Hello. Although I have been reading this forum for many years, this is my first post. As the title says, I recently failed emissions. I have a '95 GMC Safari with 4.3 CPI and 4L60E. It has about 165,000 miles on the original engine.

Let me apologize up front. After 5 hours of doing searches and reading posts I haven't found what I need. So please forgive me it this subject has been gone over a hundred times.

Here's what I did find. I read some talk about a possible leak in the intake manifold and possibly a leak in the exhaust. I haven't ruled out the intake and I did rule out any exhaust leak. I remember hearing about spraying brake cleaner around the intake to see if any would get sucked in and raise the rpm. Is this a good way to do it? Something else that I've read is about the vacuum lines to the map sensor. However, this map sensor plugs right into the intake manifold so there isn't any vacuum line going to it.

The emissions test says that I'm running rich, which the OBD scanner confirms. The test results show 52 parts per million and allowable for my year in Colorado is 20 parts per million. I've replaced the O2 sensor and the map sensor and I'm still running rich.

My map sensor reads about 1.75 volts at idle and O2 sensor reads between 800 and 900 millivolts. When I'm crusing at 65 mph the map sensor reads about 3.5 volts and the O2 sensor goes from 20 millivolts up to 900 millivolts. The rich/lean flag reads rich at idle but goes from rich to lean on cruise which is consistent with the numbers.

Everything is basically the same after I changed the the sensors. I'm stumped at this point so any help would be greatly appreciated.

Thanks,
Michael

 

The board Thirdgen.org is oriented to '82 through '92 f-body vehicles (Firebird & Camaro). There is some lee-way in this if it is related to these vehicles. Unfortunately your post is far from that vehicle group.

The fullsizechevy.com board may have some better information. If anyone has suggestions to fixing his vehicle please PM Intenseman.

RBob.