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1997 nissan power loss

weird!!! 128k miles, sometimes when pulling hills loses power and engine sounds like there is an exhaust leak- a “roaring” noise. Intermittnet. Not burning oil, not missing, not sputtering or anything just this intermittent roaaring noise from engine and loss of power on hills. I keep the oil changed, gas and air filters, gets the same lousy (17) gas mileage it always has…

hint? I recently drove it 1700 miles pulling a load, towards the end of the trip is when this started. It still starts and runs without fail otherwise, no check engine light, ever.

Some engines need back pressure, I don’t know the specifics of your car but would start with an inspection of the exhaust system and motor mounts.

The “roaring” may be the sound of the engine revving way high because the transmission is slipping. Is there a tachometer for you to watch?

its a 5 sp 4wd (hubs) 2.4, 4cyl, I do watch the tachometer all the time, the difference w/ this situation is that it takes it up past 4-4500rpm before you feel like you can shift without the power going away again, (keeping the momentum for a smooth transistion between gears and the rapid accel response it used to have)then at flat highway it runs pretty steady at 32-3400rpm at 55-65mph, and around 36-3700 in 5th gear at 75-80. I usually shift down into a lower gear around 2500rpm cause it seems like less is really lugging it, losing all momemtum. It idles smooth at 1100-, just runs so good all otherwise.
I took it on a 500 mile round trip-flat and mountainous this last week. On the flat freeway, in the wind, was 75mph, down to 3rd sometimes pulling hills, the roaring noise starting (on the flats) fluctuating, yet I held the speed, tach, and gas pedal the same, then the roaring noise started winding down, literally like you think it’s gonna die? but yet your still just going good. The noise suddenly stopped and the truck jumped up to 80mph and 4krpm in seconds, I let off the gas to 75 and it went back to the more better 3200rpm… held it there, the noise came back on, tach up, ??? it does kinda feel like its starving for air or fuel or something when its doing the hill- low power thing…
help? and thanks allot. I’m a single old 53 year old lady, I don’t have a ton o money, (I love my truck, change my own oil, filters, etc…) and I’m real apprehensive about shops. I love cartalk.

thanks, awhile back the catalytic converter was taken off and (cleaned maybe?) because the tips of the o2 senser had burned-fallen off inside it and I had a ringy-rattle on the decelerate till we figured that one out. the o2 senser is less than a year old now. I posted another reply in detail of what the particulars are of the truck now… I’m going to have the codes read at the dealer this week cause I cant help suspect it’s an egr or something electrical to do with regulating air-exhaust, partially clogged? If my valves-stc were burnt wouldn’t it be burning oil? thanks again!

I have a theory: The roaring is caused by fuel burning in the exhaust manifold and catalytic converter. How? Further theory: a cylinder (or, more) is not burning its fuel, and it burns in the exhaust manifold and catalytic converter. Where is it getting its ignition (spark) in the exhaust manifold? Good question.
The fuel injectors may be sticking and or have bad spray patterns. If fuel is spayed in large droplets into the cylinders, they can’t mix with air (not enough time). The droplets of fuel pass into the exhaust manifold where they do have enough time to burn (or, continuing to burn).
Take your vehicle to an auto parts store (Advance, or Auto Zone, etc.), and ask them to read the trouble codes. Bring those trouble codes (like P0301) here for advice.
Take your vehicle to an independent shop (much cheaper, and you will get to talk to a real, live, mechanic), and ask about a “Fuel system cleaning” (about $100). This will clean those fuel injectors.

I took it to the dealer yesterday, no codes from the computer, they said it was the “fan clutch”. Sounds plausible I guess, it never gets hot though.

Now, you need to take it to a good garage. The fan clutch-----------what about the fan clutch? Are you, and we, supposed to fill in the blank about the fan clutch? It seems so.
Ask around for a good independent garage. The dealer said nothing about the loss of power on hills, did they? Save cash. Go independent (garage).