My check engine light came on at 135,000. Scan showed code P0171, lean condition. Replaced gas cap,front O2 sensor, reset computer, after 60-80 miles light comes back on. Since light first came on engine has been hard to start. Always cranks on second or third try. Mileage also dropped to 19-20mpg. Is mass air flow next?

 

No, unless you want to keep throwing money at this problem. Could be dirty/clogged fuel injectors, an injector balance test would tell you for sure. Could be ECM programming. I would get the injectors flushed first.

 

Injectors may be partially clogged would be my thinking..... especially with that high a mileage.

 

Will it run ok once started and on the highway with dirty/clogged injectors?

 

Just had this problem with my fathers 07 hhr. it was a bad fuel pressure regulator (part of the fuel pump) not holding fuel rail presure with the engine off. If the fuel pressure bleeds off to 0 with the engine off the next time you try to start the car it will have a realy long crank time. you can check this with a fuel pressure gauge. sometimes these fail and cause problems when running other times it just give you starting problems. On my fathers car it also set a lean code be cause the running fuel pressure was low. The car still ran ok down the road but he did have a big inprovment it drivabilty after the full pump was replaced. hope this helps good luck.

 

When the switch is turned on and the fuel pump runs and cuts off, would that pressure the injector rails?

 

Just checked the fuel rail pressure, 35 to 40 psi, but when the engine is turned off, pressure drops to zero immediately.

 

yep thats the same problem, you need to replace the fuel pump in the tank. if you turn the key on and off quickly about three time then start the car it may start better in the mean time until you replace the fuel pump. turning it on and off a few times charges the fuel rail. To anser the question from your post before the power used by starting the engine robs some power to the fuel pump making it crank a long time the engine will start when the rail pressure finaly comes up.

 

How about, turn key on & let pump, pump up.. then start vehicle.

 

With the gauge on the rail, when you turn the key on the first time, no pressure. Second time pressure goes up to 38psi until the pump cuts off and the pressure drops to zero, third time pressure comes up and engine starts. If you try to start while the pressure is up it cranks fine.