exhaust valve doesnt open in 2nd gear only, P1448

If you know the car speed, and the engine RPM, then you can calculate the gear the car is in. That is how it knows.

As for why bypass valve does not open in second gear, that is a new one. Weird. The RPM at which the bypass opens is different for each gear so maybe that is a clue. Did you check the TCU for the middle valve?

 

Mitchell means the Bypass Valve Temperature ECU. A temperature probe (thermocouple) downstream of the valve on USA/Australian cars sends a signal to a temperature ECU (the same unit as the cat SDECUs/Slow Down ECU) which then sends temperature data to the engine Motronics ECU. This should tell the ECU when the valve is open. Out of range data or no data from the TCU will generate a fault code.

However, I don't know why Mitchell is saying your valve problem is being caused by a TCU. Your problem seems gear specific.

 

Do you have an OEM bypass valve or a Capristo valve? The Capristo valve defaults to open if electrics or vacuum are lost.

 

If it is an OEM bypass ....
Does it open in first gear?
give it some extra gas and try to get it to open in the 3-4k range in first, then shift at maybe 7k+ into second pushing on the throttle full open after swiftly getting into 2nd. It should open at around 3k or whatever. 3rd opens later I believe and then 4/5/6 open back down around the 3k range. If 1st and 3rd open and you are going aggressively through the gears, check your hoses for small leaks (use a pressure gauge).

If you are modertate to spirited in 1st but no valve open and do the same in second, it proably won't open or if it does it will be way up past 6k from my experience. 3rd/4th+ easy to open with just some throttle and being over the minimum RPM. 1st is easy from a stop and a lively clutch release with full throttle. For me, 2nd almost always required a lively 1st gear first.

 

Aren't there any published parameters for bypass valve operation from Ferrari? It would make sense that the 2.7 cars would operate all the same and the 5.2 cars likewise.

 

You did not tell us that you were in there doing stuff...

 

They rarely do ha ha

 

I hate that trying to diagnose something after the owner changes a bunch of stuff.
I am not perfect though and have probably done the same thing

 

??? I don't think Thomas' statement explicitly says he did anything or if it was done intentionally. It could have been his Capristo exhaust mechanic who mixed up the plugs.

Thomas, your thermocouples may be hooked up correctly. I got a P1445 code when I had mine swapped over (unintentionally). The thermocouple ECUs don't appear to have any markings. Does anyone know if horizontal one in the higher position is meant to be the bypass valve thermocouple ECU? I have done Motronics ECU to thermocouple ECU wiring checks in the past, but this doesn't tell you which thermocouple ECU is supposed to be in which position. The plugs attached to the thermocouple ECUs may have been swapped over in the past.

For reference, pin 73 on the Motronics ECU is wired to the bypass valve thermocouple ECU.

The operation of the bypass valve on the 5.2 is a bit of a mystery (at least to me). The workshop manual text for the 2.7 and the 5.2 is not the same in regards to valve operation (and you can't say, without a doubt, that one is the same as the other). The 5.2 text doesn't include most of the text found in the 2.7 section.

(2.7)
The valve opening/closing is determined by the Motronics system, so that the best counter-pressure can be reached at the exhaust in all conditions"
"The ECU of the left bank controls solenoid valves, that open depending on engine revolutions and the engaged gear, though only at full power"
"1st, 2nd, 4th, 5th, 6th: Closed up to 2750rpm. 3rd gear: Closed up to 4000rpm)"

How does the ECU determine if the car is at full power? (or is this just a bad translation from Italian?)
Does "up to" mean "until"... or does it mean "may be open earlier depending on conditions"?
There are no pressure sensors in the exhaust, so I'm assuming that pressures were measured during car development (and equated to gears/rpm and ???)

(5.2) All the 5.2 manual says is basically this...
"... the valve opening/closing is determined by the Motronics system so that the best counter-pressure can be reached at the exhaust in all conditions"
"Note: on the USA [and Australian] version, the by-pass valve operation is controlled by the ECU through a third thermocouple detecting temperature downstream of the valve. The temperature increase caused by the exhaust gases informs the the Motronics ECU about the performed valve opening through the thermocouple and the relevant ECU"

How can a thermocouple downstream of the valve control anything? All it can do is detect exhaust temperature after the valve has opened. Or is the part of the muffler reserved for bypass somehow exposed to normal (un-bypassed) exhaust gas pressure/temperature?

 

If its a 2.7 swap the ecu side to side see if that helps. If not you have a bad sensor somewhere

 

Now you've lost me. That doesn't make sense... unless you moved both plugs on one thermocouple ECU to the other ECU (simulating swapping over the ECUs)... or you suspected the plugs were swapped over by mistake. Yes, the bypass and cat ECUs are the same part number.

If there's a known problem with OEM bypass valves and Capristos... and Capristo bypass valves fix that problem, then shouldn't we be trying to find out what the difference between them is? It can't be as simple as having one default to open when there is a failure of vacuum and/or electric power.

We also need to know what the workshop manual means by "power". Throttle position? Intake air flow?