Signs Of A Bad Plenum?
 

What are some common signs of this problem? I noticed my MPG during this winter have dropped from 13/14 in the summer to around 10/11 for the winter, but i'm going off of the information on the display on the head unit, I haven't actually done it any other way to test my real MPG.

The truck does have 230k miles on it, but doesn't seem to lose oil, as from the time we got it in Aug to changing it in Feb it was low by about a quart, but the oil in it was pitch black, so I assume it just maybe broke down (hopefully). No clue when the oil was previously changed.

Under the hood is really clean for 14 years old, and from the looks of all the fluids under the hood except the engine oil, all of them have been changed recently, as they still hold their color, and what not.

The transmission has been rebuilt, and I am more than certain the previous owner took care of the truck. Or so it seems lol, I am just worried with the low MPG during this cold winter, the quart loss over 6 months and about 2-3k miles, that it may be a sign of a bad plenum.

Another thing i read that could be a sign of a bad plenum is a ping from the engine, I don't know exactly what this is, but when driving everything sounds fine, but if I heavily accelerate, like a sudden quick MPH gain from like 40-55 by pushing the gas pedal heavily, I hear pinging/ticking from the engine it sounds more like the lifters are rapid clicking.

This is only while heavily accelerating tho, normal acceleration I do not get the sound.

If you look at the top of this forum you will see the end all be all plenum thread. It will answer all of your questions about the plenum problems.


As for the lower gas mileage in the winter, its not that uncommon for gas mileage to go down some because most gas stations switch over to a winter blend of gas and it will effect your gas mileage a little. Also very cold weather by it self will also effect your gas mileage. Once the weather warms up your gas mileage should go back up.

Only way to really know for sure is to pull the air intake and look down the throttle body...it's easier if you just remove the whole throttle body which isn't a bad idea because it probably needs to be cleaned anyway. Once you have it off, take a flashlight and look down towards the back of the intake manifold and see if you have any oil in there...

I may have a mechanic look at it, I think the lifter noise is just a noisy lifter, I noticed it more after a fresh oil change with new oil, the old oil was black and probably a little too old. but i'm just hoping the 2 quarts loss of very bad looking oil was because it was old and not do to the plenum.

I got the vehicle at 228k miles, and from the looks of the engine it had been pretty well kept and taken care of, so theres a probability he ran into this issue and hopefully the plenum has already been replaced lol. Because from what I read this issue usually strikes well around the 100k mark.

Iff you have a mechanic look at it be sure to tell him to look at the plenum specifically. Ive talked to dodge "master" mechanics that had no idea these things have a plenum problem

Not every engine has the problem, but, odds arent in your favor at 228 miles. Youre getting great mileage though ;) lol im not kidding. I get 10mpg year round

These things should have a "Bad Plenum" light on the dash.

Oil doesnt just disappear when it gets old... It's either leaking from a gasket or being burned in the engine, plenum or worn rings/valves.

My exhaust never smoked and the engine is clean, I don't know how long it went without being changed, regardless it's been changed and from what I can tell with 400 miles on the oil so far, there has been no loss, I will keep an eye on it every week until I 3,000 miles, I always thought over time oil breaks down and this you need to add more, I never thought that was a sign of some kind of leak.

Oil itself doesn't break down... the additives do, and it gets dirty (carries carbon and other contaminants) that will lead to component wear.

Molecules that make up the oil combine with oxygen and impurities to form several oxidation products. Many of which are acidic in nature. So it's more of a chemical change in composition of the oil "matter is neither created or destroyed" that requires it be changed at regular intervals or you get sludge and engine wear.

i almost positive your plenum gasket is blown with that many mile on your engine,i just replaced mine and i gotta tell ya,its a very poor design from dodge,the reason you get pinging is because its basically a huge vaccum leak causing a lean condition in the engine..

I'm thinking if I did it would of happened long ago, and the previous owner took good care of the engine, so maybe it has already happened and been repaired lol, for now I'll keep an eye on my oil level until 3,000 miles, I'm starting to pick my MPG back up, and it really doesn't seem like it's lost power or chugs along horribly, in fact the power alone seemed to increase after I tuned it up last week, and honestly I don't know what kind of sound it is, I'm trying not to worry much about it atm, and will just keep an eye on the things affected by a bad plenum gasket, I only bought the truck for $1500 and have put about $2500 into it cosmetically and some repairs, and I am much of a novice to replace the gasket myself and don't have the $800+ to get a mechanic to fix it.

looking down the tb doesn't really do anything for you, ya there may be oil in there because of bad plenum but there will prob be some even if the plenum if fine, it gets drawn in by the pcv, better to take a long magnet and see if it sticks to the bottom, if it does you have the stock plate

I don't know if this could bee good sign, but I just took the old spark plugs I replaced, out of storage, as I saved them, they have wear for spark plugs but they all look completely fine where they fire, I looked for any signs of both oil build up and carbon build up or any type of build up from this picture: http://forums.themustangsource.com/a...4100345224.jpg, and they all look like the normal condition, I'd say the plugs easily had at least maybe 8k miles on them

Here's a pic of the old ones:

Besides wear I don't see any sign of a spark plug going bad lol.

In the end I am just going to keep an eye on my oil consumption, among other things, I would assume that with 230k miles on the truck the plenum would of blown at least 100k miles ago, and from both the condition of the truck and it's engine, I am assuming for the most part that maybe the previous owner had this issue fixed, the truck and engine is in great shape for 14 years old and 230k miles.

Besides the really dark oil being 2 quarts low in a truck with 230k miles on it before I changed it (6 months after I got it, should of changed it sooner), I will just monitor my oil levels weekly and go from there, the old spark plugs in the truck looked in great condition with no signs of any type of fouling from carbon build up, or anything the latter. I am not sure I really hear a ping per say, it may just be me being overly paranoid at the engine reving up on RPM's, I tend to err on the worst side instead of the better side of caution, so I worry a lot.

My truck handles hill's really well, and doesn't seem to have any loss of power, as a matter of fact after changing oil, plugs, wires, rotor and distributor, battery, it seems my truck is running better than it was when I got it 6 months ago (I'm strapped for cash so some of these maintenance things took me a bit to take care of).

And it also seems that my MPG is starting to pick back up at least according to the HUD information, I have never monitored it in real time, I may try that, but atm it's reading at 11.7MPG for winter gas.

I will err on the side of caution, but for now I am going to just keep an eye on things.