Help/advice for 176 code

[jimbolin]

I keep getting a 176 code after it warms up to operating temp.This weekend I replaced upper and lower intake gaskets ,finding a small vacum leak on lower but after putting it all back together it still codes.It has been suggested that my cats could be plugged enough to throw code.Before I change the cats is there anything else I should check?It has 280k on the original cats and I have changed all the sensors and PCM correcting a rich condition so I'm thinking a plugged cat is not beyond the realm of posibility.The vehicle runs great with no other issues.

 

[MrShorty]

CM 176 is the only code you are getting? I'd be tempted to switch the two O2 sensors and see if the code follows the sensor or not. If it follows the sensor, the sensor itself is probably bad. If it says on the left side, then it's either in the wiring or something else specific to the left side.

 

[jimbolin]

I already did the O2 swap and same thing.When I did the intake gasket I did notice that pcv hose was not tight on valve maybe causing a vacuum leak showing up on that side?
This might be a long shot but I have heard that coils can cause an eratic spark that could make it go lean on one side or the other.When I put my induction timing light on individual wires and watch the light the left side spark is not the same as right.The corresponding plugs on that side are showing they are running leaner than the others also.Would'nt the coils throw code?

 

[MrShorty]

You have a lean code left (that stays on the left side). The spark plugs are also saying lean, which suggests the O2 sensor is fine.

I have heard of cases where a misfire (maybe from a faulty coil) could trigger a lean code. The coils don't have their own codes, so an erratic coil pack could conceivably trigger this code, but I would also expect other symptoms consistent with a misfire. Bad fuel delivery (maybe from a bad injector) on that side could conceivably do the same thing.

How is the left side spark different from the right?

At this point, I'm not sure where I'd go with it. I'd probably look at the injectors closer to make sure the left side injectors are firing right. Maybe look deeper into the differences in spark you are seeing and see what that indicates.

 

[jimbolin]

I appreciate the responses.The injectors all looked the same and clean by magnifying glass standards.I have put a stethoscope on them and a few are a little noisier than the others.Something I did not mention is that when it was very cold with the engine never getting up to normal operating temps it would not code. Only when the temp comes up does it do it.Temperature related maybe?I have changed all sensors with the exception of air temp sensor and purge solenoid.
As far as checking the spark differences when using my timing light the right side is a definite single flash at each firing.When put on the left the flash is "spattered".

 

[MrShorty]

I'm not sure what would cause the spark to be erratic on one side. Coil pack seems most likely. Another thought I just had, while I don't know why it would only effect one side, but is that side of the engine adequately grounded?

 

[jimbolin]

I put the timing light on it again last night to check each wire and the two cylinders that appear lean had a definite miss according to light.I .Would a miss fire from the coil cause it to go lean?
I have checked all the grounds I could find when I started having all my issues.

 

[MrShorty]

.Would a miss fire from the coil cause it to go lean?

It could cause the O2 sensor to read lean. The O2 sensor looks at unburned O2 in the exhaust to determine rich/lean. Since a misfire doesn't consume any O2, the excess O2 can make the O2 sensor think lean.

 

[jimbolin]

That makes sense.I have learned in the past not to do too many things at one time so I am going to start with ignition wires.They are the original wires and a little less costly to replace and then go from there.