# gas mileage down 3mpg...could it be the MAS?



## svasica (Jul 22, 2004)

The gas mileage on my car has suffered quite a bit since I first got it about 4 months ago. I use to get about 30mpg and now get about 27mpg. The only thing I can think of is that the CAI I put on the car (Hotshot) may have let water in and maybe got on the MAS? How would I clean or check the MAS to see if there is water or any other damage on it? There is also another sensor on the CAI...the temp sensor i think? Could this cause this type of problem also?


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## Zac (Mar 10, 2004)

I believe season change in fuel can explain why your MPG is down somewhat.


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## svasica (Jul 22, 2004)

I also feel a considerable decline in power, more than what fuel change would do. How would I go about checking the mass air meter to see if its messed up from water or other form of damage?


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## BlackoutSpecV (May 8, 2002)

svasica said:


> I also feel a considerable decline in power, more than what fuel change would do. How would I go about checking the mass air meter to see if its messed up from water or other form of damage?


If the MAF was damaged you would be in limp mode (IE the SES light would be on). If you feel that you are down power I would do 2 things. First check the filter on the CAI, then check all the couplings to make sure you do not have leaks. If the filter is clean and the CAI is connected tight, they I would suggest going back to stock air box and see if that fixes your problem. If the back to stock option does not fix the problem you should take the car in.


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## caveman (Dec 20, 2003)

BlackoutSpecV said:


> If the MAF was damaged you would be in limp mode (IE the SES light would be on). If you feel that you are down power I would do 2 things. First check the filter on the CAI, then check all the couplings to make sure you do not have leaks. If the filter is clean and the CAI is connected tight, they I would suggest going back to stock air box and see if that fixes your problem. If the back to stock option does not fix the problem you should take the car in.



I'm interested in how your car will run with the stock air box back on. I think CAI's are a huge scam in the tunner market now days. Reason 1: The notion that you are getting a cold air intake is a joke in it'self because anyone who installes a open cone filter is going to suck in hot air from the engine bay. Reason 2: (this sort of backs up 1 in the DSM tunning world where we have nice loggers n such, people who have cut the air box so the cone filter is open get higher intake temps on the logger. The best way DSMers keep the intake cool once a open cone filter is used is to build a custom air box that blocks hot air from engine. Reason 3: Some MAFs have trouble monitoring/counting air with a CAI setup if there is some sort of bend before the MAF. One of my closest friends who has a old school 5.0 got rid of his CAI because he would have had to pay a lot of money to have a MAF calibrated for the CAI that was on his car. He put the stock air box back on his car and he got a lot more low end and mid range throttle responce and torque.

I don't have the dyno sheet to back this up, but I've read that on a DSM, dynoing a injen intake pipe lost HP compared to the stock intake pipe.

Go ahead guys, flame away, but I say don't wast hundreds of buxs on a CAI system for your car. Just get a in box K&N filter. I don't see how anyone but the engineer of the MAF used would know the effects of a CAI. The stock MAF might acually have trouble with a CAI, but it won't with the stock box. Since there is no real HP gain from a CAI anyway, why not just use a in box high flow filter? A in box high flow filter will flow more air then the stock air filter and you can get more gains with your header. Also, instead of buying a whole cat back exhaust, save money and only replace the stock cat and muffler. I did this on a turbo talon on a budget and I got massive gains. Greated that was with a turbo, installing a larger size exhaust on a NA 2.5 isn't going to give any HP gains, but installing a high flow cat(s), and a higher flowing muffler will. Again, flame away.

The 2.5 engine is not going to produce massive power from the stock HP, and the budget mods are going to work well. You would be better off spending money on tires, suspention, and brakes becuase you can greatly improve them over stock, but the 2.5 engine will never be a power monster unless the whole engine is rebuilt.

Let the flames start. Just keep in mind, I've been in to tunning for some time now and I'm not a expert in this engine, but overall, things don't change that greatly from car to car. I'm really not happy with Nissans current build quality and service, but I can say this, the 2.5 engine in our Spec V (with spec V gearing) probably has one of the best if not the best throttle responce and torque out of any NA 4cyl before. Screwing with CAI's and not knowing the effects of the MAF and installing larger size exhaust's can mess up the torque and throttle reponse. I've seen in happen many times before. Since you can't pull on all cars with the Spec V, you can build it to loose them in the curves and have much later braking. For autox and off road legal racing.

EDIT: I just wanted to add a little on the whole stock air box vrs a CAI. On some cars a CAI will add HP over a stock air box. Some cars from the factory have a extreamly small air box and air filter with very little air getting to the air box in the first place. In a case like this, a CAI would be a better choice because much more air will be able to make it to the throttle plate and intake manifold compared to a factory restrictive air box. The stock air box and stock rubber intake on the Spec V are already large. The stock air box has two intake tubes to grab cool air, the surface area of the stock filter is large, and the stock intake pipe after the air box is large with no restriction. The car already has a good setup from the factory. So it is a case by case thing. I'm not suggesting that good usefull CAI's don't exist, BUT they are way to popular and too many people automaticly assume that the first thing they should do is get a CAI. In some cases, it is more of a bling bling thing and less of a performance adder. In some cases, a CAI can acually hurt HP.


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## BlackoutSpecV (May 8, 2002)

That post was way to long (so I did not read it all). 

The simple fact is that time and time again a true CAI (pulling air from outside the engine bay, not a WAI that you described) has been proven to deliver cooler air (all be it not COLD as advertised). Also the Dyno's have show loss of low end and gain of high end power.... there are many cars that have been dyno proven to loose power with intakes... this is a car by car basis.

You should do a little research on the specific motor, the QR25 does not compare to the DSM's.

::EDIT:: 
All that being said, your right there are much better mods.


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## Zac (Mar 10, 2004)

Ehh, supposedly a cai also helps gas mileage...no, maybe your not gonna get a lot of power from it but what can you expect of a bolt on? You do raise a good point.
Bolt ons are not mods. lol


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## svasica (Jul 22, 2004)

Look gentleman, I did not start this thread to start a debate on whether the CAI is worth the money or if it does add any power.

I KNOW it does because I too have an old school 5.0....well, I built it up to a 331 stroker so its actually more like a 5.4. But anyway, I have a CAI on the mustang and I dynoed b4 and after with the CAI, and yes it did make more power. 

Granted, on the smaller 2.0 engine for the Nissan, it will hurt low end torque/power, but on the top end there is no debating that it WILL add power simply because you have more air flowing into the engine....let alone the fact that the air coming in is cooler than the air you would be getting from the engine compartment.....and all the good ole gear heads here know that a cold air charge is denser and will produce more power. 

When I first installed the CAI on my Sentra, it felt a lot more powerful than it does now, and had atleast the same gas mileage as before the CAI. Heres the complete story gentleman on how I believe the MAS got screwed up: After the remnants of one of those hurricanes passed over NJ a couple months ago, my road flooded...as did my car, partially...the water got to the top of the tires I hear. Anyway, obviously the filter would have gotten submerged in this case. I believe that afterwards, when I started the car, water must have gotten up somehow into the CAI and probably screwed up one of the sensors in the CAI, most likely the MAS.

All I was asking is how do I check the MAS for damage.....if you can't answer, please don't flame about how you think the CAI is a waste and what not, save it for another thread!


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## caveman (Dec 20, 2003)

svasica said:


> Look gentleman, I did not start this thread to start a debate on whether the CAI is worth the money or if it does add any power.
> 
> I KNOW it does because I too have an old school 5.0....well, I built it up to a 331 stroker so its actually more like a 5.4. But anyway, I have a CAI on the mustang and I dynoed b4 and after with the CAI, and yes it did make more power.
> 
> ...



You must not of really read my post. I posted a reason as to why a CAI system might not work with your MAF. You are jumping to the conclution that your MAF is bad when you don't even have a CEL. Without a CEL, Nissan's diagnostics might not be able to answer your question.

Moderators, just delete my fucking accout. I am getting sick and tired of the aditude of the Sentra forums. I'm not going to wast my time here anymore!


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## Zac (Mar 10, 2004)

Ide imagine diagnostivs viaa OBDII that autozone can do for free may help also


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## BlackoutSpecV (May 8, 2002)

caveman said:


> I am getting sick and tired of the aditude of the Sentra forums. I'm not going to wast my time here anymore!


I'm with this guy... learn to read, I said if there is no light the MAF is okay. Dont belive me, go buy one (for about $600) and see if it fixes your problem. MAF's dont get repaired, they go out, if its out its out, but you would have an SES light. 


BlackoutSpecV said:


> If the MAF was damaged you would be in limp mode (IE the SES light would be on). If you feel that you are down power I would do 2 things. First check the filter on the CAI, then check all the couplings to make sure you do not have leaks. If the filter is clean and the CAI is connected tight, they I would suggest going back to stock air box and see if that fixes your problem. If the back to stock option does not fix the problem you should take the car in.


Did you do this?


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## Greg200SE-R (Feb 5, 2003)

caveman said:


> I think CAI's are a huge scam in the tunner market now days...
> Go ahead guys, flame away, but I say don't wast hundreds of buxs on a CAI system for your car...
> Again, flame away.
> Let the flames start.





svasica said:


> Look gentleman, I did not start this thread to start a debate on whether the CAI is worth the money or if it does add any power.
> All I was asking is how do I check the MAS for damage.....if you can't answer, please don't flame about how you think the CAI is a waste and what not, save it for another thread!





caveman said:


> Moderators, just delete my fucking accout. I am getting sick and tired of the aditude of the Sentra forums. I'm not going to wast my time here anymore!


Sounds like you were EXPECTING some negative responses to your post caveman... so what's the problem here. The guy who originally posted had some simple questions and even tho they were answered pretty well he just got more info than was necessary. He obviously wants to keep his CAI. Chill.

Like BlackoutSpecV said, it's well known that any "breathing" mod generally loses low-end (because of increase in flow) and gains high-end (also becasue of increased flow). Since the QR25 is such a torque monster, of course you'll feel the CAIs effects because you spend almost all of your time driving at low to mid RMS - where the loss of torque occurs. Now, since you subconsciously are pressing the gas pedal a little more to get the same acceleration compared to before, voila, you end up using more gas. Also, the ECU, after time, may have slightly increased fuel delivery to match the increased airflow. 

Tuning is an excerise in compromises. Gain something, lose something. The most basic one is gain horsepower, lose gas mileage. Simple as that.


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## caveman (Dec 20, 2003)

Any experianced tunner would not do anything to loose low end torque and throttle reponce. If you want to do real racing, you want the best 0-60' time in the 1/4 and if you want to autox, you want the low end power to get out of the corners the fastest. Loss of low end torque and top end gains are good for about one thing. Ricer street racing and for ricer flybye's.

Since the Spec V has already been proven to be pretty limited to power, please consitor this basic formula that just about every young ricer tunner would laugh at. This is what I would do if I really wanted to race my Spec V.

K&N filter
header with no cat
stock exhaust with a high flow main cat. You can get them already made to screw in a o2 sensor on the front and back. Magnalow sells them. Read up on emissions laws tho. A shop can only legaly change your cat if your car is x amount of years old or it has x amount of miles OR if your cat is dammaged. So, if you run over a rock or a sledge hammer, you can get a new cat.

Then I would just get a better muffler. I prefer Magnaflow, but others make good ones too. The main restriction in your exhaust are the cats and stock muffler, not the exhaust size. 

After a few basic breather mods, I would spend the rest of the money on usefull mods like brakes and suspention. Even better tires would help out in the corners. The real gains are going to be had with making the car brake late and corner great. CAIs that cost over $200 and costly cat back exhaust systems are not. At least not for a Spec V.


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## Greg200SE-R (Feb 5, 2003)

caveman said:


> Any experianced tunner would not do anything to loose low end torque and throttle reponce. If you want to do real racing, you want the best 0-60' time in the 1/4 and if you want to autox, you want the low end power to get out of the corners the fastest. Loss of low end torque and top end gains are good for about one thing. Ricer street racing and for ricer flybye's.


Here's yet another basic compromise in engine design. Design for good low-end and you compromise on high-end, and vice-versa. there is no one way to tune for competition but consider this. Split your tach in half and augment the half you'd be spending the most time during your choice of driving (be it 1/4 mile, autocross, ricer flyby's or strictly daily driving). Daily driving and perhaps autocross/tight turns would see a lot of time in the lower half. Most motorsports, however, would see more key time in the upper half and would benefit from breathing mods shifting some torque from lower to higher RPMs. Losing low-end sucks but generally torque will do much more work at higher RPMs than lower - assuming the engine can take advantage of it. 


caveman said:


> Since the Spec V has already been proven to be pretty limited to power, please consitor this basic formula that just about every young ricer tunner would laugh at. This is what I would do if I really wanted to race my Spec V.
> 
> K&N filter
> header with no cat
> ...


This is a good formula for keeping as much low-end as possible. Sounds like a purist's approach to tuning, and I admire that. At WOT though, this QR sounds like it will be restricted to a degree. 


caveman said:


> fter a few basic breather mods, I would spend the rest of the money on usefull mods like brakes and suspention. Even better tires would help out in the corners. The real gains are going to be had with making the car brake late and corner great. CAIs that cost over $200 and costly cat back exhaust systems are not. At least not for a Spec V.


By the way, a cold air intake (those with a long tube, not just a heat isolating box) are acoustically tuned to augment a certain part(s) of the RPM range, normally in the low-end. Breathing mods may not gain much HP individually, but work together as a system. The QR unfortunately is so low-end focused that PEAK hp gains on paper aren't as impressive as they could be.


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## Terry S (Nov 8, 2004)

Doesn't a CAI provide a more unstable MAF reading and add more air at the same time on a N/A engine? With a N/A engine, the more air = leaner condition and slightly more power. However your AFR's will be all over the place (which some good tuning can fix).

Turbocharged DSM's (4g63t) is different with the CAI because its turbocharged and putting a CAI on without modifying the AFR's will cause an unstable MAF reading thereby lowering power on a whole.

Terry S


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## Greg200SE-R (Feb 5, 2003)

Terry S said:


> Doesn't a CAI provide a more unstable MAF reading and add more air at the same time on a N/A engine? With a N/A engine, the more air = leaner condition and slightly more power. However your AFR's will be all over the place (which some good tuning can fix).
> 
> Turbocharged DSM's (4g63t) is different with the CAI because its turbocharged and putting a CAI on without modifying the AFR's will cause an unstable MAF reading thereby lowering power on a whole.
> 
> Terry S


A CAI won't "add" more air than stock... CAIs may be able to flow more air, but when called for. The engine is constantly pulling in air but most of the time the throttle is blocking that flow. So most of the time it's like sipping water from a straw - a bigger straw will allow you to work less, but won't automatically give you too much water just cause it's bigger. However, when you are thirsty the bigger straw comes in handy just like a free-flowing intake helps at open throttle. The ECU will calculate the correct amount of fuel for the measured air intake. 

The 4G63 uses a MAP sensor (Manifold Absolute Pressure) and works differently than our Mass Air Flow sensor. Our MAFs measure the amount of air going past a heated wire through a certain size passageway. We can alter our intakes as long as the passageway (MAF housing) stays the same. A MAP sensor measures the pressure of the air in the intake manifold (pressure in the case of turbo... it would be a vacuum if NA). In this case, yes, changes on the intake that affect the air pressure can throw off the sensors readings.


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## Coheed (Oct 12, 2004)

svasica said:


> The gas mileage on my car has suffered quite a bit since I first got it about 4 months ago. I use to get about 30mpg and now get about 27mpg. The only thing I can think of is that the CAI I put on the car (Hotshot) may have let water in and maybe got on the MAS? How would I clean or check the MAS to see if there is water or any other damage on it? There is also another sensor on the CAI...the temp sensor i think? Could this cause this type of problem also?


Always check tire pressure to make sure it is correct


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