New Engine, New Vibration

Finally got my '99 4.6L stroker running this weekend ( Accurate Power kit)

Stroker now has 30.6 miles on it since I started it yesterday.

From the get go things just didn't feel right. At first I was thinking it was just running 'rough'. I indexed the distributor which I think helped with a bit of a miss, but nothing for the 'rough' feel.

I think my "rough" engine is actually a vibrating something.

While driving any slightly loose plastic interior trim pieces audibly rattle from the vibration. It's not tooth rattling, but it is VERY noticeable. Definitely not 'right'.

I did install new M.O.R.E. motor mounts. I know these will stiffer than stock, but I haven't even heard of poly vibrating like this.

Vibration is engine speed related only. Stuck it in neutral at 75 and the vibration was still there but still followed engine RPM.

Occurs with clutch in or out.

So I'm thinking the main areas that could cause vibration would be:
-Flywheel ( this was resurfaced )
-Clutch pressure plate ( New Centerforce II )
-Harmonic Balancer ( Original )

-Something internal?? ( I sure hope not...)

How the heck to you isolation these and diagnose a vibration?

Thanks for the help.

I'm getting excited about this thing now that I have felt the power I felt tonight without getting on it and with it not being broken in yet. But I'm really dubious about driving it with this vibration going on.

-Adam-
'99 XJ Sport

Why-oh-why, after all the time and money you put into a stroker engine, are you running the old vibration damper (harmonic balancer)? I'm not saying that's the problem, but it still doesn't make sense.

Question for a question: Is your stroker based on the "heavy" or "light" crankshaft? I'm not sure if the heavy one might need a different flywheel or not. I think any I-6 engine is basically neutral balanced and it shouldn't matter, but it's a thought.

Have you tried removing each spark plug wire (one at a time) while idling, to see if removing one of them doesn't affect the idle speed and/or roughness? That's usually a good way to check for a dead cylinder.

I assume you have the spark plug wires in the correct order? 1-5-3-6-2-4. With certain pairs revered the engine will run, but you'll wish it didn't. I found this out thae hard way, many years ago.

Have you indexed the distributor? I think I saw some discussion about this when you posted on the Stroker's group, but I don't remember what you said.

Are all injetors working? Have you checked them with a noid light? Are the injectors are connected to the correct wires?

Its probably just the more motor mounts I picked up the poly tranny mount for mine it lasted almost a whole week before I took it back off...The easy way to see if its the mounts is to try holding the motor at verying rpms in 100-200 levels starting at idle I have found the I6 has a sweet spot at about 14-1600 rpms then there were no vibes on mine but at idle it was horrible...
luck
themud

Eagle said:

Why-oh-why, after all the time and money you put into a stroker engine, are you running the old vibration damper (harmonic balancer)? I'm not saying that's the problem, but it still doesn't make sense.

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Thats one of those things that I'm asking myself too. The original motor only had 63K on it. Balancer 'looks' fine. So the answer is, of course. $$$...

Question for a question: Is your stroker based on the "heavy" or "light" crankshaft? I'm not sure if the heavy one might need a different flywheel or not. I think any I-6 engine is basically neutral balanced and it shouldn't matter, but it's a thought.

Click to expand...

It's the light crank.

Have you tried removing each spark plug wire (one at a time) while idling, to see if removing one of them doesn't affect the idle speed and/or roughness? That's usually a good way to check for a dead cylinder.

Click to expand...

I have not tried this yet, but I intend to. Looking at the plugs, they all look to be functioning fine, so I'm not expecting to find a dead cylinder, but I'm going to rule out the easy stuff.

I assume you have the spark plug wires in the correct order? 1-5-3-6-2-4.

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I did verify this. Multiple times.

Have you indexed the distributor? I think I saw some discussion about this when you posted on the Stroker's group, but I don't remember what you said.

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Yes. Twice :banghead: It seemed to help it run better, but did nothing with the vibration.

Are all injetors working? Have you checked them with a noid light? Are the injectors are connected to the correct wires?

Click to expand...

not familier with a noid light. I did have to re-wire the injector plugs so there is a possibility that there is a weak connection. Just don't know a good way to check it.
I would be very interested in learning more about this.

themud said:

Its probably just the more motor mounts

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Really? I have heard many say that the M.O.R.E.'s, while worse than stock, are not that bad, and way better than poly.

I might just put my stock ones back on to check if there is a change.

Thanks.
-Adam-