Hello all...My 2001 Blazer seems to put out a lot of black smoke from the exhaust on acceleration. I have done all the tune up (plugs, wires, cap, rotor, fuel & air filter) plus changed IAC valve and front two o2 sensors (after getting SES codes). Engine has 150k miles and allthough I haven't done an actual compression check on it, it does seem to have good compression (sufficient power,easy start, & smooth idle). Could this be the back o2 semsor even with no further SES codes? I'm a long time mechanic and own my own automotive parts store but this one has me stumped. Obviously a rich condition but from where? Any suggestions?

 

I wouldn't go throwing any more sensors at it. The upstream (furthest front) O2 sensors are the only ones that have anything to do with engine fuel management. The rearmost O2 sensor is only for catalyst monitoring.

Have you cleaned the EGR valve?

 

No, not yet. I may try that. In the past on vehicles I have serviced with EGR problems, I had driveability issues that resembled a vacuum leak. No symptoms like that with this vehicle. Also on others with EGR problems I have received an SES code (0401--EGR flow insuffcient) but again no codes on this Blazer. I may try the cleaning the EGR to see if that helps. Thanks for the tips. This is a great forum; I'm glad I found it.

 

Well I cleaned the EGR , didn't appear to bad, re-installed but no help on the running of the vehicle. I did pull the connector to the MAF and nothing changed. Shoulded I have received an SES code? Shouldn't the idle have changed? The engine idle did not change.

Now a few days later, out of the clear blue, engine starts running slugish on acceleration and SES light came on. A check shows P0171 & P0300. Should I attempt to clean the MAF and see if that does it or just replace it?

 

well if you unplugged it withthe valvebolted to the holes you idle wouldn't go way up because you wouldnt have a vacum leak. As for the code I think you should have I got one for running without it for like 4 seconds.

 

OK...I cleaned the mass air sensor and checked the voltage to the unit (12.2). The sensor didn't seem that dirty for 150k miles and having never been done (but I'm a big believer in keeping clean filters which should keep the sensor clean).
Cleared the codes and they came back (0171 & 0300). Do you think it could be in the injector assembly? Its the original. Is there a code that would display specifically for the injector unit? This one has me baffled. I'll take any and all suggestions, Pleaseeeeee. Thanks.

 

A code P0171 may mean that one or more of the following has happened:
[ul][*]The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.[*]There could be a vacuum leak downstream of the MAF sensor.[*]Dirty fuel filter[/ul]
A code P0300 may mean that one or more of the following has happened:
[ul][*]Faulty spark plugs or wires[*]Faulty coil (pack)[*]Faulty oxygen sensor(s)[*]Faulty fuel injector(s)[*]Burned exhaust valve[*]Faulty catalytic converter(s)[*]Stuck/blocked EGR valve / passages[*]Faulty camshaft position sensor[*]Defective computer [/ul]

 

I'll try the coil pack and re-post the results. To replace the cam sensor, is that just a simple bolt on procedure or is there any special tools required?

 

Well I replaced the coil and no help. Does the cam and crank sensor take any special tools to remove?

 

Well, black smoke means your running rich. If you have a K&N filter please throw it away its useless. When you over oil that filter you've ruined the MAF sensor so it needs to be replaced also, when you erase the codes and they come right back you've got problems. I would start with the spark plugs and wires. then check to see if your injectors need survicing.