Is your 355 exhaust bypass wired open?..

If the slowdown light is due to overheating, then that is consistent with Capristo's finding that sticking the bypass valve open causes hot exhaust gases to recirculate, at least with exhaust systems that don't employ separate chambers for main and bypass.

 

think about it. the reason it was over heating was because the HOT exhaust flowing over the sensor for a longer time longer time will produce heat soak. The readings should be higher just becuase it is open. it has nothing to do with recirulation and everything to do with hot exhaust hitting the thermo. if it is always closed until 4000 rpm the temp should be lower just cruising around town. the light came on under 4000 Rpm because the open valve let hot exhaust to hit the thermo when it should have not seen any if closed. My only question is will the upper thermo throw the slowdown light if it is to hot ? if not then the cats saw more heat because the lack of air flow. this might be the reason the headers melt. so if the answer is NO it will not then the cats overheated and that is another problem you could have wiring open the bypass. i do not beleave in the sucking air back but i can see overheating causing some issues that might seem like backflow.

 

The bypass valve thermoprobe confirms for the the 5.2 Motronic that the valve is opening and closing when it should. If it is too hot, when it expects the valve to be closed, it will set a "check engine" as well if it is too cold, when it expects the valve to be open. I am unsure if it will also throw a "slow down" light in conjunction with the valve open when it expects it to be closed. Some more people would need to try leaving their valve open to test that theory.

 

The Tubi Style Evolution exhaust for the F355 (I believe) mimics the exhaust routing of the original Capristo F355 exhaust.

http://www.scuderiasystems.com/prod-special-tubi355evo.html

 

I think you are mistaken again....here is the quote from "Joefab"

"Several years ago I CNC machine a billet 2ndary Valve bypass for the top vacuum valve as a prototype new part to resell for Fabspeed customers. This billet peice eliminated the top exhaust gas vlave that stays closed for added backpressure on the 355's dual outlet headers. Well the car sounded absolutely great but my "butt Dyno" said she felt lazy and low to mid-RPMS.............felt strong from high rpm to redd-line. Well before Fabspeed reales any & all products we DYNO test and verify power and torque as normal procedure in order to offer a best possible product. Put the car on the chassis DYNO and its lost a ton of torque and power in the mid-range. It was so depressing that I ripped the pice out and restore it back to the stock 2ndary valve. FYI- so unless you only need max RPM top end race track power that involves sweeping the tach from 5700 to 7000+ just make sure your vacuum lines and exhaust gas valve is working properly. Everything else is up to you. "

 

Nope, I don't think you have a clear understanding of the catalyst protection circuit, which is also used on the bypass valve on the 1996 to 1999 5.2 Motronic F355s sold in North America...it is very likely just the Motronic "seeing" the valve stuck open when it should be closed, such as at idle or part throttle. If it is open all the time, the thermoprobe will be hot constantly...the Motronic expects it to be less hot at idle and part throttle, and will set a "check engine" light, and very likely is activating the "slow down" light.

 

yes i would think the same thing. not worth the extra sound. easier just to add highflow cats or test pipes.

 

According to Goth the thermocouple doesn't tell the ECU it's 'cold' just when it's hot when it's not supposed to be. Simply removing the thermocouple (leaving it plugged in) and capping the bung makes for no CEL.


Rob

 

Rob if the reading is to hot does it throw the slowdown light? i have asking and been getting round about answers.

 

I can confirm it will throw a "check engine" light if it colder than it should be...for example an inoperative bypass valve. I had a bad connector to the vacuum solenoid recently (Capristo bypass valve and exhaust) and the valve was not opening. I got a CE light upon the 3rd drive cycle of an inoperative bypass valve. I immediately found and repaired the connector issue using extra parts from Dave Helms gold connector kit.

 

+1, it would be nice if we can confidently confirm that too hot on the bypass thermoprobe signals a slowdown light in addition to the CE light. We have one poster in this thread who has seen this, and I do recall in another thread someone claiming to have seen this. But it would be nice to know for certain, and this is not just an anomally.

 

Are there any driving effects should the by-pass valve not be working? Like from shifting from 1 to second at or around 4k rmp or vis vera? Aside from the check engine light and fault code.

ciao,

SRR

 

i

all that i can say is that with it open you will get the PO1448 CODE. The funny thing is that the one nght i had it open the CEL came on (after a 30 mile drive) with no slowdown light and i drove about 50 miles more with no slowdown light and the cel on. In the morning a started the car pulled the code and saw why is was on. (open valve) and let it warm up. The first 5 min i always drive like a granny shortshifting and sometimes skipping gears until the oil heats up. the slowdown light came on in the first 5min of driving. the only thing i can think is that the car might run a little ricerh until the car is at full temp and that miht heat up the headers and cats enough because of fuel not burned to turn this light on. both cats are working fine and without the valve open i do not get any CEL codes like PO432 etc... after i closed the valve 5 miles down the road the slowdown light went off and stayed off for 500 miles and is still off. long story i think the top thermo saw to much heat on the slow warmup drive and turned on the slowdown light but i do not know for sure the top thermo does this if is to hot. If it does not turn on the light then the valve being open heated up my cats enough to trigger the light. there are alot of reasons why this would happen. i am not sure i really care because the car runs perfect with the valve working. i have no CEL or slowdown but i just wanted to give feedback to what my car did with the valve wired open.

thx
Mark

 

I am going to say you got a CEL with a closed bypass because the main cats/thermocouples were getting overheated by flowing all the exhaust with a stuck bypass valve and not because the bypass thermocouple was 'cold.'

I will remove mine (thermocouple) and see if it throws a light with a wired open valve. I will report back after a few miles.



Rob

 

I disagree Rob. Prior to this happening (last Friday), I had just had (the day before (Thursday)) the entire catalyst protection system checked out at Ferrari of Seattle, including an SD1 check and voltage check at each of the thermoprobes with a 'jiggle' test of all the connectors to confirm the catalyst protection circuitry was working properly (I was getting an intermittent P1448 "pending" code stored in the Motronic the prior few weeks). The connector to the vacuum solenoid valve failed immediately after I got the car back that evening, and threw the CE light the next day. If, as you assume, I had overheated cats, I most definitely would have had "slow down" lights and "check engine" codes for such. But instead, I had a "hard" (not pending) P1448 code for "catalyst bypass flap circuit" only. No "slow down" lights for overheated cats, because my catalysts were not overheating. To overheat, requires excess unburnt fuel to cook off in the cats...how is that going to happen from a non working bypass valve?...there is no change in the fuel mixture or combustion....the valve is down stream.

I would surmise that to get overheated cats requires an ignition problem or running really rich.

I repaired the connector myself, this past Monday evening and driven at least 6 or 7 drive cycles, with no further issues. Valve works fine and the Capristo howls like a banshee.