New user - new to me 2003 Pathfinder with RPM issue

[thelastkeg]

Hey folks, I just picked up a questionable, but too cheap to pass up, 2003 Pathfinder. It's been sitting for not more than a year. A mechanic was paid to install a used engine, and it hasn't been used since. No paperwork on the engine replacement. It's a 2wd, but it has a 4wd cluster which shows 218k miles. Maybe that's the cluster from the donor? Who knows. It runs and drives good except for an RPM issue. No smoke. It does have an exhaust leak on the passenger side somewhere near the manifold. It's in overall good condition with very good Yokohama tires, and I drove it home for $500. The issue is that the RPMs will only go high if the accelerator is pressed slowly. It'll rev up to 5000 and probably more in park if pressed slowly. But in park or driving if the accelerator is quickly floored, or if while driving you try to accelerate at a rate needed for merging onto a highway, it cuts out. Sort of like a rev limiter I guess, in that it'll rev, drop, rev, drop, etc. but the cycle isn't as fast as what you'd hear in a performance car. It'll stop doing that if I let off the pedal and then will accelerate slowly if I press it back down slowly. I don't think it's in limp mode because speed isn't limited, I got up to 50 or so on the drive home. Do y'all have any ideas of where to begin to check? Thanks in advance for any advice.

[VStar650CL]

Sounds a lot like low fuel pressure or fuel volume, but does the MIL work and is it lit, and have you scanned it for codes?

[thelastkeg]

Thanks for the reply. The light isn't on so I haven't scanned it, but I will scan it this weekend. How would I go about checking to see if the pump is delivering adequate pressure and volume under load? Or would it be a good idea to rule that out by just purchasing a new fuel pump and installing it since it doesn't seem to be that difficult or pricey. None of my other vehicles have a fuel pump access door like this one does. Not having to drop the tank is great.

[VStar650CL]

You could just replace the pump, and check the condition of the connector while you're in there (integral Nissan pumps are infamous for charring the ground terminals). Make sure the MIL works, it should light up with key-on. It wouldn't be the first time I saw somebody kill one to try to sell a car, and on older models killing it is pretty easy.

[thelastkeg]

MIL light is not illuminated! There were 6 codes, some minor ones. PO304 for cylinder 4 misfire and P1130 for the Swirl Control Valve were the two that seemed important and they immediately came back after clearing the codes. Googling P1130 returned a post where someone had a similar RPM fluctuation with this code and it was fixed once the valve was replaced and the code cleared.

Thinking about it being a fuel delivery issue, I looked at the live data, but wasn’t sure how to interpret the fuel data to see if it was operating within the required range.

[VStar650CL]

There's no fuel pressure PID because there's no pressure sensor. That's why fuel problems generally produce generic "lean" codes if they produce any codes at all. The P1130 won't make it run badly, lots of people drive around with the swirl valve (most of us Nissniks call it a Power Valve) disconnected. If it's stuck open it will limit your low end torque, if it's stuck shut it will limit your peak RPM. The P0304 is serious business if it's a serious misfire, dead misses will kill the catalyst on that bank in a hurry. Get to the bottom of that before anything else. It's suspicious that the MIL is out with a misfire and a dead Power Valve, it's possible the engine ate a loose screw from the butterfly and #4 cylinder was damaged.

[thelastkeg]

Well those particular codes may come back, but they’re gone for now after a couple of 5 mile test drives.

After clearing the codes, it would still not rev correctly. Unplugging and resetting the TPS would make it rev correctly, until the swirl and misfire codes came back on, then it wouldn’t rev right. The misfire ended up just being the electrical connector on the #4 coil wasn’t seated. The misfire code hasn’t come back, neither has the swirl, and the acceleration is correct. The exhaust leaks ended up just being 4 bolt holes in the passenger side catalytic converter, like maybe where a heat shield goes.

It’s now showing a PO328 and P0420, which are new. But it seems to be running just fine so I probably won’t worry about those for now. I haven’t had any Nissans since my stint with Hardbody trucks years ago, but this little Pathfinder seems like it’ll be a good daily beater.

[VStar650CL]

P0328 is a knock sensor code, I wouldn't worry about it. Nissans from the late 90's and early 00's will sometimes throw that even with a brand new knock, but it really only means anything if you happen to get really crappy gas.

The P0420 is a different story. It may be from the converters sitting long enough to get crusty, but it could also be the reason the previous owner disabled the MIL. So it's possible the cat has been bad for a long time. Nissan engines which have IVT's are all "Miller cycle" types, including your VQ. Miller cycling eliminates the EGR system by manipulating cam angles to make the engine re-inhale some exhaust gas during overlap. That's a great idea except if a catalytic converter melts. Then it can cause molten converter material to stick an exhaust valve open followed by a cascade of molten metal. The results aren't pretty and it's uniformly fatal to the engine. I'd recommend first running some Cataclean through both cats to dispense any crust which may have accumulated. Then point an IR thermometer at the cats after a 15~20 mile drive to get them fully lit. If a cat is working at all, the outlet flange will always be warmer than the inlet flange. Even if the temperature difference is small, the cat still has a little life and probably isn't in danger of disintegration. If the inlet is warmer than the outlet, it's time to bite the bullet and change it.

[thelastkeg]

Both cat MIL lights are on now. Still running good. I don’t have a thermometer yet, but they aren’t glowing and don’t seem any hotter than a typical exhaust. Will get a thermometer eventually and check temps.

Turns out when the engine was replaced they had the swirl valve vacuum lines crossed, and when that swirl code popped up it would put it limp mode. After a week of driving with the vacuum lines fixed, the swirl code has not come back and neither has the acceleration issue.

[VStar650CL]

Both cat MIL lights are on now. Still running good. I don’t have a thermometer yet, but they aren’t glowing and don’t seem any hotter than a typical exhaust. Will get a thermometer eventually and check temps.

They should be hotter than a typical exhaust. That's the whole point.