Engine won't rev past 4500rpm even in neutral?

[yhelothar]

FIXED!! It was a clogged cat!

I have a 2000 Nissan Quest. Lately it developed a problem where the engine doesn't want to rev past 4000-4500 RPM which causes problems for climbing uphill. I notice this happens even in neutral. The power seems to be diminished as well. This is after waiting for the engine to fully heat up.

What are the likely culprits?

Update 1: Cleaned MAF sensor, new tank of gas - no help

Update 2 : I got the bluetooth OBDII and the IR thermometer. No codes reported by OBDII. Running the test feature in the Torque Pro app showed a few misfires. http://i.imgur.com/eWwbPf7.png
Not sure if it's significant. It did have a misfire code a year ago and I replaced the plugs and it fixed it.

I looked under the van and there's actually two cats. I tested pre and post temp of the second cat. Pre temp is ~600F, post temp is ~300F, so that does strongly support a clogged cat. I'm gonna unbolt it and see how much it helps.

I hope it's just one of them. It's going to suck buying two California cats.

Update 3: I unbolted the second cat. It didn't help. Maybe the first cat is the culprit. I thought the first one was ok because it tested 600F post cat.

Update 4: I just took out the first cat as well and ran it straight pipe. The thing got really peppy! The power definitely came back, and then some! There were loose metal parts in the first cat. I shook out quite a few metal scraps. I got the first cat replaced while the second cat was fine. Power is back and the engine is responsive now! It was the misfire from worn plugs two years ago that melted the cat. After replacing the plugs, it took about a year before the power diminished.

 

[NutBucket]

Wait, which one is it? Many cars will not rev to redline in neutral.

Now if you're feeling diminished power that's a different issue. I can't imagine revving to 4000 rpm to climb a hill unless its really steep or you're carrying a full load. Can you provide more detail on the issue, like when you noticed it, etc?

 

[yhelothar]

Here are two videos.

In the first video, I'm at WOT from 0:04 to 0:25. It feels like there is power loss as it takes a while even to rev to 4000. Once it hits 4000RPM, it seems like there's fuel cutoff. You could see the RPM sometimes dropping a bit to 3800 and then climbing back up to 4000.
https://youtu.be/-fjJ9TEbDOU

Here, I tried revving the engine in neutral. It won't go up past 4000RPM. Oddly though, I tried it a couple minutes earlier and it hit 5000RPM. Then I took it out for a drive and now it'd only hit 4000RPM again.
https://youtu.be/TZlTiSDQJZg


So far, I tried making sure there is enough air getting to the engine. I took out the air filter and it didn't help.

This is my mom's minivan. She noticed it a few days ago. It's a pretty old van and the engine doesn't have that much power. It needs to rev to get any kind of power.

 

[disappoint]

Maybe a vacuum leak somewhere after the MAF sensor.

 

[NutBucket]

Is it running right otherwise? When did this start? It almost sounds like a bad tank of gas.

 

[yhelothar]

I just tried cleaning the MAF sensor with rubbing alcohol and a swab. There were a few places the swab couldn't reach well. But from what I could clean, it didn't help. I bought a can of MAF cleaner and I'll be testing it out later.

It drives normally when I keep the RPM's below 3000. I was able to drive on the freeway at 75 easily that way.

 

[twinrider1]

Try it in Low gear.

 

[yhelothar]

Try it in Low gear.

Yup, I did. It even happens in neutral. See the videos. There's more power in higher gears when I keep the RPMs under 3000.

 

[boomerang]

From here behind my keyboard I'm voting for a plugged converter. It would be a good idea to check fuel pressure too.

 

[NutBucket]

That's a good guess boomerang.

Wait, if you mom noticed it a few days ago...when was the last time she bought gas. I'm still going with this theory.

 

[WackyDan]

From here behind my keyboard I'm voting for a plugged converter. It would be a good idea to check fuel pressure too.

I second this theory along with putting a code scanner on it just to see if there are any additional clues.

 

[Rifter]

its not throwing any codes?

 

[KIAman]

This sounds like what limp mode would do in a lot of cars. Have you pulled the codes yet?

 

[bruceb]

Could also be a plugged fuel filter or the sock on the intank fuel pump pickup. A bad O2 Upstream sensor (these are the ones by the engine, before the converter) can also cause a loss of power on a lot of vehicles.

 

[dave_the_nerd]

Hint @ OP: If you don't have a codescanner, you can get a wifi one for $15 on amazon that will talk to your cell phone.

 

[dtgoodwin]

I had a Chrysler minivan I was helping a neighbor with. It had a bad idle and a small oil leak. The plugs were overdue, so I replaced them but there was no change in idle quality. I took it for a drive and it behaved similar to yours - it didn't want to rev to even 3K. I thought it was a plugged converter from the misfiring. It turned out their oil pressure sender was bad, and when the engine was warm the oil light would flicker at idle. Not being familiar with what that meant, they would add a quart of oil. When I drained the oil, there was more than 16 quarts in there. I'm surprised that there was only a little oil coming from one valve cover gasket which I replaced. After a new filter and the proper amount of oil it ran like it should - no shaky idle, normal power, and surprisingly, no oil leaks.

 

[yhelothar]

I just tried cleaning out the MAF sensor with the MAF cleaner. No bueno.
I tried filling up the gas tank as well. The car sit for around 6 months and my mom added a bit more a few weeks ago. There could've been quite a bit of old gasoline in there. So far on the 3 mile drive back home, the power haven't been restored.

From here behind my keyboard I'm voting for a plugged converter. It would be a good idea to check fuel pressure too.

Do I check for both of these with the OBD scanner?

I second this theory along with putting a code scanner on it just to see if there are any additional clues.

I'm not getting a check engine light. But I sold my scanner with my last car. I just ordered another one. I'll check in a few days.

Could also be a plugged fuel filter or the sock on the intank fuel pump pickup. A bad O2 Upstream sensor (these are the ones by the engine, before the converter) can also cause a loss of power on a lot of vehicles.

Do I check for these with the OBD scanner?

 

[NutBucket]

Eh, 6 months isn't really enough time for gas to go bad. Did a rodent build a nest in the exhaust? LOL

 

[natto fire]

I am in the plugged cat or other airflow camp. Fuel is usually abundant in modern EFI systems, and they usually have port injection, so not likely injector failure.

 

[DaTT]

I tend to lean to the side of plugged cat.

I had a plugged cat once (from a misfire), and eventually it wouldn't rev past 2500 rpm. Cat would glow red hot as well.

 

[bruceb]

I stand by my suggestion of a plugged fuel pump pickup sock. But the only way to get to it is to remove the pump from the tank. On some vehicles you can do this without dropping the tank. A mechanical fuel pressure gauge or a very good scan tool that can show real time data, can tell you what the fuel pressure is.

 

[DaTT]

I stand by my suggestion of a plugged fuel pump pickup sock. But the only way to get to it is to remove the pump from the tank. On some vehicles you can do this without dropping the tank. A mechanical fuel pressure gauge or a very good scan tool that can show real time data, can tell you what the fuel pressure is.

Would this not cause hesitation and misfire?

 

[bruceb]

Maybe, but misfires are usually an ignition issue.

 

[96Firebird]

I had a plugged cat on my old Firebird, no misfire issues but definite lack of power and wouldn't climb to higher RPMs. Made it tough to drive since it was a stick. Also smelled like rotting eggs, notice any odd smells from the van?

 

[yhelothar]

I had a plugged cat on my old Firebird, no misfire issues but definite lack of power and wouldn't climb to higher RPMs. Made it tough to drive since it was a stick. Also smelled like rotting eggs, notice any odd smells from the van?

Yes! It's been smelling like burning oil or exhaust for quite a while.

Anyways, I ordered an infrared temperature thermometer and a bluetooth OBD reader android off amazon. I'm going to run through a few of these checks on the clogged cat.
https://www.2carpros.com/articles/how-to-test-a-catalytic-converter