Rhythmic vibrations from 383

[AndrewP]

Evening everyone,

I have this annoying vibration from my engine that can be felt throughout the whole car.

A bit of history...the propshaft has had UJ's replaced, shaft has been re-balanced, engine mounts have been replaced with the Mity Mounts.

The problem is the vibration is rhythmic and vibrates throughout the whole car at around 1500 rpm and above.

The video is shot in my garage, in N (not moving) and hopefully you can see the indicator stalk wobbling/vibrating.

Any ideas?

https://youtu.be/9GUHCVVRCHs" onclick="window.open(this.href);return false;

Thanks

Andrew

[Dave 1141]

Hi Andrew,

Not trying to state the bloody obvious but are all your HT leads OK and fully connected? It's certainly got the shakes!

[AndrewP]

All new leads and plugs, new dist cap and electronic ignition.
Ive not put the spark tester on the leads to make sure each is firing however...task#1

I did run a while back a compression test and it all appeared within 5%-10% of each other.

Would 1 cylinder down case this you think? I know diagnosis over the internet is tricky, but on my youtube clip, does the engine sound like its got a plug or misfiring? (I really have no idea as I have no point of reference other than a 4 pot, and when one cylinder doesnt fire on that, you know about it as its 25% of the engine out of action..with a V8, one cylinder down is 12.5% so is it as noticeable??)

Thanks for any input.

Cheers

Andrew

[shaun]

For my two pennyworth, I had a similarish problem.
Engine not running smoothly but no obvious problems.
All plug leads appeared to be connected but after further inspection, no.8 looked ok but the metal clip that is hidden by the rubber boot had pushed back inside the boot and was not actually clipped onto the top of the spark plug. It was touching but in the fullness of time it warmed up and the boot became more pliable and contact was lost.

Solved eventually.

[Grant]

From the sound on the video Andrew I think you have 1 cylinder misfiring.. but obviously I could be wrong.. check it out

[AndrewP]

Thanks guys,

Gives me something to do in the garage tonight

I`ll pull the plugs, check them out and then do a compression check and then pop the spark tester on each and see what comes of the checks. I can also check for any tracking (with the lights off) as Id assume if there were any bad joints, then I should see the blue glow/spark jumping somewhere it shouldnt!
I might check the engine earth as well...

Wonder why its rhythmic however...if it was misfiring each cycle, then I would have thought it would be more periodic and consistent rather than the seeming building up and then down, up and down.

[thomaslk]

Before you start the deep dive with pulling the plugs etc what about a quick check with the infrared thermometer?
A misfiring / non-firing cylinder might be identified with lower exhaust port temperature.
Just an idea ...
rgds
Thomas

[slotcarone]

Post a video of the engine running while letting it idle and crack the throttle. Then we may be able to better diagnose the issue. Has nothing to do with the drive shaft or u joints. The car is not moving. Did this problem start suddenly? Gradually?

[AndrewP]

Ahhhh....I feel somewhat embarrassed and annoyed at the same time. I know I said I had new leads...well 12 months ago I did but Dave/Shaun were on the money..

So...first plug I get to and the boot disintegrates to dust! The leads are only 12 - 18 months old and 3 out of the 8 crumbled and another the actual crimp came off (whether that or the boots disintegrating caused the problem..who knows?).

Anyway...will look at getting the Accel leads with the ceramic ends. Buy once, buy well as they say as they are not cheap...plus Ive ordered a set of heat socks to go over the ends..oh and a proper crimp tool for the leads. I tried to make do with the el-cheapo ones but they need to squeeze and crimp at the same time to get a good crimp so ordered a proper ratchet set.

I`ll report back once its all on and running (smoothly I hope!)

Thanks all for the replies. Hopefully this'll sort it out.

Cheers

Andrew

[AndrewP]

Quick Q on the leads...

In peoples experience, are the socks enough to go over a set of 45 degree boots (spark plug end) and keep them from disintegrating?

I know the ultimate solution seems to be the ceramic ended ones, but the price difference between a good set of silicon leads + heat 'socks' and the Accel leads is significant enough for me to ask (I have to factor in the additional cost for shipping which increases the total cost by nearly 30%).

I dont have SS headers BTW...just the normal cast standard OEM ones.

Appreciate any opinions on this.

[RayR]

You'll probably get a variety of answers but here's my 10 cents worth.

I have had Taylor leads with 90 degree boots on for close to 20 years and 100k miles and no problems, had them all off a year ago and was going to replace but elected not to, some have discoloured but none brittle. I run most of the boots pointing down with a loop back up in the lead. I have steel headers, don't know if cast iron is better or worse for boots. Most of the running would be 'open' road driving but some town stuff including traffic jams in Phoenix and California in the summer.

[slotcarone]

Andrew I have had my Interceptor since 1986. I recently changed the spark plug wires that were on the car for probably 20 years. It was still running fine. IMO you just need a quality wire set and make sure to route the wires as originally done also making sure they are away from the manifolds at the plug end. You may have to shorten a couple of wires at the distributor end for proper fit.

[Grant]

As said above by Ray and SlotMan .. no need for anything special.. me too, I don't have any ceramic/heat boots etc.. just run the boots pointing down, front 2 cylinder cables (each side of engine) to the front and up and the rear 2 (each side) to the rear and up, keep them beneath the exhaust mani, come up away from exhaust mani as much as you can Andrew ,you need to-be hogging the front and back face of the engine, I buy the ones you put the ends on yourself and this way you can get them routed just fine Andrew

[AndrewP]

Thanks all.

New leads ordered. They are the DIY sort so I can run them to the correct length as Grant describes.

Fingers crossed it sorts the wibbly wobbly engine.

[Clive Bishop]

For my two pennyworth, I had a similarish problem.
Engine not running smoothly but no obvious problems.
All plug leads appeared to be connected but after further inspection, no.8 looked ok but the metal clip that is hidden by the rubber boot had pushed back inside the boot and was not actually clipped onto the top of the spark plug. It was touching but in the fullness of time it warmed up and the boot became more pliable and contact was lost.

Solved eventually.

Can agree with Shaun, had the same thing that plugs appeared to be all OK but when the engine was warm the air expanded in the tip of the lead and so the contact was lost. Only issue was it had to be a plug lead which is hard to get to especially when the engine was still hot!!