Hey All,

Last week I installed a new oxygen sensor, and a new ECU from a 1989 (same year as my van) 302 4x4 truck with AOD. Mine has a C6.

The results? Pretty much the same, although now she runs great when cold, but after a few miles of warming up, she seems to run too lean. She suffers in part throttle acceleration, what I'd call a lean surge. Pressing on the gas doesn't produce any forward momentum, she just labors harder and doesn't pull very smoothly. No backfiring or anything, just feels starved for gas. If I floor it, she pulls smoother, but still feels as if the timing is retarded. Again, when cold (and presumably richer) she doesn't have this weak part-throttle condition.

The engine still starts perfectly hot or cold. Idles fine. Taking off from a start is fine until you push the throttle a little heavier, then the lean condition makes itself known.

My check engine light has not come on since I did the swap. I figured I'd give it a couple tankfuls of gas to let the new ECU 'adapt' to its new surroundings, but nothing seems to be changing. I am on my 2nd tankful now, ready for my 3rd. Gas mileage does not appear to be any better.

Is there a way to bring the ECU back to its initial calibration? Any other thoughts?

Thanks again in advance,

Steve S.
Seattle, WA

 

You can pull the fuses that go to the ECU, or pull the negative battery cable off for about 5 minutes. With the fuse route, you don't lose your radio presets, but you have to pull a couple of fuses (don't ask me which ones). That should get your ECu back to default.

 

Thank you for that. So, when my Ebay ECU arrived, was it in its default condition, having been disconnected from any power source for at least a few days?

Steve S.
Seattle, WA
'89 E250

 

Quite possibly, yes, it could have been in default. The aforementioned tricks are only good if you are starting over after a repair.

Any leaks around the intake manifold? Try spraying some carb cleaner around the gaskets to see if the idle changes.