Do I have a slight misfire? Or? Video included

I was coming home from a nice 80 mile drive when cruising at 70mph I noticed a sudden faint occasional flutter coming from the exhaust. No CEL or slowdown, no loss of power but once back in town under low rpm there was definitely a flutter that would come and go. Idle seemed smooth but leaving a stoplight i now felt a slight hesitation right off idle and then everything smooths out. I hear my bypass rattling along with a whistling noise sometimes that accompanies the exhaust. It currently has capristo stage 3 with aftermarket cats. Any thoughts? Here is a video of idle and rev with holding idle for a few seconds. Right after I rev and hold it for a few seconds you'll hear me rev it again and i felt and heard a slight pop and suck noise for a second that you'll hear in the video. Thanks to anyone that can help me!


Rob

Video:

https://youtu.be/QJ1EtiVABGs

 

Wow that flywheel clutch area sure sounds like a bag of marbles. The engine itself doesn't sound bad, its hard to say revving in neutral without a load on the motor. Could have a light miss...

 

Try cleaning the airflow meter, with afm spray. Also, start keeping an eye on the wires to the crank trigger.

 

Also burnt headers make the engine backfire because the 02 sensor mixture is all bamboozled. So, since you have a capristo exhaust, it may be hard to hear but try to have a close listen when cold to ascertain..

 

What sound sound I listen for if a header may have cracked? As for the clutch/flywheel I'm assuming that's a throwout bearing?

 

It could just be the kluber grease leaked out of the dual mass flywheel, or noisy bearings. That death rattle on shutdown seem to lean more towards flywheel. It probably wont fall apart on you but it will surely sound rough.

Regarding headers, Listen for a tapping raspy exhaust leak sound, or smoke test that system and see if you have any gasket/header leaks. feel around the clamshells /all joints /bypass pipe/cat joints while the car is cold.

This is important to take care of but it may not even be your headers. Doesn't hurt to check!

 

Or the oxy sensors could just need replacment. Doesnt need to be a bad header causing it.

The death rattle is the dual mass flywheel.

 

So I see the term "death rattle".... Assuming that's not good. New flywheel? Or can I go way from the dual mass?

 

That rattle sounds like the bypass valve. When its running get a screw driver and push on the actustor arm and see if the noise goes away.

Otherwise id say its clutch related.

 

Agree with all comments here, it could reallly be many things, 02 sensor, vaccum leak, intake boot leaks post maf etc. Fuel filter, injectors, cam sensors connections. Lets list them all.

Tie the bypass open with something and go for a ride. Give it a good italian tune up 8550 rpm shifts. See how she runs after that. What year is this bad boy? If its a 95 disconnect both 02 sensors and see if that smooths her out Per Dave Helms.

Pull the plugs, see how they look and pay attention to #2 and #7.

Internet diagnosis is fun!

 

The flywheel may need to just be taken apart cleaned regreased and put back together.

Of course thats not in the ferrari workshop manual

 

Thanks for the quick responses! The car is a '95 MY, I will attempt to wire open the bypass valve but I'll get the obligatory dumb question out of the way..... Where is it located exactly?

 

On the 95 you can see the bypass easily, it's sticking out between the airboxs via a hole in the exhaust heat shield. People use chicken wire to hold the valve in an open state.

 

I have a feeling my neighbors are about to hate me just a tad lol... Will it trip a CEL by doing so?

 

I wouldn't advise opening the valve for anything other than eliminating the buzzing sound so you can diagnose your other potential issue. I'm a fan of the working bypass valve and think it adds to the character of the 355.

 

Tying the valve open temporarily is a great diagnostic way of eliminating the valve as a source of noise vs clutch area.

Since you have a 95 unplug the 02 sensors I think they are located somewhere on the inside shocktower for that model. If this makes the engine smooth then your problem lies with either a defective 02 sensors, or an exhaust leak which is throwing the mix off.


Quick and easy stuff here. If that doesn't work pull plugs and inspect ignition system next.

 

I'll try this in the morning the only tricky part is that it's so subtle.. It would be easy if i could feel the miss while revving or under normal driving but it runs perfect. It's just a flutter that I can't really explain.. Could the bypass valve being loose cause a flutter sound in the exhaust?

 

First test to see if opening it removes your noise.

If so you could tie it open and.go.for a.drive and see if you feel the flutter.

If its still there youll know.

If the noise stays its not thst if it gies away it is that.
Just quick trouble shooting.

I just used a long flat head and pushed on the actuating arm to actuate it noise went away. So I found my culprit quickly.

Or use a Vaccum pump but screw driver was faster.

I was working on my car this winter, I found my bypass had been wired open, so I removed the wire.
First time starting it after the work I did on the exhaust kit was vibrating and just making damn noise from the rear exhaust area, I remembered that stupid valve and opened it up noise went away.

Race cars don't have the bypass why must we suffer haha

 

I go with the clutch springs, flywheel needs regressing. Just my personal opinion.

 

Rattling cats.

http://www.ferrarichat.com/forum/348-355-sponsored-bradan/419762-what-noise-any-help-appreciated-3.html

 

That rattle is loud enough it shouldn't be to hard to find, Put a stethoscope on the pumkin and the cats and try what PHROGS said

 

Picked up the chicken wire and man it's a ***** to get that tied down! I have to pull the arm up towards me to open up the bypass, is that correct? I had read where I had to push down but it only opens when I get the flathead under it and push it up towards me. Also, I can also say for sure the rattling is coming out of the pumpkin. However i do notice now when I blip the throttle from idle there's a light squeal/chirp that happens and goes away instantly. Very strange..

On the bypass, how do you guys tie those things open? Mine is very stiff and I didn't see anything to tie it to?

 

I don't hear a misfire but may be more noticeable under load? Seems to idle pretty smooth. My 95 with the same exhaust setup seems a bit more choppy at idle.

https://www.youtube.com/watch?v=tYbdJLfPxfw

 

UPDATE:

Wired the bypass open and it was still there so that ruled it out. Still no convincing miss but i took it on a small drive and upon stopping at a light, once I pushed the clutch in and it went to 1k, it dipped slightly to 700rpm and the check engine 1-4 came on for just a second and went off. Pulling away when I went into 2nd gear around 3500rpm it came on again for a split second and went off again. The rest of the drive was normal... Thoughts?

 

Plug a obd in and see if your fuel trims are out. Maybe you will see 1 bank running rich or at the vary least it may have logged a pending code.