I have a 2003 auto with 87k miles, currently burning some oil but less than a quart every 1k miles. My car feels fine at low rpms, but recently I've had an issue where when I first get on the freeway leaving work, and try to accelerate up a steep hill to pass someone, the car just can't go. It downshifts and the RPMs rise, but there just isn't any power there. At first it was only happening on the uphill part of the freeway, but it happened the other day on a flat section.

I just did a test on a hilly freeway near my house. I was able to get on the freeway and go from 0 - 90mh without any problems whatsoever (uphill even), then after cruising at 90 for a minute I went down to 70mph, then tried to accelerate again, and the problem happened again.

A week ago it threw a random misfire code, but after I checked and cleared it there haven't been any codes thrown. Spark plugs were changed 20k miles ago, and I took it to a shop who said they couldn't find anything wrong with it while driving around with a scantool hooked up (of course they didn't bother to drive on the freeway where I said it always loses power).

The only other thing I noticed is that my PCV valve and the hose leading away from the valve seem to be covered in soot, but they've been like that for longer than this has been happening. I had replaced my PCV valve and the hoses with silicone hoses as they looked pretty beat up, in the hopes that the PCV valve was causing my oil consumption, but it didn't make a difference.

Any ideas? I tried to bring it to another mechanic and they didn't end up having time to look it, and I can't just leave it somewhere for days as I need it for work. I'm going to pull the plugs later today and see if they look fouled, but that doesn't seem likely since the car pulls hard at first. My only other guess is a fuel pump / filter problem, but I don't know how to check that.

 

RPM's increase (engine revs) but no power? (to the ground)

*edit*

Transmission?

 

He said auto, most likely internal slippage. Try each gear and see if it slips in each or only one.

 

When was the last time you have had the AT serviced?Fluid change etc?
Most AT owners are lax about servicing their trannies.Could be with your miles,you still have not changed the fluid(or,previous owner did not).With all the electronics on a Z,there could be many things other than the fluid causing the trans to slip.I'd take it to a trans shop for some diagnostic check.

 

This. When was the last time you changed your AT tran fluid?

 

It's actually been 55k miles since it was last changed, which I didn't think was bad for these cars. However, I did a lot of mileage at high speeds on steep roads, so maybe I should be changing it more often? I'll go check the level later today, it looks like having a Nissan consult-II device would make it easier to check while the fluid is hot (so you can make sure you're in the appropriate range), but I'll try checking it cold then after driving around for 5 mins.

 

My car has now been in the shop for a couple of days. They were thinking clogged cats but they sent it out to a muffler shop who inspected the cats and said they were fine. Apparently it's not the fuel pump, and now they're thinking it might be a tranny issue.

I've found used transmissions for $700 - $900, but the real ***** will be the cost of the labor to install it. I'm still not sure if that's the problem, but I should be hearing back later today. It didn't really feel like a tranny issue, but then again the only auto failure I've ever dealt with was my Acura TLs 3rd gear clutch packs, which caused it to slip in 3rd gear.

 

Find a new mechanic, they shouldnt have to take it to a muffler shop to check cats if they have the right equipment to deal with this kind of problem. ATX can be diagnosed with proper scanner and road test.

 

I forgot to follow up on this, but I figured I'd post the resolution in case anyone finds this thread through search. It ended up being clogged cats, but it took the mechanic forever to figure it out because they only seemed to have flow issues once they got hot. In the end, I should have just purchased a $70 pair of test pipes and tested it out myself, would have been much quicker and cheaper.