Weird vibration problem Watch

CurlyBen
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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
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Mr. Petrol Head
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(Original post by CurlyBen)
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
If it was engine/transmission mounts then there would be sudden shake or judder with hard acceleration. Try changing the transmission fluid and see if the problem goes away. Try inspecting for any computer error codes that might help you to diagnose the issue.
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Pegasus2
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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.
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CurlyBen
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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...
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JC.
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Audiable or a sensation or both?
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CurlyBen
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(Original post by JC.)
Audiable or a sensation or both?
Primarily a sensation, but audible (and visible - rear view mirror and steering wheel slightly buzzing) at around 1500 and 2000rpm
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JC.
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(Original post by CurlyBen)
Primarily a sensation, but audible (and visible - rear view mirror and steering wheel slightly buzzing) at around 1500 and 2000rpm
Harmonic ballancer?
Ballance weight shed from the flex plate / torque converter?
Engine mount / stabiliser?

Then you're into stupid stuff like
Heat shield?
Failed exhaust mount?
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XMaramena
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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.
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CurlyBen
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(Original post by JC.)
Harmonic ballancer?
Ballance weight shed from the flex plate / torque converter?
Engine mount / stabiliser?

Then you're into stupid stuff like
Heat shield?
Failed exhaust mount?
Interesting that you mention the flex plate. A bit of digging around shows that the 3.8 V6 changed from internally to externally balanced flex plates in 2000. My car is a 2002... but the engine isn't original, and I don't know the age of the car the engine came from. I don't think it's a mismatch in the flex plates (I've driven 15,000 miles since the engine swap without noticing the issue) but it does mean I don't know which engine it has. Harmonic balancer and engine mounts were my original thoughts... haven't worked out how to rule them in or out though. Need to get crawling underneath I think.

(Original post by XMaramena)
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.
Alignment was done about 5,000 miles ago, but in any case would only be an issue with the car moving! The vibration occurs in neutral/stationary so I've more or less ruled out anything aft of the torque converter.

Thanks for the replies!
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JC.
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(Original post by CurlyBen)
Interesting that you mention the flex plate. A bit of digging around shows that the 3.8 V6 changed from internally to externally balanced flex plates in 2000. My car is a 2002... but the engine isn't original, and I don't know the age of the car the engine came from. I don't think it's a mismatch in the flex plates (I've driven 15,000 miles since the engine swap without noticing the issue) but it does mean I don't know which engine it has. Harmonic balancer and engine mounts were my original thoughts... haven't worked out how to rule them in or out though. Need to get crawling underneath I think.

Thanks for the replies!
In the MOPAR world the engine number will decode to tell you the date the block was cast and the plant it came from.
Have you looked into seeing if there's similar sites out there for fords?

Pop the trans shield off and see if there's a balance weight sat in the bottom?
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JC.
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Another thought...
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?
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CAElite
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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.
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CurlyBen
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Been on a different island from the car recently, so haven't had a chance to have a look yet... Hopefully I'll get a bit of time to poke around this weekend.

(Original post by JC.)
In the MOPAR world the engine number will decode to tell you the date the block was cast and the plant it came from.
Have you looked into seeing if there's similar sites out there for fords?

Pop the trans shield off and see if there's a balance weight sat in the bottom?
Another thought...
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?
Yep there does seem to be a pattern for Ford castings, I'll dig around and find out what I've got. Not sure on the torque converter, but my suspicion is they probably split it at the flex plate. It was a quick and dirty job, but it was about $3000 less than anything else I'd been quoted! (Yes, it is that Mustang... most trouble I've ever had from a car!) At the same time I've driven 10-15,000 miles since the engine swap without noticing the vibration so I'm inclined to think that it's not incompatible parts but something else that's changed.

What's the 360 going into?

(Original post by CAElite)
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.
Funnily enough I've been wondering whether it's a combustion issue. The idle is a bit rough, especially from cold, and I've had some OBD codes relating to poor catalyst operation. I thought they'd been solved by changing the aft lambda sensor, but I got a recurrence the other day. I'm going to have a look at the fuel trims on the two banks and see if there's a discrepancy.
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CurlyBen
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(Original post by JC.)
...
Any suggestions for tracking down the cause of a misfire? I suspect that may be the cause of the vibration issue - I found a misfire recorded when I hooked up a scan tool, and switching to higher octane fuel (which isn't necessary according to the owner's manual) seems to have almost, but not quite, eliminated it.

Also got a couple of brake issues to look at and the roof hydraulics have failed for the third time... Fix Or Repair Daily doesn't quite cover it!
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