1996-1998 cobra engine vibration

[Ray429]

first thanks for being accepted to the group.
Second, I’ve got a 96 cobra that has a unexplainable engine vibration at 1600-1900 rpm. I recently replaced and upgraded all the front suspension, i went to full tubular setup with coil overs. I also replaced the clutch resurfaced the flywheel, and went to adjustable quadrant, cable and adjuster. I got the clutch from a local company that i have used for previous drag & race cars. I contacted them and they said it may be out of balance. So i took the flywheel, clutch, and pressure plate to them. I marked it how it was lined up on the car to make sure they would see how i had it. It was out by 3/4 oz, they balanced the flywheel and pressure plate to 0oz. The vibration got better, but its still present. Any ideals?

 

[98 svt]

Have you tried rotating the driveshaft?

 

[Ray429]

No. I marked it before I took it off and put it back in the same way. The vibration happens while the car isn’t moving too. Also pushing the clutch in while in the rpm window makes no difference.

 

[Mark99GT]

I was gonna ask about the drive shaft too. How do the motor mounts look?

 

[Ray429]

Changed to solid/poly mounts. I’ve used same k member on other cars. And I know you can/will pick up some vibration or harmonics from poly or solid mounts. But I’ve never had it cause this kinda vibration. And the car had none. Even with factory mounts that where worn.

 

[Ray429]

These are the active faults, I have removed all egr, and secondary air injection equipment. I don't see these causing the issue though.

 

[01yellercobra]

Did you go with poly or solid? Big difference between the two. What brand did you go with? If they're poly are you sure none of the metal in the mount is touching. I haven't seen it happen, but you never know.

Are you sure you don't have a miss?

 

[Ray429]

Did you go with poly or solid? Big difference between the two. What brand did you go with? If they're poly are you sure none of the metal in the mount is touching. I haven't seen it happen, but you never know.

Are you sure you don't have a miss?

So I have solid motor mount plates and poly eyelet bushings that connect the plate to the k member. AJE brand. I've crawled around under it and can't find anything touching where it shouldn't be. I did pull the plug wires one at time while running, each of them made a noticeable difference when unplugged. I don't think there is a miss.

 

[01yellercobra]

I'm guessing eyelet bushing is on the stud and sits between the motor mount and K member mount?

 

[Ray429]

I'm guessing eyelet bushing is on the stud and sits between the motor mount and K member mount?

The plate attaches to the motor mount location on the block, and it has a bracket that matches the eyelet location on the k member the poly bushings are on both side of the eyelet. A 1/2 grade 8 clamps the bracket through the eyelet center hole.

 

[01yellercobra]

That doesn't sound like a stock set up. It might just be the durometer of the bushing.

 

[Ray429]

That doesn't sound like a stock set up. It might just be the durometer of the bushing.

if you zoom in you can see what im trying to explain, lol
its not a stock type system.

 

[01yellercobra]

Yeah, it sounds like it's a mix of the set up and durometer of the bushings. There isn't as much bushing there to dampen the NVH. But I bet the engine is solid in there.

 

[Ray429]

Yeah, it sounds like it's a mix of the set up and durometer of the bushings. There isn't as much bushing there to dampen the NVH. But I bet the engine is solid in there.

It's definitely solid lol. But I've used this setup before and not noticed this issue. And I know, you will pick up nvh from solid or poly mounts. But I've not seen it cause a nvh issue that is so specific to 300 rpm. I'm wondering if i may have an issue with the crank damper.

 

[hotcobra03]

I just messed around on a friend's car.

Bad vibration sitting still and in gear sitting still..

Motor had 4 mounts,all looked good.

I took them all off, and had engine on jack,
Started engine and it was smooth as glass .

New mounts did fix problem .

So like maybe something is touching causing this

 

[04DeadShort]

Years ago my friends stock 96 Cobra developed a vibration around 2200rpm and clear up around 2900rpm. We swapped everything besides the engine. Nothing fixed it. Finally he bought a reman engine and we swapped it out. Vibration was gone. Tore original engine apart to inspect. Found #6 cylinder had a bent rod. We were both shocked beyond belief but it was obvious it was bent. Hope this isn't your issue, highly doubt it since you redid the front end suspension but this was my experience with a odd vibration.

 

[Ray429]

I just messed around on a friend's car.

Bad vibration sitting still and in gear sitting still..

Motor had 4 mounts,all looked good.

I took them all off, and had engine on jack,
Started engine and it was smooth as glass .

New mounts did fix problem .

So like maybe something is touching causing this

I just got back from ponies in the smokies, I'm going to get the car back off the ground and check again. But I checked everything for clearance and fitment issues multiple times already. I haven't found anything rubbing or touching up to this point.

 

[Ray429]

Years ago my friends stock 96 Cobra developed a vibration around 2200rpm and clear up around 2900rpm. We swapped everything besides the engine. Nothing fixed it. Finally he bought a reman engine and we swapped it out. Vibration was gone. Tore original engine apart to inspect. Found #6 cylinder had a bent rod. We were both shocked beyond belief but it was obvious it was bent. Hope this isn't your issue, highly doubt it since you redid the front end suspension but this was my experience with a odd vibration.

Did the vibration start randomly one day, or was it something that was always noticeable?

 

[04DeadShort]

Did the vibration start randomly one day, or was it something that was always noticeable?

He believes it happened during a cold crank one morning. He also believes the new MSD wires he installed a few weeks prior had something to do with it. He said the car would run fine but on occasion it would make a faint pre-ignition knock under a load. Engine was factory stock. He had just gave the car a tune-up. Fresh plugs and wires but he went with MSD wires instead of OEM or Ford Racing wires. He changed the wires back to stock type and the car did run better. But vibration was still there around 2800rpm. That's when the long journey of replacing everything began. Little over a year later after we had swapped the engines is when we finally found our answer.

 

[Ray429]

He believes it happened during a cold crank one morning. He also believes the new MSD wires he installed a few weeks prior had something to do with it. He said the car would run fine but on occasion it would make a faint pre-ignition knock under a load. Engine was factory stock. He had just gave the car a tune-up. Fresh plugs and wires but he went with MSD wires instead of OEM or Ford Racing wires. He changed the wires back to stock type and the car did run better. But vibration was still there around 2800rpm. That's when the long journey of replacing everything began. Little over a year later after we had swapped the engines is when we finally found our answer.

Dang. That sucks. I put new plugs in mine. And it made no difference. I don’t get any audible noises, even during the vibration. I think I may try to remove the belt, crank pulley and dampner. And start it back up. See if that has any effect on it. Maybe it’ll get better or worse. I’m out of things to try now. I’ll have to live with it or take the motor out.