70MPH downhill in neutral truck rapidly slows down

First time doing this in this truck for troubleshooting. Did it in the old Nissan just to test the drag.

 

You could raise vehicle one tire at a time and spin it. Seeif one drags more than the other? Maybe you have a sticking caliper?

 

Not saying it is related, but reminds me a bit of this thread
https://www.tacomaworld.com/threads/4x4-stuck-causing-drastic-mpg-loss.454350/

 

Is there some sort of descent control nanny turned on?

 

“Tacoma Coast Guard” is already taken. D13 has good people, too!

But you may not be far off - I’m guessing here, but maybe the Hill Assist Control may have come into play and applied braking? - I tried letting my truck coast backwards a bit on a hill (while still in drive) to have another try at a boulder as I have done a lot before in my Gen 1 Taco, and only went a few feet and the HAC activated and the brakes automatically grabbed hold. I had to put it into reverse to complete the maneuver.

 

Going to 4H then back to 2H cleared it up? Sounds like the problem is in the transfer case or the front differential. Next time it happens try a very sharp turn if you don't get hopping then the front axle is not locked so it is most likely the transfer case.

 

I didn’t think of that - probably the best answer as I reread OPs description now that I had my first cup of coffee and my comprehension is better. I assumed he was not engaged in 4WD.

Time for a dealer checkup on that system, having it locked like that is going to wear things out.

 

Sorry I screwed that Quote up

 

This seems very possible and need to keep sharp eye on this

 

Just for some more discription and operation :
The 4H light comes on when the front differential locks so that is why it is possible to have the transfer case partially engaged with no instrument panel indication.

 

Hmmm .. . . Mine flashes as soon as the rotary switch is moved. It goes solid when it's fully engaged.

G.

 

I hope it’s not the case, but if there’s a problem with that system, maybe it only tells you it’s fully engaged or intermittently? I dunno, Maybe a good time to have a pro check it.

 

Absolutely. The flashing is caused by switch position and disagreement with the front diff fork sensor. If the switch is in 2H and the transfer case is partially engaged there will be no flashing.

 

Mexican overdrive
I've done that also but not in my Tacoma. If the throttle is closed Tacoma shuts off fuel so it uses less than Mexican overdrive.

 

Saltines typically have nothing to contribute

 

It's wasting gas to put it in neutral when going downhill? I've always thought the opposite, which is the whole point of doing it... No?

 

Putting a auto in neutral when coasting I've always been told is a definite no no. I believe it has something to do with transmission fluid not able to circulate through the transmission. I could be wrong though.

 

Depending on how step the hill is, your idle may go up in an auto placed in numeral going downhill. To boost brake pressure if you need to stop, since it knows the engine isn't helping. I use 'knows' relatively. Old auto's don't do that.

On the flashing 4H, I switch back and forth allot and anytime I go from 2H to 4H and back, and the transfer case it's not where I told it to be the 4H flashes.

 

Possibly bad gas?

 

When in gear and going downhill, no fuel is needed to keep the engine turning with the foot off the gas. When in neutral, under the same scenario, a little bit of fuel is needed to keep the engine turning.