Hi guys. I think my problem has changed enough that it warrants a new thread; I think my old one became confusing...

The situation is: Check Engine Light reads code 51: Engine running lean

However: Engine is gulping gas to the tune of 17 mpg.

O2 sensors are new and working. What else can fool my engine into thinking it's running lean and using too much gas? Or, can running lean possibly decrease fuel mileage?

Thanks!

 

Have you tested the injectors? or the fuel pump module?

 

Hey, thanks for the response!

No, I haven't checked the fuel injectors; I don't know how. Nonetheless, they seem to be working pretty darned well seeing how much gas she's drinking...

I did replace the fuel pump relay recently, in response to a thrown code 42. Hasn't seemed to have any effect on fuel economy, though. Fuel pump seems to be working alright, I can hear it pressurize and all...

I'm thinking maybe the MAP, PCV valve, or (thanks to you guys' advice already) a dirty EGR valve. It really seems as though something is telling the car it's running lean although it isn't. I haven't noticed any particular power or idle problems that would be abnormal for such an old car. Idle is a little rough, and there is some vibration during deacceleration but I didn't find it alarming for a car at 156,000 miles...

 

Hmmmmmm....decided to try replacing the MAP today, and when I took it off, the sensor was covered in oil...it seems as though there is a lot of oil in my intake manifold...Anyone know what can cause this?

I replaced the PCV valve while I was at it, and found out that the longer PCV hose (from the valve cover to the PCV valve itself) is cracked at its connection with the valve cover (someone electrical taped it back together), and there was quite a lot of oil and crud around and on the connection there...

Give anyone any clues??

 

EDIT: just read your last post that you made while I was making mine lol. I'll have to think a little bit.

 

well I think a bad PCV valve makes your engine consume more fuel and also thats the only direct passage from your breather box to your intake.

 

you have the valve cover with two ports coming out of it? the coil pack bolts right up on top of the valve cover and not on a metal bracket? If that's the case, there is a hose coming off the back of the valve cover to the bottom of the intake tube right above the throttle body tucked up under and out of the way. That's the only other way it could possibly happen.

 

Ok, could it be either of these?

Throttle Position Sensor? Haven't had any hesitation problems, though. Car has died at idle when low on gas a couple times, and shifts a bit hard occasionally...

Fuel Filter? (This one makes no sense to me but people will not stop suggesting it, so I assume there must be some merit here. But if the fuel filter was clogged, yes the car would run lean, but how could it be burning gas so fast??? Argh!)

 

maybe the knock sensor, im only guessing but when an engine runs lean it starts to ping and knock. maybe the sensor is your culprit. making the engine think it is lean and dumping in fuel. its a toss up but to me it kinda makes sense.

 

no, that would give u a code for engine misfire or engine knock. not lean condition...Possibly, could you have your o2 sensors backwards?