355 Replacement slow down cat ECU prototype

Thanks Bob,
Interesting to see in real time.

Can the OP solve the mystery of the 1448 bypass valve code ?
I’ve been running the Goth Simulation Box with success, but would like to know what the computer is looking for on that circuit too.

Test pipes and Capristo BV = CEL.....without Goth’s Box


Thanks
Skipp

 

It may only react to high temperature values when the valve is supposed to be closed (indicating a valve stuck open). The thermocouple seems to be on the wrong side of the valve to check for (bypass) cat overheat and it may not react fast enough to an increase in temperature when the valve opens for brief periods.

I'm surprised the Kiwi cars don't have the bypass ECU (The Aussies do). No Aussie imports?

 

As I understand, the exhaust ECU for the bypass line is the same as the other two. The engine ECU knows what to do with the bypass valve based on the signal it receives from this third exhaust ECU. Or is there a separate black box controlling the bypass valve?

 

It appears that engine ECU Pin 64 controls the bypass valve, via Pin 8 of the 41091 connector.

 

I have a video I did of the BP location output in a normal, error free condition on my car. I’ll dig it up so you can see the values.

The sdecu at that location does not control the BP valve nor does its output values affect whether it opens or closes. It just monitors temps via the TC like the others do.

We don’t know what throws the 1448 code but we do know that in some installs where primary cats have been removed and straight pipes installed that there is some reversion of exhaust emissions that creates some voltage outputs that throw that code.

I believe the goth box was transmitting a constant 1.5 v signal to keep the ecu happy.

 

I forgot I owe you a little kit to tap that output with goths box installed. I’ll get on that skipp

 

wbt,

Here is the video I did of the BP output in my car. All functions normally and the BP valve works. It starts at warm idle and progresses until I got on some roads where I could step on it. You'll see the BP operation and voltages starting around the 5 minute mark.

As I said above, we really don't know what the motronics is looking for that causes the 1448 code. Maybe it needs 1.5v to indicate it opens? I believe Goths BP box which Skipp has installed puts out a constant 1.5v. I am sending him a positap and some wire so he can tell us for sure.


Bob

 

Thanks Bob,
Looking forward to solving this mystery

 

Looking at Bob’s video shows the voltage range.
When I was trouble shooting this a couple years ago, there was some debate about whether the 1448 was being triggered by too low of a voltage reading based on the cats being removed leading to lower heat to the thermocouple.

 

Or maybe 1.5 is a happy medium, somewhere between high temperatures generated by heatsoak (with the valve closed) and a higher temperature, say, 1.6, for an extended time period indicating a stuck open valve.

Unfortunately, the guy who designed this system has probably long since retired, so the debate will probably continue for some time.

Do you mean the removal of the bypass cats? I'm one of those (lucky) people who have no bypass cats, standard thermocouple TCU, but no message.

 

I’m talking about the regular cats, not the bypass cats.

 

My earlier reply was incorrect (I don't have a 355) when I said that the engine ECU opens and closes the bypass valve based on the signal from the bypass Ehx. ECU. It is actually the other way around - the ECU opens/closes the bypass valve (based on engine rpm and possibly load) and then it looks at the signal (temperature) from the bypass Ehx. ECU which works in the same way as the left and right Ehx. ECUs - its output voltage is 100 x the Thermocouple voltage.

The engine ECU is probably not looking for any specific voltages (bypass gas temperatures) from the bypass Exh. ECU for the bypass open and closed positions but probably looking at the difference between the average of the left and right exhaust temperatures and the temperature in the bypass. If this difference is not within the range that the engine ECU expects (this is what we don't know), it throws the code. When the bypass valve is closed, the ECU expects large difference (how large?); when the valve opens, the difference should be small (how small?). If all Thermocouples, the Exh. ECU-s and the bypass valve are good and the code 1448 still appears, I believe it means that, when the bypass valve opens, there is either too much or too little exhaust flowing through the bypass. In such a case, the problem would be in the construction of the (modified or aftermarket) exhaust system, probably in what back pressures the system creates for the normal gas flow and for the bypass gas flow.

 

So now we have a 3rd theory We need to get the Bosch designer out of retirement.

 

I assumed that the engine ECU expects to see the voltage from the bypass ExECU representing what is actually happening downstream of the bypass valve.

If a "special" black box to fool the engine ECU is to be developed, I would start from the following assumptions:

1. Bypass Valve Closed - low temperature at the bypass Thermocouple point, i.e. the general temperature of the muffler; if it is assumed that this is about 150C at low engine speeds up to 3000 rpm (while the bypass valve is closed), the output from the bypass ExECU would be about 0.6 Volt.

2. Bypass Valve Open - the question is whether the bypass gas temperature is somewhat higher or somewhat lower than the main exhaust flow temperatures (left & right) when they are relieved of some flow by the open bypass; I would first assume that the bypass temp is somewhat lower.

The "special" box could then be designed to perform as follows:

1. No connection to the bypass Thermocouple (abandoned).

2. Connect the left and right ExECU output signals to the special box.

3. Connect the bypass solenoid valve signal (off or on) to the special box.

4. The logic of the special box could be:

a) Bypass Valve Closed - send a fixed 0.6 Volts signal to the engine ECU.

b) Bypass Valve Open - send a signal to the engine ECU that is equal to the average voltage of the left and right ExECUs minus, say, 0.5 volts.

The special box would then have to be tested to see whether the engine ECU throws the code or not. If it does, further tests would need to be done by slightly varying the fixed 0.6 Volts at bypass valve closed (probably a bit upwards) and the "minus" voltage when the valve is open (try with -0.3, -0.8 etc) or try even with a small "plus" voltage as the bypass gas temp might actually be slightly higher than the temp of the main gas flow (but unlikely, I think).

I think that "wbt" can easily design such circuit and, for the prototype, provide means of varying the fixed and the "minus" voltages so that their correct settings can be determined during trials (by a volunteer).

 

Maybe...

We have goths fake out box installed in Skipp’s car and it solved the1448 issue for him so let’s just see what it’s doing.

Stay tuned.

 

So, other than cost, what's the reason for a different SD ECU? The old black epoxy ones were replaced on my car in 2006 and the new green epoxy have been fine every since. The car has like 20k miles on it since they were replaced. If its a moisture getting in issue because the epoxy cracks why not just spray them with several coats of Plasti Dip or Flexseal.

 

The reason is to fake out the system, so you can run various exhaust options.

 

The Goth BPV Box abandons the thermocouple. Once DrBob sends me the test kit, we should know. I wasn’t going to publish Goths secrets publicly, but he’s long gone at this point. So, the community deserves to know.

 

The op's design prototype is a box that functions like OEM. I don't believe it is intended to fake out the system, just an alternative to the OEM box. From most of what I have read about failures of the OEM ECUs I think his premise is wrong. Failures seem mostly with the older black epoxy boxes.

Whether he can design a box like Goth's isn't the point of the current prototype. I'm sure he could given the parameters. The thing about Goth's BPV box is that it doesn't appear to be "smart" so with no input I'm not sure exactly what it could do other than provide a constant or some kind of oscillating output signal. I suspect maybe the latter.

 

It's a great project. "wbt" has already developed the main part (the sensitive and very accurate 100 times linear amplifier, already good as the 355 SDECU) from where, with a simple add-on engineering, he can easily build the 348 (NLA) SDECU. And the 355 SDECU may soon also become NLA.

 

Agree.

 

Goth is still out there and may have some of his ecu's available. I passed the info on to him via another Stooge. Maybe he will join in on the thread.

 

Wow! Ricambi is asking $500+ for these now. Last time I checked they were around $300.