How smart is the emissions management system. - Alfa Romeo Forum
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(Post Link) post #1 of 11 Old 17-05-13 Thread Starter
MGG
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How smart is the emissions management system.

I am faced with a challenge. The challenge is to save a lot of money by not getting my 156 2L JTS tuned once I replace the catalytic converters with a performance manifold. It wouldn't be so bad if I didn't have lower wishbone replacement on my mind.

I have heard about spark plug defoulers but I don’t think their behaviour can be adequately controlled.

I have found out how to easily make an electronic simulator which generates a square wave with a 0.9v amplitude and 3 second duration. It could be adapted further to change the reference voltage if necessary. Has anyone had experience with electronic simulators?
There is a lot of inconclusive information out there on what is the acceptance criteria for post cat oxygen sensors and how they affect the fuel trim. So I am looking for any information that may help me make an informed decision about the effectiveness of simulators.

I have read in the service manual that post cat sensors do have an effect on the fuel trim but it does not state how they feedback into the system. I assume they cannot provide an absolute value for the fuel ratio due to inconsistencies present within the catalytic converters so their effect must be somewhat limited.

If I understand correctly, providing the engine management system with a post cat oscillating signal around 0.45v would have the same effect as tuning out the post cat signal during a remap. The only advantage remapping has, that I can see, is the engine will have improved mapped parameters for whatever changes have taken place. I am guessing that the effectiveness of an engine with simulators instead of a remap is highly dependent upon the accuracy of the pre cat sensors.

Any thoughts? Other than put in a new converter as I have unfortunately been there and done that.

(Mechanical Engineer + Mechanic - Alfa)*time = ln(Bad News)
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This post needs moving to the 'Boffins' section!..

..
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(Post Link) post #3 of 11 Old 17-05-13 Thread Starter
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I was confused over where to put it. It could be put it in the modifications section but then again there are a few people out there possibly looking to deal with a failing catalytic converter of which I was once one.
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The problem you are going to find is that most of the members on here are from the UK and our annual MOT testing system is getting very strict as regards CAT removal so I would think that the number of people experimenting with removing them will be quite low.
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I would have thought a closed loop system was pretty hard to spoof. The sensor is providing an oxygen level to the ECU, and the ECU is trimming fuel base on it. Because your cat is absent, the exhaust stream will have more Oxygen than expected (and more unburnt fuel & CO), so the ECU will be presumably trying to richen the mixture to reduce the oxygen percentage. If you attempt to send a constant signal back, then it will simply tune to a set point, which may or may not be right at any other point in the map. What you need is a method of scaling the voltage produced by the lambda sensor back to a level that indicates a good mixture. So if the lambda is reading 4.5v, you read 4.0v - you base your spoofed on the real reading.

I would have thought this was possible with some basic electronics, but it is a very long time since I have done this sort of stuff!
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I think it is a bit "dangerous" to give a total spoof signal to the ECU - a modified signal, sure, but totally synthetic

I would just put the new exhaust in - place the Lamda's where they used to be - many-a-times it will not give faults. If it drives fine - 1st quantify how much worse it is and if it is needed to adjust - also remember that you might be driving harder than before as you like the noise of the new exhaust.

My SW V6 has the pre- and post cat lamda's put back in place (cats absent) and it works 100%.
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(Post Link) post #7 of 11 Old 17-05-13 Thread Starter
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I going to give it a go and report back on the results. I will compare the readings using fiatecuscan and place a small fast blow fuse in the circuit to prevent an expensive mistake. The worst that can happen is that I send one of the trimming values through the roof and that will trigger the car into open loop for sure.
At least this way everyone can learn from either my mistake or success.
I am surprised that your v6 didn't have an issue Gertie, maybe it has something to do with how they are positioned.
A remap is not out of the question for me but I still feel they are slighty overpriced in New Zealand for what is, after all only about a days work.
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(Post Link) post #8 of 11 Old 17-05-13 Thread Starter
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rxe, I found some free software on the internet for simulating circuits called LTspice and I must say, it is rather good. It was quite intuitive and plotted the circuit's transient output nicely.
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The lambda's after the cat need to give a "rich" signal at all times when you are applying throttle, and lean when you lift off.

The management might not care id the mixture stays rich which lift-off, but if it sees lean when throttle is applied it'll conclude the cat is faulty.
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(Post Link) post #10 of 11 Old 18-05-13 Thread Starter
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I have just driven the car with one of the post cat sensors replaced by my simulator and it seems to be working. I have driven up hill under heavy throttle and lightly around town with no troubles at all. So fingers crossed.

Edit: Just attached a plot to compare the simulator to the standard o2 sensor at idle. From this I have deduced that I must change the value of one of my resistor so the average of the red signal is equivalent to the blue. I also compared the stored additive and multiplicative factors between the banks and they are approximately the same so far.
Attached Images
File Type: jpg Signal.JPG (62.4 KB, 30 views)

Last edited by MGG; 18-05-13 at 05:46.
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(Post Link) post #11 of 11 Old 18-05-13 Thread Starter
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Here is the circuit I used
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