355 Capristo bypass valve slow to close

Strange. The signal from the ECU should be the same throughout this period (no voltage, no effort expended by the ECU). All you have done is interfere with the vacuum system. I'm not sure of the internals of the solenoid valve, but I'd say the solenoid valve shouldn't have changed state, either. Engine vacuum just goes straight through the valve.

The solenoid valve is providing vacuum (some at least). Wouldn't this point to a faulty bypass valve? Did you inspect the vacuum hose running from the solenoid valve to the exhaust bypass valve? Could it be leaking when the car warms up? I assume the kit comes with a new hose, however.

That's the inline plug for the RH ECU. You need the one for the LH ECU. There is one for each ECU. Anyway, thanks for the photo. It's good to know what it looks like. From what you've told me above, however, it would be difficult to come up with an electrical-related theory. I have one, but it's far-fetched.

Maybe if you have time, could you locate the pin on the LH inline plug related to the bypass solenoid? I know it's pin 9, but I don't know how the plug is oriented. Pin 9 could be in one of 4 locations (see diagram below)

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Just put one probe of your ohmmeter on pin 21 of the LH Motronic ECU connector and the other probe on one of the 4 positions show above (in pink) on the fixed (ECU) side of inline connector. This will be good for future reference (and I could add this detail to my wiring diagrams).

 

Just wondering if your Secondary Air solenoid valve is leaking vaccum when the car has warmed up.

Another suggestion. Temporarily clamp off the vacuum hose on the Secondary Air solenoid valve, preferably after the car has warmed up). It may otherwise generate a CEL.

See "X" in the photo below.

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@IvanRico 's photo "borrowed". Thanks Ivan.

 

My mistake. I assumed a 2 x 12 pin configuration. That plug is a 3 x 8. But having said that, there is no way I can match up the OEM wiring diagrams with that plug. In the diagrams, the wires are in two groups. The wires/pins in your photo are in 3 groups. Anyway, thanks for the pic.

Going by the OEM wiring diagrams, the pin 9 should be in one of two spots

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Yours looks like this:

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That means that all three of my 2.7 engine-related wiring diagrams are wrong.
By the way, your photo appears to show the solenoid side of the plug?



Did you check all the pins to see if any others matched?

Yes, sorry didn't make it clear that I was worried the (OEM) secondary air solenoid valve was leaking (so less vacuum for the exhaust bypass valve solenoid valve). Clamping off the exhaust bypass solenoid valve vacuum will of course stop the exhaust bypass valve working.

It's hard to see in the parts diagrams and on the car, but there is a thin metal pipe welded to the secondary air (thicker pipe). The rubber/silicone pipe from the exhaust bypass solenoid valve going to the exhaust bypass valve capsule should be attached to this metal pipe. I've shown the pipe below, but it doesn't look like it's hooked up.

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You may have to remove some airbox plumbing to see the pipe. Anyway, if that's ok, maybe you could repeat the clamping exercise (on the secondary air solenoid vacuum pipe)?

(EDIT: it's possible that your aftermarket silicon pipe bypasses the metal pipe and runs straight to the exhaust bypass valve capsule)

 

The workshop manual doesn't show that thin metal pipe, but a direct connection between the solenoid and the bypass valve.

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Your installation may be the same as the image above, in which case, you won't have to worry about any damage to the thin metal pipe. If you can't find the thin metal pipe under all the airbox stuff, you could try temporarily running the vaccuum hose directly to the bypass valve. The metal pipe is probably just a better route to stop the hose touching any hot metal parts and to make the plumbing look more cosmetically appealing.

 

Here's a photo of the vacuum hose plumbing (thanks to @Lionworks Auto )

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The rubber hose seems to go to the top (secondary air pipe), but it is actually connected to a small pipe sandwiched between the upper and lower secondary air pipes.

 

As Ian said, if you pop off the vacuum line and then re attack it you aren't altering the position of the solenoid. This seems to rule out an electrical problem in my mind. There are tow other possibilities. When you detach the vacuum line, if left open, it may reduce the vacuum level in the canister and then it takes time to rebuild. Or, and this is what I think, possible the valve is defective and sticking open. I.e., it a mechanical problem.

 

Thanks for letting me know. This is a real mystery then why the diagrams don't match the plugs. How sure are you that you had your multimeter probe on pin 21? Did you get continuity between the ECU (pin 21) and the solenoid valve with the 3 x 8 inline plug connected?

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Ugh.. that's a lot of hoses. Are there any hoses which feel soft and squishy? I had a problem on one of my other cars. The vacuum hoses were collapsing when they were warm. My Ferrari hoses, however, are like rock.

 

You said it take a long time to close when you start the car cold. Put a T in the vacuum line going to the valve can connect the vacuum gauge to it. Start the car cold and watch the vacuum level. If it stabilizes to some level and the valve remains open for some time, then closes without a change in the vacuum level I would conclude it's a problem with the valve.

 

If you do, don't forget to reinstall the OEM solenoid as well (if you still have it).

Cool. Thanks. It seems that only that inline plug is mixed up in the diagrams. Sorry for the distraction (it does seem to be a "mechanical" issue rather than an electrical issue)

 

At one point, you said this:

Is this long closure time due to a good vacuum or something sticking? I've been trying to get my head around this for half an hour.

Vacuum is required for Capristo bypass valve closure, but with no signal from the Motronic ECU to open the valve (engine off), the Capristo solenoid valve should allow reservoir vacuum to keep the exhaust bypass valve closed. To me, this seems like a properly sealed vacuum system. However, I suppose other things could cause this behaviour (with a poor vacuum). e.g. Sticky Capristo exhaust bypass valve (perhaps temperature related)?

Vacuum from the engine may be weak and it might be taking the vacuum reservoir a long time to charge. I suppose the black and white one-way valves may be limiting vacuum "flow". However, you reiterated above that the valve closes quickly when you start a cold car, suggesting a good instant supply from the engine. But is it a good instant supply or is the engine vacuum simply topping up a reservoir which still has some pressure in it?

 

I guess I misread you 1st post.

Sticks open when hot? Still seems mechanical to me after everything else posted.