Hello I am a newer member of the s-chassis community but not to the 240sx. This is my third one (two s13 single slammers) my first s14 95. I have done all the mods/ engine work either my self or with the over site of a senior mechanic. Anyway so my concern is this: I know for idle stock afrs should be 14.7. Which when I first installed my wide band the innovative LC-1 that's what it was reading so everybody was happy. And at WOT it would read low 12's so it seemed to be doing its job. I have checked an array of things with no success. I tried switching out all my plugs with a back up set of ngks with no change. I checked for vacuum leaks and I can find any. I have no CEL's right now and no exhaust leaks that I can hear or see ( when its cold).Right now it seems to run 16.5 at idle, 14.5s around 1.75k and to get progressively lower with higher rpms which is what you would want to see as the motor needs more fuel. Im going to be getting a timing light and compression tester on next pay day to see if that sheds any light on the issue. I just rebuilt this motor about 500miles ago and I don't want to have any detinations. Heres my mod list.

OBX headers
2.5' full exhaust with high flow cat
cold air intake
s13 cams
megan motor and tranny mounts
11lb fly wheel and stage 1 clutch
one piece drive shaft
electric fan with koyo style radiatior
egr delete with resistor bypass
ngk plug wires
walbro 255lph fuel pump
z32 fuel filter
and LC1 wide band
kyb gr-2 on lowering springs
strut towers front/rear
16x9 rims on kumos
etc

 

Update, I have checked the maf for good voltages in/out and also in/out for the tps which I adjusted to .44v. Afr seems better but now im throwing a code which I still need to look up. tried to do a compression test but the tester was junk it kept purging air on its own over 100psi. Still working on getting a timing light. Oh btw distributor cap and rotor are new as well as cone air filter.

 

I don't know if im chasing a ghost or what. I found the code i was throwing was for the knock sensor. Its a new oem sensor i put in 3 months ago. From reading its piezoelectric so there is only one pin for signal on the ecu. The sub harness is good, i will verify the ohms of the sensor tomorrow. I reset the ecu again as well. Need some help if this is a serious issue or just a possible glitch of the wide band. oh and timing is about 25 degrees.

 

well if any thing this will help others with the same type of issues. basically im down to a possible vacuum problem or the fuel system. The knock sensor tested out at 550k ohms and is sending a signal back to the ecu. Rechecked maf, tps, o2, ignition timing, and did a visual inspection of every vacuum line I could find. The second symptom of this is I am getting some random hesitation in the power band but it seems to go away once I back off the throttle. Any comments positive or negative would be helpful incase there is something I have over looked.

 

Ok new update, I just replaced all 4 injectors with the refurbished stock ones for now. I also did new push caps and rubber gromits for the intake manifold. It seems to be better around 15.5ish but still not the golden 14.7. Once my fuel pressure gauge comes in I will be checking fuel pressure to verify the pump is still good and not clogged. If that's good the only thing left in the system would be the fpr unless any body can think of anything that might cause this. Also I will be resetting my wideband again to see if there is any change with the new injectors.

 

Well to end this post with an answer it seems that resetting the ecu and letting it adjust to the injectors did the trick. I am still dealing with the knock sensor issue but my guess is that its losing the signal in the harness. Anyways with my timing slightly retarded from the knock sensor code im reading about 14.2-3 ish at idle now. I did get my fuel pressure gauge installed but by that point the cars AFR's were already resolved. I hope that my troubleshooting and issues can maybe help my fellow 240 drivers in the future . Now for my next venture BOOOSSSSTTTT!