weird engine vibration at low RPMs

[tevake]

I know that I've brought this all on myself. I was out driving my 1980 SC last week, and thinking to myself that WoW this car sure is running good. In fact its been running well since the engine was out last winter for a new clutch, and seals, etc.
Now I didn't say this out loud and certainly not to any one else. But sure enough shortly after I thought this is when I started to notice this off sound / feeling vibration in the engine. Its from about 2K rpms up to 2700 rpms. then it smooths out sounds and feels fine. You can feel it with the engine in neutral at those revs. or while driving in gear. It kind of peaks at 2300 revs tapering down as the revs climb thru 2800 revs. There is a slight flatulent , off song sound in the exhaust note, while this is happening.

Its been 5 or 6 days now. First I checked the engine running in the dark to see if there were sparks jumping around. The wires are less than a year old and it looked fine, all dark in there.

Today I pulled the plugs to see if any were fouled. They all seem fine, so I cleaned them up and reinstalled.

Then drove 12mi or to my usual gas station. topped off with a little more than a half tank and added a bottle of techron injector cleaner. Thinking about some of the different stations I had filled at recently, H'm.

Well that hasn't smoothed it out yet.

Whats next to check? Sound familiar to any one?

Thanks for any help!
Richard

[DRACO A5OG]

While the engine was out was the engine mounts replaced?

Was the fuel filter changed while in there?

[tevake]

Yes new motor and trany mounts. fuel filter is a little more than a year old. Fuel Accumulator is fairly new. Injectors are one year old.

This was a sudden onset.

[bkreigsr]

sounds ignition related. my guesses:
check to see all wires are fully seated in the cap,
they have good contacts on the dizzy ends.
check for carbon tracks inside the cap,
and lastly replace the cap.
Bill K

[Joe Bob]

Does the engine sound like a playing card in the spokes of a bicycle? Kind of like ffffpppphhttt?

Check your headstuds.....

[Josh D]

Are you running the A/C when it's doing this?

[tobluforu]

Did they balence the clutch/PP, etc together? The reason I ask is because I have the same thing right after I did my clutch job and I did not balence them, damn!

[tevake]

There is no AC on the car.

The noise is in the exhaust sound. And just in that narrow rev range.

We did not balance the clutch when installing, but I have use the car a lot since this was done, and it has been running smoothly till now.
It does feel like a balance issue, except for the exhaust sound.

I just had a look in the dist. cap it and the rotor are fairly new and looking good.

I am hoping that a bit more driving with the injector cleaner will have some effect.

Thanks for the replies
Richard

[kidrock]

Originally Posted by joe bob

does the engine sound like a playing card in the spokes of a bicycle? Kind of like ffffpppphhttt?

Check your headstuds.....

+1

[snbush67]

Richard,

Did you get this sorted out? I am coming to Kauai for business next Wednesday and was trying to remember who on this board was from there.

Shane

[tevake]

Hey Shane, Its just me and Jed ( ARCS in AK) that are active on the forum over here.
Where on Kauai are you going to be? Heading up to the north shore by any chance? Will you have any free time? Maybe we can get together.

Yes the SC is running well again. It was the spark plug wires. I took the very old crusty ones off my project car and switched them for the less than one year old top of the line OEM ones in the coupe and viola smooth running.

Let me know what your plans are.

Cheers Richard

[snbush67]

I will be in Lehui for a project, just on Wednesday and Thursday. I would love to meet up and talk story. I have never been to your island before. I was going to offer to bring along the MSD plug wires I had before my rebuild if you wanted them, but I guess you got it worked out.

Anyways, I am very flexible if you and possibly Jed wanted to meet up, let me know where is best, I will have rental wheels.

[tevake]

Well if you haven't seen Kauai before maybe you would like to drive up to the north shore for a look around and dinner at our house in Haena wed. after work. I could meet you part way here to show you some cool back roads and sights.

Cheers Richard