Larry Bialecki
New Member
For 6 months I have been chasing down a problem with my 93 ATX. (See other input to the
forum under my name.) The vehicle has 171K miles on it and I am the second owner, getting
it with 79K on it. It has had no scheduled maintenance with the exception of the timing
change, no ATX repair, and no major breakdowns. In the beginning of the summer I started
to have shifting problems. The 3 to 2 downshift was acting up during a power downshift.
The ATX would try to downshift but
would take too much time to get to second and feel like it was slipping. A 647 error was
generated and the ATX would change shifting schedule from then on, no longer ever trying
to shift into third regardless of going up or down. This condition would clear after turning
off the ignition. I spent a lot of time trying to determine the cause of the problem, flushing
out the ATX, changing the Vehicle Velocity Sensor, considering pulling and inspecting the ATX
valve body. There was never any gunk or parts in the ATX pan and no signs of slipping.
I got to the point where I would just manually down shift when I suspected that a 3 to 2
power downshift would be required.
At the same time this was all happening, I was also experiencing some loss of power,
although I only realize this by hindsight. It appears that I lost about 20% of my power.
I could tell this because my gas mileage dropped from 24 to 21 MPG and I could no longer
climb the same hill, under the same conditions, in overdrive as before with out dropping down
to third. I also started to get an occasional engine light during city driving which lasted for
about 30 seconds and indicated both O2 sensors were bad (error 281 and 289). Replacing
the O2 sensors did not stop the occasional engine light. There were no other engine light
indications. I also replaced the fuel pump and plugs.
Based on comments from the forum regarding other SHO problems I decided to look at the
MAF sensor. I used a dremel to cut notches into the screws and carefully removed the sensor.
And guess what I saw? The sensor elements were covered on the air inlet side with black
soot, which was only obvious when looking under a magnifying glass. I used carburetor
cleaner to CARAFULLY clean off the soot and then reinstalled the sensor. At the same time
I poured some injector cleaner into the tank and added Slick 50 Transmission fix to the ATX.
After a month of driving now I am very pleased. No more O2 light. No downshift out of
overdrive, just like before under the same conditions. And, my 3 to 2 downshift problem
seams to have gone away. Gas mileage is backup to 24 with an occasional 27 MPG.
Because I never drove the SHO aggressively (I am an old fart) I cannot tell if acceleration
from is better. I think that cleaning the MAF sensor now allows the SHO to run at best true
mixture giving me full power and stopping unnecessary power down shift requests.
The ATX probably still has a problem but it is not over exercised with excessive power
downshift requests.
Sorry about the length of this input but I though the forum would be interested in my
experience. I will keep the forum updated on any addition mechanical repair experience
I have with the SHO. I appreciate the forum availability.
forum under my name.) The vehicle has 171K miles on it and I am the second owner, getting
it with 79K on it. It has had no scheduled maintenance with the exception of the timing
change, no ATX repair, and no major breakdowns. In the beginning of the summer I started
to have shifting problems. The 3 to 2 downshift was acting up during a power downshift.
The ATX would try to downshift but
would take too much time to get to second and feel like it was slipping. A 647 error was
generated and the ATX would change shifting schedule from then on, no longer ever trying
to shift into third regardless of going up or down. This condition would clear after turning
off the ignition. I spent a lot of time trying to determine the cause of the problem, flushing
out the ATX, changing the Vehicle Velocity Sensor, considering pulling and inspecting the ATX
valve body. There was never any gunk or parts in the ATX pan and no signs of slipping.
I got to the point where I would just manually down shift when I suspected that a 3 to 2
power downshift would be required.
At the same time this was all happening, I was also experiencing some loss of power,
although I only realize this by hindsight. It appears that I lost about 20% of my power.
I could tell this because my gas mileage dropped from 24 to 21 MPG and I could no longer
climb the same hill, under the same conditions, in overdrive as before with out dropping down
to third. I also started to get an occasional engine light during city driving which lasted for
about 30 seconds and indicated both O2 sensors were bad (error 281 and 289). Replacing
the O2 sensors did not stop the occasional engine light. There were no other engine light
indications. I also replaced the fuel pump and plugs.
Based on comments from the forum regarding other SHO problems I decided to look at the
MAF sensor. I used a dremel to cut notches into the screws and carefully removed the sensor.
And guess what I saw? The sensor elements were covered on the air inlet side with black
soot, which was only obvious when looking under a magnifying glass. I used carburetor
cleaner to CARAFULLY clean off the soot and then reinstalled the sensor. At the same time
I poured some injector cleaner into the tank and added Slick 50 Transmission fix to the ATX.
After a month of driving now I am very pleased. No more O2 light. No downshift out of
overdrive, just like before under the same conditions. And, my 3 to 2 downshift problem
seams to have gone away. Gas mileage is backup to 24 with an occasional 27 MPG.
Because I never drove the SHO aggressively (I am an old fart) I cannot tell if acceleration
from is better. I think that cleaning the MAF sensor now allows the SHO to run at best true
mixture giving me full power and stopping unnecessary power down shift requests.
The ATX probably still has a problem but it is not over exercised with excessive power
downshift requests.
Sorry about the length of this input but I though the forum would be interested in my
experience. I will keep the forum updated on any addition mechanical repair experience
I have with the SHO. I appreciate the forum availability.
Your writing was long but interesting and not boring as most long readings. Thank you for you observation, my '93 was also putting of the CE light and gas millage was crappy I read the codes and it was the MAF sensor issue code, so I cleaned it up with berrymens carb cleaner really good and carefully and every since, restored power, better gas millage, and no CE light 
