# 03 Sentra - need diagnosing help!!!



## jbarnesiii88 (May 14, 2014)

Hello. I am trying to diagnose a problem which is eluding me and I finally need help. My brother has a 2003 Sentra SE-R Spec V and at random intervals his engine starts to sputter, loses alot of power and gives off a horrid smell in the passenger compartment. If he does not rev the engine higher, his car dies most of the time. This problem only occurs at normal operating temp. His vehicle does use oil, maybe a quart/500 mi, but i've never ran into these symptoms with a car using alot of oil.
The dealership gave him DTCs for high idle and a IAC code, but a new throttle body was put on previously, and the PCM was reflashed multiple times. No positive results. The mechanics are stumped, and my bro was stuck with a useless $96.00 bill. My turn.
Before I smelled the thing for myself, I did not believe him, but I knew it sputtered. I originally thought it was a vacuum leak. I checked for leaks in vacuum lines, fuel injectors, around the manifold, any possible area that involves vacuum and air exchange. Found nothing. Not even a slightly corroded hose. 
Next I gave it a tune up. No results. However, his NEW plugs with only 20 miles on them were showing signs of running lean. 
So now im on his air intake and fuel system. I ran some fuel cleaner through. Nothing. When I looked in his combustion chamber when I changed the plugs,  his cylinder walls and piston head were clean, so no top engine cleaner was needed.
He has a short cold air intake installed. The filter sits behind the battery, which is pretty close to the engine. There doesnt seem to be much ram air flow in the engine bay around the battery area so it would naturally be a higher temp area. One of my concerns was that the intake is sucking in hot air which, in turn, is making the engine run hotter and mess with the fuel/ air mix since hot air is less dense. Could this be the problem or helping the problem fall within the parameters? I was thinking about making a CAI filter heat shield similar to the shields that come with alot of after market intakes. I was also thinking about making a single, short ram air tube that is positioned behind the driver side fog lamp and through the fog lamp upper access port that will help move some cooler air towards the filter and intake pipe. 

The smell I cannot even describe. Its not the smell of a cat going bad, its not coolant, oil, ps fluid, brake fluid, gas or anything I have smelled before. Now, the thing I havent smelled in my career is burning/burned coolant. This gets me thinking that he could possibly have a small head gasket leak. Is this a possibility? 
As a side note, I do notice that the car starts to disply these symptoms when the cooling fans turn on at normal operating temp. So im leaning more towards a head gasket. Please help!!!


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## vafiatx19 (Nov 5, 2013)

Coolant has kinda sweet smell. It sounds like the catalytic converter going bad. I had a ford ranger with similar symptoms. It had a rotten egg smell but it could be what the converter is made of and what type. It did do the sputtering and overheating. After a lot of money thrown in parts and sensors and stuff me and a friend removed it and made a straight pipe in its place. Problem solved.


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## jbarnesiii88 (May 14, 2014)

His rear cat is fine and his pre-cat has already been replaced because of the recall. The cats on his car are the typical combs so a bad cat would smell like rotten eggs, yes. However, this smell is more pungent, dense, and sharper like smelling salts. I talked to my team about it today and they told me it might possibly be a coil pack going bad (oddly they are genuine Nissan packs and only weeks old) which is causing a misfire. But I dont smell any unused gasoline expelling from the exhaust and the gas mileage is within normal range. Is it even possible that this specific misfire happens ONLY when the car is at operating temp? All misfires I've diagnosed and fixed happened at any and every temp (from cold start to operating temp). Im gonna start on his CAI shield and coil pack testing tomorrow. I'll let you guys know how it goes. If anyone else experienced this problem on this specific vehicle please let me know. Thanks!


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## worthirt (May 21, 2013)

This may sound completly crazy, but here it is. Have you looked at the battery and the charging system? I have a 94 that my battery was going bad on, the car would do all kinds of crazy stuff. Have you looked at the IACV and MAF, they may be a little gummed up. MAF is the big one, many CAIs use oil impregenated filters on them, some of that oil blows into the air intake and gets onto the MAF sensor wires, also it travels up into the IACV and causes it to get stuck.


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## rogoman (Dec 16, 2004)

jbarnesiii88 said:


> Before I smelled the thing for myself, I did not believe him, but I knew it sputtered. I originally thought it was a vacuum leak. I checked for leaks in vacuum lines, fuel injectors, around the manifold, any possible area that involves vacuum and air exchange. Found nothing. Not even a slightly corroded hose.
> Next I gave it a tune up. No results. However, his NEW plugs with only 20 miles on them were showing signs of running lean.
> So now im on his air intake and fuel system. I ran some fuel cleaner through. Nothing. When I looked in his combustion chamber when I changed the plugs, his cylinder walls and piston head were clean, so no top engine cleaner was needed.
> He has a short cold air intake installed. The filter sits behind the battery, which is pretty close to the engine. There doesnt seem to be much ram air flow in the engine bay around the battery area so it would naturally be a higher temp area. One of my concerns was that the intake is sucking in hot air which, in turn, is making the engine run hotter and mess with the fuel/ air mix since hot air is less dense. Could this be the problem or helping the problem fall within the parameters?


If you suspect a blown head gasket, perform a compression test on every cylinder.

Are you using the proper spark plugs? They should be OEM NGKs. Stay away from aftermarket plugs such as Bosch. Nissan engines don't run very well with aftermarket plugs.

Many CAI setups cause more problems then they are worth. They don't give you any noticeable performance increase except just a lot more noise. Was the MAF relocated with the CAI installation? If so, it could throw the air flow calibration off. Maybe your best bet is to remove the CAI and reinstall the OEM intake system. 

To do a proper test for a possible vacuum leak, use a vacuum gauge. Attach the 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.
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Here are some vacuum gauge readings and their indications:
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Low & steady: Late ign timing/valve timing, low compression

Very low: Vacuum leak

High & steady: Early ignition timing

Gradual drop in reading from idle to higher RPMs: Excessive back pressure in exhaust system 

Intermittent fluctuation at idle: Ignition miss, sticking valve 

Needle fluctuates as engine speed increases: Ignition miss, blown head gasket, leaking valve or weak valve spring


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## jbarnesiii88 (May 14, 2014)

worthirt said:


> This may sound completly crazy, but here it is. Have you looked at the battery and the charging system? I have a 94 that my battery was going bad on, the car would do all kinds of crazy stuff. Have you looked at the IACV and MAF, they may be a little gummed up. MAF is the big one, many CAIs use oil impregenated filters on them, some of that oil blows into the air intake and gets onto the MAF sensor wires, also it travels up into the IACV and causes it to get stuck.


I did check the charging system but not the battery because it is fairly new. Ill give that a try. Yes it does have a oil impregnated filter but I use the K&N filter recharge kit on all my CAIs so it shouldnt be sucking the oil, but I will check the MAF first because that does make more sense given the situation. IAC is good. Thanks. Will update results later today after I test the coils as well.


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## worthirt (May 21, 2013)

If the filter is over oiled (it happens alot, and is really easy to do) it will go into the air system and screw up the MAF.


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## jbarnesiii88 (May 14, 2014)

rogoman said:


> Are you using the proper spark plugs? They should be OEM NGK
> 
> Was the MAF relocated with the CAI installation? If so, it could throw the air flow calibration off. Maybe your best bet is to remove the CAI and reinstall the OEM


Yes they are the the factory recommended NGK plugs. I also gapped them slightly more because of the way he drives. The gap is set to and 8% increase. I stay away from Bosch completely. Had previous negative results on my cars so the only Bosch items I but are their excellent power tools  

It appears the MAF is located at the exact same spot. I will install the factory intake as well and see how that goes.

As for vacuum, my gauge was within spec at all RPM ranges. I will definately spray around the manifold. I will also check the EGR ports for blockage while im around that area.
Will post later the results.
Thanks


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