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What was the inquiry? I may have missed it

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Hi Rockfanged, it was "decreasing fuel economy-trans not shifting into overdrive". I seem to have difficulty in searching for this and many other subjects, it seems the Caddyinfo site has changed. Let me know if I posted it in the wrong place.....thanks     Bill in VT

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Hmm. Not sure.

This is the 99 Deville right?

Engine light on? 

Has it ever thrown the Torque convertor death code P0741?

Please give me the engine RPMs at cruising speed 55mph flat. 42 mph flat. Engine up to temp.

Engine revolutions should drop at 41 mph if cruising. From about 1500 down to about 1300. I will compare what you provide with my 97 Deville. 

GM FAN FOREVER

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This is my 1990 Deville, 51k miles. There are no codes stored, and the RPM's at 55mph are 2000, it will shift into 4th gear as it should, just not OD. Although it did shift fine for the 1st 3000 miles or so. This car is a creampuff, and well worth fixing. Is it difficult (and might it help) to change the trans filter and gasket? I can get the tranny to shift into OD manually by using the OBD and in the correct mode, push in the "warmer" button. Any suggestions? 

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I could help more if this was the 99, but I will try to help

I do not know which tranny they used on those, Whether they are electronically controlled in the early 90s.

Is the coolant getting up to temperature? At least 170*f. If the coolant is not getting to temp it will not go into overdrive.

Not sure that a fluid and filter change would help but it sure couldn't hurt. Should not be very difficult. Inspect solenoids while you have the pan off. I have seen things hit the pan and break solenoids

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Thanks. I'm getting it out on the road again this week, and will check the temp via the OBD. I hadn't thought of, or considered the engine temp being a factor, as the heater is working fine, and the temp is displayed via the OBD in Celsius. I found the Celsius range should be 93-100 degrees. I'll let you know! It could be a faulty thermostat, causing it to run rich as well.    Bill in VT

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Another thing I would check is the brake light switch.

If its failed either brake lights or OD wont work.

Used to be a big issue with GM trucks back then.

Just a thought in case it was mentioned and i missed it.

93 DeVille-13 Chevy Impala

72 GTO - 77 Triumph Bonneville

84 Z-28

Syracuse NY

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OK! So, here's the deal....I am quite ecstatic, because, I checked the engine temp while cruising, level ground, and up a few steep hills, and discovered the engine temp WAS in fact running cool. (Although the heater SEEMED to be OK, in the cold weather). So I installed a new 195 degree thermostat, and WOW! The temp is back up to normal, the exhaust is no longer chokingly rich smelling, the engine runs and idles smoother than ever, and best of all, the OD works properly and my fuel mileage is back to normal. SERIOUSLY. I am totally shocked that such a simple remedy could fix all these issues. And of course, I realize I am REALLY lucky, thanks to your help. I hope anybody else who may experience this problem reads this and is as fortunate. Thanks Rockfangd! And Sonjaab too.....      Bill in VT       PS I still have the '99 Deville as well

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Excellent. Glad to hear. Like I said before I must have missed the original thread. Thanks for updating this

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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