Chrysler 300C & SRT8 Forums banner

1 - 12 of 12 Posts

·
Registered
Joined
·
71 Posts
Discussion Starter #1
So I got a puzzler. Don't even know how serious it could be. I have some theories but I'd like to just provide the symptoms and see what some of you guys think about them. I recently drove without the radio on and heard and felt something I hadn't noticed before. So I have a 2005 with the 5.7, and the five speed automatic, and 3.90:1 rear end. In fifth gear I'm up over 2k rpms going 55-60mph and I noticed at that speed, if I backed off the gas and then gave it very light throttle input, like as little as possible but still pressing the pedal, I got a funny noise almost like the engine bogging and I felt a vibration in the steering wheel, not the floors, pedals, seat etc, just the steering wheel. The more I play around, I can duplicate it in any gear at almost any speed, but just letting the car coast for a minute and then feather the gas ever so slightly. If I give it more gas it goes away. If I hammer it, I don't notice it happening. If I go through all the gears just giving it some gas, then I also won't notice it. Today I got it to do the noise and vibration going uphill, by backing off the gas until I was giving just barely any throttle. I also took note when I was going down a very steep hill, I was coming to a stop sign and was on the break, I could feel it shift down through the gears and aid in slowing the car, and I felt no vibration and heard no noise. I also don't hear or feel anything if I let it coast down a hill and build speed on its own and bump through the gears under its own momentum.

Also the auto stick thing was broken when I got the car so I can't shift it manually to observe anything that way.

Curious what you guys think about what's going on. Oh yeah, if I'm cruising in high gear and get it to do the thing, it will keep on doing it for ever unless I let off the gas completely, or give it more gas. I think I noticed it cruising in that state under cruise control at 60mph today.
 

·
Registered
Joined
·
209 Posts
Best guess, the left engine mount has worn out. The left mount both pulls and pushes going forward. Usually it's either pressed down by the weight of the engine while not on the throttle or pulled on by the torque of the engine when on the throttle. When you find that light throttle point you've balanced it's weight and torque and it can vibrate. The engine mount is mounted on the front structure near the steering rack and isolated from the rest of the body so you feel it only in the steering.
 
  • Like
Reactions: Greg N

·
Registered
Joined
·
71 Posts
Discussion Starter #3
Best guess, the left engine mount has worn out. The left mount both pulls and pushes going forward. Usually it's either pressed down by the weight of the engine while not on the throttle or pulled on by the torque of the engine when on the throttle. When you find that light throttle point you've balanced it's weight and torque and it can vibrate. The engine mount is mounted on the front structure near the steering rack and isolated from the rest of the body so you feel it only in the steering.
After reading your guess, I tested the symptoms again on the way to work this morning. I noticed that if I really try, I can sometimes feel it in the floor and through my hand on the door panel, but much more vaguely than the steering wheel. I also noticed it going through a dip in the freeway where I was on steady low throttle but the car transitioned through the dip I heard and felt it, almost put me in mind of something grinding briefly, although I doubt/hope it's not actual grinding that's just the nearest sensation I can think of. I got in the parking lot and tried while in park tried to raise the rpms by feathering the throttle. I kinda might have felt the steering wheel vibrate buy I didn't hear the tell tale noise. Then I tried to rev it and back off and rev it again. I'd bring it slowly up to around 3k and then let it drop and then push the gas a little again to catch it and raise the rpm before it hit idle. Every time I hit the gas, no matter what rpm it had dropped too when I reved again, the steering wheel definitely vibrated for a moment, each time, but I didn't hear it the same way I do when it's in gear with a load on the engine.

Also listening too it, it kinda sounds like the noise is on the left, but I used to hear it from the front and sometimes kinda had the right side in mind, so I don't know if I'm fooling myself with a biased expectation after reading your guess. But so far your guess seems better than any of the theories I had bouncing around my head.

The only other guess I got from a friend was a lifter issue, but that was before I had as good a handle on the symptoms too. I can kinda describe the noise it makes as like an engine bogging, like when I drove the ten speed trainer truck at work and tried to climb a grade in too high of a gear, but just not nearly that loud.
 

·
Registered
Joined
·
209 Posts
I noticed that if I really try, I can sometimes feel it in the floor and through my hand on the door panel, but much more vaguely than the steering wheel. I also noticed it going through a dip in the freeway where I was on steady low throttle but the car transitioned through the dip I heard and felt it,
This fits the mount theory. The engine is mounted via a metal and rubber mount to the K-member which holds the front suspension, steering and engine. That K-member is mounted to the body through another set of rubber mounts. So enough vibration will first be felt in the steering and then transferred to the body. It'll also be effected by loads on the front suspension in particular loads that would twist the K-member or bounce the engine.

I got in the parking lot and tried while in park tried to raise the rpms by feathering the throttle. I kinda might have felt the steering wheel vibrate buy I didn't hear the tell tale noise. Then I tried to rev it and back off and rev it again. I'd bring it slowly up to around 3k and then let it drop and then push the gas a little again to catch it and raise the rpm before it hit idle. Every time I hit the gas, no matter what rpm it had dropped too when I reved again, the steering wheel definitely vibrated for a moment, each time, but I didn't hear it the same way I do when it's in gear with a load on the engine.
This fits as well, notice if you rev the engine quickly in park the whole car will rock to the right. This is caused by the engine pulling on the left mount while it accelerates it's own internal mass.

If my theory is correct you should be able to do it stationary. Hold the brake with your left foot, put it in drive and feather the throttle with your right. You should be able to do it and hold it just as you would while driving. Then try reverse, it's unlikely you'd be able to in reverse. The loads are opposite in reverse so it's pulling on the right mount.

Also listening too it, it kinda sounds like the noise is on the left, but I used to hear it from the front and sometimes kinda had the right side in mind, so I don't know if I'm fooling myself with a biased expectation after reading your guess.
Car noises are tricky to hear, they bounce around. If you really want to pinpoint a noise. Drive by a hard barrier or through a tunnel with the windows open. The sound will bounce off the barrier. Keep in mind that if the barrier is on the right it'll sound like it's on the right. Need to try both sides equally/separately or find a place like a small tunnel where the car can be centered.

The only other guess I got from a friend was a lifter issue, but that was before I had as good a handle on the symptoms too. I can kinda describe the noise it makes as like an engine bogging, like when I drove the ten speed trainer truck at work and tried to climb a grade in too high of a gear, but just not nearly that loud.
There's no way this is a lifter issue, that wouldn't be load sensitive. It could be a tune-up issue. A lean miss, a cylinder failing to fire during the transition from coast to load where the engine is rather lean.
 

·
Registered
Joined
·
71 Posts
Discussion Starter #5 (Edited)
This fits the mount theory. The engine is mounted via a metal and rubber mount to the K-member which holds the front suspension, steering and engine. That K-member is mounted to the body through another set of rubber mounts. So enough vibration will first be felt in the steering and then transferred to the body. It'll also be effected by loads on the front suspension in particular loads that would twist the K-member or bounce the engine.


This fits as well, notice if you rev the engine quickly in park the whole car will rock to the right. This is caused by the engine pulling on the left mount while it accelerates it's own internal mass.

If my theory is correct you should be able to do it stationary. Hold the brake with your left foot, put it in drive and feather the throttle with your right. You should be able to do it and hold it just as you would while driving. Then try reverse, it's unlikely you'd be able to in reverse. The loads are opposite in reverse so it's pulling on the right mount.


Car noises are tricky to hear, they bounce around. If you really want to pinpoint a noise. Drive by a hard barrier or through a tunnel with the windows open. The sound will bounce off the barrier. Keep in mind that if the barrier is on the right it'll sound like it's on the right. Need to try both sides equally/separately or find a place like a small tunnel where the car can be centered.


There's no way this is a lifter issue, that wouldn't be load sensitive. It could be a tune-up issue. A lean miss, a cylinder failing to fire during the transition from coast to load where the engine is rather lean.
The lifter theory came about before I had as good a handle on it. By dip in the free way, I meant kind of like a small valley. I'm going to try the test in reverse and see what happens. But even in reverse the crank still rotates the same way, wouldn't it still lift the same side of the engine?

The noise is also too low to be heard with the windows open, at any speed. The wind noise just drowns it out.

The other parts I forgot to add that I had told my friend was that holding the car still in gear and on the brake it makes the same sort of sound and vibration a lot of times but as the idle slows down, so does the frequency of the sensation and noise, so it's directly from the engine I think.

Also the car recently had an engine flush done because it was burning a lot of oil. The flush helped, I was also overfilling it cause of an error with the dipstick. But the car was clearly abused by the previous owner and the flush brought out a lot of bits of hard carbon deposits.
 

·
Registered
Joined
·
209 Posts
But even in reverse the crank still rotates the same way, wouldn't it still lift the same side of the engine?
In gear most of the rotational loading is from the driveline.
 
  • Like
Reactions: Greg N

·
Registered
Joined
·
71 Posts
Discussion Starter #7
In gear most of the rotational loading is from the driveline.
I just added some other details, dunno if you caught them. I'm definitely gonna have the mounts checked out. I like your theory, just wanted to give a little more background for the other, and why it could conceivably have an unhappy motor in general.
 

·
Registered
Joined
·
209 Posts
it was burning a lot of oil
These engines burn oil, it's probably the single biggest unaddressed flaw. The PCV system does a poor job separating oil droplets from the PCV venting. In stock form these droplets end up going into the intake manifold and are eventually consumed. Many people will install catch cans in the PCV system to catch the oil before it makes it to the intake. But I've yet to see a catch can with a drain back to the pan so they fill with oil as the oil level drops and it has to be manually dealt with.

It's my personal belief that this PCV flaw is a big contributor to things like the lifter issue. They consume so much oil that if not topped off between changes the level will get too low. This is further exacerbated by the 7000mi oil change interval if using the factory warning. An owner who never pops the hood and just goes in for a change when the car tells them to might only have 3qts left in the engine at that point.

Dealing with the PCV is on my to-do list, I don't have an ideal solution yet.
 

·
Registered
Joined
·
71 Posts
Discussion Starter #9
These engines burn oil, it's probably the single biggest unaddressed flaw. The PCV system does a poor job separating oil droplets from the PCV venting. In stock form these droplets end up going into the intake manifold and are eventually consumed. Many people will install catch cans in the PCV system to catch the oil before it makes it to the intake. But I've yet to see a catch can with a drain back to the pan so they fill with oil as the oil level drops and it has to be manually dealt with.

It's my personal belief that this PCV flaw is a big contributor to things like the lifter issue. They consume so much oil that if not topped off between changes the level will get too low. This is further exacerbated by the 7000mi oil change interval if using the factory warning. An owner who never pops the hood and just goes in for a change when the car tells them to might only have 3qts left in the engine at that point.

Dealing with the PCV is on my to-do list, I don't have an ideal solution yet.
In my case the factory dip stick broke like a lot of them do and the replacement seems to not be super accurate. If I have exactly 7qts in the motor it sits right on the add line. I noticed the oil level dropping cause of the PC and carboned up rings I think. Like close to 1000miles/qt. Then I started topping it up the the add line obsessively, and it kept blowing out the intake, and also some trace amounts into my air box. After I did the flush and changed my own oil, I noticed how the dip stick is off, and I haven't had to add oil nearly as frequent after figuring that one out. It's also now blowing oil down my breather nearly as much. But when I was keeping it over filled I pulled the throttle body once and the breather was soaked with black slime. I wonder about a lifter being dirty from the previous owner letting it get all carboned up, and I haven't cleaned the throttle body yet since getting the oil consumption under control, so I wonder if it's a bad mount/bushing, or possibly actually an unhappy engine. But I'm getting zero fault codes. I mostly hope it's not an early indication of something in the trans going bad. The car does still seem to shift good, and I would think a trans or drive line issue would get worse with more throttle input, and again I got zero fault codes?

I do also have a wheel bearing or something going bad at the rear. On another thread I talked about how I had a 7.9" V6 rear end installed in the car, and the axel seals are already dripping now, 9 months later, still not enough to effect the oil level on the diff in measurable amount, but enough to make streaks on my exhaust pipes. And also right after the diff got swapped a wheel hub went bad. The car also has 125k miles so I would think it's about due for some hubs, if it's anything like the trucks I've owned lately. And usually when one goes bad, the other is not far behind. I get a low rumble that starts about 70mph and sorta comes and goes as i increase speed, but never really fully goes away. I had it on the lift at the mechanic shop last Monday, and we both felt and shook all the things underneath and couldn't find any play in anything and the roads were too wet and noisy for him to hear the noise. So maybe next week when I'm home... But those are some of the issues on my old doo doo box.
 

·
Registered
Joined
·
829 Posts
So I got a puzzler. Don't even know how serious it could be. I have some theories but I'd like to just provide the symptoms and see what some of you guys think about them. I recently drove without the radio on and heard and felt something I hadn't noticed before. So I have a 2005 with the 5.7, and the five speed automatic, and 3.90:1 rear end. In fifth gear I'm up over 2k rpms going 55-60mph and I noticed at that speed, if I backed off the gas and then gave it very light throttle input, like as little as possible but still pressing the pedal, I got a funny noise almost like the engine bogging and I felt a vibration in the steering wheel, not the floors, pedals, seat etc, just the steering wheel. The more I play around, I can duplicate it in any gear at almost any speed, but just letting the car coast for a minute and then feather the gas ever so slightly. If I give it more gas it goes away. If I hammer it, I don't notice it happening. If I go through all the gears just giving it some gas, then I also won't notice it. Today I got it to do the noise and vibration going uphill, by backing off the gas until I was giving just barely any throttle. I also took note when I was going down a very steep hill, I was coming to a stop sign and was on the break, I could feel it shift down through the gears and aid in slowing the car, and I felt no vibration and heard no noise. I also don't hear or feel anything if I let it coast down a hill and build speed on its own and bump through the gears under its own momentum.

Also the auto stick thing was broken when I got the car so I can't shift it manually to observe anything that way.

Curious what you guys think about what's going on. Oh yeah, if I'm cruising in high gear and get it to do the thing, it will keep on doing it for ever unless I let off the gas completely, or give it more gas. I think I noticed it cruising in that state under cruise control at 60mph today.
I think you're just experiencing the MDS....cruising at 55-60 mph your MDS will activate and you'll be running on 4 cylinders. If you press the gas just slightly, you can feel/hear the engine lug. Pressing it a little more, or stomping on it, turns off the MDS and resumes firing in all 8 cylinders. I'm not sure if the EVIC on your 2005 shows when you are in Economy mode (MDS active) or Performance mode (MDS deactivated)...I think I read once that the early hemis had a little light on the instrument panel that indicated whether MDS is on or off...but you might keep an eye on that to see if it corresponds to what you're feeling and hearing.
 

·
Registered
Joined
·
71 Posts
Discussion Starter #11 (Edited)
I think you're just experiencing the MDS....cruising at 55-60 mph your MDS will activate and you'll be running on 4 cylinders. If you press the gas just slightly, you can feel/hear the engine lug. Pressing it a little more, or stomping on it, turns off the MDS and resumes firing in all 8 cylinders. I'm not sure if the EVIC on your 2005 shows when you are in Economy mode (MDS active) or Performance mode (MDS deactivated)...I think I read once that the early hemis had a little light on the instrument panel that indicated whether MDS is on or off...but you might keep an eye on that to see if it corresponds to what you're feeling and hearing.
I didn't know they had mds in 05. I know it doesn't show in that hidden evic menu. But that makes sense if it is on the 05.

I also haven't had time to pull the throttle body and clean it after soaking it in oil for a few thousand miles of extreem blow bye. So I wonder if an extra dirty throttle body could make it run shitty on eco mode.
 

·
Registered
Joined
·
744 Posts
I didn't know they had mds in 05. I know it doesn't show in that hidden evic menu. But that makes sense if it is on the 05.

I also haven't had time to pull the throttle body and clean it after soaking it in oil for a few thousand miles of extreem blow bye. So I wonder if an extra dirty throttle body could make it run shitty on eco mode.
That's not a bad idea, Greg. It only takes about five minutes to pull the throttle body.

You do have MDS, and no, there is no indication as to whether it's on or off.
 
1 - 12 of 12 Posts
Top