# Rough idle / no power / won’t rev past 2000rpm



## ChrisJ1286 (5 mo ago)

Hello all new member here looking for help. This is not your typical bad cam / crank sensor or dirty maf etc issue. 2.5 w/ 105k miles and I am the original owner, always well maintained and cared for. Randomly one day when driving normally the motor started to stumble and struggle under any load very badly to the point where it almost isn’t drivable unless your idling in gear and barely touching the throttle. I have NO codes whatsoever. Parts I have already changed are cam sensor, crank sensor, coils & plugs, fuel pump, throttle body, checked and cleaned MAF, Ohm’d out all fuel injectors and all are within spec at 14.5-14.7 ohms. The car will start and idle no problem although a little rough. It will NOT run with the MAF unplugged. While idling if you unplug any coil or fuel injector there is a drastic change in sound and obvious misfire which leads me to believe all the associated wiring is fine. I do not have a smoke tester but I sprayed everything with carb cleaner while idling and there was no change in idle indicating a vacuum leak. All sensors and the throttle body were replaced with OEM Denso and Hitachi parts. I’m at a loss at this point and I don’t want to keep throwing parts at it as I’m already nearly $700 in and there’s not too much left really besides the VVT solenoids and the intake manifold runner solenoid/valve which I do not believe are the problem as I’m pretty sure any of those would throw a code. Any help would be greatly appreciated, it would be a shame to junk this thing with only 105k miles in it.
Thanks in advance


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## Oldcivicjoe (Jun 21, 2021)

Does the engine rev fine in neutral? Does the exhaust sound normal, or like it's got an extra muffler on it?


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## VStar650CL (Nov 12, 2020)

First thing I'd try is spraying some supplemental fuel down the barrel (Brakleen, Gumout, etc) and see if it will take the throttle. That will rule a fuel problem conclusively in or out. I'd also check engine vacuum to make sure the cat hasn't collapsed, an exhaust blockage will show up as more-or-less normal vacuum at idle but it will plunge as you try to accelerate. You could also check voltage coming out of the IPDM from the ECM Relay (if it has crummy contacts then the ECM may be going "in and out of consciousness" which can cause a "barely-running" condition with no codes). Checking voltage drop on the block and chassis grounds would also be a good idea. If all of that checks out, then I think you'll need to look at the engine parameters with a streaming scanner to get some clues about what's abnormal.


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## ChrisJ1286 (5 mo ago)

Oldcivicjoe said:


> Does the engine rev fine in neutral? Does the exhaust sound normal, or like it's got an extra muffler on it?


No it does not rev fine in neutral either. Exhaust sounds fine though.


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## ChrisJ1286 (5 mo ago)

VStar650CL said:


> First thing I'd try is spraying some supplemental fuel down the barrel (Brakleen, Gumout, etc) and see if it will take the throttle. That will rule a fuel problem conclusively in or out. I'd also check engine vacuum to make sure the cat hasn't collapsed, an exhaust blockage will show up as more-or-less normal vacuum at idle but it will plunge as you try to accelerate. You could also check voltage coming out of the IPDM from the ECM Relay (if it has crummy contacts then the ECM may be going "in and out of consciousness" which can cause a "barely-running" condition with no codes). Checking voltage drop on the block and chassis grounds would also be a good idea. If all of that checks out, then I think you'll need to look at the engine parameters with a streaming scanner to get some clues about what's abnormal.


I initially thought cat possibly failed but the exhaust sounds and feels fine and I would think if it collapsed or failed it would set a code for inefficient cat or something along those lines. I also forgot to mention I cleaned battery cable connections and put a brand new battery in it as well as having it on a tender while it sits. Voltage seems fine on the little code reader I have when viewing live data. No dimming lights or anything when opening/closing windows with headlights & a/c etc on so I believe grounds are all good but I will double check everything.

I just ordered an autel maxicom, been getting by for many years with a little code reader but I think it’s time to upgrade and now I can justify it.
Thanks for the suggestions so far.


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## VStar650CL (Nov 12, 2020)

ChrisJ1286 said:


> I initially thought cat possibly failed but the exhaust sounds and feels fine and I would think if it collapsed or failed it would set a code for inefficient cat or something along those lines.


It takes time and driving for a cat to set codes, and the car is half-dead. I'd throw a vacuum gauge on it.


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## ChrisJ1286 (5 mo ago)

VStar650CL said:


> It takes time and driving for a cat to set codes, and the car is half-dead. I'd throw a vacuum gauge on it.


Going to tomorrow. Is it common for these things to jump timing or have cam phasers go bad?


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## Oldcivicjoe (Jun 21, 2021)

Not common I would say, but it happens, nearly always see a cam/crank correlation code when they jump time unless a cam or crank sensor is bad. And in every case I've seen them jump time the guides were torched long before the timing jump actually happened, usually from cheap lube and tune oil changes with the wrong weight oil.


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## VStar650CL (Nov 12, 2020)

ChrisJ1286 said:


> Going to tomorrow. Is it common for these things to jump timing or have cam phasers go bad?


Joe has that right, but jumped chains are pretty rare on QR25's and phaser issues are just about unheard of. Issues with IVT/EVT are usually from oil pressure in the front cover and not the chain or phasers. If it has jumped time it should show up as low compression.


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## ChrisJ1286 (5 mo ago)

Couldn’t find my vacuum gauge think I lent it to someone awhile ago and never got it back so I ordered another one, should be here tomorrow. But I checked all cylinders with an inspection camera and no visible signs of damage or coolant indicating a head gasket leak. I did a compression test and it looked good all cylinders 148-150.

Also with the car running I sprayed some carb cleaner in the intake with someone in the car giving some gas and it would NOT take it at all it immediately stalled out several times.

I have a decent Fluke IR thermometer so I let the car run and I took some temp readings of the cat and to me they seem high but I’ve never done that and honestly don’t know what they should be or what’s normal. Right at the top of the cat near the o2 sensor I was getting around 810 degrees and at the other end of it I was only seeing 450-500 degrees depending where I took the reading. I did hear a slight rattle underneath the car with it running so I’m really starting to think it might be the cat. Let me know what you guys think.
Thanks again


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## VStar650CL (Nov 12, 2020)

The back side of the cat should be hotter than the front, not cooler. Try pulling the A/F Sensor (front O2) and see if that lets it rev. If so, your cat is trashed.


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## rogoman (Dec 16, 2004)

ChrisJ1286 said:


> Couldn’t find my vacuum gauge think I lent it to someone awhile ago and never got it back so I ordered another one, should be here tomorrow. But I checked all cylinders with an inspection camera and no visible signs of damage or coolant indicating a head gasket leak. I did a compression test and it looked good all cylinders 148-150.
> 
> Also with the car running I sprayed some carb cleaner in the intake with someone in the car giving some gas and it would NOT take it at all it immediately stalled out several times.


Spraying starting fluid into the intake while the engine is running is like full choking an engine.

A typical symptom of an engine running in fail-safe mode is limited revs beyond 2500 rpm as set by the ECU. However you're saying there were no DTCs to indicate a fail-safe condition. Here are some things to check that might give you a fail-safe like symptom:

- Incorrect fuel pressure. Tee-in a temporary fuel pressure gauge between the fuel feed hose and the fuel rail. The reading at idle should be 51 psi.
- There may be a major intake system vacuum leak. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
- Check your engine grounds. With the car running, put a voltmeter on the lowest scale and measure from the block to the negative battery post. It should read no more than 50 millivolts (0.05V).

Since you replaced the throttle body and cleaned the MAF, you should perform an IAVL (Idle Air Volume Learn) procedure. That's what the IAVL does, it re-matches the MAF to the ECM.

Here's an easy way to test for a bad CAT: Connect a vacuum gauge to a source of full vacuum (unmetered) on the intake manifold or throttle body. Note the reading at idle, then raise and hold engine speed at 2,500. The needle will drop when you first open the throttle, but should then rise and stabilize. If the vacuum reading starts to drop, pressure may be backing up in the exhaust system.


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## ChrisJ1286 (5 mo ago)

Altima clogged cat







youtube.com





Can’t even get it rev to 2500. Seems to be getting worse every time I start it. Also noticed the car gets hot extremely fast.


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## VStar650CL (Nov 12, 2020)

Pull the front O2. That will let the engine breathe and tell you _instantly_ if the exhaust is restricted.


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## Oldcivicjoe (Jun 21, 2021)

All the signs of a plugged cat, its officially worth it to pull and inspect.


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## ChrisJ1286 (5 mo ago)

Confirmed cat is clogged. Pulled front o2 and car revs clean to 5000+ and vacuum is just about normal. Thanks all for the help, hopefully this thread will help someone else in the future at some point. Will update with pics of it once I pull it out.


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## Maximat (11 mo ago)

Hard to figure how the convertor would "go bad" just like that. The operating surface on the inside is a real fine honeycomb that has to get clogged up to prevent air flow.
If his was plugged, it couldn't breathe... right.... and even unplugging the sensor wire wouldn't cause the breathing to improve. 
Physically being plugged... oil fouled would be my guess. If it hasn't been "burning oil", how would it get to the point of being physically plugged.

years ago, I had a 86 Dodge D50 pickup, with a little Mitsubishi 4 cylinder engine. When i got it, it wouldn't hit a lick. I did everything possible under the hood to check the problem. It was getting fire and fuel.

This went on for a few years. I'd get frustrated and push it out of the shop and let it set. One day, I pushed it back in and was playing with it. A friend was there, so I had him set in the cab and try to start it while I sprayed a little gasoline in the carburetor.
The rays of the sun were playing across the top of the engine at just the right angle... and every time the engine turned over, I could see puffs of fuel popping out of the carb throat!!!! 

I held my hand over the carb... and it had barely any suction...not like it ought to.

I ran to the back and held my hand over the tail pipe...He turned the engine over... no pressure came out the tail pipe!!!!

I crawled under the truck, disconnected the muffler from the engine exhaust. Nothing!!!!

I disconnected the exhaust pipe from the manifold mounted cat convertor..... no air flow!!!!!

I really didn't even know there was a convertor in there... it's hidden. I took a foot long ½" drill bit and drilled a hole up through that converter material and told him to hit the starter.

That SOB fired right up and sprayed crap out of the manifold all over the floor. I then took a rod and tore out all the cat material and cleaned it all out.

That thing ran like a champ after that.

Turns out one of the exhaust valves had burnt and was passing oily/unburnt fuel right out of the cylinder onto the cat surface... and over the years it had gave it a coating, which effectively plugged it up, and it couldn't breath. Just that little half inch hole gave it enough flow to let it start!!!!


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## ChrisJ1286 (5 mo ago)

I didn’t just unplug the sensor I pulled it out, it is pre catalytic converter right off the manifold primaries and it accomplished the same thing that drilling a hole in yours did, gave it just enough to breathe and run. The car ran fine prior to this issue. I’m thinking it was partially plugged up and then possibly started to break apart and then just about completely blocked itself up. Apparently this is a fairly common problem with these cars.


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## VStar650CL (Nov 12, 2020)

ChrisJ1286 said:


> I’m thinking it was partially plugged up and then possibly started to break apart and then just about completely blocked itself up. Apparently this is a fairly common problem with these cars.


It probably had a meltdown, literally. They hit a critical temperature and hundreds of the honeycombs all plug up at once. You're actually fortunate that it didn't go volcanic and suck debris back into the engine, Nissan engines are practically all Miller-cycle and "cat inhalation" is 100% fatal when it happens. This is the result:


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## ChrisJ1286 (5 mo ago)




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## VStar650CL (Nov 12, 2020)

That will do it.


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## 1.8TTony (5 mo ago)

If you have emissions inspection, you can hollow out the other cat and install these in the downstream O2 sensor locations to prevent the CEL from turning on......remove them temporarily to pass smog test....reinstall after the test.


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## balmrmartin (4 mo ago)

ChrisJ1286 said:


> Hello all new member here looking for help. This is not your typical bad cam / crank sensor or dirty maf etc issue. 2.5 w/ 105k miles and I am the original owner, always well maintained and cared for. Randomly one day when driving normally the motor started to stumble and struggle under any load very badly to the point where it almost isn’t drivable unless your idling in gear and barely touching the throttle. I have NO codes whatsoever. Parts I have already changed are cam sensor, crank sensor, coils & plugs, fuel pump, throttle body, checked and cleaned MAF, Ohm’d out all fuel injectors and all are within spec at 14.5-14.7 ohms. The car will start and idle no problem although a little rough. It will NOT run with the MAF unplugged. While idling if you unplug any coil or fuel injector there is a drastic change in sound and obvious misfire which leads me to believe all the associated wiring is fine. I do not have a smoke tester but I sprayed everything with carb cleaner while idling and there was no change in idle indicating a vacuum leak. All sensors and the throttle body were replaced with OEM Denso and Hitachi parts. I’m at a loss at this point and I don’t want to keep throwing parts at it as I’m already nearly $700 in and there’s not too much left really besides the VVT solenoids and the intake manifold runner solenoid/valve which I do not believe are the problem as I’m pretty sure any of those would throw a code. Any help would be greatly appreciated, it would be a shame to junk this thing with only 105k miles in it.
> Speed Test
> Thanks in advance


Does the exhaust sound normal, or like it's got an extra muffler on it?


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