Bypass Valve Removed = Slowdown Light? | FerrariChat
Buy

Bypass Valve Removed = Slowdown Light?

Discussion in '348/355' started by Genyosai, May 12, 2009.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. Genyosai

    Genyosai Formula Junior

    May 28, 2008
    501
    SC
    Full Name:
    Nicholas
    #1 Genyosai, May 12, 2009
    I have a 98 F355 Spyder in which I've upgraded the headers, cats, muffler, and y-pipe. In addition, I removed the bypass valve and replaced with a straight pipe. Once again, my car is a 98 and has a thermocouple in the muffler immediately after the bypass valve. I've never had a slowdown warning until the bypass removal, so I'm assuming it's the reading coming from the bypass valve thermocouple.

    My question is....

    Will this slowdown (blinking) warning throw my car into limp mode as will a slowdown indicator caused by an overheated cat? The only reason I've removed the valve is because mine was making so much noise AND the soonest I can get my hands on a Capristo unit may be 2 to 3 weeks. In other words.... I wanted to drive my car :)

    Thanks,

    Nick
     
  2. Monteman

    Monteman Formula 3
    Rossa Subscribed

    Feb 9, 2006
    2,345
    Santa Barbara, CA
    Full Name:
    Monte
    #2 Monteman, May 13, 2009
    Does the slow down light come on as soon as you start it up? Mine has done that a couple of times after I've worked on it and then goes off after driving about 20 minutes and really warming it up. Once it's off, it doesn't come back on again. I suspect that it happens because I've unhooked the power to do the engine work and it is relearning but not certain. If it truly is the cats overheating, then it would only come on when the car is warmed up and being driven. Otherwise I suspect it's due to the work you did and it's relearning the settings. I'd be curious to confirm this from someone who really knows the ECU system.
     
  3. J. Salmon

    J. Salmon F1 Rookie
    Owner Rossa Subscribed

    Aug 27, 2005
    4,367
    VA
    #3 J. Salmon, May 13, 2009
    I have a Capristo that is a Euro version, and it lacks the thermocoupler bung after the valve. I simply zip-tied the sensor out of the way. It does throw a CEL, but it does not through a slow down or put the car into limp mode.
     
  4. J. Salmon

    J. Salmon F1 Rookie
    Owner Rossa Subscribed

    Aug 27, 2005
    4,367
    VA
    #4 J. Salmon, May 13, 2009
    The symptoms you are describing sound like the case on one or both of your cat temp ECUs is cracking and letting moisture in. You can read many a thread on it here, and it happened to me. I removed mine, cleaned and sealed the cases with silicone, and have since not had any problems. I'd take a look and see - the cracks were easily visible.
     
  5. UConn Husky

    UConn Husky F1 Rookie

    Nov 11, 2006
    4,424
    CT
    Full Name:
    Jay
    #5 UConn Husky, May 13, 2009
    Makes sense, the TC saw a higher temp when the valve was supposed to be closed and threw a CEL. Check out Goth's new exhaust system thread, in there he mentions that if you remove the TC completely and plug the hole you won't get a CEL (apparently the ECU doesn't worry about low temp, there's just a high limit).
     
  6. Genyosai

    Genyosai Formula Junior

    May 28, 2008
    501
    SC
    Full Name:
    Nicholas
    #6 Genyosai, May 13, 2009
    Last edited: May 13, 2009
    The light does not come on as soon as I start the car. It starts to blink only when I've been driving for about 5-10 minutes. My car has 3 cat ECUs. The one that I suspect is the one that does nothing more than monitor the thermocouple after the bypass valve. Since I have just a straight pipe in its place, I'm assuming that I get the blinking slowdown light because the car is detecting hot air at this point even when the valve 'shouldn't' be open.

    I am running a full exhaust upgrade; Fabspeed headers, Fabspeed y-pipe, Hyper flow cats, and Larini Exhaust. The Larini does have the bung after the bypass valve for the valve thermocouple, therefore it's plugged into the exhaust. I'm going to try disconnecting the thermocouple from the bypass valve ECU to see if that makes the light go away. Hopefully this will produce only a check-engine light, but no slowdown or limp mode. By the way... all of my cat ECUs are new (3 weeks old).

    I'll be glad when Nick's Forza gets some more Capristo bypass valves in stock :)

    --Nick
     
  7. gothspeed

    gothspeed F1 World Champ

    May 26, 2006
    10,244
    U.S.A.
    Full Name:
    goth
    #7 gothspeed, May 13, 2009
    +1 ........ :) ............ what is causing the OPs CEL is the absence of the 'by-pass valve' itself ...... when the valve is missing the cats and o2 sensors will not see the exhaust they want to see at low RPMs and will throw a code.

    My CEL light works fine ........ but I have only the by-pass 'thermocouple' out of exhaust circulation. I have had it like this for well over two years and still no CEL :). My car is a 5.2 motronic.
     
  8. Genyosai

    Genyosai Formula Junior

    May 28, 2008
    501
    SC
    Full Name:
    Nicholas
    #8 Genyosai, May 13, 2009
    One thing I forgot to mention is that I have NOT thrown an actual check-engine as of yet. I suspect that will come after a few more starts. I only have the blinking slowdown indicator which I'm sure is being generated by the bypass valve TC ECU.

    Goth:
    Enlighten me. What does OP stand for?

    Thanks,

    Nick
     
  9. gothspeed

    gothspeed F1 World Champ

    May 26, 2006
    10,244
    U.S.A.
    Full Name:
    goth
    #9 gothspeed, May 13, 2009
    OP stands for 'original poster' or 'the guy that started the thread' ;) ............. I have only researched the 'logic' of how our exhaust sensors cause a CEL ............. if you are getting a 'slow down light' ....... it is caused by something else all together .......... it could be bad connections or a bad cat ECU ....... :eek:
     
  10. Genyosai

    Genyosai Formula Junior

    May 28, 2008
    501
    SC
    Full Name:
    Nicholas
    #10 Genyosai, May 13, 2009
    Last edited: May 13, 2009
    Latest update:

    I think maybe the slowdown light was coincidental to my bypass valve removal and actually had nothing to do with the slow down light starting to blink. I put the valve back into place today, started the car for the first time, and the light began to blink immediately. I tried unplugging the TC after the bypass valve to see if maybe it had gone bad, but the light still blinks. I tried unplugging other TC connectors, but the light still blinks.

    According to the owner's manual, a blinking slowdown indicator means that the exhaust gas temps are getting too high and to drive slowly. A slowdown light that stays on means the the temps have reached a dangerous level and driving should be stopped immediately.

    Well, I doubt the exhaust is getting too hot, causing the blinking light as soon as the car is started. Does anyone know if this blinking light at first start also indicates a failed TC or ECU? I hope not an ECU, as I recently replaced all three of mine a few weeks ago. Do the thermocouples ever go bad???

    Thanks,

    Nick
     
  11. Genyosai

    Genyosai Formula Junior

    May 28, 2008
    501
    SC
    Full Name:
    Nicholas
    #11 Genyosai, May 15, 2009
    I replaced the thermocouple at the bypass valve. At first, the slowdown still blinked at startup. I killed the power for 10 minutes, reconnected power, then let the car idle for 10 minutes. After all of this, the light was still flashing. So, I decided to take it for a spin anyway, knowing that there was no real overheating issue. Well, before I got out of my driveway, the light stopped.

    As of right now, after a 20 minute, hard drive; I have no slowdown light and no check engine!

    I'm now running fabspeed headers (coated), fabspeed heat shields, fabspeed y-pipe, larini exhaust, and K&N mufflers. I can feel the top-end power increase since the fabspeed y-pipe install. The exhaust note on the top end is much nicer, too.

    I think I'll install the fabspeed carbon air boxes and air-intake muffler delete next. Anyone have any ideas on an ecu upgrade? Powerchip of course claims a 30hp increase AND a money-back guarantee if not satisfied.

    Could it hurt to try??

    Thanks,

    Nick
     

Share This Page