2005 4L power loss

Unusual power loss (not just normal loss due to thinner air) in the mid RPM range, at highway speeds, most noticeable above 6,000'.

Caviats:
1) I have put 106,000 miles on the truck since I purchased it new in '05.
2) I'm familiar with O2 / air pressure issues and their role in power loss at hi elevation/altitude, and drove the vehicle thousands of miles at these higher elevations w/o this more recent, abnormal power loss.
3) The vehicle is a 2005, 4.0L, 6M, 4dr, TRD, tow package.

Synopsis:
Eight + months ago when I was away at work a Jiffy Lube told my wife during an oil change, that the truck's injectors were real dirty. We had noticed the signifigant loss of power (downshifting sometimes does not allow speed limit) recently so I took the truck to the local (Durango, CO) dealership and told them the situation. They agreed, and did a fuel injector flush, and service. No change to power loss. Took it back, the dealership said the (one or more) catalytic converter(s) were bad. (no check engine light). After consulting TWF, and other resourses it seemed that the cats were bad; made sense to me. I had a local guy reset my ECU, clean off my MAF, and did a test drive; still the same. He agreed it was probably the cats so I had him put on a Doug Thorley setup. I still can't notice a change to the original issue!

So, what gives?

 

Was your truck brought to Colorado from a lower elevation? And did it ever perform adequately at higher altitudes?

It can be frustrating to spend money without actually resolving the original issue. The advice you got so far was likely just guessing. Try to find someone who actually knows.

Maybe someone else here knows, but do our engines have air pressure altitude sensors? Perhaps it's not compensating for the thinner air.

I also put on a header (LCE), but learned that a less restrictive muffler created a loss in low rpm torque, so I put the stock exhaust back on but kept the header. With that setup on the dyno, the header not only produced a modest increase in torque, it also lowered the peak at which it was reached from 3,800 to 3,150.

 

I am going to guess a fuel filter problem.

 

Do you have any of the cats left in the system?

G

 

Gadget:
I have no cats in the system, pulled all four and replaced with Doug Thorley headers, and y-pipe to the stock exhaust. There was quite a bit of armchair/internet research, none showed I should have signifigant power loss or gain, but it eliminated the cats, and seemed like an overall improvement.

Tooter:
The truck has been sea level to 14,000'+. It lived and operated at 6,000-10,000' for about a year before the noticable power loss; beyond the normal altitude loss.

Torspd:
I've been looking throught the fuel filter topics. Any way to see if fuel is being limited before it hits the engine when at full power? I have no dyno anywhere near, and don't know off-hand if a normal scantool/OBDII reader can see this.

Thanks, all.

 

Okay, I'm trying to revitalize this short thread.
My '05 4.0L taco is experiencing a loss of power at the high end. When I am requiring max power in 5th/6th gear, up mountain passes, etc. the truck just won't produce.

No CEL.

1) fuel injection system flush n clean (dealer said it was this; it was(is)n't)
2) cleaned MAF sensor, reset ECU (didn't make any noteworthy change)
3) put Doug Thorley headers on, pulled all the cats. (dealer said it was this, now. TWF, and others said it was this, still no CEL or codes related. This did nothing).
Where I'm at now:
A) Keep hearing/reading "maybe fuel filter" (haven't figured out how to test yet, not doing this replacement yet as I'm sick of getting burned by throwing parts at the truck)
B) Hearing/reading a bit about maybe the PCV valve. Will deal with it today.
C) Have been told to do the plugs (don't believe this is the issue. Could it only effect the high-end perf of the eng?)
D) Been told that if a cat/cats were in fact bad then they could have fouled the muffler, and since I still have the orig muffler on, it could be bad/clogged. How much pressure should I feel putting my hand to the exhaust?
E) No reading that the second row of O2 sensors (downstream of the cats) do need to function properly/or be simulated so the ECU provides proper mix. Anyone had issues with this? The CEL has been on since I pulled the cats, and it says the cats suck. But before I pulled them research pointed to it not mattering... Hmm.

Any thoughts are welcome as I'm getting pissed at my inability to determine the root cause of my truck's power loss. I love this vehicle, and try to maintain it, but this problem has been persistent over a year, and even with a lot of input/research/$ I have no solutions. Thanks ahead of time.

 

Do you have any audible vacuum leaks?

You do have over 100k on the odometer. Depending on a variety of factors with your fueling and driving, your filter could be extremely clogged. Cleaning the injectors and fuel system after a dirty filter doesn't fix anything. As the fuel still has to go through the filter.

Regardless if it doesn't completely solve your issue or not, you have a substantial issue there. The filter needs to be changed, and the cheapest way to do that is from www.Dezod.com or www.URDUSA.com

I cannot say this is the absolute fix for your truck. I can say that I replaced other people's with the aftermarket upgrade, and their "issues" went away.

If you don't have any CEL's, except for No cats, then that is where I say start.

You might be able to tell if fuel is being limited by watching the long-term and short-term fuel trims.

If your throttle body is really dirty behind the flap, that can cause issues.

If your air filter is extremely dirty, that can be an issue.

If your headers are loose and you have exhaust leaks, that can be another issue.

You still have things to check.

 

Thanks for the info Torspd. I pushed another post about the exact same thing, yesterday. Lots of good advice. I'll update in a couple weeks, as I'm off on vacation for a bit. Talk more soon.