7747 - lean code has me stumped

[Dieselsj]

1987 454 7747 ECU

Been logging and tuning and truck is driving great. I have a specific set of circumstances - high gear, 45mph where I can trigger a CEL with a lean code every single time. I can do the same thing a gear lower at just under 40mph (puts system in same cell for MAP/RPM).

I went on a nice long drive with the TunerPro dashboard up and logging turned on. I set up my parameters - 45mph in 5th gear and bam there is the CEL and the TunerPro dash is showing me 128 on both the INT and BLM.

HOW?!?!?!

My thinking based on knowing the ECU uses data from surrounding cells is that one of those cells is way off. So I adjusted speed to get data in the surrounding cells, rode the brake to get into different MAP cells, etc. All the surrounding cells were in the mid 120's to the low 130's for BLM and/or INT.

One funky thing...I saw the INT flash to 160 for a second then drop back down. I could NOT get that 160 to come up again no matter what I did.

Thoughts? Ideas?

[brian617]

What does your o2 voltage look like?

[Dieselsj]

What does your o2 voltage look like?

Dang it...didn't even think to check. I was too focused on the BLM/INT numbers. I'll go back through the logs and see.

[Dieselsj]

Just to come back with an update. The O2 voltage was dropping to like under 0.100mv and would sit there. No matter how much I increased the VE I could not get that to change. Then I started to get a hesitation, then a stumble, and then it went back into the lean surge that I had a few months ago. Dang injectors went bad. Installed new injectors today and all issues solved again.