Mileage improvement from transmission failure

[jwgary]

I haven't gotten any bites over in the 2nd Gen forums so maybe someone will take notice here.

I have a failure in my transmission governor pressure sensor or solenoid (I haven't had the time to troubleshoot it yet). The reason I know is that it acts just like it did last time it happened where I start out in 3rd gear. The strange thing is that I got really good mileage on the last tank of fuel since it stopped working. The ovhd computer said 22. 8 mpg (mine has always checked well against a calculated MPG) and I calculated 22. 5. The computer only gets the last 400 miles so more of that is after the failure than calculating on the whole tank. This is the first time I have ever gone 625 miles before the low fuel light (1/8th of a tank) came on. With the DTE added to my ODO I would have hit empty at around 750 miles.

Maybe I am on to something. Could the smooth transition from 0-35 mph help mileage? I'm going to watch it a bit more since I won't be able to do the repair for a few more weeks. Of course it is a bit of an annoyance when starting on an uphill grade, but most of my driving is on the freeway and unloaded so it's not all that bad. I'm thinking of tapping into the circuit after the repair to switch between economy mode and low end torque mode.

Has anyone else who has had this common failure experienced a similar mileage improvement?

 

[TFucili]

You've created a poor man's CVT

 

[rbattelle]

Am I understanding correctly - you're starting in 3rd all the time?

Interesting that improved the fuel economy! Although I'd be concerned about burning your transmission fluid up, since it's got to absorb a lot of energy when you take off from a stop in 3rd gear.

Ryan

 

[jwgary]

I don't do a lot of stop and go driving. My commute is about 30 miles with about 25 of that being freeway at a constant 60 mph. Mileage on this tank is not looking as good so maybe I just got a "good" tank of fuel last time. the CVT thing is basically what I have. The torque converter amplifies torque at high differences of engine and drivetrain speeds and gets closer to 1:1 as they match. The feel is not much different from driving my mom's Murano with a CVT.

 

[rbattelle]

The torque converter amplifies torque at high differences of engine and drivetrain speeds and gets closer to 1:1 as they match.

I am not familiar with the concept of a torque converter as a torque amplifier. In my opinion, a torque converter does not amplify engine torque, regardless the difference between the engine speed and the wheel speed. Rather, in my opinion, a torque converter transmits power from the engine to the transmission input shaft using a fluid which absorbs excess energy from the engine until a wheel speed commensurate with the engine speed is obtained. In effect, it functions as an axial pump with the "stator" vanes mounted on the transmission input shaft (the blades are attached to the engine flywheel).



That's merely my opinion.



If you're starting off in 3rd gear, where does the excess energy go before your wheel speed and engine speed are matched? In my opinion, it is absorbed by the transmission fluid, which will get very hot very fast.



Ryan

 

[Tinman]

Your trans is in limp mode. And yes, it probably is a solenoid or pressure sensor. I had that happen once and it's an easy fix. Any mileage gains you might be getting (and I don't see how) will be negated by the trans re-build you'll have to do if you keep driving it that way. When mine went out,

Bill Kondalay told me to not drive the truck until it was fixed. Of course the stock TC is much looser than the STT, but I won't risk it.

 

[jwgary]

I have done this repair before and yes it is an easy one. I just have to get the time to do it. Maybe this weekend. The last time it went out was in the winter so I had a little more cooling going on.

Ryan, the stator vanes in the TC provide the torque multiplication. That's the difference between a torque converter and a standard fluid coupling. As far as heat generation, the slipping is not any more than what it feels like when you pull a trailer that's loaded down. It takes the extra RPM and a little more time to get the beast moving. After getting to about 10-15 mph it drives like normal. I also drive like a grandpa when taking off from a stop and always try to do a rolling stop if I can. That probably contributes to the mileage increase as well.

 

[rbattelle]

I also drive like a grandpa

That's nothing, I drive like grandma! :-laf



Ryan

 

[jwgary]

Update

So, it takes about two weeks to go through a tank of fuel and I filled up on the test drive to get everything warmed up after the replacement of the governor solenoid and pressure sensor/thermistor. The last tank calculated and computer said 21. 6 MPG. That's a little closer to average, but I was still at 630 miles with the low fuel light turning on only 5 miles away from the station. I'll post again when I fill up in another two weeks to compare the fixed mileage.

I do think that even if this works as a mileage improvement it isn't a way to work. I forgot that after a while the transmission likes to stay in 1st gear a long time and you have to get over 20 mph before it will shift to 2nd. I quickly made the repair after it started doing that (only drove home from work). Maybe there is a way to get into the PCM and force a shift. You could at least manually select that you don't start in 1st, but 2nd instead. The 5 and 6-speed guys do this all the time - granted they have more gears.

 

[Skydiver]

I got y'all beat. I drive my 96 Regal 3. 8 like a Great Grandma. The gov. fuel mileage is rated for 27 hiway. I get 30. 5 combined.



What is diesel any way?lol

 

[jwgary]

Post Repair Update

I filled up yesterday for the first time since the repair. My mileage was 21. 7 so I guess my high mileage was just a fluke. I'm getting basically the same now as I did on the last tank that was all pre-repair. It is somewhat fun trying to see how high I can get the mileage to go by keeping my foot out of it.