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Discussion Starter #1
Hey everyone, been gone for a bit due to life, but still loving the T&C. But now I've got a couple of issues. It has popped a P0456 code, and I've found that it's an Evap System code. Yeah, fun to figure out what it might actually be. Now, on my last tank of gas, I only got 13.3 mpg. Could the two issues be related? Or is it more likely that the bad mileage is due to probably needing spark plugs. It's got just over 100k on it, and I'm guessing they haven't been changed.

Thanks!
Adam
 

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Well, they could be related. If the engine is pulling fresh air when it is supposed be be a vacuum sucking gas fumes, it would richen up the mixture to compensate, and then add the older sparkplugs with a wider gap not burning as it should, bad gas mileage could occur. Check the return lines for cracks and sponginess, replace where necessary, get it back together properly. After you find whatever and change the sparkplugs and would recommend sparkplug wires, too, disconnect the battery to clear the code and allow the engine to restart the computer at factory settings instead of trying to overcompensate for the current rich condition, may reset itself and run better faster.
 

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It has popped a P0456 code, and I've found that it's an Evap System code. Yeah, fun to figure out what it might actually be.
Starting in model year 2002 Chrysler used NVLD (natural vacuum leak detection) to monitor evaporative emissions. You could have a leak in a hose in the evaporative emissions system. Some of the ends of the hoses are on the top side of the fuel tank and pressed against the body so access is difficult. I do NOT think you have a hose leak.

This is a video that shows how to test Chrysler NVLD systems. The vehicle in the video is NOT a minivan so individual components for your vehicle are located in different positions on the chassis but the theory behind operation is the same.

http://www.youtube.com/watch?v=5YjhQO2EHvw




This link discusses how NVLD functions on Chrysler vehicles. Scroll to 03-14-2010, 12:20 AM netnathan


http://www.lxforums.com/board/f77/code-p0456-small-emissions-leak-209389/


I suspect that you do NOT have a leak in an emissions hose. I think the NVLD switch has malfunctioned and is not passing current when cooling occurs in the fuel tank, a slight vacuum is created and the switch closes but is NOT passing an electrical signal to the PCM (powertrain control module). Over time I believe corrosion and/or carbon buildup on the switch contacts occurs and causes the switch to fail its function.

This is not easy to diagnose and requires a patient, methodical approach. I do NOT suggest using the shotgun approach and replacing components randomly. You will spend a lot of money needlessly.




Now, on my last tank of gas, I only got 13.3 mpg. Could the two issues be related? Or is it more likely that the bad mileage is due to probably needing spark plugs. It's got just over 100k on it, and I'm guessing they haven't been changed.
I think your higher than normal fuel consumption is unrelated to the NVLD problem / code P0456 stated. I would suspect the intake manifold absolute pressure (MAP) sensor is failing, giving erroneous values to the PCM which is causing the PCM to enrichen the fuel mixture to the fuel injectors more than necessary. I would suggest using a facility that has the proper equipment to look at the freeze frame data of the PCM and analyze the fuel trim values. Hopefully this would show a manifold absolute pressure sensor that is failing. I would ask others on this forum: can one spot a MAP sensor failure through analysis of fuel trim freeze frame data?
 

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Can we take for granted you've eliminated dragging brakes, change in your typical driving route, and your driving habits? Any maintenance done just prior to this?

At 100k miles the plugs are due so you won't loose anything by changing them. However, whether or not that is the cause of that much of an MPG loss is questionable unless they are so bad you feel a miss and have starting problems. They'd have to be very bad in my book. The P0456 is even less of a culprit target.

As AllanC suggested the best thing you could do is to get a capabale scanner on it that can read fuel trim data. It will show what is happening and when. If you go the shotgun route, the upstream O2 sensor would be first on my list. It is the key component in determining air/fuel mixture. Proper AF mix is essential to good mileage.
 

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Before shotgunning parts, I'd replace the plugs and wires. Possibly the O2 sensor. But start with the plugs & wires first. That gives you a good base to work from.

If fuel mileage is still low, then further diagnostics will be needed.
 

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Doug D said:
Before shotgunning parts, I'd replace the plugs and wires. Possibly the O2 sensor. But start with the plugs & wires first. That gives you a good base to work from.

If fuel mileage is still low, then further diagnostics will be needed.
+1
 

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I would treat the evaporative system code as a separate issue. Generally evaporative emissions do not affect driveability or fuel economy.
This was the changeover period from LDP to NVLD. Your underhood vacuum map label should indicate the components and the routing between them and would ID which system you have.
 

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Discussion Starter #8
Thanks for all the replies. I will start looking into all things suggested. I probably won't be able to ge to the plugs until this next weekend. One if you mentioned starting issues. It does occasionally take longer cranking to get it to kick over. I will check to see which system it has and plan on doing the plugs and report back.

Thanks!
 

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Discussion Starter #9
Oh, just for curiosity, what is everyone's choice for spark plugs? I tend to go with NGK but like to try and stick with OE when I can.
 

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I would go with the OEM recommended plug. They function fine for 100K miles and that's hard to beat given the labor intensive plug change.
 

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Discussion Starter #11
valiant67 said:
I would go with the OEM recommended plug. They function fine for 100K miles and that's hard to beat given the labor intensive plug change.
That's my plan. I just haven't taken time to see what OEM for this one is yet. Haven't gotten a service manual yet either.
 

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Discussion Starter #13
ImperialCrown said:
There is probably an underhood label with the plug type and gap listed on it.
Took a quick look when I went to lunch and its there. Didn't take enough time to determine which evap system it has.
 

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Discussion Starter #15
Sorry for the long time getting back to this. Due to busy family life and a slight fear of getting to the back plugs, I have yet to change them. I do have the new plugs, and I did have enough time last Friday to pull one of the fronts for a look. I'm certain these are a big part of my mileage issue as the electrode was domed, the gap was wide, and it was very grey all around. I'm hoping I get them swapped in the next couple of days. If I get a chance and think about it, I will post a pic of the plug.
 

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If it has Mopar printed along the plug wires, there should also be a date code. The last digit is the year of manufacture. If they are older than 3-4 years old, I would replace them as well.
The correct Champion spark plug should be RE14PLP5.
 

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When is the last time the air filter has been changed?

Also check the gap on the old spark plugs to see what they are worn out to. If the gap is larger then .80 then I would suggest replacing a coil pack. I have seen coil packs burn out because of a large gap on the plugs.
 

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Discussion Starter #18
I changed the air filter the last time I changed the oil or that would have been my first guess. I will take a look at the wires and the gap when I get back in there. Thanks guys.
 

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Discussion Starter #19
Honestly, how tough is it to get the backside plugs changed? I know I'm going to be doing it blind, and that doesn't really bother me too much. I've got long, skinny arms, so that should help. Is there anything I can take off to make it a little easier? Thanks.
 

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Removing the wiper linkage module may offer a little more room, but won't really give you a direct visual.
mWRxVNZTTnCKnscOuFk53Jw.jpg
It does have to be done by feel. Follow the plug wire to the plug (on a cool engine) and remove it from the plug (try to remember how for in you reached for each plug). Do one plug and wire at a time.
If you lose your reckoning on where the last plug was, they can almost be seen easier from underneath or possibly with a mirror.
The first time doing this is always the learning curve.
 
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