Okay, not sure if this is actually an issue or not, but here goes...

After pulling my transmission and installing a new flexplate, a better torque converter, and a new transmission mount, the amount of vibrations in my cab on cold startup have increased dramatically. It's not noticeable when the engine is at normal idle speed, just when the engine is running at high idle after a cold start.

I had some vibration with my old torque converter, transmission mount and flexplate, but not this much. Here's the question: Should I be worried about an improperly balanced flexplate or converter, or just chalk it up to a new transmission mount transferring more vibration to the rest of the truck?

A couple other factors that may or may not be useful:

- The flexplate is a Pioneer FRA210
- The torque converter is a Roadrunner Billet Towmaster
- I also have new engine mounts that I installed earlier this year. I noticed a slight increase in vibration after installing them, but nothing like what I have now.
- All the driveline mounts are "Marmon Ride Control" brand.
- The vibration is NOT noticable when driving, only when the vehicle is in park or neutral and the engine is revved above idle.

Thanks to anyone who can help!

 

Have you checked to make sure the exhaust pipes aren't rubbing anywhere? I get a vibration only at high idle because mine will rub on the transmission crossmember. It goes away after the vehicle has warmed up though.

 

Thank you for the response, and that's a good idea. My exhaust is banged up and is very likely rubbing on something. Eventually I need to just redo it completely, it has about 20 different leaks in it from the awful welds where somebody deleted the catalytic converter and welded in a piece of straight pipe instead.

However, I kind of doubt it's causing the majority of the vibration. This feels like it's coming from the driveline. It's a pulsing vibration, and can be felt most in the seat and steering column. The steering wheel shakes a little at certain speeds.

I should also note, above about 2000-2500 RPM, the vibration is gone. It's only at certain speeds between 2500 and idle that it's felt. On cold startup my engine starts at high idle, and then randomly revs between half throttle and normal idle for about 20 seconds before settling down.

This truck is a 1994 F150 XL, 4.9, E4OD. Should have specified that in my original post.

 

Yeah, it's probably not your exhaust if its a pulsing vibration. That to me means something is out of balance, could be driveshaft too. But I'm a bit confused. In your first post, you said there's no vibration while driving, only during cold start-up while at high idle. Your last post you mentioned you can feel the vibration in your steering wheel at certain speeds, maybe I'm misunderstanding? But it sounds like you have multiple issues going on here if you're having random idle issues. Is the CEL coming on or flashing? Have you checked for codes?

 

Correct, the vibration is not noticable while driving. When the engine reaches certain speeds during its high idle/warmup period, you can see the steering wheel shake as the vibration reaches certain frequencies. If you're holding on to the steering wheel, you can feel the vibration through it.

 

And the CEL on this truck comes on and goes off randomly whenever it feels like it. It's never on when I cold start the truck, usually comes on and goes off randomly while I'm driving. Never checked the codes, I was going to take it in to have them checked but couldn't get the CEL to come on by the time I arrived.

I know a number of emissions components have been removed or disconnected, some of which could possibly trigger the CEL.

For what it's worth, it's not coming on any more frequently since I did the transmission work.

 

what truck and engine??
if it is OBD-ll it will have a stored code even if the CEL is not lit.
it is possible the wrong flexplate was installed, different years use different balance weight flexplates.