QuestionQUESTION: I can't pass state emission test, lots of unburnt fuel, you can smell it too when you get outside. Runs great, new O2 sensor, tune-up, wires cap rotor, plugs, filters. Checked fuel pressure, good. No leak-down, No smoke on cold start-up. poor gas mileage, 18 highway, but runs strong. 245K but had some head work done at 100K. DEQ tested about 2.5X above the passable CO and hydrocarbons. What next?
ANSWER: Robert,
The fuel pressure regulator is probably blown. If the fuel pressure is good then you probably have a defective fuel injector or two. Get a fuel pressure regulator and a Haynes Manual and check it out. With the car running check the pressure and then turn the key off. If the pressure drops suddenly then you have a leaky injector or two. Pull the plugs and note which are wet and black and you will know which injectors that need to be replaced.
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QUESTION: This 3L motor has throttle body injection, the fuel pressure was good and did not drop quickly after turned off.
AnswerRobert,
If the fuel pressure is good and the injectors are not leaking means that the throttle position switch could be out of range as in need of replacement or adjustment. Another cause is a old oxygen sensor that is lazy. That is, over the years it has become coated telling the computer it is running lean. When, in fact, it is running rich. But, it cannot tell due to the coating. Another cause is timing not being set to specifications. But, the first two are more common. Oxygen sensors are only good for fifty-thousand miles and yours are probably way overdue.
