Code 171 is system to lean "1" code 174 system to lean "2" code 420 catalyst system efficiency below code 530 a/c refrigerant pressure sensor "A" sounds like o2 sensors are bad or vacuum leak
SOURCE: 1999 Dodge Ram 1500 Extended Cab 4x4
YOU'RE GONNA HATE THIS BUT IT DOES SOUND LIKE A FUEL ISSUE. HOWEVER HERE'S THE CATCH.....THE FURL FILTER IS IN THE GAS TANK CONNECTED TO THE FUEL PUMP. YOU HAVE TO DROP THE TANK OR TAKE THE BED OFF TO GET TO IT. AND YOU CAN ONLY GET THE NEW FILTER AT THE DEALER. THE LOCAL PARTS STORE DOESN'T CARRY THESE. BUT I'M NOT SURE ABOUT NAPA, THEY MIGHT. YOU MIGHT ALSO WANT TO CHECK FOR A VAC. LEAK AROUND THE THROTTLE BODY. LASTLY WHEN WAS THE LAST TIME YOU DID ANYTHING TO THE TRANS.? MIGHT WANT TO LOOK INTO THAT.
SOURCE: 1985 Ford F-150 Truck (EFI) Fuel Problems
i actually have a 1985 302 efi... there are 2 pumps one one the rail right under drivers door and one in the tank.. there are also two filters... one just behind the pump one the rail.. its actually inside a canister that you open with a oil filter wrench then it has a paper element inside..then there is a inline filter that is actually part of the high pressure line the hose is about 3 feet long and runs from your front pump up to the fuel rail agaist the firewall...this one is really hard to find (Buy) good luck wish i hade a carb
SOURCE: 1985 Ford F-150 Truck (EFI) Fuel Problems
Same problem with my 85 F-150 5.0 EFI---turned out that the fuel pump relay under the hood was teriffically corroded on the inside (I opened up the relay to look inside). When I checked the voltage at the fuel pump it would show 3.5-6 volts instead of 12 volts.
I was thinking fuel blockage or perhaps failure of the in-tank pumps. Sometimes the truck would start and run, othertimes it would neither start nor run. Typically, if running it would stay running until turned off (where the relay had to break).
Changing the green fuel pump relay fixed the problem--12 volts now at the pump and no reoccurance.
Good luck--let me know if this fixed your F-150.
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SOURCE: My 1998 ford mustang v6 3.8l .. is hard to start
So what you saying is it's hard to start cold right? Something in computer system not allowing excess fuel to injectors when cold. Probably sensor Get auto electrician to sort it out otherwise you end up replacing things that there is nothing wrong with They got the right gear
SOURCE: 1998 ford mustang 3.8 v6 starting problems.
it's your upper intake manifold gasket. it has a crack in it and needs to be replaced. your getting to much air and not enough gas. mine did the same thing.
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