Emissions device logic in stock Mustang ECU - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 9 Old 01-23-2018, 11:47 AM Thread Starter
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Emissions device logic in stock Mustang ECU

So here's a rarely asked question. I am planning an MS3 install in the near future. Now, my EGR will get deleted, but i intend to run cats and may keep my smog pump.

Now, before i can figure out how to control it, i want to understand the parameters in which is operates on the stock setup. In general, i know that during warmup, the air pump diverts air to the heads to the top pair of cats, and after warmup, diverts to the main pair of cats. Since i'll ultimately be running a high flow pipe with 2 cats, it doesn't make sense to feel air to the heads, so i'll plumb directly to the h-pipe. However, it appears that flow can be stopped completely. Under what circumstances would the ecu close the bypass valve and block all flow from the air pump?

Second question revolves around charcoal canister and EVAP purge. I know i can just vent it, but if i choose to keep it intact, under what circumstances does the factory ECU close/open the purge valve on the system?


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post #2 of 9 Old 01-25-2018, 05:17 PM
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Now, before i can figure out how to control it, i want to understand the parameters in which is operates on the stock setup. In general, i know that during warmup, the air pump diverts air to the heads to the top pair of cats, and after warmup, diverts to the main pair of cats. Since i'll ultimately be running a high flow pipe with 2 cats, it doesn't make sense to feel air to the heads, so i'll plumb directly to the h-pipe. However, it appears that flow can be stopped completely. Under what circumstances would the ecu close the bypass valve and block all flow from the air pump?
When you go wide open throttle it vents the air to the atmosphere to reduce the parasitic drag caused by the smog pump. The first valve after the smog pump also know as TAB (Thermactor Air Bypass valve) either sends the air to the TAD (Thermactor Air Diverter valve) or it sends it to the atmosphere. If you look at the bottom of the TAB valve you will see that its open with something that looks like a filter.

I had a breakdown some where on how the EVAP is used but I'm missing it right now. I've been looking into the same thing taking some of the programmable inputs the new ECU's have and using them to control the smog equipment.

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post #3 of 9 Old 01-25-2018, 07:20 PM Thread Starter
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Now, before i can figure out how to control it, i want to understand the parameters in which is operates on the stock setup. In general, i know that during warmup, the air pump diverts air to the heads to the top pair of cats, and after warmup, diverts to the main pair of cats. Since i'll ultimately be running a high flow pipe with 2 cats, it doesn't make sense to feel air to the heads, so i'll plumb directly to the h-pipe. However, it appears that flow can be stopped completely. Under what circumstances would the ecu close the bypass valve and block all flow from the air pump?
When you go wide open throttle it vents the air to the atmosphere to reduce the parasitic drag caused by the smog pump. The first valve after the smog pump also know as TAB (Thermactor Air Bypass valve) either sends the air to the TAD (Thermactor Air Diverter valve) or it sends it to the atmosphere. If you look at the bottom of the TAB valve you will see that its open with something that looks like a filter.

I had a breakdown some where on how the EVAP is used but I'm missing it right now. I've been looking into the same thing taking some of the programmable inputs the new ECU's have and using them to control the smog equipment.
Thanks for the response.That actually makes sense.

So with a 2 cat mid-pipe, my feeling is that it's not really necessary to route air from the pump to the heads since the two pre cats are not present. If so, it would be pretty easy to just plumb up a single line to the mid pipe from the pump and just put the bypass inline and wire it up to a wot trigger. Could even use the WOT relay for the AC to do so vs the MS.

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post #4 of 9 Old 01-26-2018, 10:36 AM
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Thanks for the response.That actually makes sense.

So with a 2 cat mid-pipe, my feeling is that it's not really necessary to route air from the pump to the heads since the two pre cats are not present. If so, it would be pretty easy to just plumb up a single line to the mid pipe from the pump and just put the bypass inline and wire it up to a wot trigger. Could even use the WOT relay for the AC to do so vs the MS.
No problem I've been in the same boat trying to figure out how to make a modern EFI system control the smog stuff. The one thing I have learned with the new EFI systems a good set of cats and tune you should be able to pass a smog test at the tail pipe fine. The only part for me is making the car look the part which really isn't that hard from what I'm finding. Its one of the things that I really don't understand about the smog laws if the car blows clean what does it matter how its doing it. I'm looking at going with the Pro-M system in my car right now. I have looked at the PiMPxs from stinger but for what I want the Pro-M system is the way to go for me.
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post #5 of 9 Old 01-26-2018, 11:28 AM Thread Starter
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No problem I've been in the same boat trying to figure out how to make a modern EFI system control the smog stuff. The one thing I have learned with the new EFI systems a good set of cats and tune you should be able to pass a smog test at the tail pipe fine. The only part for me is making the car look the part which really isn't that hard from what I'm finding. Its one of the things that I really don't understand about the smog laws if the car blows clean what does it matter how its doing it. I'm looking at going with the Pro-M system in my car right now. I have looked at the PiMPxs from stinger but for what I want the Pro-M system is the way to go for me.
I fortunately do not need to pass an actual sniffer, and aside from looking to see if there are cats on the car, the hood never gets popped, so i do have some leeway.

My concern really is keeping my expensive bassani catted mid-pipe happy if it requires an air pump (it may not so i could just delete the setup completely)

Also trying to figure out what to do with EVAP purge, but from what i see, that should be fairly easy to handle...i just don't know how it's handled by the factory ECU. At what times is the vent solenoid open, and what times is it closed? I know i could delete this as well...but i'm not at that point yet.

Egr, i'll just delete it. Sounds like the MS can handle that just fine.

EDIT: I just got a response from bassani stating i do not need to run the air pump. Looks like i'll just remove it then.
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post #6 of 9 Old 01-26-2018, 02:01 PM
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See my old thread about the charcoal canister

https://forums.corral.net/forums/engi...questions.html

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post #7 of 9 Old 01-26-2018, 02:37 PM
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I had saved some diagrams, that might be helpful:



Attached Images
File Type: gif ThermactorAirSystem65_zpsb18eb681.gif (48.8 KB, 49 views)
File Type: jpg Vacuum-Diagram-Fox.jpg (58.3 KB, 49 views)

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post #8 of 9 Old 01-26-2018, 03:04 PM Thread Starter
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Thank you. Most helpful. I like you want to keep the car in a state that i could easily put back most of the emissions stuff, as who knows what will happen in the future. If my state gets more strict, i may have to put an A9L back in, pass my inspection, and then switch back. So basically i want to keep things somewhat in a ready-state

Only question remains is when does the factory charcoal canister valve open and close in the stock A9x programming?

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post #9 of 9 Old 02-03-2018, 01:31 PM
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you want me to scan the pertinent section of the GUFX and send it to you?

if so, pm your email

there is a fair bit of logic in it

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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