2008 GT, new exhaust, big mileage drop, help!

[Raven6]

Hello, I am new to this forum.
I have a 2008 Mustang GT, 4.6L 3V 5Spd manual.
Previous engine mods were:
K&N Aircharger
AiRaid throttle body spacer
Jet MAF sensor

With this setup I was consistently seeing an average of 19-22 MPG during all normal driving conditions city and hwy. Oh, and 87 octane always.

I added on 8/6/09:
BBK stainless steel Long tube ceramic coated headers
BBK Off-Road X-Pipe
Dynomax Racing Bullet Cat back exhaust kit.
MIL Eliminators

Now I am getting 16-17.5 MPG

I thought after all these years and reading that mileage should stay the same or improve slightly. My exhaust also smells like it's burning very rich.
Can anyone give me some insight?


Thank you in advance!

 

[302GTS]

In all honesty, are you getting on it more often/revving higher before shifting than normal? When I first got my exhaust done, I was constantly shifting at 3,000 rpms, and going WOT any chance I had, just to hear the sound of it. I know it sounds dumb, but it might be the issue.

 

[Raven6]

STOMP ON IT!!

LOL, I understand, I did that on the first day and saw the mileage dip down to 15.8. No today, I topped off, reset everything and went about some "normal" driving. I made sure to watch my shift point and not WOT, especially from low rpm. I am running between I'd say about 1,800-2000r's out to about 2,800, maybe 3 max at times, which is the way I always drove it. Unless I was on it.
I'm not sure, what it is. I suspect a possible exhaust leak only because I start to hear a little bit of a tinny air sound coming out of the rear left if I go past 3k-r's at all

 

[Justin01]

I'm sure a tune would help. Certainly couldn't hurt it. The long tubes will change your mix ratios so it's best to have it done anyway.

 

[Raven6]

Yeah, the constant things I am hearing is "tune" and give the engine time to adjust, drive it, and the computer will catch up.

Maybe that's the case. I am a little frustrated though, bbk advertises all of this stuff as "tuneless upgrades" So does Jet and K&N. I shouldn't have to tune it to make it run right, just to take full advantage of all the upgrades. I just don't understand why I've lost 3-4 MPG. I am going to send my opening comment to bbk and see what they say, and summit as well, I bought from them..

I appreciate all the feedback, a community of like minds, and 2nd eyes is priceless!

 

[Justin01]

dropin k&n - ok
tb spacer - ok
mid-pipe - ok
catback - ok

Changing the manifolds to a long tube header.......well I've always heard you need a tune with that one. I needed one on an older stang (98) after the swap to get the air:fuel corrected. Don't know how much things have changed, but if you want the full advantage of your new toys and want them to operate as efficiently as possible, a tune is what you need to look at next.

 

[mustangdave]

Does your off road x-pipe have the O2 sensors reinstalled in it? If not, the computer cannot adjust your air/fuel ratio.

 

[Raven6]

I agree, You need a tune to take full advantage and I plan on going there, I just didn't figure I needed to at the time of install. I would have waited a little longer so I had the coin to do it all at once. Now I have to scrape some bucks up to get a programmer. Luckily summer is almost over and I can probably have it done by next season.

I talked to Summit racing and they suggested I take out the JET MAF, unplug the battery for 10 minutes, put the stock MAF back in and see if there is a difference. He also said it sounds like an exhaust leak, which was my 1st thought. I didn't expect my installers to be that incompetent though...
I will take the car to another exhaust place on Monday for a free inspection.

I have an email into bbk as well, I will update this thread with their response as well.

 

[Raven6]

O2 answer

Yes all the sensors are in place and MIL eliminators have been installed.

You know, at one point the installer swapped the front sensors with the rear sensors because his cables weren't long enough. "He goes they look the same expect they are different colors, so I just swapped them so the cables would reach." I told him they were color coded for front and rear and specific and I verified that. So he then had to extend the cables to hook them up right, I am wondering if he forgot to put the sensors back in the right places.. I would think I would have a check engine light if he didn't
The sensors are blue pair and green pair, does anyone know if the blue pair is front or back or vice versa? Then I can double check myself to see if that's messed up.

 

[Raven6]

ok, so turns out, it's the leads that are color coded, not the sensors themselves. They do have different part numbers on the sensors themselves. I'll post that so if anyone ever needs it you've got it.
Front o2 sensor middle number: 9F472
Rear o2 sensor middle number: 9G444

I will need to disconnect the sensors and make sure they are correctly installed.

BBK got back to me as well, this is their response:
I find that the more bolt-on's I install, the harder I drive to enjoy them....

I wonder if the car needs a tune now that you've added all of the stuff with the aftermarket MAF. It may be limiting the adaptability of the ECU.


There's that MAF again. Gonna give that a try.

Word.

 

[Justin01]

The MAF seems to be a constant not a variable. If you had it on before, it shouldn't be a problem after exhaust mods. Probs with the O2 sensors, wires, or MIL eliminators will throw the engine check light. I had a bad MIL elim from dallas mustang, then after the fix had a bad/faulty wire connector after the x-pipe install. Would think you would have gotten a check light if they screwed that up. I'm still voting for a tune, but if you find out what it is, please give me some closure.

 

[mustangdave]

How can your car throw a code if you have MIL eliminators? ...which I didn't even know they made for these cars.

 

[Justin01]

How can your car throw a code if you have MIL eliminators?

My case was the MIL eliminators were bad, but it was for a 98 GT. The MIL eliminators were not telling the computer the O2 sensor was functioning normally cause it was a busted unit.

 

[mustangford289]

Longtubes

I have longtubes and a tune....there is no noticeable change in fuel economy from stock. I do have the forward o2 sensors installed and the rear sensors are shut off in the tune.

 

[Raven6]

Last night I put the stock MAF back in and went for a drive. I got a solid 19 highway driving. I usually get about 21 on that drive but this is better then the 17 I was seeing before. The exhaust still reaks and gives one a headache if the wind is right. I am working on the tuner, doing research and what not. I plan to do a normal commute tomorrow, check the mileage, swap the MAF's again, and repeat to see if there really is something with the Jet MAF.
Regardless, I think I am going to need a good tuner to deal with the mods and tweak the air/fuel, not to mention monitor for other issues.
I would hate to scrape together the money for the tuner and tunes and then find it's something else. The only other option I can think of would be to take it to the dealer or someone else with a computer. The dealer will probably shun me considering the off-road x pipe.

 

[Raven6]

Mil Elims

They don't make them for the current cars per say. You can still buy them for the 96-04 models. I did some research and found that the sensors haven't been changed. I verified that the 04 mils worked for someone else, then I bought them for myself.

 

[Justin01]

They don't make them for the current cars per say. You can still buy them for the 96-04 models. I did some research and found that the sensors haven't been changed. I verified that the 04 mils worked for someone else, then I bought them for myself.

A tune will eliminate the need for those, if it's an issue for you. You are doing the mileage estimates with a pencil right? Not the computer I hope? The exhaust stank will go away after some more miles. Sucks how many things effect gas mileage when you are trying to figure out comparisons though, headwind, temp, right foot, traffic, etc.

 

[Dan02gt]

Long tubes move the front O2 sensors too far down the exhaust path, which throws off your A/F ratio. This is because the exhaust has more time to cool before it reaches the sensors causing false readings. From what I understand they need to be around 12" from the exhaust ports to function optimally. Like others have said your going to need a good tune to even get back close to what you had before.

 

[Raven6]

Dan, Thank you for that response, that makes some sense. I could understand needing a tune to some extent, but details like that help me to grasp the specifics. These sensors are I'm guessing about 14 inches further down from where they were before. That issue combined with all of the changes made, as other members have pointed out, I could use a tune.

Mileage estimates I am doing with both computer and pencil. My computer is pretty close surprisingly.

Justin, you are right about the tuner eliminating the need for mils. I bought the mils with the intention of not getting a tune until next season. They were to trick the computer and get rid of the engine check light until then. There's some money that should have been put towards the tuner. It's a learning experience, I prefer getting paid to learn, not the other way around


I am erked now because I am strapped and can only spend about 400 bucks on the tuner. The ones I like are 600-1200 bucks, which means buy one now, and spend more later one the cooler one.... sigh. Maybe I'll be able to sell it, or does anyone have one for sale?

 

[Raven6]

New question

Ok, I have to verify one more thing. I talked to a CS Rep at American Muscle regarding a SCT tuning setup and my MAF issue.

The guy on the phone recommended I return the JET MAF, pocket the money, and rely on the stock MAF with a tuner. He said that even though I am reading a broader range of flow and may be adding more air, I will have to add more fuel and that I am really not going to see a benefit to running the Jet MAF until I go super charger anyway.

This makes some sense to me, however I did see a mileage and performance increase when I installed the JET MAF, that was Pre-exhaust anyway.

I am getting the Tuner either way, returning the MAF makes it easier on the pocket book. But should I? The tuner and custom tunes can accommodate for the non-stock or Stock MAF's either way. So I guess the question is, is the guy right about performance? That until I supercharge there isn't a need for a better MAF anyway? I do notice that procharger uses the stock MAF on their setups, so the stock one may even be good enough in that situation.

So return it or not?
Recommendations? Votes?