So before my little ram air setup i was running around 26/27 mpg. After the ram air, i got a horrible 20/21 mpg. The extra air wasn't worth the mileage i was losing.

After removing the ram-air setup, i topped off the tank with some gas, and 210 miles later i'm still getting the same weak mileage. The same WITH the ram air.

The only thing i haven't touched was a custom tubing that replaced the y tube that goes from intake box to the hole where the restrictor would be but that's not a ram air.

Could my ECU still be reading all that extra air cuz of my ramair even without it? So i'm running rich? I unplugged the battery for about five minutes to sort of reset the ecu (i dont know if that works on nissans but on hondas they do) so hopefully it'll go back to the original air fuel settings.

Any other suggestions? I haven't done anything else between making the ramair, gassed up, removing and gassing up again.

 

I dont think the ram air mod is where the problem lies

 

the ram air doesnt actually pressure any air into the engine... it just provides cooler air from the atmosphere... as raine said, sounds like the problem lies somewhere else

 

I've read that the O2 sensor although not completly bad to throw a code can infact give a weak signal to the ecu, increasing fuel richness, and lowering your MPG.
I tested this theory myself a week ago by replacing my o2 sensor. After a few start ups and driving about 30miles, my MPG increased from 19MPG to about 25MPG. I've calculated this through one week of driving use.
Reading the FSM the O2 signal weakens pretty much because of the intense heat in the exhaust. The heat from the exhaust literally wears down the platinum coating that is in the O2 which would weaken the signal. After about 3000miles of driving the o2 sensor is only 65% efficient in controlling the signal for the A/F ratio. At about 30,000miles the O2 sensor is only 20% effective in sending the signal that controls the A/F ratio.
Another way you can signicantly drop MPG is through advancing the timing to your engine via distributor without advancing the cams as well. When you advance the distributor without advancing the cams, it literally chokes the engine and raises hydro carbon levels. Hydro carbons are produced when there isn't enough air to fuel that will mix with a lean fuel dump, actually increasing the richness of the engine, and also decreasing gas mileage. Since detonation occurrs earlier and the cams havent been advanced to dump earlier the engines vacuum potential decreases.
You can also be getting weak MPG through your TPS (Throttle positioning sensor), this sensor is located at the Throttle Body. The TPS tells the ECU the position of the Throttle in order to dump an amount of fuel through the fuel cycle, (it's relative to calculation with the MAF,TPS, and O2...............
Now in any case if it was tyour MAF you would be throwing a code right off the spot. Anything dealing with smog emissions would throw a code off the spot. If by chance you have removed any of your smog emissions equipment thinking that you were getting a performance gainer, THINK again. Put it all back including the AIV, the AIV although you think it does nothing is actually part of the vacuum circuit to the EGR/BPT........
But if you have the 95 and up OBD 2 disregard what I said about the AIV and follow what I said before.

 

Vinnie and his super posts lol

 

DAMN..... I am assuming by the LOL that I shouldn't of posted soooo much info...... I just try to include everything I know so that I won't have to repost, and be a posting ***** like some others around here....

 

would I get a check engine light if the o2 sensor is broken?

I think i'll runa self diagnostic one day.

 

When the O2 sensor can no longer throw a voltage signal to the ecu, the check engine light will come on. But that doesn't mean that it isn't working effectively now for you. I picked up a BOSCH O2 sensor from pep boy's for $22.00, If I were you just save your self the headache.
On another note running a diagnostic may be good after all, I failed to mention that when the thermostat stops working the check engine light sometimes doesn't go on, but it will throw a code. Actron code scanner book is cheap at under $30, it will diagnose any code for OBD2.

 

O2's tend to get lazy. They typically produce a 5volt signal to the ECU. However, if you look at the signal with a scope, you'll that it emits a sign wave where the voltage fluctuate between 0 and 1v (edit...did a little more research) . A good O2 sensor should fluctuate between 0 and 1v about 8 times in 10 seconds when the O2 is fully heated and engine is running at normal operating temp and at 2500rpm - 3000rpm. Lower voltage equates to lean mixture and higher voltage equates to a richer mixture.

My S14 has 99k miles and is on its original O2 still. Up until about a two months ago, I was getting terible fuel economy. About 20mpg at best driving mostly highway. I checked her out a little more in depth and found that the the timing was way retarded. I advanced the timing from the stock setting about 3 degrees on my 100% stock motor. Not only did I gain much more power, my fuel economy immediately jumped to 25mpg. Now, two months later, I'm at 26.5 miles per gallon. Your ECU takes some time to learn your fuel trim and driving habits. It's not a good idea to unpliug your batter, IMO, to "reset" anything. If anything, it'll make it worse.

Check your timing. Remember, retarded timing will not only cause you to lose power and fuel economy, it also causes your motor to run warmer. Advanced timing can gain power, reduce temperatures, and gain fuel economy. However, advancing too far can cause your engine to knock and ping more.

It's been a while since I've "wrenched" so my voltage info may be off a little.

Just my $02.

EDITED FOR MORE DETAILS AND CORRECTIONS.