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HybridZ

1977 280z


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I have no idea since you have not given any information.  But when I drove my Z from Colorado to California, my mileage dropped to less than 20mpg and it ran rich, so I replaced the filter and that fixed it.

 

If you want useful help with your issue you need to give details on your car.  Engine, fuel injection, modifications, history.  Even if it's completely unmodified, you need to say what the issues are, when they started, what you have done...

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Follow the electrical leads from the water temperature sensor where it's installed in the thermostat housing.  About 18" down the lead and into the larger part of the harness you should see/feel a "small lump" in the harness.  Strip away th insulation and you'll find the aluminum bullet connectors where the wires from the engine temperature sensor connect into the harness.  Those aluminum connectors corrode over the years causing higher resistance in the circuit which tells the ECU the engine is cold and to run richer.  Pull the connectors apart, thoroughly clean them, coat them in dielectric grease and reassemble.  That will eliminate that as a source of the engine running rich.  My '77 was running so rich my plugs were wet with fuel and I was getting 5.5 MPG when I finally discovered  the "lump".

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Your cold start injector could be leaking too, to cause a rich condition.  There's a few possibilities.  Can you describe how it's running?  is there any surging?   you said it flagged on timing,  That could certainly cause rich running. get a light and time it according to the FSM. I think it was something like 10 deg BTDC, but you would need to look it up.

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