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'88 Ford F-250 5.8L HEGO fixed lean

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4 years 1 month ago #38570 by Cactus Jack
'88 Ford F-250 5.8L HEGO fixed lean was created by Cactus Jack
Have an '88 F-250, 5.8L over 8500# version, with a new Bosch HEGO that is fixed lean but does respond to propane enrichment.
No vacuum, Thermactor, EGR or exhaust system leaks. IAC functions correctly. Engine and vehicle are totally stock and otherwse in good condition.
Although the 0.0volt HEGO reading indicates engine is running lean, spark plugs are black and slightly sooty suggesting a rich fueling condition in the cylinders.
Any suggestions?

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