Last April when i bought my 4runner, i was getting about 17mpg (between 16.8 and 17.2)

Well i did the deckplate mod and it went down to about 15.5-16 and that was fine.

Well i decided to give the seafoam treatment a try, and saw almost no results. Really i am not sure if anything happened even at first.

But since then my gas mileage has been getting worse and worse, and the last fill up i got about 13.5mpg. I figured it might be the winter air, and cold temps affecting it. Or the bad quality gas in the winter.



Well 2 weeks ago I decided i would put the cap on my deckplate, and maybe get that 1.5mpg back since it was getting to cost a lot.
After 2 weeks i used up a tank of gas, and got 246miles on a tank, and 13.61 gallons of gas used.

Turns out to be 18 MPG

Huge increase. I honestly can't believe that little 4" hole is causing this much of a difference now. It originally accounted for 1.5 mpg, but is now account for 4.5

Really strange. It really makes me want to see what my mileage will be in april, with my deckplate capped off and the ISR mod reversed, just to see what it would have been last year after the seafoam.

This is just really weird though, has anyone heard of this before?

 

Most decreases due to the deckplate mod around here are due to one putting their foot in it everywhere they go. However, even if you did do that, that much of a mpg difference just isn't right. Something else has got to be up. I would get a few more tanks worth of data before I made a conclusion that the deckplate was responsible for this. It is an interesting coincidence though...one I never experienced (my mpg didn't change at all).

 

I would say you need new O2 sensors..

 

Ya I just installed my deckplate this week. I filled up my tank the same day I think and noticed my MPG's were horrible, 36 miles on 1/4 tank.

Maybe it was just me flooring it liking the loud intake but kinda scared me. So today I just thought about re-setting the ECU, dont know if it will do anything technically but does seem like its helping a little.

I also changed from 89 to 87 for my gas. Theres many things that could cause my loss in MPG and will need more time to figure it out for sure.

But I hear ya man, kinda odd

 

Actually resetting the ECU does do something. I have seen what it does on a Scan Tool (with my laptop hooked up) and it totally messes with the fuel trim. In fact, after I reset the ECU my mpg goes to heck, then comes back again after a tank or so.

Pull the NEG cable and step on the brake. It's the best way to clear the ECU immediately.

 

hmm didnt know the need for the brake. Ive just pulled it off for like a few minutes then put it back on. Well of course re-setting wiped my miles and I forgot to write it down so I need to start on a new tank and figure out why its doing so bad. Like I said I there were lots of variables so I will work on it the next several tanks.

 

Performing a deck plate mod will induce additional air flow in the engine, the o2 sensors will see this and increase the dwell time of the injectors therefore could be using more fuel to compensate. Which could comes out to more performance and lower mileage.

 

i use to get around 18mpg and it looks like im getting about 21mpg now ? if i keep my foot out of it

 

Seafoam??? What is that?

I may throw my silencer back on and screw the deckplate back on to see what happens to mine. A little reset to the ECU.......

At this point in time......I can't afford ANYTHING that deceases my mileage.
I'm at the pump all too often with that little 18.5 gallon tank.
I'll let you know what I come up with after 2 tanks because I'm sure the first will be bad.

I'll take 18-19 MPG over 15-16 and some loud noise under the hood or the tailpipe anyday..:

 

True, in a way, but if more power is available at less throttle position (which someone has yet to confirm for certain with this mod) then the same amount of fuel would be needed to do the same work; a large decrease like this just wouldn't make sense. An example would be a hill that you drive each day before and after the deckplate mod. Remember also that the ECU (in conjunction with a number of sensors) is fighting to keep the engine at a stoichiometric mixture (14.7:1) in closed loop mode no matter what.

Once someone gets past the awe factor of the deckplate mod, a 2 - 5 mpg decrease is definitely indicating another problem.

 

I noticed a significant decrease in my mileage as well right after the deck plate mod. Mine dropped to between 12.3mpg and 13.4mpg from 14.8mpg to 16.6mpg. I will have to do some more calculating before making any definite conclusions, but the drop was immediately after the deck plate install, no changes in driving habits.

 

I did my deck plate mod about 3 or 4 years ago. Before ever driving it after performing the modification, I reset the ECU by disconnecting the battery for no less than 15 minutes, just like the instructions I used from 4x4Wire said to do. Never had any drop in fuel mileage at all. If anything, I gained a slight bit. Strange to hear you guys are having these decreases. Only thing that's ever significantly decresed my mpg was a set of Bridgestone Revos!:bounce2:

 

Really? Have you tried searching?


Chadbob;

Creating the _capability_ for the engine to suck more air shouldn't drop your gas mileage. _Using_ the capability will.

Check for a dropped vacuum hose, air leak downstream of the MAF, etc. Something's making the truck run rich.

 

well i guess i forgot to say i also have a trueflow filter the isr mod and a magnaflow muffler

 

Ya I have a Trueflow and catback and Im guessing my decrease is coming from my foot work.

Is the O2 sensor going to notice the intake O2 change? I didnt know it would change the effect in the exhaust. I jus tneed to read up on that sensor I guess.

 

Everyone forgets about the simple fact that the gain in performance can't happen without a loss in mileage. By increasing the air flow, the engine must compensate by adding more fuel. It's very hard to stay off the throttle, but if you really want to increase your mileage, you'll need to do just the opposite and install a restrictor plate, reducing the air flow.....

 

Well, the O2 sensor will continue to do its job in that it'll monitor the exhaust for oxygen levels. Having more air in up front won't necessarily mean that there's more oxygen in the exhaust.

I think that CJM saying "new O2 sensors" is more about looking at the specific symptom and not getting sidetracked by the deckplate having gone in. Ya' know? A hosed front O2 sensor can lead to bad gas mileage, and a deckplate going in is just a "distraction" in the diagnosis.

 

Ok I hear ya

 

Of course, but cutting that hole in the box increases air flow simply because of less air resistance. So even if i am not giving it any more gas than before, it will suck air in with much more ease.

And with the ISR still in tact it is definitely much louder than stock, and i still got 18mpg... so it wasn't me hammering on it all the time. In fact i never really let the RPM's get high enough to here it hardly any louder than it was before the isr and deckplate mods..... Especially the past 10-12 gas tanks, i have been used the the noise as well.

And btw, i wasn't at all including my mudding and beach trips. If i include those i got at times 10 mpg.....

 

Hmmm... The 3.4L in this installation is known to be starved for air, that's been proven. If I create a way to get more air into the engine, then that doesn't mean it will _take in_ more air.


Correct, but 800CFM is still 800CFM, you have to "ask" for more airflow.

More air flow will create more fuel flow, which will create more power. With the deckplate mod the engine will get what it needs, when required, which is when asked.


Here's an extreme example...

Expand the airbox hole to 2 feet in size (theoretical)... Just because the hole is larger, doesn't mean that the engine will take in more air. But, the converse of reducing the hole to, say, nil (i.e., put the deckplate in) _does_ mean that the engine will be starved for air.

Regardless, we're talking about a mod that finds 6hp and you've seen a drop of 3.5mpg. 6hp won't cost you 3.5mpg (20% of your previsou mileage). Something else is going on.