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4Runner RPM change in mornings

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Old 11-14-2018, 07:07 AM
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4Runner RPM change in mornings

I have a 95 4Runner 3.0 auto, 176k miles. Engine and heads were just rebuilt, new plugs, new coolant temp sensor, new O2 sensor, TPS was tested and works correctly, and the transmission was rebuilt last year.

Iíve noticed when I go home from work in the afternoons my RPMís at 70mph are about 2900-3k and I get good gas mileage, however when I go to work in the mornings, my RPMís at 70mph are roughly 3400-3600k and my gas mileage tanks. Obviously there is a temperature change between the morning and afternoon, but I live in AZ so the temps in the morning have been 50 and 70ís in the afternoon.

Does anyone have any idea why the change in RPMís and gas mileage at different times in the day?
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Old 11-14-2018, 08:28 AM
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Up hill down hill, head wind, air density..

Or you need to warm up the engine longer so it enters closed loop and uses the oxygen sensor.
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Old 11-14-2018, 09:35 AM
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Everything is flat, on the freeway, no headwind. Itís a 40 minute drive to work so it has plenty of time to warm up. Maybe itís not going into closed loop at freeway speeds when I start driving cold?
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Old 11-14-2018, 11:15 AM
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Sorry I missed a few details there.

The RPM shift is due to either not switching to overdrive, or the torque converter not locking. The first is temperature dependant, the second is load based (so the wind and hills still apply).
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Old 11-14-2018, 11:22 AM
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Originally Posted by DFowl View Post
Everything is flat, on the freeway, no headwind. Itís a 40 minute drive to work so it has plenty of time to warm up. Maybe itís not going into closed loop at freeway speeds when I start driving cold?
Almost no where is dead flat, check GPS or a typographical map. Even a light breeze on the front end makes a difference, get on a bicycle and try going from 10-15-17 mph. Another bit is the air density 50-70į, it's substantial thicker in the morning due to the cold and any moisture..

Anyways hook up your volt meter to the transmission diagnostic. It will output a voltage that can be compared to the shift position.

Another quick check is the vafm air temp, it will have an effect on the fuel mixture. Which was probably a red herring on my part not noting your rpm to speed correlation.
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Old 11-14-2018, 01:01 PM
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I figured it might just be the cold and dense air in the mornings, I just wanted to make sure this wasnít a common and/or fixable issue. I just picked this 4Runner up not too long ago so Iím getting used to itís quirks.

Thanks for the input guys!
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Old 11-14-2018, 01:18 PM
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Originally Posted by Co_94_PU View Post
...The RPM shift is due to either not switching to overdrive, or the torque converter not locking. The first is temperature dependant, the second is load based (so the wind and hills still apply).
I (we all) assume you have an automatic transmission. At 70, the transmission should be in overdrive and lockup, unless you pulling a pretty steep hill (6% or so), or going into one hellacious headwind. You can both hear the lockup and see it on the tach. Driving that fast out of lock up, or in 3d, will really affect fuel economy. Once you're in lockup, the relationship between rpm and mph is fixed by the gear ratio; wind and hills don't make a difference.

But the best method, as suggested by Co_94_PU, is to just ask your transmission. You do that with a voltmeter. Either use your multimeter (you'll need long enough leads to get the meter inside the cab), or drop $5 on my patented Gear Shift Indicator. https://www.yotatech.com/forums/f116...icator-303218/
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Old 11-14-2018, 01:24 PM
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Thanks Scope! Yes itís an auto and Iíll give your little gadget a try!
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Old 11-14-2018, 03:49 PM
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When you're driving to work and the RPMs are higher, if you click the OD button off, does the engine RPM increase? If not, then it's not going into OD.
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Old 11-14-2018, 03:53 PM
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Robert, I click OD off and it jumps RPMís. Itís definitely in OD, just different RPM range in the mornings.
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Old 11-16-2018, 12:47 AM
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Originally Posted by DFowl View Post
Robert, I click OD off and it jumps RPMís. Itís definitely in OD, just different RPM range in the mornings.
Well, that is kind of impossible, unless you have a electrical gremlin that is showing the wrong tach speed at times. That can be traced to GND.

I also have a V6 Auto that doesn't go into OD - check engine light will come on then too. Still stumped. So it's in the garage just sitting around. Good luck!
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Old 11-16-2018, 06:10 AM
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Originally Posted by ev13wt View Post
Well, that is kind of impossible, ...
Even once in OD, Lockup can be on or off. With Lockup off, it's driving through the torque converter, so rpm can change with load.
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Old 11-16-2018, 02:17 PM
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Scope,
it seems you are correct about OD lockup. Lockup isnít engaging in OD. It just happened to me again driving to work, this time in the afternoon though. Lockup was engaging just fine in OD but I had to drop down a gear for a slight incline then it wouldnít go back into lockup when it went back into OD. What could cause this?
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Old 11-16-2018, 07:08 PM
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The transmission won't lock up when it is "cold." Perhaps you're not warming up fast enough (thermostat?) Or perhaps the transmission temp sensor http://web.archive.org/web/201408160...34electron.pdf is dying.
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