302 EFI running rich

[A Cobra guy]

My 302 is running rich, WAY rich. it will cut out sometimes coming of idle, the exhaust pipes are black.

The set is as follows and was running fine until mid last season when this problem began.

Stock 302 long block. It is an Explorer P-head engine I have had since new. the intake, computer, wireing and all sensors are from a 91 Mustang. This combo was working fine for nearly 25,000 miles.

I have replaced the Throtle Pos. sensor and the Idle air bypass control.

Any ideas?

[blykins]

Oxygen sensor?

[HighPlainsDrifter]

Hi,
Yeh, take out the oxygen sensors in the exhaust pipes, if they are any color but red/tan in color they are hooped and you will go into full rich at idle. Any parts store will have them.
Perry.

[A Cobra guy]

Perry,
What do you mean by "Hooped"? The Ox. sensors are fairly new (Less than 25,000 miles) but are black due to the rich condition. The car runs worst at mid temperaturs. I have checked the voltage at the engin temp sensor and it seems to be within specs. Could it be too much fuel preasure? I have an adjustable unit that seems to be keeping the preasure pretty high. Since the engine is so stock I think perhaps I should go back to a stock regulator.

I am thinking about switching the intake over to a Mass-Flo system by Quality Roadsters. Before I do that I want to get all the other sensors sorted out to reduce variables during the conversion.

Harvey

[HighPlainsDrifter]

Harvey,
Yes for a stock efi the fuel pressure should be 39 lbs without the vacuum line on and 30 lbs with the line on running at idle,you need to do this 1st. Too much fuel will wreck the oxygen sensors and the cats. If the oxygen sensors are black they are NOT working and should be replaced as the computer will go into rich warm up [choke] mode if it doesn't get the signal from the oxygen sensors. The only time they are not used is under full throttle so all other times you will be too rich.
Perry.
ps- a mass air system will do nothing for a stock engine,you only need it if you run a performance cam.

[A Cobra guy]

Thanks for the tips. I'll get onthem in the next few days.

As to the Mas-flo system the change would be just for cosmetics. I'm not expecting a horsepower gain.