Hi all,

I'm hoping someone on here might be able to help me diagnose a vibration in my car.

It started when the car was supercharged, there seemed to be one day where under load and high rpm there was a new vibration in the car which I felt through the seat.

This seems to have continued on and not gone away with anything I've done or changed, happens around 4500rpm onwards, I daren't continue revving to redline in case something gives, so I couldn't say whether the vibration reduces after say 6000rpm.

I get a huge vibration through my drivers seat, my missus claims she never feels it as a passenger but I don't know whether to believe that.

Happens whether I'm moving, stationary, in neutral or in gear. So it's not gearbox/diff related. Simply revving the car in neutral will reproduce the issue.

In terms of AFR's they all look good, nothing seems wrong there, and so far as I know I've never had det, tuned with my knockbox and only ever run fairly gentle timing with this being my first forced induction project, don't currently have a knock sensor.

Having spoken to a few mates already, it's clearly a resonant frequency of something with the engine being perfectly smooth until this point. So what could it be?

I've replaced the crank pulley with another in the theory that the supercharger belt might of ruined the harmonic dampener, this didn't really seem to sort the issue, but that said, the replacement crank pulley wasn't new itself.

I've checked for the downpipe touching anything and it doesn't.

The flywheel and clutch have recently been changed which didn't have any impact.

The engine mounts appear to have been changed before I bought the car, that said, how do you know if they're worn out already? will there be visible signs of wear?

Cam belt is fine and tensioned ok.

Water pump is new last year.

Then I'm onto actual engine components, could I have a bent rod? would this only show up at certain rpms? Is it possible to have done this with an M45?

What other engine components could potentially run perfectly smooth until certain rpms?

I'm open to any suggestions on what it could be, I did many searches of this forum relating vibrations and came across sort of similar ones but there was no definitive answer and were all in the 2000-3500 rpm range, from a couple of years back. This has been going on for about 7/8 months maybe longer so I'd like to get to the bottom of it!

Car is a '94 Eunos 1.8.

Thanks,
-Lew

 

remove mounts. inspect.
if not mounts, and not harmonic damper, might be clutch/pressure plate

 

So do you reckon there's good mileage in it being engine mounts? Is there any way to inspect without fully removing them, something I've never done on the car and wouldn't know where to start to be honest.

Clutch and Pressure plate were recently (few weeks) replaced with competition clutch products. So I sort of cancelled that out.

 

comp clutch sucks. there is a possiblility it is out of balance, or something fell off or broke off on it, seen it before many times.

also you can strap the engine to a cherry picker and raise it slightly with it still bolted down on the mounts, if they are ripped should be relatively easy to see. otherwise you need to remove and inspect. they are likely torn (also common).

 

have you done a clutch job recently?

 

The vibration started waaaayy before the clutch change, I'd say a good 8/9 months probably. Whereas the clutch was only done a few weeks ago. That's why I don't think it's anything to do with that.

Engine mounts are starting to seem like possible candidates. How much should the engine move about when the car is revved?

 

Moves more than you think it would on stock mounts.

I expected mine to be in two pieces after 120k of stock MK2.5 clutch judder, but they looked like new.

I think the mounts tearing thing is less common than generally thought.

 

Moves more than you think it would on stock mounts.

I expected mine to be in two pieces after 120k of stock MK2.5 clutch judder, but they looked like new.

I think the mounts tearing thing is less common than generally thought.

 

Perhaps you have deeper issues? LOL.

Seriously, motor mounts are likely and inexpensive/free to check. I'd start there.

Also, make sure your PPF is properly torqued at both ends. It would have been loosened or removed for the clutch job.

 

Hah... I never let her drive this car, she'd boot it, hit the vibration, and probably stuff it into a wall in a sweaty mess.

How would the PPF affect it though, if it's happening when the car is in neutral and stationary?

 

ppf supports the engine and transmission from rear. if it is loose that would also contribute to lots of vibration and wobble. though that's unlikely because if it was loose your shifter would be going up and down about a foot every time you shifted, and complete the "car sex machine" theme you've got going here

 

FTFY

 

Nope definitely don't have any shifter issues.

So, does anyone have knowledge of potential engine problems? I can't stress how smooth the engine is until 4500rpm, there's no clicking or knocking noises.

If I compression test it, would that potentially show up a bent rod? or should I look at poking a rod into the cylinders and testing the depth of TDC for each piston? will that be accurate enough?

 

I was thinking last night, if one of my HT leads was corroded where it clips onto the coil pack, could that be affecting the spark at higher RPM's? could the vibration from the engine be that cylinder 4 isn't firing right?

I'm almost certain that the car feels less powerfull once the vibration starts. Weak spark could explain this?

 

That's plausible. Is the condition of your ignition system in question?

 

The plugs are relatively new, probably 3/4 months old maybe, and they were gapped correctly.

However, the Magnecor leads I have, I'm sure that the metal on cylinder 4 is heavily corroded IIRC looked like the metal had gone a bluey colour. As for the coil pack... no idea!

I also remember once that once it sounded like I'd hit the rev limiter, almost like a cylinder or two hadn't fired right and all the fuel had gone straight into the exhaust and crackled.

 

In that case, I change my comment to "That's likely." Get fresh leads and go from there.

 

Ordered myself some replacement leads, will have to see how I get on!

 

Make sure to clean the coil pack lead sockets with a metal bottle brush and use dielectric grease at both ends.

Over here, we just cruise down to the parts store and pick up a set of leads. Are they harder to come by over there?

 

Not really, I just don't normally get much spare time atm, so it's easier for them to arrive to me! Good shout on the grease.