This is really annoying me, I can't work out what's going on. Car is a 4th gen Mustang with a 3.8 V6 and 4 speed 4R70W automatic transmission.
For the last few weeks I've been noticing a 'rumble' every now and then. At first I thought it was only in 3rd gear so just drove to keep it out of 3rd as much as possible, but I've now realised it occurs in neutral and other gears.
So, what do I know?
- It's low frequency, probably 1-2 cycles per second. Intensity is variable and I think it's related to power, rather than engine speed. It's much more noticeable at 1,500rpm when driving (which is why it often appeared when I was in 3rd), and I can't feel it well enough at other speeds to be sure whether it's the amplitude or frequency (or both) that's changing
- Testing it in neutral/park/held on the brakes: it's not noticeable at idle. About 1400 RPM it starts, intensifies at 1500, drops off a bit, peaks at 2000, then rapidly becomes unnoticeable
- It doesn't seem to occur when cold. It's hard to be certain due to the roads around here, but in neutral it doesn't occur at all from a cold start. After 20 minutes driving it's definitely there
- It doesn't seem to be affected by air con, and the harmonic balancer visually looks OK
- Transmission fluid is at the right level, pink and doesn't smell burned. The fact it occurs in neutral rules out anything behind the torque converter, and I haven't noticed any other torque converter issues
Any great ideas? I suppose it might be an engine mount, but they're buried under a lot of engine so I've not got at them yet
Could just be a loose component in the engine bay.
Try an localise it first.
Get a friend and go through the rev range with him or you listening to the engine compartment. Then try in the cabin, doors open and then shut. Don't forget it could be under the car itself.
The fact it doesn't occur when hold could mean that s parts expand as they warm, something becomes free to move.
The hot/cold thing might have been a bit of a red herring, I now think it does occur, it just tends to be much less distinct as the engine is typically under less load when cold (I live 1500' up a mountain!). I think mounts or the harmonic balancer are the most likely culprits now...
Audiable or a sensation or both?
Has nobody mentioned wheel alignment, or have I just missed it? Stress on the axle can cause misalignment between parallel wheels which can result in exactly the vibrations you're describing. Vibration sensation can alter due to phase alterations caused by increasing rotation frequency (or speed, in this sense), and alignment.
Was the torque converter from the car re-used or did the donor engine come with a converter?
The converter has to match the flexplate too. Whilst it might physically fit it might not neccesarily be balanced.
Running into this issue myself, a smallblock 360 wont fit where a 318 used to be and allow you to reuse the original converter without using a special flexplate that is balanced to compensate for the converter not being balanced.
Either way, you still need to work out what you have and get the trans shielf off, eh?
Presumably this is the mustang that you pm'd me about last year?
Ive had this happen in an older Astra at idle. (2004ish 1.6)
It used to have a kind of steady vibration that faded in and out at idle that was only noticable when the engine was hot (electric choke off). I took apart the intake manifold and inlet track and soaked it in brake cleaner then jetwashed the whole lot. It was full of crap, uneven airflow passing through the manifold can cause your engine to stutter very mildly without much hesitation or loss of power. Its a super easy fix, on a V the inlet mani should sit right on top of the block with 4-6 bolts holding it in, be sure to disconnect any breather lines whilst taking it off as they can go brittle and snap if the car is a few years old.
EDIT: Never thought, i know nothing about US fords. If the engine has any sort of variable inlet timing DONT do this fix as you will most likely **** the manifold! If its just a normal metal mani then you will be fine, its worth a try.