I have an 89 F-150 with a 300 I-6 EFI with 185,000 miles. I have been getting a code that says it is running rich, and mpg has dropped a bit. There has been no noticable drop in power, and it burns no oil at all between changes. Since it is fuel injected, I don't think there is any way to lean it out. This only started after it got real cold. I put in 5 new plugs recently, one seems to be welded in. It sounds fine, no skipping or anything. The other plugs looked alright when I took them out, just old. I am thinking about trying to get the other plug out, and then add an MSD or Jacobs ignition system to get a more complete burn. Could the choke plate be getting stuck partially closed? Can't think of much else. Please help. Thanks

Rob

 

A dirty air filter can cause the engine to run rich. I hope it is something simple like that.

 

I would recommend replacing the Coolant Temp Sensor @ 12 bucks...It's job is to tell the computer if the engine is running to lean/rich.

 

Thanks for the advice. Pastmaster, that is exactly what I was thinking, except the sensor was $24 at Napa. I will be doing it this week and hopefully it will fix it. Could this have caused any excessive carbon buildups? I am thinking about running some type of fuel injector cleaner or something. Any recommendations? Would high test gas do the same?

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Rob
89 F150 4X4
300 I-6, 5 spd
For Off Road Driving

 

Also have you replace you'r O2 sensor. That can cause some probles to.

 

I really don't know about the carbon buildup. I replaced my sensor last summer, when I replaced the hoses and did a complete flush...You could tell a definant difference.

Also, you might consider completely cleaning the throttle, with a brush and TB cleaner...It perks up reponce, and cures hesitation/surging. It may help you out.