Attn 6 MT OWNERS (again)

Well Toyota wants to do nothing. Says “operates as designed “. Ha! Really? So again I say if anybody else has same issue turn it in. All mechanics acknowledged the problem.

 

Do you have a video of the rpm gauge as you're cycling through the gears while driving? I'd love to see what it looks like for personal knowledge.

 

I have the same issue with my Tacoma. I just did fluids at 30k miles and rear diff (like a lot of these trucks apparently) was almost a quart short. I pumped in new fluid till it started coming out the fill plug. Who knows if this is the placebo effect but I swear I haven’t felt the surge/stutter/whatever since then.

My fake theory is that the rear diff fluid needs to be full to reach a sort of “resonant frequency” and move throughout the diff in a non-sloshy fashion, any this smooth-sloshing removes binding in the drivetrain, removing the felt “surge.”

 

I have a couple from a long time ago. Those clock at about 8sec. I did get a 7.2s but could not film and do the run on the Torque app at the same time.

Pre-tune:

 

I mean of the OPs engine bogging down in lower rmp

 

Sorry! I guessed poorly.

 

As others have noted, the issue primarily involves ignition timing. After extensive experimentation with the stock tune, here are my findings:

• Disabling ACIS: This has a significant impact. When the ACIS (Acoustic Control Induction System) flap alters the intake runner length, it appears to affect ignition, which is already close to the knocking threshold. This can lead to detonation and cause the engine to abruptly pull timing. By disabling ACIS, this issue is partially mitigated, resulting in a smoother running engine. Although there is a slight power loss in the mid-range, it is barely noticeable, and I find the trade-off worthwhile.

• Valve Timing: Reducing the intake valve advance to a maximum of 65° fully resolves the stuttering at highway speeds on 6th gear below 3000 RPM.

• Ignition Maps: There are three ignition maps—Base, Low, and High—and the truck transitions between them during driving mostly depending on load and rpm. From my observations, the Base and High maps are primarily used. The High map appears well-tuned, while the Base and Low maps are problematic, likely optimized for fuel economy on automatic transmissions. This issue persists even with high-octane fuel but is more pronounced when using low-octane fuel. The knock learn value oscillates noticeably as you drive. There is also a Base Retard map that I have adjusted, which has improved performance, though I have yet to modify the other maps.

My next step is to refine the ignition maps further. I’ve noticed that my truck tends to detect knocking between 1000 and 2000 RPM, causing the knock learn value to drop, which slightly retards the total timing. Conversely, from 2000 to 3000 RPM, the knock feedback detects overly retarded timing and attempts to advance it, leading to the knock learn value fluctuating up and down during driving. This inconsistency makes timing inaccurate, particularly under part-throttle loads. I am also going to ease the transition between maps, specially around 1000-2000 RPM range.

I’m currently busy with other commitments, but I’m making gradual progress. Once I have a reliable set of tables that resolve the issue, I will share them here for anyone to use, including professional tuners.

For reference, I live in south Florida at sea level with crazy humidity.

 

Hey Julian that’s awesome! I’m goin on a test ride with service manager and head tech. If I show them your post, do you think they will even have a clue? I know nothing about what you are talking about. Ha! These “adjustments” aren’t something that can be done by dealer personnel I assume.

 

Sorry julman…

 

They won't have a clue. Unless Toyota releases a TSB (unlikely at this point) they can't do anything about it.

I think the bottom of the issue is this engine was tuned for an automatic transmissions, then adapted for a manual. If you drive it like an automatic you will rarely hit the power bands for a given throttle input that we can do in manual transmissions.

Automatic transmissions will either try to keep rpm as low as possible or downshift as soon as you get on the throttle. So very rarely (if never) you will hit for example a 70% load on 2nd gear at 2500rpm because it will downshift right away before you hit that load.

Another example, on the highway on our manuals we can push the throttle all the way in 6th gear and feel as the engine is misfiring. An automatic will never get into that situation, it will downshift to 4th gear right away, bumping rpms into the 3500, where the engine is super happy.

Automatic transmissions can also hide the acis transition perfectly, it happens probably during downshifting, so you never notice it.

 

Interesting. I think this adds and explains further some of the odd, quirky behavior of this drivetrain I experience time to time with my 3.5 auto. Between the Atkinson cycle, ACIS, Valve timing, Ignition maps, surging/bucking during engine breaking some times, bucking the odd time under heavy acceleration, auto transmission that locks, unlocks and can even do a partial unlock amongst a plethora of other emissions/MPG saving items, can make for an odd experience at times.

I drove stock for 3.5 years and OTT for the last 6 months. Even with the tune the inherit idiosyncrasies are still there to some degree IMO. But much more reduced.

Before and after the tune, some days the truck would drive wonderfully, other days quirky. However much better with the tune.

I guess the 6M with the 3.5 still has some of the same traits as our auto. I would have loved the 6M but not practical for our family tho.

 

My 21 was barely passable as being 'nice to drive'. Have driven quite a few cogswappers over the years...the one in the third gen Taco is the most unforgiving of any of them (includes an 85 Dodge Omni 4sp). Throttle delay coupled with a revvy engine, accumulator and questionable ratios make it just so-so to me. Way too much effort involved to make nice shifts compared to other manuals I've driven. It felt like it wanted to be nice, but never really was. Have to admit I had expected better. I got the MT because there was no way I was willing to suffer the auto.

My own analysis concluded that a throttle cable and a clutch cable would greatly improve things.

 

I honestly have no clue what most folks are talking about in this thread. Stock or tuned my truck is a joy to drive, city or highway. My only minor complaint on stock tune was the throttle response when trying to revmatch.

Full disclosure, i have been using at least 91E0 Octane after dealers fill. Now, running SFOB on Chevron 94 (Flashed my ECU after about a year on stock tune), the truck is an absolute beast. I do use my truck as a truck, towing, carrying heavy loads, offroad, etc.

 

I feel the same as you as my truck does not exhibit any misfiring.

 

Sadly we lost 91E0 in Ontario recently so I only got a year with 91E0 on the Tacoma but ran it for many years in our Audi and my motorcycles. It is sorely missed.

 

Some people don't experience the issue at all, and some of us do experience really badly, even after trying multiple tunes the issue just comes back after a couple days, then it goes away, then it comes back. It is very frustrating. It can get so bad that we even get the "nose dive" as people describe it, which is basically you start to accelerate, the truck looses briefly all power after 1 or 2 seconds causing the nose of the truck to dive, and then it regains power again lifting the nose. Believe me, I am extremely busy with work and life, I would not be spending this amount of time tweaking the stock tune to make the engine perform "normal" if this was not a problem.

When I discovered that reducing valve timing to 65 max resolved the sputtering issue on the highway, I mentioned this to Matt from OVTune, and he told me literally this: "yes I know of this issue you are describing. Some trucks do this and some do not. Higher octane gas also helps with this problem but the permanent solution is to lower the intake cam advance like you have done.".

 

I drive a 1998 F350 manual for work the other day and it was honestly a pleasure compared to my Tacoma.

Pushing the gas pedal and getting a constant acceleration with no lurching was a joy I’d long forgotten..

 

I don’t get the nose dive on mine…. When you do all this tune settings do you have it on a scope or dyno at all? Does anything show up as a glitch. Guessing a tune would cancel warranty. Guy at Toyota corporate customer service said I am the only one stating this issue.

 

The only data point I see changing are the knock feedback and knock learn, that is how I concluded it was all ignition timing related. If you do the nose dive many times in a row, the knock learn eventually adjusts and the truck stops doing it, but then you do a pull in 2nd gear 70% load and the engine feels like absolute crap between 2000 and 3200rpm because of the retarded timing. The evidence timing is overly retarded is the knock feedback becomes positive, which means it is letting the computer know timing can be advanced. Then if you do this same 2nd gear pull many times in a row, the knock learn eventually adjusts and the engine feels better on that range, but you get the nose dive again down low.

The proper solution is to change the maps so timing is more retarded down low, and a bit more advanced during mid-throttle between 2000 and 3200rpm (more or less). That way the computer does not have to compensate all the time with the knock feedback and learn. Unfortunately, this is not super simple because as I mentioned before, there are multiple ignition and compensation tables, so it is not a single point you need to adjust but many, and it is very unclear when the truck will use one vs the other. It will take a while but it is doable.

Another bad news is I am not sure how universal my resulting tables will be. They will be basically tables for my truck, at sea level, high humidity. It may turn out perfect for me but not for others.

 

Yes, I don't mind the low torque at low rpm, I've driven many manual cars with no torque down low and I get used to it. What I hate is the unpredictability of the engine, sputtering and lurching without any logical reason.