Wired bypass valve open, pro’s and con’s

Before putting the 355 to rest for the winter I decided to try wiring the bypass valve open. I basically wanted to se if I should repair it or if I could actually live with it open all the time. I asked about the possibility of error codes at when picking it up after yearly service and the mechanic told me that all European cars can be set open without any problem. This is my conclusions:

Since I am driving a lot with my ears, listening to the sound of the engine, it made the driving easier since the sound is more consistent.
Sound is better and I love it while driving at moderate speeds and on twisty roads
On highway however it gets annoying and I wanted the bypass closed
I have decided to fix the bypass to get rid of the buzzing but what I really would like to have is both! I would like to decide when to have it open all the time and when it should be on automatic. Any on have an idea of how to do this?

 

You are talking about the exhaust bypass on the top pipe when looking through the black hole right down the middle right? Mine is completely removed and a piece of straight pipe bolted in place. I have seen it for sale once before but cant remember where.

 

I have one...It's made by Tubi. Machined stainless steel. Sounds awesome!

 

On a Motronic 5.2 (don't know the pin number for 2.7 but the principle is the same) the exhaust bypass valve is commanded by the wire on pin 64 (cf diagram).
When the conditions are met (full open throtle and rpm above 4000) the ECU open the valve by grounding pin 64.
So, you can add a switch which connect the valve wire either to the ECU (normal mode) or directly to ground (forced open mode). cf modified diagram!

Quite easy, you can even install the switch and do that from the passenger compartment because the ECU and the wire are there. It should be noted that under certain conditions (iddle, ...) vacuum may be not sufficient to fully open the valve. Also, no CEL with Euro cars ....
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Has anyone actually tried this? Sounds like an interesting project for the winter. Would love to hear from someone who has done this, where do I find the correct wires, ideas of where to put the switch….

 

I have done it for temporary investigation .... my exhaust valve is now maintained open by a pipe collar (cf picture). It is also an easy way which can be installed and removed even with air intake installed.

The wire you need to access to can be found at Motronic level (cf picture). This one is behind the passenger seat (LHD car). It is one of the wires which go to the white connector you can see close to the ECU. I do not remember the color but it is easy to find disconnecting this connector and Motronic one, and checking continuity with pin 64.
In my case the switch was flying but it can be easily installed in the ashtray ... if you are non smoker !!
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Thank you for sharing this information. How come you didn’t keep it that way? Didn’t it work as you expected or was it for some other reason?

 

A nice solution would be to have it connected to the sportmode setting, maybe this would be posible?

 

I removed it from my car because I enjoy the sound with the valve open and have never been bored by it doing too much sound. Also, on mine, the valve was barely open at idle because of vacuum level. So I choose the solution you have seen ... can be removed and installed in minutes.

It should be very easy to connect it to the sport mode selection. The sport mode selection switch is, among others, commanding the light in the dash board. A simple solution could be to connect a small 12V-1RT relay in parallel with this lamp, and then to use the relay contacts to ground or not the valve commanding wire. Depending you have a F1 or not, the logic and thus the contact you have to use on the relay will be different (not familiar with F1 but it seems that light is on in sport mode while it is on in comfort mode with manual gear). I can provide you with a diagram if that is not clear enough.

 

Hi Eric
It all sounds great to me, got to try this out!
My car is an F1, and as you point out the light is on as I set the car in sport mode. If you have the knowledge and would be so kind to help me with a diagram on how to make the connection I would be very grateful. I am not very good when it comes to car electronics but have a friend who are working with electronics, I think he can help me out.

 

Hi Johan
here it is and some explanations !!
- the two wires connected to the sport mode light can be easily found at dash pod level. This wiring diagram is from early (95) non-f1 355, I have not found more recent diagram, but the principle is there.
- the relay should be a small 12V relay availlable in every electronic shop. I would't use a standard car relay because you do not need a 30A breaking capability for valve commanding and the coil of these relays has a low resistance. I would choose a relay with about 1 kilo-ohm coil resistance to be almost transparent (small amount of extra current) wrt sport mode selection switch circuit.
- do not forget the diode, in the correct orientation. It prevents high voltage spike to be generated at the exact moment the relay is opened.
- the contacts of the relay must be connected exactly as the manual switch on my previous diagram. I have represented a connexion for a F1 car in the comfort mode. When the switch is set in sport mode, the light is on, the relay is commanded, the valve wire is grounded and ... the exhaust valve is open !!!
Happy mod and keep me aware
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Great info, thanks Eric. I'll post back after trying it out.

 

Now this is what I was looking for. Does anyone have a picture of the actual wire? I am going to do this over the winter also. But that Tubi pipe also sounds good. Anyone got pictures or a link?

 

My exhaust has been wired open for quite some time now. Only problem is the CEL is triggered the 3rd time it is started( US cars). Mine is up for smog test so I will unwire it, have the CEL reset and the car tested. Yes it will be wired open as soon as I return from testing. I did notice quicker throttle responce at lower rpm's. That never hurts. It seems the car likes a bit less backpressure than stock.


Darrell.