Low Speed emmisions failure - HELP!

89 Merc Grand Marquis is repeatedly failing the emissions test that has recently been effected in Austin. I've replaced the two lower cats (this car has 4 !!), and both O2 sensors. the car still idols funny (high/normal/high) and is failing by 6 TIMES the legal limit. 200ppm hydrocarbons - pass - and the car is releasing 1200 at idol speed. the mechanic refuses to suggest any other repairs (because i'm doing them myself i'm sure) and i NEED to get the car to pass inspection. Any ideas?????
Thank you!!

sounds like a ignition module problem


89 Merc Grand Marquis is repeatedly failing the emissions test that has recently been effected in Austin. I've replaced the two lower cats (this car has 4 !!), and both O2 sensors. the car still idols funny (high/normal/high) and is failing by 6 TIMES the legal limit. 200ppm hydrocarbons - pass - and the car is releasing 1200 at idol speed. the mechanic refuses to suggest any other repairs (because i'm doing them myself i'm sure) and i NEED to get the car to pass inspection. Any ideas?????
Thank you!!

Could you add more detail please? I've been told the issue could be caused by vaccum leak, EGR or PVC valve, Catallitic converters, and o2 sensors. i'm trying to narrow it down, and no one has mentioned the ignition module, to be honest i don't even know what that is. if these details help - the car has 90,000 original miles and was garage kept in a northern state for the majority of its life. the pipes have also been replaced from the lower cats back.
Thanks

Have the fuel pressure checked. It sounds like it is running way too rich. If the pressures are high, it can cause the readings. Vacuum leaks can affect the O2 sensors and make them trick the computer to add more fuel too.

Thanks Way2old, i hadn't heard that one before - yes i think it's safe to say the car is running WAY too rich!! how would i go about checking the fuel pressure, or is something that would have to be done at a shop? Also, what do you think about reekor's idea that it could be the ignition module? additionally, do you think i can eliminate any of the other possible causes for an emmisions issue - upper, cats, egr etc. Appreciate any ideas -thanks!

If you can borrow a fuel pressure gauge you can check it yourself. Some parts houses have a loan a tool program. There is a schraeder valve on the fuel rail that the gauge screws into to read the pressures. It should be about 40-42 psi with key on and engine not running. With the engine running it should drop about 10 psi to 30-32. Reeker may be right also. If the module does not trigger the coil properly it can cause unburnt fuel to enter the exhaust and cause problem You may also want to look at the MAP sensor.