EECV uncontrollable AFRs

Hi all,

I'm brand new to Gearhead. I have been getting into tuning EFI and it looks like I am at the right place for some sage advice.

I am in New Zealand and own two Aussie Ford Falcons - a 2001 AU2 XR6 VCT and a rare 1995 EF XR6 wagon. Both run the 4.0 SOHC inline six derived ultimately from the 200-250 American Ford six of the 1960's in front of an automatic. It's an all-round great engine. It has hemispherical combustion chambers, hydraulic roller cam, dual-path intake manifold and coilpack ignition, and produces 220-230 hp factory (the higher figure is for the AU2 VCT with variable cam timing). It's robust and will rev to 6000 rpm all day long (with the rev limiter increased). A number of US first-gen Mustang owners are swapping the Aussie engine in place of the factory six.

The engine uses the EECV speed-density ECU - the same box used in Mustangs of that era - so the code has long been cracked and there is a heap of information and support for tuning it. The strategy and definitions are very similar. I have a tuning pack and J3 chip from TI Performance and have used Tunerpro RT to tune my wagon for about six years. The wagon is (was) my daily driver, but I also use it for DYO drag racing over the summer. It's not super fast (best ET 15.12), but it's huge fun and wins a few races. I am a member of two Aussie Ford forums - Fordmods and Australian Ford Forums - but they have been unable to help with the problem I am having with it.

A few years ago, it gradually drifted leaner and leaner - I had to regularly increase the fuel table, to the point that eventually the 190cc injectors could not flow enough fuel at high revs. I replaced the injectors with 267cc '931' injectors (same as GM LT1) and adjusted the tune to suit. That gave the extra range I needed, but didn't stop the drift. Then, about a year ago, the AFRs became effectively uncontrollable in some situations. At idle and cruise it sometimes goes so rich that it dies. And on overrun, with very low MAP, it goes so lean that it flames out and stalls. I doesn't matter what I do to the fuel tune - the AFRs don't change. I am running a wide-band O2 for data-logging, so have not run closed loop for years - the EFI is running purely off the fuel tables in the tune. Does anyone know what can cause these symptoms?

The engine is quite mildly modified - headers, cat delete, cam one step hotter, skimmed head for more compression, cold air induction, larger throttle body - just the basics. These mods are well within the range of the factory ECU and injectors - with the right EFI tuning.

In chasing this problem, as well as replacing the injectors, I have replaced the:
- fuel pump
- fuel filter
- fuel pressure regulator
- MAP sensor
- temp sensor
- cam angle sensor
- coilpack
- plug wires
- spark plugs
- crank angle sensor
- idle air control solenoid/valve
- throttle position sensor
- ECU (twice)
and probably a lot more that I have forgotten.

I have checked for vacuum leaks multiple times. I even replaced the WBO2 sensor thinking that it might be giving me false readings, but it was fine.

I don't know where else to look or what else to do. It's doing my head in. As it tends to die at inopportune times, I can't rely on it, so it has been parked up for over six months. It's a fun drive, and I miss my drag racing, so I need to get it sorted soon. Any help you guys and gals can provide would be much appreciated.

Thanks, all.