I posted this on the "Tech/Perf" forum too.

I have a '95 coupe with 47K miles, auto. Last week it started stumbling and missing and idling very rough. I babied it home and noted very black soot on the rear bumper fascia and black soot coming out of the exhaust (both sides.) I ran codes and "H-64" came up, translating to a "Lean oxygen sensor, left bank." I cleared the code and started the car and drove it around the block. Ran fine for a few minutes and then it repeated the problem. I again obtained codes and got the "H-64" again. OK.

The fella at AutoZone researched and found the factory original part number and asked: "Front or rear sensor, left or right?"

Front or rear . . . left or right???? I saw only one in the factory manual, and it was located on the exhaust header in front of the cat.

Anyways . . . a "lean" reading would not equate to black soot coming out of both pipes, right?

I did a cursory under hood check for the obvious: leaks, wires, hissing, knocks, etc.

Before I open the Snap-On box and start turning wrenches, I thought I should check with the "gurus" here and get a few recommendations and maybe narrow this problem down.

The car ran great with absolutely no problems. . .up 'til now. I do not "dog" my car either.

Any thoughts?

Thanks in advance, Gary

 

All I can give you is: Lean O2 readings cause the fuel mixture to go RICH, trying to FIX the lean condition. The O2 sensor reads lean, this could be an O2 sensor gone bad or it could be a lean condition in the fuel management system. Can you get a scanner on the car and read the O2 sensors?

 

Thanks for the reply. Seems kinda odd that a lean translates to rich, but who am I to argue? I think the O-2 sensors are heated, so that may explain why the car ran OK for the first few minutes (until the sendors either heated up or not) and then ran like crap.

I do not have exotic scanners - I just read the codes from the speedo unit.

If you, or any other readers, have further hints, I welcome them. Weather is getting nicer and I plan to drive more often.

Gary

 

If the O2 sensor comes back with a LEAN condition, the ECM tries to FIX that lean condition by going richer. If the O2 sensor is defective it will not ever be happy and the ecm will go FULL RICH.
If the O2 sensor is working correctly then something is wrong in the fuel delivery system.
That is why everybody says to troubleshoot before replacing parts.
Does that make any sense?

 

The car has 2 operating modes(MORE really but not important right now)
Closed Loop and Open Loop.
When the car starts it uses parameters hard coded into the Chip. After warm up(I am not sure when exactly) the ECM uses data provided by all the sensors to constantly monitor the engine management system and make changes to whatever needs to be changed to keep the engine running properly. IE: Injector Pulse Width, Timing, Etc.

 

using a laptop w/scanning software may give better insight as to 02's, blm etc. being the culprit.