what could cause this? Exhaust leak, spark plugs, sensors? How to tell???

 

In which Cells, and under what operating conditions are the BLM's = 128?

 

The blem long term average is 128 on datamaster. Through out the rpm range the blems are 128. Idle is 128 and all part throttle conditions are 128.

 

Is it going into closed loop? Almost sounds like you "reset" the PCM, and it isn't going into closed loop and "learning". It would be extremely unusual to see both banks at 128 in all 18 cells.

 

Yeah after about 2 minutes or so it goes into closed loop. I was told that my crappy bosch platinums might be the culprit. I just bought a set of NGK TR55's and put a set of duals on, as soon as I get the car back I'll let you know what its doing. If it still is I'm stumped...

 

If your blms are 128, the car isn't running rich. Mine were at 108 and it was rich. The lower, the richer.

 

well then how come my exhaust tips are black and it smells rich? I think it's because my spark plugs are junk, I can hear a miss at idle I think. I just got a set of duals on so I know it's not an exhaust leak. Its got to be the plugs or the opti,.

 

if the cars blms are between 108 and 160 the car is not running lean its runing 14.7. its just showing you how much its correcting and acctually if the blms are under 128 then its pulling out fuel. not adding

 

The best way to check it is the old fashioned way. Pull the plugs. They are better than trying to judge by blms. 97z is right too, if between those 2 numbers the car is still running at the target a/f ratio(although not stoich). At least that is what the pcm thinks but that is a whole other subject.

 

I'll repeat what I already said.... if would be EXTREMELY unusual to have the BLM's at exactly 128 on both banks, in all 18 Cells. I'll go out on a limb and say it absolutely impossible, unless you reset the PCM and the "learning" is disabled, or it isn't going into closed loop. Defys logic.

 

Ok I understand that, thanks. Now is there anything that might throw the BLM readings off? What would cause a miss at idle? Plugs, valve lash, opti?

 

Blowby, intake leak, plugs, any ignition component, O2 sensors, etc.