355 Exhaust Bypass Valve Solenoid Wiring

Good point about one failing closed. I could probably clamp the hose to isolate the problem valve. I think I’ll order two for the reason you stated. Crazy that this may have been the issue the whole time. I feel dumb because I think @yelcab even advised I change these on my header thread or maybe it was this thread.

My F1 indicator is headed to Ricambi to get a new segment display while I’m away on business and the check valves should be waiting for me when I get home. What am I going to do with myself when the car is behaving?

 

Anybody know the ID of the vacuum lines running from the intake to the vacuum reservoir? I might as well order some extra and make sure I get the right size throwaway check valves. Thanks.

 

Mainly looking at #16. Just looking for something to temporarily add a single check valve to before the reservoir without having to cut the lines on there now, so I’ll order some generic AEM tubing length.

 

Brilliant. The Ferrari check valves are back ordered. Do you think 3/8” barbs will fit the tubing properly? I ordered some already, but now worry I ordered the wrong size. Frustrating not being able to just go measure for what I need.

 

Awesome, thanks. For some reason I thought they were bigger. I got some 1/4” check valves, so they should work. I could have sworn those hoses were a larger ID and the hose leading to the bypass valve was closer to 4mm ID. My memory is acting its age.

 

Awesome, thank you. Mine were all snug and the tubing seems like it may be relatively new. I decided to order two sizes of check valves since they’re cheap and one is bound to fit. I’d love to be able to test things out while I’m home for ~24 hours this week, but I don’t think my F1 indicator will be back by then and it’s probably not a great idea to try to power the car up without any of the gauge cluster hooked up. I’ve read enough to know how picky these cars are about electronics. Appreciate the help again. Can’t wait to report that the bypass valve is working the way it was designed.

 

Mine are labeled with the same manufacturer and other data that is shown on a Ferrari parts distributor’s website that shows a photo of the tubing for sale. I guess it’s possible they are original, but their elasticity is still very good. Hard to say. I did briefly try to remove a tube from the union, but it was on there tightly and I was worried the union would be brittle and break. I guess I might as well go for it this week and if it breaks, I can order a new one during my next business trip. I should have a bunch of parts filtering in over the next few weeks. Any time I find something broken, I replace it right away. I don’t want to build up a backlog of parts I need to order “some day.” That cracked tube from the idle air valve, for example, is headed my way this week. No skimping on this car.

 

Man, you guys are insanely helpful. This forum is such a great resource. Thanks!

 

I finally made it home from my business trip and got a chance to work on the car. The factory check valves were here waiting for me and I promptly pulled the old ones off and checked them by sucking on each side. They free-flowed when I sucked on either side, so they were definitely shot. I got to work on replacing them with the new ones and was ready to go for a drive to see if we had solved the stupid bypass valve problem. I asked the wife to come with me so she could hear what the car is really supposed to sound like.

We left the neighborhood and got the car thoroughly warmed up and then I stomped on the throttle AND…none of that sweet Marinello music I was expecting. I tried again…and again…and again. The bypass valve was not doing anything. I pulled into a parking lot to make sure I hadn’t forgotten to connect a hose somewhere, but everything looked fine. I tried my old trick of engine braking at high RPM’s and then stomping on the throttle. That didn’t work either, so I immediately suspected the command was not being sent or received at the bypass valve solenoid. I headed home my tail between my legs and felt defeated.

I checked all of the vacuum lines and everything was holding vacuum where it was supposed to. When I disconnected the hoses from the vacuum reservoir, I could actually hear the thing suck a bunch of air in (I know, physics says atmospheric pressure was pushing the air in, but whatever). The vacuum portion of the system truly seemed fine, so I focused in on the electrical. I disconnected the solenoid, checked its resistance, and checked voltage at the connector. Everything checked out, so I thought maybe the connection itself was dirty. I did a quick cleaning and hooked everything back up and headed back out for a drive. I stepped on the throttle coming out of a roundabout AND…IT STARTED SCREAMING! I tried it again and again in different gears and different RPM’s. It was working exactly like it’s supposed to.

In the end, this was simply old, worn out check valves. I’m glad I chased all of the other stuff because I learned a lot, but the solution was ultimately very simple. Thanks to everybody for the help along the way. Next up is an electrical problem I’ll post about soon. It might be a tougher one to solve, but I think we’ll get there. Hoping it isn’t too much $$$

 

Just wanted to post a quick update on the bypass valve situation. After replacing the check valves, the bypass valve was working around 70% of the time. When it wasn’t working, I’d stop, unplug the bypass valve solenoid, and plug it back in. It worked each time after that. Seemed to be an issue with the connection.

I ordered some deoxit and applied it to the pins and connector plug. Since doing that, the bypass valve has worked 100% of the time. I don’t want to jinx it, but the problem seems to be completely solved.

So, for those following along, this was basically a vacuum issue where the engine was creating sufficient vacuum, but the reservoir was not holding a volume of vacuum because the check valves were allowing it to leak out. Additionally, the electrical connection to the bypass valve solenoid was intermittent and would not consistently cause the bypass valve solenoid to send vacuum to the bypass valve.

The TPS is working as it should and was never the issue. Along the way, I did tighten up a loose throttle cable, which helped eliminate a dead spot when pressing the accelerator pedal. I love how a problem in one system leads to checking multiple other systems to see what’s up. I checked for any diagnostic codes today and there is nothing active or pending. I also recharged the air conditioning, which is working very well. The car is becoming a dream to drive. Love it.