wasting fuel?

nascar john

Registered User
gentlemen, i drive a 94 auto that is bone stock. i drive only around town on surface streets with the car in drive. the car upshifts and downshifts quite a bit due to speeding up and slowing down. i had a fellow sccoa member tell me that is wasting a lot of fuel due to the computer richening my fuel each time the trans goes into od[fourth gear]. i realize ,that by not using fourth, i am saving wear and tear on the trans, but is the computer richening the mixture? i am confused since, in od with my driving style the rpm's are at 1600 and in fourth they drop to 1100. you all know the cost of fuel so a mile or two extra per gallon can be a cost saving. any comments?
 
gentlemen, i drive a 94 auto that is bone stock. i drive only around town on surface streets with the car in drive. the car upshifts and downshifts quite a bit due to speeding up and slowing down. i had a fellow sccoa member tell me that is wasting a lot of fuel due to the computer richening my fuel each time the trans goes into od[fourth gear]. i realize ,that by not using fourth, i am saving wear and tear on the trans, but is the computer richening the mixture? i am confused since, in od with my driving style the rpm's are at 1600 and in fourth they drop to 1100. you all know the cost of fuel so a mile or two extra per gallon can be a cost saving. any comments?


Ummmmm...if you don't use 4th/OD, and the system supposedly goes rich when it goes into 4th/OD, how can you be worried about wasting fuel? You can't get there from here :confused:

'in od with my driving style the rpm's are at 1600 and in fourth they drop to 1100' - Can't be done. As you said, OD is 4th... You must mean 1600 in 'D' (3rd) and 1100 in 'OD' (4th)...?

AFAIK, 'L' is 1st - 'D' is 1st, 2nd & 3rd. - OD is 1st, 2nd, 3rd, & 4th. 'R' is for the rock you are likely to hit when backing up and 'P' is for sissies. Seems like you are confused what OD/'overdrive' is and what it is used for. :)

I don't agree that you are 'saving wear and tear' by avoiding OD or whatever. If you're using the trans, it is obviously seeing wear.

I stay in OD, letting the trans decide when to otherwise shift, except only when on a steep grade and/or traffic force the system to 'hunt' back and forth for a gear...then I drop down. I'll hit the other positions every few months just to exercise the internals and monitor trans operation.

The test is your mileage? What is the low average MPG for you? Mine is 17.

Keep the tires inflated - I run slightly above spec. Don't treat the trunk like an attic and stick to some sort of routine maintenance schedule and you'll be doing the most you can towards better mileage.
 
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Wow!!!! talk about being nasty! :eek:

During a shift you may see some enrichment to compensate for the sudden load the motor will see, but once the shift is complete your AFR will go back to around 14.6. The other factor during a shift is timing is adjusted to lower the amount of torque going into the transmission.

If I was going through the streets and the car is going in and out of OD then I'd lock it out and stay in D (which is 3rd). Running a motor in that type of situation at 1100 rpm's is not the most healthy thing for the bearings especially with changing loads. This could make your car run hotter as well as it will be lugging so it will be working harder. If the lugging gets high enough, the computer will actually switch to open loop mode and enrich the fuel.

The best thing to do is try one tank of gas with OD on in those situations, then try another tank of gas and shut OD off.

Frit
 
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AFAIK, 'L' is 1st - 'D' is 1st, 2nd & 3rd. - OD is 1st, 2nd, 3rd, & 4th. 'R' is for the rock you are likely to hit when backing up and 'P' is for sissies. Seems like you are confused what OD/'overdrive' is and what it is used for. :)
A '94 auto will be a 4R70W. It should be the same shift sequence as on my '95 V8. 1 is 1st, 2 is 2nd, D is 1st, 2nd, 3rd and 4th. If the button on the shifter is activated it locks out OD so that D is 1st, 2nd and 3rd.
 
tinman_72> A '94 auto will be a 4R70W.

Thanks, but '4th' is still OD, right? - that still doesn't explain his claim of "...in od with my driving style the rpm's are at 1600 and in fourth they drop to 1100."

Is it possible his trans is borked or you think he's maybe confused about what the OD button does...?
 
No, I think you are just confused because he uses the terms overdrive and fourth to describe that gear above third. He even wrote at one point, "...computer richening my fuel each time the trans goes into od[fourth gear]...", indicating that he knows they are the same thing.

You know, I just re-read what you pointed out and I see what you are saying. Maybe he meant "in D the rpm's are at 1600 and in fourth they drop"
 
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tinman_72> Maybe he meant "in D the rpm's are at 1600 and in fourth they drop"

Now we're cookin'...except since you cleared it up that he has an OD button rather than an OD shifter position, I'm thinking his understanding of when OD is engaged might just be opposite the reality :)
 
fuel

thanks guys, you cleared up the issue-sorry for my typo, i'll lock out the od for a tank or 2 and report any savings
john
 
fuel

i rnn a tank of fuel with the od locked out and lost 2 miles per gallon. guess i'll let the trans search for the gear it wants. thanks for your input guys
 
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