Late model EFI engines in classics withOUT catalytic converters...

[Kern Dog]

If you used a stock computer from the donor vehicle, how would the PCM in the vehicle maintain a proper air/fuel ratio?
I am unsure.... would the engine stay in closed loop? Would the Air/Fuel ratio be essentially preset and not continuously adjusted as I understand that they are with a completely intact system?
I assume that in the donor vehicle, if the converters were removed, the MIL/Check Engine light would always be on and the codes for no signal from the O2 sensors would register. I'm curious how the engine would run right without the feedback from the O2 sensors due to the converters being gone. Even if you remove the O2 sensors, it seems like there would still be some issues.
Would you need some type of custom "tune" for the system?

 

[kiwigtx]

I don't know a lot about the computer changes ....but I can tell you from experience first-hand that if the Cats are removed, and no alterations are made to the tune in the computer, the engine warning light will be continually on.

I have a 6-cyl Falcon that has this issue, and I ended up getting a cheater O2 sensor dummy extension bung that reduces the CO content entering the O2 sensor. Not ideal, but it's not worth spending a ton of cash on a car worth two-thirds of bugger-all. For the most part the extension works. The PO would just disconnect the battery for an hour or more to extinguish the light. I suspect he had just re-connected when I looked at the car before buying it.

 

[moparedtn]

The first o2 sensor (before the cat) is the one that is instrumental in getting air/fuel correct.
The second one (after the cat) simply monitors efficiency of the cat for emissions compliance.
They sell "simulators" or "emulators" to use in place of the 2nd sensor when cats are removed;
lots of them out there, various levels of quality of course.

 

[RemCharger]

Cats removed gives you a P0420 and P0430. Which only tells you the converters aren't converting .

 

[moparedtn]

Cats removed gives you a P0420 and P0430. Which only tells you the converters aren't converting .

Yup and a Check Engine light, of course...