Check Engine light is back on.
Thread Starter
|
New User
Joined: Mar 2003
Posts: 13
Likes: 0
Check Engine light is back on.
A couple of weeks ago, my check engine light came on. I went to a local parts store, and they read my codes. P0171 - system too lean. So i read what you guys had to say from other postings, and came up with the fuel filter. So i switched it out, and cleared the codes. But 2 days later, the check engine light came back on.
So does anybody have any suggestions on where to start next - o2 sensors, all of them(3?) or start with one. converters? - do they usually go bad. Gas cap maybe?
My gas mileage didn't seem bad until after i changed the filter, now it seems to be a little worse.
thanks in advance.
1999 F150 4.2L automatic - 85,000 miles.
So does anybody have any suggestions on where to start next - o2 sensors, all of them(3?) or start with one. converters? - do they usually go bad. Gas cap maybe?
My gas mileage didn't seem bad until after i changed the filter, now it seems to be a little worse.
thanks in advance.
1999 F150 4.2L automatic - 85,000 miles.
Last edited by Wiseman; May 6, 2003 at 11:10 AM.
Freshman User
Joined: Apr 2003
Posts: 40
Likes: 0
Check Engine light is back on.
Since this is trouble code P0171 this is for Bank1 (meaning the bank of cylinders starting with cylinder one). This means that there is something wrong with this bank only. Therefore, I would look for a vacuum leak on that side of the intake manifold.
To check if the O2 sensor is bad you can use an ohm meter (follow the shop manual). Also, you may be able to swap with another sensor from the other bank (if it is the same part number) to see if a code comes up with P0174 (bank 2 too lean). This would indicate possibly that the O2 sensor was bad. This might save you some money on buying a new O2 sensor.
To check if the O2 sensor is bad you can use an ohm meter (follow the shop manual). Also, you may be able to swap with another sensor from the other bank (if it is the same part number) to see if a code comes up with P0174 (bank 2 too lean). This would indicate possibly that the O2 sensor was bad. This might save you some money on buying a new O2 sensor.
Thread Starter
|
New User
Joined: Mar 2003
Posts: 13
Likes: 0
Check Engine light is back on.
Thanks for the information. I'll take a look at the vacuum lines. So....., i'm not very mechanically inclined - on the 4.2L, is the bank 1 on the drivers side or the passenger side. Also, my guess was that i had (3) o2 sensors, is this correct, 1 on each side, and 1 after the pipes join?
Also, are there alot of vacuum lines to deal with?
once again, thanks for the info.
Also, are there alot of vacuum lines to deal with?
once again, thanks for the info.
Freshman User
Joined: Apr 2003
Posts: 40
Likes: 0
Check Engine light is back on.
Not being very familiar with the 4.2L, I can't explain where hoses and O2 sensors are located. But here are some general rules.
Bank 1 is the set of cylinders on the passenger side.
Look for any vacuum lines going to the passenger side of the intake manifold or rocker arm cover. I say this since you are getting a lean reading on this side and not from the driver's side of the motor.
O2 sensors, you will have to crawl under the truck and look. There may on be 3 sensors. Typically there is a sensor on each side of the motor between the exhaust manifold and the catalytic converter. Then there is usually a sensor between the last catalytic converter (if two CATs) and the muffler (closer to the CAT). Typically the two front O2 sensors are identical. Thus you can swap them with each other to see if the sensor is bad (if you don't have the custom socket for O2 sensors, I believe a 22MM open end wrench will work).
Bank 1 is the set of cylinders on the passenger side.
Look for any vacuum lines going to the passenger side of the intake manifold or rocker arm cover. I say this since you are getting a lean reading on this side and not from the driver's side of the motor.
O2 sensors, you will have to crawl under the truck and look. There may on be 3 sensors. Typically there is a sensor on each side of the motor between the exhaust manifold and the catalytic converter. Then there is usually a sensor between the last catalytic converter (if two CATs) and the muffler (closer to the CAT). Typically the two front O2 sensors are identical. Thus you can swap them with each other to see if the sensor is bad (if you don't have the custom socket for O2 sensors, I believe a 22MM open end wrench will work).
Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
Check Engine light is back on.
The O2 behind the cat isnt used as an O2. It is a catalyst monitor. It checks to make sure the cat is working properly.
Like kjester said you should check for vacuum leaks. Besides the hoses etc you can take some spray carb cleaner such as Carb Medic and, with the engine running, spray it at the intake manifold where it joins up with the heads and anywhere else there is vacuum. If the idle changes with the Carb Medic you've found your leak.
I wouldnt be surprised if you just had one bad O2 though.
Like kjester said you should check for vacuum leaks. Besides the hoses etc you can take some spray carb cleaner such as Carb Medic and, with the engine running, spray it at the intake manifold where it joins up with the heads and anywhere else there is vacuum. If the idle changes with the Carb Medic you've found your leak.
I wouldnt be surprised if you just had one bad O2 though.
Freshman User
Joined: Apr 2003
Posts: 36
Likes: 0
From: Kennett, Mo
Check Engine light is back on.
We get that "check engine" warning occasionally in our "98 Mustang GT. I had it checked and got the same lean indicator. It turned out that a little water in the tank, or some low grade fuel causes the problem. A little octane boost with a new tank of gas corrects the problem. Try running some of the higher octane fuel.
Trending Topics
Thread Starter
|
New User
Joined: Mar 2003
Posts: 13
Likes: 0
Check Engine light is back on.
Thanks for the info. I've tried that once before, but the light came back on after about 10 min. But i haven't tried it since i put the new fuel filter in. it's worth a shot. I like to try all of the small fix-it items first.
All of these suggestions are great - haven't had time to tear into it yet, but probably saturday.
Thanks.
All of these suggestions are great - haven't had time to tear into it yet, but probably saturday.
Thanks.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Thread Starter
|
New User
Joined: Mar 2003
Posts: 13
Likes: 0
Check Engine light is back on.
Hey, thanks again for all the info, i found the problem, with your guy's help, and a little carb spray. It was the PCV valve vacuum hose, it had a hole in it right on an elbow, just under the throttle body? I think thats what it was called. So far i haven't had the light come back on, it's been 2 days.
thanks again.
thanks again.
New User
Joined: Jul 2007
Posts: 1
Likes: 0
Second the common problem.....
I checked all the forums and tried all the solutions for codes P0171 & P0174, fuel filter, MAF sensor, Egr system, everything short of upper/lower intake manifold gaskets, and finally found a post for the little rubber elbow off the intake manifold. Kind of an out of sight, out of mind location, especially under an E150 van's hood! Was the cheapest part to replace, even right from a Ford dealer, and it solved the problem! The parts man at the dealership didn't have to even look anything up. I just told him I needed the little rubber elbow on a 4.2L engine, that connected the intake manifold to the PCV valve, and he turned, walked down an aisle, grabbed one, came back and dropped it on the counter in front of me. Sounds like a big seller to me!
