'98 F150 w/4.2L Automatic and 134K miles.

Bought the truck a few days ago after it had reportedly been sitting for a year. Drove it home about 60 miles. The next day when I started it, the CEL came on. I put in premium fuel and Lucas, then had a problem with hard starting and running rough. When I had the codes checked at Autozone, it came back P0171. I tried a new coil and a new passenger side o2 senser "after the cat. converter". Neither made any difference in the CEL or the intermittent start problem.

I had to get it inspected, so unhooked the battery to reset the ECU. Inspection went fine, and I drove another 65 miles with no problems. I went to start it today, and the CEL came on again, but the starting problem has not returned.

I don't understand why this light comes on at start rather than during the 60+ miles of operation.

I also don't understand what might be involved in my mysterious hard starting problem. Is it possible the ECU is going out?

I would appreciate any expert opinion.

 

Its premature to jump to the ECU at this time. The PO171, bank 1 system lean, is telling us the mixture is lean so lets go for the free-bee stuff, like its sucking in air someplace. Check PCV hoses, the elbows crack and will suck in air if and when they want. Check other areas with carb spray while idleing, look for increase in RPM.

 

How on earth do you get at that pcv valve and hose on the passenger side without removing the intake?

 

Don't have the hands on experience on the 98 mine is a 02 with a different intake. Suggest sending Bucko a PM just in case he has missed this thread. Don't remember which year he has but perhaps he has the intel you need.

 

Thanks for taking your time to reply.