[Tiger2008]

I have a 2008 SE Plus. For the first four years that I have had this car, I could normally get 400 miles per tank. Now, I am lucky to get 300 miles.

I regularly have the oil changed...same brand of oil and filter each time. I have also replaced the air filter (twice) recently.

About a year ago, I changed the plugs. I was at 150,000 and thought that they needed their first change. I took out the NGKs and replaced with Champion. That was a mistake. My local service center owner/friend just about shot me. He told me to always put the factory-supplied type back in (NGK...quite a bit more $, but not terrible). It didn't run bad with the Champions, but MPG did go down. At that time, I had his crew put new NGKs back in. A few weeks before he put those in, the P1004 code came up. He ran some tests (looked good) and tried to clear it, but couldn't. I searched on here for remedies and found that cleaning the throttle bottle might help. There I found yellow gunk all inside of it. It had the consistency of ketchup. It even made its way up to the air filter. After this cleaning, the code was bugging me, so I took it to the former Dodge dealer where I bought it and asked the service manager about it. He said that there were 2 bulletins about the P1004 and that I would have to take it to the new Dodge dealer to determine what the real issue was. P1004 is a code for the short runner valve. So, after the plug change to NGK by my friend, I took it to the Dodge dealer. I hadn't had good runnings with them in the past, so I was hesitant. They informed me that the short runner valve was seized. The only remedy was to replace the entire intake manifold/plenum. They asked if I had ever changed the timing belt (no) and suggested that I replace it and the water pump at the same time. No problem! I had a Dodge 10% discount and a few other discounts, so the price wasn't terrible at all (they even gave me a free courtesy car!).

Now, replaced air filter, new intake manifold, new belt, new water pump, new NGK plugs and still losing MPG. I have never changed the gas grade...always regular unleaded. Any ideas?

 

[Part Deux]

Short runner valve seized?

That's rich... for them. No such thing

Start calculated mpg, not miles per tank. fuelly.com is an excellent tool for tracking mpg.

Winter fuel is worse than summer fuel. You will see a decrease.

Cue the magic additive that solves the world issues in 3.2...

Srsly, I would find another dealer to check things out. Something's wrong and the first dealer ripped you off. If in fact they wrote up short runner valve seized, I'd be calling your state attorney general's office. There is no such thing.

 

[Ron380]

Might be a dumb question, but have you been checking your tire pressures? Low tire pressure will lower your mileage also.

 

[Ddaddy]

Short runner valve seized?

That's rich... for them. No such thing

Start calculated mpg, not miles per tank. fuelly.com is an excellent tool for tracking mpg.

Winter fuel is worse than summer fuel. You will see a decrease.

Cue the magic additive that solves the world issues in 3.2...

Srsly, I would find another dealer to check things out. Something's wrong and the first dealer ripped you off. If in fact they wrote up short runner valve seized, I'd be calling your state attorney general's office. There is no such thing.

The V6 has a short runner valve and it is a known issue with it failing to operate properly (seized). I can only assume the OP has a 3.5L HO V6 since he also mentioned the plugs and timing belt that the 3.5L engine uses.

 

[Ron380]

It's a 2008 SE Plus, therefore it does have the 3.5L V6!

 

[Ddaddy]

It would also be helpful to know the magnitude of the MPG loss. What was it before and what is it now?

A 1-2 MPG loss will indicate much different probable causes than a 7-8 MPG loss does.

 

[Part Deux]

wth is a short runner valve?

 

[Ddaddy]

wth is a short runner valve?

The 3.5L engine (and now the 392) uses an adjustable intake that switches between short runner tubes and long runner tubes to change the intake configuration. This system is basically two different manifolds in one, controlled by runner valves. The long runner flow path is used at low rpms to gain additional torque. The short runner flow path is used at high rpms to gain additional horsepower.

 

[Black-N-Tan]

My first thought is,They did a bad job. Take it back and have them redo it....or find a local mechanic to look at what they did. Does the car sound different? Louder? We need more information.

 

[Ddaddy]

My favorite quote on the 392 dual runner intake system...

"An active dual-runner-length intake manifold helps boost both low-end and high-end power, an old Mopar trick based on maximizing the natural 'supercharger effect' of the manifold."

 

[krautmaster]

My favorite quote on the 392 dual runner intake system...

"An active dual-runner-length intake manifold helps boost both low-end and high-end power, an old Mopar trick based on maximizing the natural 'supercharger effect' of the manifold."

Mopar has always played around with long tube manifolds for torque production check out these different versions over the years:

 

[Tiger2008]

Might be a dumb question, but have you been checking your tire pressures? Low tire pressure will lower your mileage also.

Checked the tire pressures this weekend. The manual and door show 30 PSI in cool weather. They are all at 30 (The LED still comes on when they're off, still though! ). It's winter where I live in Indiana. All of this started when it was fall though. It wasn't cool at that time.

 

[Tiger2008]

It's a 2008 SE Plus, therefore it does have the 3.5L V6!

You are correct, sir. I believe this was the only year for the SE Plus with the 3.5L.

 

[tgl]

The 3.5L engine (and now the 392) uses an adjustable intake that switches between short runner tubes and long runner tubes to change the intake configuration. This system is basically two different manifolds in one, controlled by runner valves. The long runner flow path is used at low rpms to gain additional torque. The short runner flow path is used at high rpms to gain additional horsepower.

Ford also did this method. This is also how my 96 SVT Mustang Cobra engine's intake was configured. The 4-cam V8's Intake Runner Control (IRC) would activate at 3250 rpm to switch between the longer path and the shorter path. In my car, the transition became a bit more noticeable as the car aged. Fuel economy was very much worse if I stayed above 3250 rpm for extended times. When I put 4.10 rear gears in it, I had to more closely monitor my tach to keep it below that line (which corresponded to the mid-70s mph) or my fuel economy would suffer.

 

[Ron380]

Fuel economy was very much worse if I stayed above 3250 rpm for extended times.

I think I've had that problem with just about every car I've owned! >

 

[Ddaddy]

Checked the tire pressures this weekend. The manual and door show 30 PSI in cool weather. They are all at 30 (The LED still comes on when they're off, still though! ). It's winter where I live in Indiana. All of this started when it was fall though. It wasn't cool at that time.

You still haven't said what the actual MPG loss is. What was it before and what is it now?

Until we know the magnitude of the loss, it's hard to make reasonable suggestions as to what it might be.

 

[Tiger2008]

I've downloaded fuelly... refueling in the am. I guess ill post my results in about 3 days. Then, i'll give ***** to whomever has the best suggestion.