355 Bypass Valve Removal Question

The bypass valve on the 5.2 triggers a service light because there is a 3rd thermal sensor where the bypass pipe joins the muffler.
Its job is to moniter exhaust temperature and if it sees a constant high temperature (ie. when the bypass valve is supposed to be closed) or low temperature (when the bypass valve is supposed to be open) the ecu triggers a check engine light to alert you to the defect(assuming the bypass valve is malfunctioning).
The 2.7 does not have the sensor and therefore there is no warning light.

 

Exactly.

 

As Carm said, it is likely your light bulb for the CE light is removed. When you first turn the ignition on, does the self test of the CE light work? Does the CE light illuminate? If it does not, then the bulb or circuit is not functional.

 

My bypass valve was definately the rattle in the rear. I played with the valve while the car was running and all of the rattles went away. Also, the car definately has a much better sound, more grunt, while holding the valve open.

Has anyone figured out how to remove this or wire it open and not get the engine light?

 

Yes, if the thermocouple senses an "always hot" condition, it will trigger the CEL with the code P1448. The sensor is there for a 'stuck open' condition, as this is what affects emissions. A 'stuck closed' condition will not trigger the CEL. This is my experience with the 5.2 motronic.

BTW don't take my word for it.....anyone can verify this by pulling the vacuum hose off the bypass valve vacuum diaphram. One would then drive past the RPMs noted in the manual where the bypass valve would 'normally' activate..... and find the CEL will not trigger. One can do this as long or as many times as one wants to prove this out.

Disclaimer/note: it may be possible to overheat the primary cats or cause other engine/exhaust issues if done for an extended period...

 

Two methods: One it to remove the CE light, not recommended, since the CE light is trigger by several other functions that just this one, so you would lose those warnings.

The second is some sort of replacement exhaust temp ECU boxes that will always give the correct signal, so they will not trip the CE light. This way you only lose the cat temp function to the CE light function, all the other CE light functions remain. Not sure where you get the ECU boxes, but threads have been posted before. They are made for various cars (this issue is not a Ferrari specific one), but not certain about Ferraris. You might have to mod one to work (changing the plugs).

 

Installed my 355 Challenge sleeve replacement for the bypass valve on my 95 355 last night. Pretty straightforward process:

1) Remove airboxes
2) Remove black heat shield
3) Loosen lock nut on bypass valve
4) Remove two long bolts connecting bypass valve to forward and rear exhaust
5) Disconnect and plug vacuum hose

The next, and only tricky part, was removing the "Y" piece of the forward exhaust in order to slide the replacement sleeve into place. Because the sleeve is recessed on both ends, you need extra clearance to slide it into place. Removal of the "Y" piece of exhaust makes this possible. Two long bolts on each side, similar to the ones holding the bypass valve in place. When all done, simply reassemble.

The whole process took me abut 90 minutes. If I had to do it a second time, and not figure things out as I went along, I think I could do the whole job in 30 minutes. And by the way, it DOES sound great!

John

 

We need this with an O2 simulator for the '99

 

Sounds like Fabspeed may have them. But I don't think it is O2 simulator that you need, it is related to exhaust temp ecu. But he may mean exhaust temp ecu, someone needs to ask them directly.

 

HI
You definetely want TO TRY to fix the rattle on the 2ndary valve 1st before you eliminate the "vacuum actuated exhaust valve". Yes any 355 screams even louder and sounds even better BUT Fabspeed machined up a replacement part the simply replace the flapper valve for all 355 cars.

We were about to make 100 sets of these on the lathe and CNC mill. But I told my guys after driving the car several hundred miles over 2 weeks that the 355 felt lazy and slower. Essentially my BUTT DYNO said something felt weaker with this bypass. Sure enough the chassis dyno showed it lost valuable torque and power at all RPM level and broken even later.

We never got any CEL lights from this modification. Perhaps something else is wrong on that car. We do have screw in 02 simulators for all 2ndary O2 sensors available to trick off CEL lights on cars with catbypass pipes or faulty catalytic converters.

If you are looking for additional top end power and more sports car sound our 2ndary 2.7 and 5.2 2ndary catbypass pipes top pipes will work great on these cars. Try to fix the flapper valve. I would guess that FErrari Challenge cars used the straight pipe as the Pierburg valves are $500 each and on a race track from 6000 to 7500 RPM power with the proper chip the cars made power while saving Ferrari money and simplifying cost and design.

happy holidays

Joe

 

Joe,
Can you explain the comment: "Sure enough the chassis dyno showed it lost valuable torque and power at all RPM level and broken even later." Particularly the part about "...and broken even later."

 

So does this mean that on my 98, I can remove the thermocouple sensor, cap off the thermocouple inlet on the exhaust, replace my bypass valve with the challenge pipe, and I should never get the CEL? Sounds logical, considering that the thermocouple at this point would never read an always-hot condition.

--Nick

 

The center thermocouple can be removed and capping the bung with no CEL ............ though on the 5.2 if you remove the bypass 'valve' itself you will get a CEL ........ not because of the thermocouple but because the primary exhaust path sensors will see errant air at lower RPMs.

 

I've never had a problem with myne, just luck I suppose.

 

Who else here has an issue with a slight exhaust leak where the bypass valve mates to the y-pipe and muffler? My stock valve leaked a little, and now my Capristo leaks a little (I test for exhaust leak before I reinstall the heat shield and air-boxes). I even have new bypass valve gaskets (the two, large metal o-rings), and the two spring-bolts are as tight as possible; still a faint leak.

Should I care??

--Nick

 

Your y-pipe is pre-loaded at an angle .......... try loosening both upper 'pinch clamps' at the header collector ..... on the header side of the flanged interface. These should allow the front flare fittings to 'slide' where they want to be. Closing the 'side gap'.

If they do not slide under their own 'pre-load' .......... then the side where your leak is ....... is the side that needs the forward flare to slide aft (rearward) ........... AND ......... the opposite side needs to go forward ....... use a 'tool' and move each flare in appropriate opposite fore/aft directions with some 'encouragement' from that tool .......... until the sidegap is closed at your by-pass valve ........

 

That makes sense, so my problem must be that I'm no longer running stock headers, y-pipe, muffler or cats. The only pinch clamps I have left are on the cats. As far as the y-pipe to header is concerned, all I have are free-spinning flanges for the two bolts at each collector.

I tried completely loosening the the y-pipe from the headers and then bolting the bypass valve bolts first. Then I tightened the y-pipe to the headers since these fittings use a "real" gasket. I still have a very small leak. The other thing I've noticed, however, is that the y-pipe side of the Capristo bypass valve has a deeper/wider guide where it actually inserts a little into the y-pipe. The Capristo valve isn't inserting completely into the y-pipe as if maybe my Fabspeed y-pipe opening isn't quite large enough for the valve to seat inside it fully.

I'l try removing the valve and grinding out the y-pipe opening a little more to see if the bypass valve will eventually insert fully so that the bypass mating face actually touches the y-pipe mating flange.

Thanks,

Nick

 

What headers are you running? I am fairly certain you still have 'pinch clamps' that hold the forward 'flare' at the upper collectors. The upper pinch clamps still use the heavy flanges. Post a picture if you can.

 

I have Fabspeed headers. The headers have the flare built in at the upper collectors with the bolt flanges before the flare. The stock headers had the pinch clamps which held the flared adapter to the upper collector. Basically, if I were to 'try' using the flare adapters from the stock setup, I'd end up with two flared areas of the collector.



--nick

 

Wow .......... you were not kidding ...... I wonder why fabspeed welds these on ? ....... the factory left them 'unwelded' for this type of adjustment (to align the y-pipe) ................. but there is still one glimmer of hope ... but you may end up with tips that stick out 'unevenly' from the bumper ........ this adjustment may either fix the tips or make them worse .....

As you mentioned you still have two pinch clamps at the bottom (aft end of cats) ...... loosen these two bottom pinch clamps and tilt the muffler forward on the side of the gap ............... this may also need encouragement with a 'primal tool(s)' ................ the pinch clamps should slide along ............. I hope this works ...... if not ...... I guess you may have to resort to your other plan of 'grinding' .....