4low and down steep hill

Hi all, i took my truck out to test the 4wd a little and get use to the truck. When i am going down a steep hill and have the truck in 4low 1st gear it wont hold the truck back at a steady speed. Its like the engine revs holds the truck back then kind of costs rpms go down then revs back and forth? Also having issues when i slow to a stop my truck lurches a little making me apply the brakes harder. Also doing it while i was backing a trailer down a allie way. Revs up and down. Is this something i should have the dealer look at?

 

Mine crawls quite nicely down hills in 4lo s1, might talk to your dealer about it.
Mind you the "crawl" is a little faster than my manual but thats to be expected with a different gear ratio. And at-mt.

 

So I talked to the dealer and they said that the down hill thing is normal. Its the transmission trying to not work to hard? Protect it I guess. In every other vehicle I have owned I never would have to push the brakes at all in 4low 1st gear. No mater the steepness of the hill. They say the other issues I am having could be a update or low fluid. So they are checking that out Monday. Thanks for the response Broccoli.

 

The only answer a dealer knows. Check with the gurus here in TW, they will have a better answer for you.

Regarding my truck, I have to apply some light/corrective braking while on 4LO when going downhill - but not much. Then again, the hill might not be as steep as yours

 

Hmm, this is something I should try in 4lo.

I went down the entirety of pikes peak pretty much all in 1st with some 2nd in normal 4x2 hi and it held a pretty constant 23-25 MPH all the way down, no lurching or coasting whatsoever. Must be a 4lo deal? Not sure about the whole protecting itself deal. I mean I was engine breaking for many many miles downhill and never had any temp issues or the like. Kept the brakes well under 100°f at the check point. Hardly touched em.

Problem is, I live in Kansas so finding a hill would be the hardest part. Haha.

I have done some 4lo but mostly pulling other trucks/SUVs out of the mud. It did seem a little more lurchy if you will but it's low gear so I kind of expected that. Similar to a tractor in low range.

 

The Dealer had my truck for a day. Looks like the tranny fluid was low. About 3/4 quart. They filled and the lurching has stopped.

 

The engine braking is wonky, my M/T does the same thing. Going down a steep hill, engine turning about 2k rpm 4lo 1st gear.. I want to slow down, so I lift off the gas. You get engine braking down to about 1300, then all of a sudden you lose it. The truck will continue like this until the revs creep back up to about 2500, then the cycle repeats. It's another little annoyance that I hope the OV tune will address!

 

Wonder if it's an otto/atkinson issues? Bouncing back and forth.

 

I'm not sure I understand what you're saying OP, but maybe you're using crawl control. The lurching seems to happen more with CC or is more noticeable as reported by some.
I had a little lurch when it was new & learning but Its all but gone now.
I add to say some ppl have found the air intake clamps loose on some vehicles and I would highly recommend everyone checks those as air would or could bypass air filter and cause all kinds of issues.

 

This is your engine going in and out of deceleration fuel cut off. Above 1300 rpm no fuel, but if below 1300 it gives it gas.

Nothing will correct that, it's your engine not wanting to stall out.

I've suggested this before with much doubt, but you can actually drive down a steep incline like described with the engine off to avoid the lurching. Since the engine is still spinning you still have power steering and brakes.

 

You should make sure this is documented, call toyota corporate and try to get a longer warranty for your drive train. Explain that you are concerned that driving with the low at fluid level, which has now been documented as low from the factory, may have caused damage, and your lawyer advised you to demand an extended power train warranty.

 

I'm not convinced. I tried cutting the engine off manually on a hill before in the same scenario, and while the braking effect was consistent, it felt and of course sounded different than when left in the run position (and yes, the power steering and brakes work, as I've told you before). Now, before you quote me and say "see, you just proved it", remember that this engine is capable of variable compression through late exhaust valve closure on the compression stroke (aka the synthetic Atkinson cycle). It could also be this that causes the weirdness.

I'm also not convinced that "nothing will correct that" when referring to supposed fuel cutoff. I'd like the folks at OV tune to tell me that, since they seem to have a pretty good handle on the 2GR-FKS ECM and it's software.

Frank

 

Well good luck with that.

This explains "supposed".

 

I get it as a general concept, and thanks for the Wiki style definition / diagram. I've looked for this in the 11k plus page 3rd gen Tacoma service manual and 2GR-FKS features document with no luck. Toyota source? Anyway, sorry to the OP for mucking up his thread.. whatever is causing this, it's annoying when off road.

 

Text and diagram are from Toyota.

Toyota engineers would not put the engine into atkinson cycle while engine braking since it would reduce the braking effect with lower cylinder pressure.

 

Cool, for the 2GR-FKS? Don't misunderstand, I'm an electronics tech by trade so I question everthing lol. The other reason for my skepticism is the severity of change in engine braking. I mean, this isn't my first 4WD vehicle, and every other one would hold back very strongly in 4lo first gear with the engine running the whole time. A couple were carbeurated, so no cutoff weirdness there. I know variuos gear ratio combinations between vehicles will make a difference...

 

I'd posted that graph here first back in 2012 so definitely not 2gr-fks. The site link no longer exists but it was definitely Toyota sourced.

It was from this site http://www.autoshop101.com/ which has links to lots of Toyota documents, but alas I can't find the specific link, they must have changed their site configuration since then.

I'm curious what OV Tune can do, my guess, if anything, they can drop the rpm where DFCO cuts back in, but would that even be within what they access and change? When will you be able to find out?

 

Search the manual using the term, "fuel-cut operation".

 

SO it's time to eat some tasty crow.. well kinda. Here are some references to "fuel cut operation" from the service PDF (thanks Splitbolt):

Edit: After reading Para 1 (d) again, it occured to me that a "momentary" fuel cutoff would be in play because this test is not performed while the veh is being driven. So the fuel cutoff would only be active for the time it takes for the engine to drop from 3500 to around idle speed (or maybe 1300?):



Now this is more in line with what we've been talking about, at least when the engine braking resumes at the high end:



I've been looking for full descriptions of fuel cut operation, but so far it's just single line references such as these.

Frank

 

Another interesting feature with fuel cut operation gleaned from the service manual - it will cut fuel when serious misfire conditions are detected in one/multiple cylinders. This is to save the Cats from overheat due to raw fuel getting in there. Makes sense.

Then I got to thinking about this in relation to possible CPS issues and members reporting severe bogging.. although I'd expect the CEL to be set at some point. Yeh I know, gotta stop.