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Vibration at idle after some exhaust and engine mounts

X

XJFLYER

NAXJA Forum User
Location
Nevada
I've got an intresting vibration that has developed in my 4.0 after completing a recent header and engine mount upgrade. When at idle and in either drive or reverse there is a significant vibration that develops throughout the vehicle. Shakes pretty bad, vibrates mirrors and steering wheel. When under the vehicle the exhaust looks like it vibrates about an inch either side of center. The funny part is once the engine warms up the vibration decreases significantly. There is no issues while in park or neutral and there doesn't seem to be any trouble with the engine. It seems to be idling smoothly at about 800rpm. And the moment I add a little power the vib goes away completely. And I'm using rubber mounts not poly.

What I've tried. Through research and trying to eliminate possibilities.

Burned 2 cans of carb cleaner searching for vacuum leaks. -> none found.

I have tested fuel pressure as I had recently also changed out the fuel pump. -> pressure normal.

Plugs are pretty new. And coil pack is only a year old.

Torque on new engine mounts seem good.

New steering pump, cause it seemed to be worse when at top center steering. ->no change

This weekend I'm going to swap out the fuel injectors to 4 port A-6 units. I was planning on doing this anyway, but maybe it could help my vibration issue too.

Any other ideas that anyone can think up? I'm at a loss on this one.

Thanks for your help.
 
The upgraded motor mounts are causing the vibes. When I added Ironman mounts with poly bushings I could feel the vibes, but I eventually got used to it and don't notice it anymore. I wouldn't sweat it, the mounts you have now are miles ahead of the OE design. I would recommend doing the tranny mount asap though, if it is badly worn it will cause the new motor mounts to wear faster.
 
You can try loosening all the engine mounts, then move forward and reverse a few feet, then tighten everything back up. Ford used to make us do this, they called it "powertrain neutralization". Might help. But as said, my poly mounts also vibrate some at idle.
 
Last thing you changed was the motor mounts and now you have vibes, I'd have to go with the others and say it's the mounts. I would hold off on the injectors until you have isolated the vibes and either fixed them or determined they are not detrimental.
 
Thanks guys.

I'll order a tranny mount this week. I've never done one of those before, better hit YouTube up over the next couple days. I'm planning on having her apart this weekend for a steering upgrade anyway. Might as well take care of it all at the same time. I'll give that "power train neutralization" a try. Maybe that will help.
 
Tranny mount (sounds a bit gross to me) will be a piece of cake. Just jack the tranny up, remove the cross member and you have access to the mount to replace it.
 
what did you torque the engine mount bolts to? My brown dog mounts didn't get torqued down. They were tightened just enough to move the washers on both sides. Maybe you have them torqued too tight
 
I think they called for 7lbs. I'll look it up. I know it wasn't much. Basically the same on these mores, just enough to to squeeze the rubber a little.
 
I have the exact same issue with my '99. Engine mounts are new and transm. mount is new. I even tried different engine mounts (Brown dog, oem Mopar, oem aftermarket) but the rough idling still remains. I also played around with loosening and tightening bolts. That made it a little bit less annoying but never really solved the problem.
 
KingIce said:
I have the exact same issue with my '99. Engine mounts are new and transm. mount is new. I even tried different engine mounts (Brown dog, oem Mopar, oem aftermarket) but the rough idling still remains. I also played around with loosening and tightening bolts. That made it a little bit less annoying but never really solved the problem.
Click to expand...

Rough idling has nothing to do with engine mounts
 
The MORE mounts I installed 10+ years ago use off the shelf rubber control arm bushings. They are stiff compared to the factory mounts, but will soften over time.
 
Its possible to preload twist into the exhaust at the header/downpipe flange, which can cause clearance problems. Try loosening the two bolts, sometimes youll see it jump free from the twist... Then try again. Its hard to explain...
 
I haven't been able to work on it yet over the holiday season. Been busy running around with family stuff. There may be something to the "rubber break in" idea. When the vib first started it happens all the time at idle in drive or reverse. Now as the engine warms up it only seems to happen when I'm slowing down at idle at intersections and such. When it just sits it's fine while warm. Still vibrates pretty bad when she's cold though. But still only at idle in reverse or drive.

I'm planning on getting under it again second week in janruary. I wanted to try the "balancing" idea. Add that to some more driving around broadening the rubber and we may have a solution.
 
Found the dam vibration. It was the a/c unit's clutch quitting! I cannot believe I spent so much frigging time digging around for it to be something that simple. I'm going to yank it off as soon as I can get the coolant dumped. Hopefully, this will be the end of the idle vibrations.
 
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