OK, Ford ECU Gods...I've got a problem.
Since installing a set of headers on my '96 F-250 460 life has been good. The absolute best bang for the buck I've spent on the truck. I also have a 3" Flowmaster 70 system after the catalytic.
There is one problem...I occasionally get a check engine light because the free-flowing exhaust system is making the ECU unhappy. It's pretty obvious why I'm getting the two error messages on the OBD-2. The first one is a "Slow response from O2 sensor" and the other is "Insufficient EGR flow". What's really happening is there isn't enough back pressure in the exhaust system to blow quite as much through the EGR pipe or through the O2 sensor as the ECU expects. Since the truck has over 60,000 miles, I replaced the two front O2 sensors anyway (grrr), but still getting the error from time to time.

Does anyone have any suggestions (other than jamming a potato into the exhaust pipe) to make the ECU happier? My real question is if an aftermarket chip can be programmed with wider limits on these and other parameters. Or is that part of a different part of the EEC-4 ECU ?

Like I said, I couldn't be happier with how the truck is running and how it's able to tow our trailers. Right now I'm not in an emissions test part of my state, but that could change in the future and this could be a problem in the future. But for right now, this is just a major annoyance I'd like to correct.

Thanks in advance.

 

Yes, a chip can be programmed to handle a wide variety of issues. It can't, hoever, take care of a fundamental problem that needs to be addressed. Ask yourself why you're not getting enough back pressure (answer: you may have gone too far with the exhaust). You're going to need to do something to get more air into the engine (free flow intake and/or ram air) and reprogram the ECU to correct the fuel mixture with the added air. If you're getting error codes now its going to be a hit-and-miss proposition with the chip until you address the fundamental problem of the exhaust --- and I'm not convinced the exhaust is the sole reason for the codes.

 

I know you're busy and thanks for taking the time to reply, Ken.

Since my earlier posting, I re-read the emission system manual and I was able to "correct" the insufficient EGR flow problem. Ford puts a restrictor in the EGR pipe between the exhaust manifold and EGR valve for the purpose of creating a pressure differential...The more EGR gas flow, the larger the pressure difference which is read by a differential sensor...so it's able to measure the flow of exhaust gas. As an experiment, I introduced a deliberate leak on the low pressure (downstream) side of the sensor.. leaving the high pressure side alone...which makes it think there is a slightly greater exhaust gas flow through the EGR pipe than there really is. That worked. No more ECU error, truck still works fine.

Yes, you're right about insufficient exhaust system backpressure being the issue, but once all the 3" pipes are welded, the muffler and headers are installed, re-working it on a guesswork basis not knowing exactly how much backpressure is "enough" is something I wanted to avoid! This was a problem that I had never read or heard about anyone else having so I couldn't anticipate it. Oh well, the fun of performance mods on computer-controlled engines.
Like I wrote, the truck runs great, I couldn't be happier with it.

The most elegant solution would be to reprogram the ECU limits (putting a T fitting and a partially pinched rubber hose in there is prolly more cost-effective ;-), you know a heck of a lot more about all the interrelated issues in ECU programming than I do, and I had no idea if it was even possible to do.

There you have it. Thanks again, Ken.