I have a 1999 F150 4X4 4.6L Auto Flareside with roughly 70k miles. My issue is I have a vibration between idle and about 1500 rpms (doesn't matter in gear or not). The engine does not miss and runs smoothly. Prior to the vibration it sounded almost like a loose heat shield rattling in the same rpm range. The vibration occurs on climbing and falling rpms in that range. I have checked the engine mounts and trans mount and appear good. Has anyone had issues with torque converter or flexplate/flywheel? Anything else I should look for?

 

Have you had your tires balances and rims checked for straightness?
Scrach that as that wouldn't cause vibration at idle only if moving.

I'm sure someone will chime in here, but how about your drive shaft not being balanced? I believe they all have weights on them and sometimes they can come off or the drive shaft being reinstalled correctly if removed.
Again just things I've heard/read on here over the years.

Just throwing out some suggestions.

Do you have factory exhaust or aftermarket? Are any of the exhaust components hitting the frame etc?

 

You say it does it even in park?

 

Park, Neutral, Drive, say 800rpms to 1500 rpms (seem the worst around 1100 rpms). It does have a aftermarket cat-back but it's not that. It's not tires or driveshaft as this does it standing still as well as driving. This shakes the whole truck and does not make any type of rattle sound anymore since vibration started.

 

I'm gonna put it on a lift tomorrow and check out some more stuff. Due to it "shaking" the whole truck and engine runs smooth I was leaning towards flexplate or torque converter but it clears up after 1500rpms which should rule those out if something is out of balance or broke. Also going to check over plugs and wires (just to rule them out) but have had the same in there for the last 15k miles with no issues. My buddy has a high end scan tool and will try that as well. Gotta say I've seen a lot but this one stumps me for now. I will report back what I find hopefully just looking for some ideas right now.

 

If it does it in neutral and park then I would think it would have to be in the motor or something related to it. Something out of balance. I wonder if maybe a weight came off the flywheel? Do they still add little weights to them to balance them?

 

Not sure...most of my experience is with pre-modular engines but if it was engine I would think the engine would break up some or miss which it doesn't. It doesn't even sputter. I know my 5.0 GT has aftermarket flywheel with weighted inserts for balance but no idea on these. I have been leaning towards flexplate (flywheel) or torque converter from the start but it's hard to stick with that due to everything being normal 1500-4500 revving or driving which you would think we get worse with more rpms.

 

Well gonna double check motor/trans mount once on lift, gonna check serpentine system including harmonic balancer, try to get a look at flywheel, and check all plugs/wires. If it's none of those I think I'm out of ideas. Thanks for input....

 

1) Idle Air Control Valve.... i.e... IAC .... unplug it at idle and see if you notice a change.

2) When was the last time your EGR to Throttle Body ports were cleaned? Basic maintenance can go a long way

 

If so, would it not shake like hell at higher rpm;s too. Never had this issue but just a speculation

 

#1 usually gives you a hanging idle if anything but worth a look.
#2 usually throws a code and runs rough but also worth a look but I usually try to clean every now and then.

Kinda what has me stumped is it still runs smooth and it really feels like it's coming from the flywheel area but also doesn't make sense that it gets better above 1500 rpms and not worse. Thanks for the added things to check out.

 

Iirc, some people have heard a "rattling" sound prior to a spark plug blowout...

 

As a check to see if the EGR is opening a small amount due to a vacuum regulator hanging open, pull the vacuum hose off the EGR and do the test.
If it clears, the EVR is hanging open and would need cleaning.
Good luck.

 

Motor/trans mounts are good, no issues with IAC or EGR system, inspection of the flywheel and torque converter showed no immediate issues. I know I failed to mention I have underdrive pulleys (been on there 2-3 years now) but inspection of those were good (not loose, distorted, or wobbling while running) but am going to try putting stock ones back on due to hearing of others having issues with them. Did not inspect spark plugs yet but that will be next on the list and if pulley swap doesn't work then probably going to pull trans as I need to change rear main seal anyways. Just figured I would give a quick update.

 

Well swapped the stock pulleys back on and didn't solve the problem. I think next step is headed for the flexplate and torque converter.