355 Capristo bypass valve slow to close

Recently I installed a Capristo exhaust bypass valve. If the car sits for a few days, it takes a second or two for the valve to close upon start-up; if driven multiple times a day, the valve sounds closed upon start-up. When I get on it and the valve opens up, it stays open for anywhere from a few minutes to maybe 15 minutes, regardless of engine rpm or throttle pressure, then just sort of closes after awhile.

The silicone (?) vacuum lines appear to be in good shape, no kinks etc., but I'm guessing there's some sort of vacuum leak somewhere. Thinking about it, even when I had the OEM valve installed, I felt like the valve would open but not with the sort of immediacy you'd expect, not like when I first bought the car 5 years ago - it seemed "weak" for lack of a better way to explain it.

I don't know a lot about the vacuum system; any thoughts on what to be looking for or how to troubleshoot? I did search around here but didn't find quite was I was looking for, and emailed Capristo a few days ago but haven't heard back yet.

Thanks for any help.

 

I'm not sure if this is normal or not. On start up after sitting for a few days, I would imagine it would take a while for the engine vacuum to charge up the vacuum canister. The vacuum would also have to operate the secondary air valve with the car being cold.
When you say it's ok on startup after you have driven the car multiple times a day, I wonder if there is still sufficient vacuum in the vacuum canister from the previous drives? If the check valves are good on the vacuum system, then there may still be some residual pressure.

The behaviour when you "get on it" seems to confuse the issue. Surely should be plenty of vacuum during a drive. Maybe the bypass valve gets sticky when the temperatures go up?

I'm not sure of the internals inside these actuators. How do they get such a large range of mechanical movement from such a small capsule diaphragm? Also, are there helper springs in particular directions? Is it easier to open a valve than to close it (or vice versa).

When you installed the capristo bypass valve, did you have to mechanically pull/push on the actuator rod to make the linkages line up. I know in my Lotus Workshop Manual, there was a warning about not pulling on the actuator rod of the turbo wastegate with tools, but to activate it using a vacuum pump. I'm wondering if there is some physical damage to the capsule diaphragm. Capristo may hit you with this question, too, if they respond.

 

Thanks for the reply, I appreciate it. Not sure I understand this question...there were no linkages to line up; I removed the OEM bypass valve as a unit and replaced it with the Capristo unit in the exhaust assembly. I did not manipulate anything on the Capristo unit, I just installed it and connected the vacuum lines to the Capristo solenoid from a diagram I sourced from another member's thread who had done it. I'm assuming everything is connected correctly as the valve does work, except for not closing correctly as the revs drop/throttle decreases.

In another post here that I can't find at the moment, I read that after the initial charging of the system, it was supposed to maintain vacuum pressure, but perhaps it isn't uncommon for that pressure to drop after a few days? I really don't know.

 

My mistake. I forgot that the capsule and valve are installed as one and no adjustment should be required. I know some folks try to adjust the linkages on the OEM valve to stop it rattling.

I believe the only things maintaining the vacuum in the "bean can" vacuum tank are cheap plastic non return valves on the vacuum hoses. Do you know if these were changed when the hoses were changed?

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I still don't understand why the problem should occur after high rpms.

 

The only vacuum line that was changed was the one supplied by Capristo that replaced the line running from the valve to the solenoid; I haven't seen nor changed those plastic one-way valves.

Going to see if I can work on this over the next couple days. I'll try swapping back in the OEM valve and see how that performs again, against what I have going on with the Capristo valve.

 

As marked...

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I got a chance this morning to run the car this morning while accessing the bypass valve (still have the Capristo valve in place). I started the car, and after a few seconds the valve closed. While idling, I took the vacuum line off the valve, it immediately opens up as it's supposed to. I put the vacuum line back on the valve and the valve stays open, but if I manually manipulate the arm to close the valve, the vacuum in the line keeps the valve closed, but sort of weakly, for lack of a better way to describe it. I put my finger over the open end of the vacuum line while off the valve, don't really feel much, but there must be vacuum or it wouldn't keep the valve closed when I manually put it in the closed position.

Is there a way to measure the vacuum? I don't know much about vacuum lines etc. Does the above still sound like a leaky one-way valve would be the culprit? Maybe I ought to order a smoke tester? Other than the valve issue the car seems to run fine.

 

Apologies for the semi-thread hijack. Maybe it’ll be helpful though.

I’ve got a problem with my Capristo exhaust + Capristo valve and remote. With the remote set to valve open (default) it closes as soon as the throttle is sufficiently depressed - nearly the opposite of how it’s supposed to work. It sounds loud at idle and hitting the gas hard will essentially mute it.

I’ve tried recently disconnecting the vacuum hose and the valve stays open while sounding glorious at all RPMs, as expected.

Any thoughts about what would be telling the valve to close when the vacuum is hooked up and actually using anything but a slightly cracked throttle?

PS - I actually think the stock exhaust valve might have exhibited the same behavior. I was new to the car and just thought the stock exhaust was timid and robbed the engine of its proper sound but come to mind I think the original valve might have been performing identically. Is this a computer fault or something mis-wired?

 

Seems unlikely that someone would tamper with the solenoid valve wiring. Are the hoses going to the right ports on the solenoid valve?

For reference, the standard Ferrari solenoid valve looks like this with power coming in on the green/black wire:

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The ECU provides an earth when the valve needs to be opened.
Did your kit come with a Capristo solenoid valve?

Make sure you have the hoses hooked up to the appropriate ports on the solenoid valve.

 

There is a way to measure vacuum using a gauge. It is measured in psi and it takes 8-10 psi to open the stock bypass valve. The Capristo valve has reverse logic where vacuum closes it and no-vacuum opens it. Using a hand pump to operate the valve is a good first step. You can also use a hand pump to check the vacuum integrity of the system and that would be a good second step.

 

Indeed it appears the hose is connected to the original solenoid and the Capristo solenoid was overlooked by the shop. I've reached out to them to get it addressed. Thanks for the nudge!

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Aha! Easy fix. Let us know how you go with the proper (Capristo) solenoid.

 

Perfect, thanks. Picked up a Mityvac on my way home today and checked the valve; starts to close at a couple psi and fully closed at 7.5-8 psi. With the car running and the vacuum line connected, valve closed as it should be, the valve stays closed when I shut the car off and is still closed 15 min later. With the car running and valve closed, as soon as I pop the vacuum line off the valve it immediately opens up as is correct. Connecting the valve end of the line to the hand pump and pressurizing the line, it easily gets to 8-10 psi and holds it. Took the car out just to double check everything, and as before, valve opens right around where it's expected to, then stays open for several minutes before closing.

If I drove around everywhere at 6000k+ rpm it'd be great; I know people wire the valve open, but it can get somewhat droney at lower rpms under load.

Any other ideas? I haven't yet replaced the one-way valve that Ian @Qavion mentioned; is there a way to test it? Any thoughts on a next thing to try? I don't know much about vacuum system troubleshooting beyond checking for obvious things like cracked lines, etc.

 

if you have changed to the solenoid valve to the capristo one and plumbed it up correctly, it should work properly. Make sure you keep the bottom connection free as per the diagram above in Qavion's post.

 

No further troubleshooting is required. A Capristo solenoid valve must be fitted. The Capristo solenoid valve operates in the opposite sense to the OEM valve. This is the way it was designed (to match the Capristo exhaust bypass valve).

The Capristo solenoid valve is normally open allowing engine vacuum to close the Capristo exhaust bypass valve. When the Motronic ECU determines the exhaust bypass valve should be open (high engine load/rpms), it electrically energises the Capristo solenoid valve, closing the solenoid valve, shutting off the vacuum and opening the Capristo exhaust bypass valve. Loss of vacuum or power will open the Capristo valve (for safety).

 

Well, that's the thing. I'm using the solenoid supplied by Capristo. I believe it's plumbed correctly; I used the description in post #1 of this post https://www.ferrarichat.com/forum/threads/exhaust-bypass-valve-capristo-355.279806/ as the included Capristo directions show a different solenoid. The valve operates correctly, it's closed upon start up, it opens when it's supposed to with a romp into the higher rev range, it just doesn't close like it's supposed to. At least, I'm assuming it's supposed to close right up once the revs drop, in other words, function exactly like the OEM valve, just using vacuum to accomplish the opposite of how the OEM valve worked.

Maybe it's the solenoid that's the problem?

 

Sorry, my mistake, I was getting you and Ivan mixed up.

If stored vacuum can hold the valve closed for 15 minutes after shutdown, it seems as though your vacuum system is good.

Have you tried contacting Capristo with your symptoms? Have they had any previous reports of, say, sticky solenoid valves?

 

Ah, makes sense.

I sent Capristo an email a few months ago with no reply, just tried again. Hope to get this sorted soon.

 

So the valve seems fine; checked the solenoid and it fires regularly with 12V. Connection to solenoid looks good. So it appears the problem is upstream of the solenoid, which makes sense, the OEM valve was opening irregularly which led me to believe it was failing, which led me to get the Capristo valve.

So...any ideas on what to check next/what tells the bypass solenoid to fire?

 

An earth provided by the Motronic ECU on the blue/yellow wire. You should have 12 volts on the other pin (with the ignition on). i.e. on the green/black wire.


If there is voltage, you might want to do continuity checks between the Motronic ECU and the solenoid plug.

 

I have a little less than 12V on the solenoid plug with the key on. I know the basics of continuity testing, but what pin/s am I checking on the Motronic? Not trying sound like an idiot, but I've never done much automotive electrical diagnosis (which is obvious). Thanks again for any help. I'm assuming it's the ECU on the pass side of the car (95 so has 2).

 

Sorry, I didn't realise you had a 95 car. The wire colours on the solenoid plug are different. Yellow is the power, blue/red is the earth from the ECU.
The exhaust bypass valve is controlled by the left hand ECU pin 21.

Your ohmmeter leads probably won't be long enough to stretch across the car between the LH ECU and the solenoid plug, so you will need a long piece of wire (say 4~6 feet). Set up the meter something like this:

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The resistance should be very low (depending on how good your connections are). You may need a piece of lockwire or fuse wire to insert into the plug socket/s. The multimeter probes may be too thick to insert into the connector sockets.

If the resistance checks are ok, on the 2.7 Motronic car, you have the option of swapping over the Motronic ECUs. This will tell you if the LH Motronic ECU is causing the problem or not.

 

Great, thanks so much for taking the time to write that up, I really appreciate it. I’m out of town tonight but will check it tomorrow afternoon once I get home, will update as soon as I know.

 

As a preliminary step, you might want to check the resistance of your test leads with all the extensions and bits of wire attached to your leads. Any additional resistance during the actual resistance check of the car's wiring will be the resistance of the blue/red wire.

Note that there is one inline connector between the solenoid plug and the Left ECU plug. A corroded or bent pin on this inline connector might cause a high resistance. I believe the inline connector is located close to the ECU (not 100% sure).

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The parts diagram above appears to show the RH ECU. The LH ECU should be a mirror version of that.

If you don't have wires and crocodile clips and such to do wiring checks, maybe it would be best to jump straight to the ECU swap. Be very careful not to bend pins on the ECUs. Also inspect that inline connector.

 

Thanks and will do! Hope to have an update tomorrow, got in late tonight.