Unwanted deceleration/drag

For about a week I've noticed the truck decelerates faster when coasting. It's gotten considerably colder here which may be a sign things are just not flowing like they used to but I'm going to investigate other culprits:

Tire pressure - OK
Alignment - Seems OK (no pull, drives straight)
Brake drag - will check
Shifting into Neutral during coasting
4x4 and 2x4 coasting differences

Any other suggestions on what this could be? I don't think its just in my head. Ill check my mileage too after this tank is empty.

Thanks,

 

Front wheel bearing?

 

Jake braking?

 

Curious to see if it's the brakes dragging. That'd be my guess.

 

Well I know the auto tranny will feel more like this when cold. I just changed ATF and experience less so far. But in 75° AZ... Check ATF level. Mine was ~1qt low and topping off combined with change has made this less noticeable.

If brake drag you'll be able to feel the drum get hot. This happened to my 4Runner. Real PITA! if so just replace ALL brake hardware, wheel cylinders and springs and shoes. With the 4Runner bad wheel cylinders stick OPEN causing the drag. Not sure if so with tacoma but would not be surprised!

Good luck!

W

 

Is this built in? I've also noticed the same thing. It almost feels like the tranny shifts out of OD and downshifts into 5th or another gear or something while coasting down a hill (do Tacos even have OD???)

 

I always figured 5th IS OD!

I keep mine in 4th until freeway over 50+/- and going up hill.

W

 

TBH, I don't understand what OD is anymore.......I understand how it works and what it's supposed to do. My last car (1990 Pontiac Bonneville) was a "4 speed with Overdrive" but it shifted like it had 5 gears, and my father-in-law's Victory Crosstour had a "6 Speed with Overdrive" but it only had 6 gears You're probably right in that 5th is the OD gear.

Either way, the truck still feels like it downshifts, or something locks up after 2 seconds of coasting....

 

5th in the manual, is 1:1

 

Many modern FI engines (including these Toyota engines) have a feature called deceleration fuel cutoff, or DFCO. It turns off the fuel injectors in certain deceleration conditions and the engine helps slow down the truck (i.e. engine braking). It's pretty effective at slowing the truck, plus it helps save gas and reduce brake wear. In order to keep the engine from stalling, the injectors will turn back on when certain speeds are reached. In OD, my truck (2.7L 4-speed auto) will go into DFCO at about 60mph and the injectors come back on around 30mph. When coasting in 3rd gear, the injectors come back on around 20mph. Your truck will probably have different speeds as it's a V6 5-speed auto.

A separate feature is auto-downshift... I have noticed pretty consistently if I coast downhill for longer periods and I apply the brakes (such as coming down a mountain grade), my 4-speed automatic transmission will shift itself from OD down into 3rd without any movement of the shift lever. It shifts back into OD after applying the throttle. Pretty sure this is a safety feature to help keep the brakes from overheating and help reduce speed too.

 

might have a caliper hanging up

 

That's what I figured, but wasn't sure of. I also thought it was part of the tow package (kind of like a downhill-assist for towing). It's definitely nice to have, but it's also a little annoying when I'm trying to maintain a certain speed while coasting down a hill. Again, a minor annoyance at worst.

Thanks for the info!

 

Is there an OBD device, Scan Gauge etc, that can indicate what gear the tranny is in?

W

 

I use Torque Pro, and it doesn't have that option. I guess I could log/look at Engine RPM and Engine Load.

 

Downhill assist has NOTHING to do with the towing package.

That is a TRD OR 4x4 09+ feature, that will keep you at 5mph or under going down hill and do braking for you when in 4lo only.


OP what you describe sounds like what others are talking about, fuel cut. Injectors shut off all the way and turns the motor into essentially a big air pump. Leaving your truck in D if you get up to cruising speed then roll off the throttle, dont touch the brakes, the truck will go into fuel cut and will actually subtly downshift through the gears till 3rd, at which point when you hit ~20 mph you can feel the fuel being fed back to the motor as you coast. Colder temps will produce a more pronounced engine braking feel as the thicker air has to be pulled through the same closed throttle body.


Next..... overdrive... jezus guys, really that much confusion. The V6 auto has 5 gears. 5th gear is "over drive" or a taller than 1:1 ratio... something like a 0.8:1. Putting the gear select in D will let the trans shift to all 5 gears, putting it into 4, only gears 1-4 will be used, putting it into 3, only gears 1-3, into 2, only gears 1-2, and L only 1st gear will be used.

The torque converter lockup will ONLY occur in 4th and 5th gears and is often felt as a second shift to those who dont know what is going on. Torque converter lockup is simply a clutch that engages so the motor output is locked to the trans input resulting in no losses due to slipping of the torque convert. People often think that the trans shifts to 4th when a slight hill or a little throttle is added to cruising speeds, when often its simply an unlocking of the lockup clutch and the "slipping" of the torque converter allowing extra rpms.

 

Anything that has an engine attached to a driveline has engine braking...

Literally the friction of the engine itself, without acceleration/increase in RPMs, causes a slow down...

 

What I meant by "built in" was what the O/D switch on Fords and the Tow/Haul switch on Chevys do. They change the shift points and/or lock the tranny out of OD when pressed (usually used when towing/hauling downhill, so sorry for the "downhill assist" terminology confusion).

 

Gotcha. My 2005 Camry had an O/D button on the gear selector so you could disable it. That what you mean?

 

Yes, exactly. I thought the engine "disabling OD" while decelerating/coasting was an added feature included with the tow packages, but I guess it's not a feature at all lol. Also, this is my first vehicle that cuts out the injectors so noticeably.
Again, thanks for the info!