Always suspected my 440 was running a tad rich. Well, now I now for sure! Hooked up an exhaust gas analyser and the CO readings are actually off the chart: around 12.5 - 14.5%, which probably translates to something like 9 AFR (10% CO = 10.79 AFR). Lovely.

This is an old Holley Pro-Jection 4Di EFI (digital, not the even older analog one). I'm really kinda fed up with it. Sure, I could replace the (narrowband) O2 probe and sealing the exhaust manifold would obviously help. I'd also need a laptop computer though which plugs into the ECU's serial port, oh and it has to run Windows 95-XP. Seems pointless.

Should I just go back to carb?

Depends on how much you have into it, what else do you have to convert to go back to carb vs cost to swap to a modern controler.

if all you need is a win xp machine that shouldn't be too hard to come by. or build.
wide band o2 isn't that expensive either. depending on what it interfaces with.

Are you looking for cheap or just better?

With the older systems (like mine) hooking up the laptop is pretty important to get a good tune. A wide band sensor also. I am pretty sure any newer kit comes with wideband (or should!). Also sealed manifolds. After I ditched gaskets and used a little high temp RTV I did not have any more header leaks.

You can get adapters to run the serial port into a USB. They are a bit if a PITA to get set up but seem to work OK thereafter.

If you want EFI you really need the wideband either added to what you already have or part of a new kit.

If not messing with matching up a computer is high on the list, sounds like it is either new self tuning kit or carb.

The thing is I don't have a portable Windows computer anymore. Sure you can pick up obsolete machines for next to nothing but they're cheap because the battery's knackered. Buying a servicable laptop is still going to cost me real money and only for tuning the car? How long is it going to last anyway? Using a wideband O2 would require an upgraded ECU (Holley Commander 950) and they don't grow on trees either :-(
It may be possible to use a Megasquirt instead but I don't know anything about those.
I originally went down the EFI route to replace the ailing Thermoquad, hoping it would improve reliability and economy. Can't say it did. Even upgraded the throttle body to Holley Commander specs and the injectors alone were something like 90 bucks each. Four needed. Also replaced the obnoxiously loud Holley fuel pump with a Walbro unit (~ 200 dollar). All feels like a waste of money now.

Ok, I still need to fix the exhaust system and replacing the O2 probe wouldn't break the bank but it is an obsolete bit of kit and I really don't want to invest in a self learning EFI system at the moment.

Sealing the exhaust manifold

running rich

hmm, I wonder.

When I went shopping for my EFI, I was pretty set on a PC controlled unit and then a friend of mine that is a buyer for a national speed supplier told me the EFI companies are moving towards the little control modules. He attends SEMA every year and showed me all the common units and told me unless I was going to race, stay with the plug and play. Since I am using the MSD Hemi Engine Control I went with the MSD EFI so any problem would only have one stop for a solution. I was convinced that PC was the way to go but maybe it is becoming old technology.

No, not just yet. A couple of no-cost things to try first:

1. Take the O2 sensor out and clean it with oven-cleaner. Put it back in and put some miles on it. They get sooted-up and don't get a "clean" signal.

2. If that doesn't work, try moving the O2 sensor further down the pipe. The farther away you get, the temp reading gets colder. To compensate it will lean the mixture to get a hotter reading. You might have to experiment a bit with placement so be prepared to drill holes and re-weld your exhaust bung a few times.

a new single wire o2 is very inexpensive

It uses a heated three wire sensor. Well, thought about it some more and decided I'll give it another shot. In a way it does work, even though it's probably running in open loop mode at the moment. I have an old 486 laptop somewhere that might be frugal enough to run of a dc-ac converter. Pretty sure I could use either the MS-DOS version or maybe Win 3.11.
I did buy a much improved aftermarket software package though (again a surprisingly substantial investment) but that needs Win 98 as a minimum requirement.
Could buy an old Toughbook (~ 150 $) but if you add a new O2 sensor that's 50% of what a perfectly serviceable Edelbrock carb would cost me (selling everything on ebay would probably pay for one!).

I'll fix the exhaust first and see how it goes.

Ok so I managed to find an old laptop but now I'm even more confused. The O2 sensor seems to be running fine. Originally it was set to run run in open loop at idle. Corrected that (it's meant to help with non stock cams) but it's still idling rich @12.5 air-to-fuel ratio (~0.9V O2 sensor reading). Took a few screenshots (literally):

I'm puzzled why the O2 sensor correction reads "0" and what am I supposed to do about the throttle position sensor? The manual only states that you can assign values from 0-255.
My test run was driving around town, so lots of idling but that's what I use the car for 90% of the time.

Ok, a new Edelbrock Thunder AVS it is then,