550 trailing throttle

floormat?

 

550 Intake manifolds come loose allowing very large air leaks at the gaskets. The engine management system compensates so well that often idle speed or Ck engine lights caused by "O2 sensor out of range" are the only symptoms. I have seen your problem also caused by poorly adjusted or sticky throttle cables (either one).

But floormat is the #1 cause.

 

Due to the light throttle return on Ferrari's they are famous for the omnipresent aftermarket floor mat creeping up and ever so slightly holding the throttle open or slowing the throttle return.

Yes, those.

An air leak after the mafs are not part of the detected intake charge (vacuum leak) so the O2 senses a lean mixture and adjusts accordingly.

On a few of the cars I have seen the leakage so large in quantity that the engine had trouble maintaining or achieving proper idle speed.

The surprising part is that even as bad as the leakage was that the motor ran well in every other way.

 

If you have the ability to watch the O2 pattern on ocilloscope or on the graphic display function of the SD1 or SD2 spray the gasket area with either aerosol carb cleaner or an unlit propane torch. The 02 pattern will go ballistic.

 

Floormat's are also known as Ferrari Cruise Control.

He's a simple test. Take out your floormat and see if it still occurs

 

In my experience the leaks come from the covers (top and sides) of the intake assembly, not the main intake/head bolts. When the leak starts to become significant, I get detonation between 5000-5500 rpm. A 550 has significant heat cycling under the bonnet which I believe causes the intakes to come loose. My exhaust has also done the same.

 

That has not been my experience. It has been at the heads and quite a few of them were leaking so bad they had sucked large portions of the gasket into the port. You are correct about the heat cycles and I suspect it is the root cause.

At least on the US cars we had a campaign or recall (don't remember which) to replace the airhorns inside the plenums because they were falling out. We had the plenums off maybe 50 of the cars and never found a loose one. It is interesting that you have had yours come loose.

 

Thanks for the tip, yet another thing to have checked regularly.

 

Now that you mention it, me as well. Thanks.