Loss of power at high end (mountain passes/near-full throttle)

So....Have you actually had someone that knows more about engines/trucks than you drive this thing? Or are you just self diagnosing?

I would hope you have done some simple things like a compression check or have the dealer plug it into a computer to check all the sensor parameters.

Seems like you have tossed a lot of needless money at this thing.

 

I pretty much have the same truck V6 manual 5 speed and use to live in Arvada.

I would always head over berthoud pass or go up through the tunnel. Even with
no load, I would end up in 3rd gear near the top of these passes.

Lower gear was no problem, and pretty peppie when coming out of the curves and giving it gas at 10'000 ft. Regular gas.

I know you have a 6 speed , I would try the same hills in a lower gear. You will always lose power in high gear on these passes. I get about half way up and when I lose speed it goes in the next lower gear. Sometimes even into 2nd on tight curves.

 

Are you sure this isn't just all "in your head" and/or are asking too much of the truck?

The only reason why I say this is because of all the things you have done haven't made a difference and you'd think if there actually was a problem, it would have been fixed by now!

I live in a valley that's only about 1,200 feet above sea level and the main highway to get out of the area has anywhere from a 5% grade to as high as an 8.5% grade with a summit of 4,000 feet. So my max height is basically your starting point!

However, just recently I had it on the highway and to get from my town to the summit is about 124 miles (basically strait up) and I was trying to average a speed of about 80mph.

Well I can tell you that almost the entire time going up, my truck/engine was screaming around 5,000rpm (I think) in 3rd or 4th gear (auto). As soon as I would lift the gas (to give it a break) and bring it into 5th gear, there was no chance, not even close, to holding the speed up.

Over that 125miles I went through A LOT of gas as I was basically stuck in 3rd - 4th gear! I could almost see the needle moving! Sure I could have gone slower, but I came from a moded turbo Subaru STi' so slowing down isn't my thing! Regardless, I must say that I was disappointed in the lack of power. But not a big deal to me as I might take that road once a year...

Anyway, are you running the fan or AC?
How about your tire pressure?
What kind of tires are you running?

I just drove 1,000 miles in my buddies stock 2007 TRD OR AC with all season stock sized tires. I can tell you 100% that his truck had more power on the highway than my 2014 TRD DCLB Sport with the Baja suspension, 2' AAL in the back and 265-75-16 Duratrac's.

On the same stretch of road, I'm NOT 100% sure as I never could test, but I believe that his truck would have handled a hill in 5th while mine would have had to shift into 4th to maintain the same speed.

Hope that helps?

Cheers,

Jay

 

What things were changed on the truck immediatly before you noticed the issue?

Do you have an O2 simulator since you have Doug Thorley long tubes, and/or do you have a check engine light for no cats?

Do you have a ScangaugeII or Ultragauge to see operating parameters?

Did you ever have the compression tested at that fancy shop? Since you didn't mention it in the most recent update.

Your truck weighs in at 4800 lbs, and had 255/85 R16's Which are around 10% taller than stock. That combo on a 3.73 really loads the engine down, especially with the altitude combined.

I am not sure what size is the stock tire, but my spare is a 245/75 R16.
This calculator right here even shows that an increase in gear ratio is necessary. http://www.tacomaworld.com/forum/tirecalc.php.

235/85R16




255/85R16





Given your combination that I mentioned above, and if everything else is fine, I think that you need to make sure your tire pressure is full, and get new gears as those will have the largest impact on your towing/hauling at speed at altitude.

 

This guy hit the nail on the head right here. Air is thinner the higher the altitude, thus reducing the output that the engine has because it is in a sense being choked of air. The computer has to make necessary adjustments.

Equate it to you this way. Why do you think many of the teams which come to play the Denver Broncos at their home field lose to them? Thinner air kills their performance.

 

Thanks for all the recent posts. In lieu of scheduling a psych exam (maybe soon), I'll answer the questions, and continue on.

I have had multiple other persons "test-drive" the truck. The latest attempt at determining if I am imagining things, or there's an actual issue was quite clear. I was living in Bend, OR this summer, having techs from the local import performance (Toyota truck folks) shop drive the vehicle at just 3,500'. They all said there's a noticeable difference in my truck and theirs (the ones they own, and work on for a living).

I fully understand how the lack of O2 causes issues to normally aspirated engines. Now I am finding that any time (seemingly less, and less dependent on high altitude) that I demand max power from the taco, I don't get it.

Yes, I have 235/85/16s, and yes, I understand the difference tire diameter, and pressure make. They're yoko geos, and have been great. I run them between 30 and 40 PSI depending on what I'm doing, and up to 55 on the rear when I have way too heavy of a trailer, and load in the back. The tires are not the issue.

Yes, if I was attempting to maintain 80MPH on a steep grade, I would expect to be in 4th at 5K (ish), or 5th around 4,000 RPM. And that would burn a lot. As it is I can't even get the thing to 5K in 4th when I'm in the conditions I'm talking about. It's like someone is holding the back of the truck, or......... the truck is not producing the power it should....

I don't have a scanguage / type system. (I did buy a little OBDII port bluetooth sender thingy, and downloaded an app to read it; never had luck with it. Probably should have bought the $30 one, not the one for $10...)

The rear O2 sensors have been replaced with the URD simulators, therefore no more CEL. But yeah, immediately after the cat-pulling, I just left the sensors out, then realized that there are some subtle things they do, and put in the sims.

Again, thanks for all the awesome thoughts, etc. I'd like to get this thing on a dyno, with an expert, to once and for all know what it's producing. Then yeah, it would be nice to check the fuel lines. Folks have hooked up some do-dads to the taco, but I'm unsure if all the sensors have been checked, or even which ones, and how to.

More later. Stay thirsty my friends..

 

I just want to be clear on the rear O2 sensors. They are both in, and the URD O2 simulator is plugged in between them and the OEM harness? I know it seems redundant, but just want to be clear. As URD's simulator doesn't replace the OEM sensors, while another brand does.

Which weight oil do you use?

Getting that App to work would really help. Then we could know if timing is being pulled, which would make the most drastic reduction in power.

Also, you didn't yet answer what was the last thing done to the truck, immediately before you noticed the issue.

 

With the app, you'd also be able to tell if the ecu is not letting the throttle open up as much as your foot is commanding it.

 

They're mountains and the Taco engine is weak sauce if not revved out. My pedal is to the floor in 5th gear to maintain 70-75mph up mountains with 300 lbs in the bed. It's not very different with nothing in the bed. 2500RPM doesn't cut it you need to be around 3,500. If I slow down I need to downshift to keep the revs up around 3,000-3,500.

A supercharger will cure this easily. Atmospheric pressure at 10,00 ft is about 10 PSI vs 14.7 at sea level. The supercharger provides about 6-8 psi of peak boost and 7-9 if you have the URD 2.85 pulley.

Supercharge the taco or get a bigger engine. Mountains are mountains, you don't cross them, they let you through.

 

Sub to add input later.

 

When going up the pass, have you tried re-setting the ECU and then driving?

Just wondering if that would allow the computer to re-learn based on the higher elevation and/or highway conditions.

Just a thought...

 

Datalogging or freeze frame data would really help us diagnose it over the web. I would bet your Air Fuel Ratio is fubar in open loop (running off the map in the ECU, not O2 sensors) and that it is running really rich. Why it is running rich is an interesting question. In open loop, the ECU ignores the o2 sensors and instead uses input from the MAF, coolant temp, intake air temp, etc to alter the amount of fuel squirted into the combustion chamber. Scan it and look at your long term fuel trim. I bet it's in the double digits. That means the ECU is dumping extra fuel in based on the inputs it's receiving. If this is the case, then there is a good chance one of the inputs for open loop is messed up, likely the MAF sensor but it could be any of them. The reason I think it's a faulty MAF sensor is that the MAF measure air density, kind of like a barometer. If it's not doing it's job and is reporting dense, sea level air to the ECU when in fact your are driving through thin mountain air...the AFR will be too rich. Maybe see if someone will swap MAF sensors with you for a day to see if the fault moves to the other truck. http://urdusa.com/p1260519174/Denso-197-6030-MAF-Sensor-for-1GR-FE-4.0L-V6-engine/product_info.html

 

I like that little quote about the mtns.

My favorite is.. You don't ever beat the mountains.

I sure miss Colorado.

 

TORSPD: Nothing had just been done to the truck, prior to noticing the power issue(s). I hadn't done any mods to the taco, at that point. It was a slow recognition that something wasn't right. Then the wife asked if something was wrong. Then I had someone else drive it. Yeah, the URD sims are just plugged in upstream of the sensors.

I'll get my act together and get a scanguage or equivalent, as the ELM327 Bluetooth device never worked for me.
Then I'll look into checking compression, and fuel lines.
The MAF was just replaced, as recommended by the fancy shop; no change in apparent performance, small change in lower trim numbers from 14 to 11 on the R, and 9 to 8 on the L.
The first things done were resetting the ECU, cleaning the intake, removing the K&N, and cleaning the MAF. That was 15,000 miles ago...

 

Have you checked your throttle position sensor?

 

Supposedly the throttle position sensor isn't the issue; per the latest, fancy mech shop. This after I queried them specifically about it. But, who knows..

 

Compression is a cheap and easy test, and low compression is a likely candidate for your symptoms. Put that at the top of your list.

Do you ever notice any loss of coolant or milky oil?

 

They are supposed to be pretty easy to check if you can get your hands on a scanguage. Their are a number of youtube vids on the subject. Just because he did not find a code relating to the sensor, does not mean it is functioning properly. If he tested the throttle while reading the position indicated by the scanguage then it can be ruled out.

 

Unless I glanced over it (just read the entire thread..), this sounds like a basic fuel filter problem. No passing power at high RPMS, under WOT, feels like something is "holding your truck back"? I'm putting my chips on it.
I grew up in the southern California mountains, and regularly worked/traveled off the mounts, and back up(500+sea level, to as high as 7500-8000ft).
I've had almost identical problems to this, across a plethora of vehicles I've owned throughout my life.

So, if it hasn't been done, I suggest this:
http://urdusa.com/Fuel-Upgrades-Fue...uel-Pump/Filter-Upgrade-Kit/product_info.html

Probably your cheapest fix (next to the plugs) that you'd have to do. PLUS, it'll make things 117% easier in the future to change the fuel filter.

 

The MAF sensor all so gets info from the baro sensor it knows how high you are and adjusts accordingly. The OP knows his truck and knows some thing is not right he has not moved to the Mt's or changed his driving habits. My suggestion is some thing that will read the sensors in real time and have a knowledgeable person read them while he is driving. Some programs allow freeze frame but again you can't drive and fiddle with the program at the same time.