouldn't the fuel trims still correct for this?
2. my engine just likes to run rich? unlikely, being N/A at about 10.2:1 comp.
LQ4, .040 gaskets, 823 heads, TR-55's
3. my MAP sensor is malfunctioning..... i say this, because it started throwing a code last week.... even though it still has consistent readings.
if you're wondering why i'm not using a wideband, i have an LC-1 and spent 3 months trying to get it to work. despite pages of help from experts on several forums, i never got it to work with EFI live using serial or analog connections. i even tested the analog output with my multimeter, and the voltage was right where it should be. so now it's sitting in a box.
Reply With Quote
Originally Posted by joecar
