6 Speed High RPM Issue

Hey all, I haven’t posted much but I’m looking to get a little insight. About a year and a half ago I purchased my 2008 Tacoma TRD Sport 6 speed manual and have have been modding it ever since. All along the way I had a bit of uncertainty on whether or not the tachometer was truly correct. Ever since purchase it seemed like the tach was reading excessively high at highway speeds (4,200rpm at 80mph on 29” tires). After installing my long travel kit, 33” KO2’s, and a scangauge, it predictable lowered the rpm at 80mph to around 4,000. Either way, these rpm numbers seem very high for the truck. It only gets more confusing when looking at the Scangauges rpm reading, which displays a much more reasonable number. I am confidant that the previous owner didn’t install any deeper gears, and I’m wondering if the stock tach is somehow miscalibrated, or if that’s just how the truck is geared stock. I’ve included a picture of the dash/scangauge at 75mph in 6th gear, notice the rpm reading on the SG vs the tach.

Any ideas?

Also, the carfax does show that the truck was imported from Canada. If that makes any difference or could potentially explain a gauge swap.

Thanks!

 

How confident are you the truck hasn't been geared? Have you checked with method that involves rotating the wheels and counting driveshaft revolutions? Short of pulling the third and counting teeth, there aren't too many ways to know for sure.

 

When installing my long travel kit, it showed no signs of ever being modified, let alone to the point of needing gears. But I guess anything is possible. I’m not familiar with the method of turning the wheels and counting the rotations, just counting the actual teeth on ring and pinion. I’ll definitely look into that method though. At this point I’m really leaning toward it being a tach calibration issue.

 

I assume the picture was taken while driving in 6th gear. That looks right for 5th gear on my 6 speed, if I down shift for acceleration to pass. It might have been re-geared. Seems like it would be about right for 4.56 gearing.

Those thoughts aside... I'm on 33s and stock gears, and the scan gauge reading seems right for a stock 6 speed rig.

 

Yeah, that picture was while in 6th gear.
Oddly I’ve found only one other thread on TW similar to this one, and the only real similarity is that both trucks were imported from Canada. Everyone in that thread insisted it must be 4.56s as well. That’s kind of why I’m thinking that it may be related to a cluster swap.
I’m definitely going to try the tire rotation method to establish an estimate of the ratio.

 

It very well could be a tach calibration issue, especially with the scan gauge reading what it is. But the counting rotations method is pretty simple, and would be a way to eliminate an unknown without disassembling anything.

 

out of All the changes that have been made..............that could have been made w/o the current owners knowledge

most would change the Speedometer reading ' mph ' or kilometres more so than the tach being ' miscalibrated '

sitting still...............in neutral or in gear the tach is only ever going to read the engine rpm

Your scan gauge & tach should be within a few RPM of each other

they both are reading Directly off the engine ECU

 

I’m assuming you’re saying that out of all the modifications, gears could have been one of them?
If so, I bought the truck stock and did all of the current modifications myself. The tach has been weird since the time of purchase (in stock form).
And I agree, in previous vehicles I’ve owned with SGs, the rpm is always spot on. Even at idle the tach reads 1200rpm while the SG reads ~780.

 

I think your scan gauge is right, and the tach is somehow off.

 

Know where in Canada the buggy originated? We have a large presence in TW...perhaps we could hunt down the previous owner and beat the info out of him



Or count rotations...


Keep us in the loop...also, we know how to change the HVAC readout from C to F...we just wont tell you that.

We're assholes in that regard

 

Something isn’t right. I‘m in a 6-speed MT, regeared to 4.56 and have a scangaugeII and my rpms are very close to showing the same. I’m around 2800 at 70mph (true speed) on 33’s. 75mph would be 3000rpm-ish.

 

Maybe it's reading in metric RPMs instead of SAE

 

That's a complete US gauge face. Maybe they swapped the whole gauge face, or maybe they swapped the whole instrument cluster. If they swapped the gauge face, maybe they didn't get the tach needle on correctly. Here is what the Canadian tach looks like. Notice r/min and the cat face. This on my (Canadian Taco, imported to US) Taco.

On mine, they only changed the speedometer face, and not the tach face. The US instrument cluster has a headlight indicator that only comes on when the headlights are on. The Canadian cluster has an icon the comes on when the park lights or headlights are on. If yours has a headlight indicator and it comes on with park lights and headlights on, you have a Canadian cluster with a US gauge face.

 

That makes sense, my headlight indicator does come on with just park lights as well as headlights.

 

There you go. I bet they didn't get the needle on correctly. It's real tricky getting all the needles on correctly.

 

That definitely seems like the most logical answer. Thanks guys!

 

that now U mention a distinct difference

there shouldnt be a 500 rpm difference between the 2

different tyre size would NOT account for that sitting still in neutral

 

another user had a similar issue of the dash reading 1k rpms high. Whats your idle rpms? 1550ish on the dash i bet once warmed up. This was due to a dash swap on the other users rig.