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3,277 Posts
Discussion Starter #1 (Edited)
1994 Single Turbo 6sp, 139K miles
stock fuel pump
stock injectors
12 volt fuel mod

All graphs below are second gear.

I was driving the other day and my Innovate SCG-1 triggered a lean fuel boost cut. I have the boost cut set to cut 100% boost and it drops me from 19.0 psi to ~8psi. I really think the SCG-1 saved my engine here. Without it, the problem would have gotten worse over time and I'm not sure I would have caught it. Definitely not immediately like the controller did.

The first graph is my Supra with No tune whatsoever. AFC zero'd out, ecu reset, etc. This graph is from a few months ago.
  • I've observed mid-10 AFR's as the baseline for my supra multiple times in the 13 years I've owned the car.
  • The AFR stays consistent mid-10's at 8psi, 15psi, etc.
  • Under WOT, the AFR's always start richening up between 6 and 7psi. That rich, no-tune state sees AFR's between 10.3 and 10.7 AFR.

TODAY - After being alerted to the lean condition:

I zero'd everything out in my tune today and did a baseline test. This was the result

I came back to the house and reset the ECU to just to be sure that there wasn't any sort of tune being preserved, and did one more test. The result is next:

One other note: I need to try re-calibrating the SCG-1 wideband 02 sensor, but the car was too hot to remove the sensor for a free air calibration after these test runs.

From everything else I've observed, the sensor is behaving properly.
  • The first graph was from 2 months ago
  • I calibrated the sensor right before that graph was recorded, so the calibration is only 2 months old.
  • AFR's at idle are right around 14.7
  • After a rev from idle, the AFR's drop down to the low 10's (as any MAF car with BOV vented to the atmosphere does)
What could this be? I can think of a few things
  • Clogged fuel filter
  • Failing FPR
  • Clogged or failing injectors
  • Fuel pump slowly failing
Everything seems fine during regular driving, it just seems like it can't keep up under WOT. Am I witnessing my fuel pump giving out?

Any input would be much appreciated.


3,277 Posts
Discussion Starter #2
Turns out it was a flow problem. The vacuum hose popped off the FPR so fuel pressure wasn't rising with boost. Easy fix!
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