bypass valve 355

Not a good idea to wire it open. Some will tell you it is ok, but it is not meant to be wired open and could cause potential problems later on. Capristo sells an aftermarket one that is a much better design than Ferrari. There is also a small adjustment that can be made to the valve sometimes to relive the rattling--A search here will show a few threads on it...

 

Wiring the valve open will not cause damage to the engine. What it will do is trigger the check engine light. Mine has been wired open for years, and the motor is PERFECT. It simply reduces backpressure, nothing more. The only problem is, I have to reset the CEL before a smog check can be performed.




Darrell.

 

DMoore: what's the code that comes up- p1448? just wondering.. thinking my car may have been wired open by previous owner. thanks

 

Wiring open on a 1995 car with 2.7 motronic will NOT set a "check engine" light, as there is no thermo probe in the Y section bypass pipe to detect the exhaust temperatures rising and falling as the valve opens and closes (1996 to 1999 5.2 Motronic cars will set a CE light). But, it would be preferable to have it operating correctly, as I think it the jury is still out on possible problems having it wired open could cause long term. First off, you CAN adjust the pre-load tension on the valve, and this can often get rid of the rattle. I suspect it is rattling mostly at idle? Remove the valve from the car, and you will see it has a turn buckle sort of arrangement and you can loosen the nut and add a couple turns of additional spring tension on the valve and reinstall. Try that first. If no luck, you can simply replace it. They are about $1600 for a factory one, or about $950 for the Capristo aftermarket replacement. Note the Capristo works slightly differently, and you have to make a very simple change to the vacuum lines. Threads are posted here on how to accomplish that if you search. I did a write up a few months ago.

Note also, there are a lot of things that can rattle other than the exhaust valve, to include the heat shields on the Y pipe and exhaust manifolds, along with the heat shields on the catalysts.

 

P1448 Catalyst Bypass Flap Circuit

Could be a problem with the exhaust valve not working, so you need to see if it may be wired open. Check that it is functioning properly, and if not, inspect the vacuum lines, and solenoid electrovalves (not sure how you test those electrovalves). Also possible the exhaust ECU is bad (that was my problem). You can verify that the exhaust ECU is bad by simply swapping the two plugs that go to it, with the two plugs that go to the exhaust ECU for the right side catalyst. The two ECU's are stacked on top of each other in the right rear area of the bumper, near the air pump. Just remember, you need to move BOTH wires from one ECU over to the other ECU, and vice versa. One plug is for the thermo probe, the other is for the power and signal back to the Motronic.

Exhaust ECU's are readily available from FoS or Ricambi America. Early exhaust ECU's are black plastic housings filled with black expoxy. The later ones are black plastic housings filled with green epoxy. The later green ones became available during 360 production. They tend to last longer, and the expoxy is less likely to crack and allow water intrusion. But, the green ones still fail, as I have had all green ones on my car since they were replaced in 2003, and one failed last summer, but no cracking of epoxy that I could see.

 

What happens if you remove the vacum line from the bypass valve, is it safe?. I read a thread on the 360/430 that it dramaticaly improves the sound (they need sound improvement badly).

 

360/430 works the other way arround, removing the vacum will make the valve closed all the tima with potential engine problems.

BTW: In europe we dont have the thermo probe in the Y section bypass pipe and can wire it open without any error...

 

Replace it with the straight challenge pipe and plug the vacume line with a golf tee or small bolt. Part #170683

 

Yeah, i have a UK spec. car, no thermo probe or third cat ecu. Keeping the bypass open is no problem