Found out why my mileage has been so trash.....

K

krakhedd

NAXJA Forum User
Location
Buffalo, NY
Ok, I felt I should share this, since I posted a thread about it a bit back.

Basically, the two causes of my horrible milage are my hood vents and a relocated IAT sensor.

I bought a new IAT last week, when the weather was in the upper-40s/lower-50s. I installed the new one in the stock location, and boom, 17MPG on 5 or 10 gallons (I forget hopw much). The temperature dropped a few days after that, into the mid- to upper-30s, and my mileage went right back down to around 10-13MPG.

I decided to see how hot my intake manifold was earlier this week, after a decent drive, immediately after I stopped the truck (still running). I know I have put my hand on a 4.0 intake manifold before in cold weather, and almost burnt my hand off. It was barely luke-warm the other day. What this indicates is that my hood vents are keeping the entire engine bay clear of hot air, to the point where even the exhaust header beneath my intake manifold is not warming up the manifold.

Just a solution to those of you who may be searching for similar answers, or are contemplating installation of hood vents and live in cold climates. I hope this helps somebody other than the stupid oil companies I am uselessly throwing money at.

Which begs my next question - anybody have a stock hood for sale? :)
 
i had the same prob and i fixed the not hot enough prob by putting cardboard right under the vents and i would run 210 motor temp the whole time and the motor was getting hot to try that its cheaper.
 
I do have this whole white/blue thing going with the rig, that might be cool. We'll have to see.

As far as cardboard....I wouldn't feel comfortable putting that under the vents. Too much moisture around these here parts, and if the cardboard started falling apart and landing on my motor...well...I dropped motor oil on a hot motor once, I was lucky enough to 1) see it happen and realize a fire had started, 2) have a fire extinguisher in the back seat, and 3) be young and fleet-of-foot enough that I think it took me about a total of 2 seconds to run from the front of the car, grab the fire extinguisher, remove the safety, and start putting the flames out.

God bless my Sundance.......
 
Hey Crackhead...

Why not build block off plates for the vents out of either thin sheetmetal or custom formed fiberglass? If doing fiberglass you can use cardboard to create the mold you want.

You could hold them down with small machine screws and wing nuts, the wing nuts on the underhood side. IF the size of the screw head is right you might even be able to have teh screw head not be seen.

Sequoia
 
krakhedd said:
Which begs my next question - anybody have a stock hood for sale? :)
Click to expand...


Go to Wal-Mart and get 3 dollar magnet sheets, put them on the under side of your hood on the vents. 1. not permanent 2. VERY easily adjusted to allow full venting, partial venting, or no venting 3. its way cheap.
 
53guy said:
Go to Wal-Mart and get 3 dollar magnet sheets, put them on the under side of your hood on the vents. 1. not permanent 2. VERY easily adjusted to allow full venting, partial venting, or no venting 3. its way cheap.
Click to expand...

Knowing what your vents look like.... I was going to say the same thing. They actually make them in the exact size you would need.

On the original post.... Im suprised that the mileage got worse. Usually cold air is better-no? On the other hand a cold iac will richen the mixture.... which is why I relocated it on my 95 2.5 yj, with the breathing mods it needed more fuel. So, thinking out loud... I guess it do understand..... must of ran good!

So, you moved the IAT back to stock?? I would assume it wouldnt be much use on a stock motor to relocate it.
 
Last edited:
not having this issue (yet i just put a hood scoop in) id say you can change the voltage to or from the iat to fix this problem
 
canadianwheeler said:
what is a IAT sensor??
Click to expand...

inlet air temperature.
 
/intake air temp (to be anal :) )


Yeah, she ran great at WOT. She actually runs better in the cold with the stock location, but once the ambient air temp hits about 40 or 45, I start losing WOT performance compared to the relocated er, ummm......location.

I'd love to get a voltage adjuster for her, this is exactly what I was looking at, but I understand as the temp gets colder, the voltage goes down. I'd need to boost the voltage at a non-linear rate vs. ambient temp as it gets colder, to correct my ultra-rich mixture. I'd also need some sort of extremely accurate O2 sensor, or a high-resistance meter I can splice in-line with one of my stock sensors, and I'd have to have an intimate knowledge of what O2 ratio my computer is aiming for given certain conditions, etc.....seems like way more trouble than it's worth.

I'd be best off, I think, just getting some of those magnetic flaps, I dunno how well they'd work though because my ghetto-fabulous hood vents are bolt-mounted to my hood, with Ultra Black RTV as a gasket :) Basically, they're not flush, especially on the underside of the hood, and there's very little surface area for the magnets to cling to. Maybe if I used magnets around the periphery I'd be ok, but still, the way I drive, I'd be afraid of something falling loose.

I don't know, I don't have a lot of time or money right now, I work all the time (I'm at the end of my lunch break right now), and don't make a hell of a lot of money doing it. I'm gonna have to figure something out involving a voltage regulator sooner or later.....
 
canadianwheeler said:
Where is the IAT sensor located?
Click to expand...

In the intake manifold. I have 2, one of which is mounted in the airstream of my custom K&N filter conversion. I'm not using that one right now, it has a plastic plug in it (that came with the new one when I bought it).
 
krakhedd said:
/intake air temp (to be anal :) )
Click to expand...


OOPS.
At work all I deal with is inlet and outlet.
Just force of habit to write it.
 
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