Lean codes, backfiring at W.O.T., no power

redwing89

redwing89

Club Member
hey guys,

i have an 89 lx with a 5.0 H/C/I. i was having some cold start idle issues with the surging and stalling... found out my maf was off calibration (bought it from a friend but didnt have the proper setup for the housing it was in. it was in a housing for a 94-96 cobra style) so i bought a new PRO-M unit, 75mm "bullet" maf, calibrated for my 24 lb injectors. i also have an SCT tuner chip i just bought, but the car will run like shit on any other tune beisdes stock, and im assuming the codes im getting for it is why.

KOER codes

21, 31, 91.

91 indicates drivers side bank running lean. i don't believe i had this code before i swapped mafs, because on heavy accel/W.O.T the car has no power, and backfires during acceleration. its never done this before i switched maf sensors. and yes i did pull the neg battery cable and let it sit for like 3 hours (i know it only needs to be disconnected for 15 minutes) now the day i had gotten the maf in the mail, and installed it on my car, it felt like it was running great, it still had some popping sounds coming out of the exhaust on decel that i didn't have before, but it felt like it wasn't lacking in power. until i ran it out of gas. so im thinking i perhaps restricted my fuel filter, and that's what is causing it to run lean. it doesnt appear to be missing at idle/ low rpms, in fact the idle is a lot nicer now and it no longer surges or stalls.

EDIT: i also swapped the 02 sensors just to see if the code would change to 41, to indicate a bad 02, but it still came out a 91. unless i was supposed to disconnect the battery before checking which i didn't do.
 
Couple of things I would try. Put a fuel pressure gauge on the car make sure it's not dropping also this happens more than people like to admit but if you didn't get all of the wax or grease off of the service port on your processor when putting the chip in It'll do some screwy stuff.
Everything your describing (obviously with the code) is a lean condition including the rolling idle.
 
okay, i replaced my fuel filter, 02's and my ECT sensor. my readings for KOER are now 31 and 91. so it is still indicating a lean condition on my drivers side bank. but when i did my cylinder balance test this time, it blinked "1" and then paused and blinked "1" agian, so is it indicating that cylinder 1 failed the test? what to check next.
 
update agian. re did the tests and now both o2s sensors read lean. so i have code 41, 91 and 31. ran cylinder balance test and it passed that time. so im kinda confused as to whats going on. maybe something is messed up with my ECM?
 
ok im really sketched out by the guys at bama that deal with the SCT tuner chips for these model cars. i called them twice with questions about my tunes and i got two different stories. but what im going to do is try and raise my fuel pressure becuase i think it is set below stock rating at 35psi. and maybe that is affecting it. but i don't really see how because when your in W.O.T. there's no vacuum and the fuel pressure should increase as well. which means at wot i should be getting about 45psi fuel pressure because that is what it shows when the vacuum line is unhooked. but ill give it a shot anyway.
 
my fuel pressure was 31 psi at idle with the hose connected. and 42 with it off. i brought it up to 39 psi with the hose connected and went for a drive, it seemed to run a lot better it didn't hesitate or backfire at all, but i still have the lean code. only its on the drivers side bank now.

i swapped my old maf back on to see what would happen, and i lost the lean codes all together but i got codes 44, 94, 31 and 13. 3 of which are smog related and the 13 code says my idle air control motor not controlling idle properly, but i know its just the maf itself because i swapped it into a stock housing when it was calibrated for a different one. so im thinking my maf is causing the lean code somehow?
 
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