I built up a 454 to replace my 350 in a GMC Suburban 4WD and was told that re-programming the ECM was a simple thing 5 years later I'm still having issues with the system despite sending it out to several tuners. It runs too rich at low power settings 13.8 and too lean at high power settings 16.0 or there about till RPMs catch up. Seems to throw the Code 13 when the mixture at low power ticks 14.0 or lower. It runs fine but the check engine light will fail my emissions. I monitor with the Wide Band Innovate system. I monitor fuel pressure and its rock steady. I have the larger TBI and new injectors. The gear ratio is 488, I pull a big boat up long high passes. The O2 sensor seems to work, monitor with a meter it swings high with a rich mixture .900VDC and Low with a Lean mixture .400VDC. Any ideas? My last tuner was at a loss but doesn't specialize in OBD1 systems. It's mostly stock 1987 vintage 9.1 compression, 500CID RV cam, Edelbrock TBI Alum, manifold no EGR, Headders, High Flow Cat, Heated 02 Sensor. How touchy are the OBD1 systems?
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