97 with P171 & 174 running lean

[Woodsman]

I'm slap out of ideas. My engine light is one from mixture too lean banks 1 & 2. The truck used to run good, then right before I started working on it, it was starting to run a little rough.

I started by putting a new MAF sensor on without reseting the light or the mixture adaptations and the engine fell on it's face, wouldn't idle and stalled when I tried to take off. I took this as a good thing because if the orig sensor was good putting a new one wouldn't change anything.

Well the light came back on. I've sprayed the intake down several times with brake cleaner with no raise in idle. None the less from what I've read I tore into the intake.

I replaced the upper and lower intake gaskets, valve cover gaskets, EGR gasket, throttle body gasket, fuel rail gasket, and the fuel filter. I even blew the rail out with compressed air. The injectors all ohm'd out to spec and appear to be in good condition.

The spark plugs all look the same, with a light colored fuzz that if i remember correctly indicates running too lean.

I replace the PCV valve at 50K miles and again last night at 103K miles. It would still rattle freely.

During that job I checked all the vacuum lines during removal, no leaks. Last night I finished and she crank right up after priming the fuel system. Ran in the garage for a bout an hour(idle-400rpm) checking fluid levels and such.

As soon as I pulled into the drive way the light came back on with the same P171 & P174.

I can't for the life of me think of anything else that could make it run lean on all cylinders???????

I'm kinda ruling out the 02 sensor it self being bad from the plugs showing lean.

Only other thought is a fuel pump thats on its way out?? But it runs as good as it did brand new, runs strong to 4000RPM on the road??

All input is appreciated and greatly needed.

Thanks

 

[mht95ranger]

Not sure if this will help or not but check the small hard plastic vacuum lines that go to the egr valve and the thingy that is bolted to to the intake. I did a tune up the other night and had trouble getting to the middle plug on the drivers side so I removed the lines and one broke. Upon inspecting it I could see that it was cracked and by me removing it the little piece left let go. Ran to the parts store for a small vacuum hose and now the truck runs like a champ.

 

[97ranger4x4]

After replacing that many parts I will suggest it before MAKG does, go to a professional. You have already wasted a few hundred in parts and time working on your truck, Spend $100 at a trustworthy mechanic or the stealership and get it diagnosed properly. then go and fix it yourself!

 

[Gotta_gofast]

I agree with 97ranger4x4. But you shouldn't "rule out" the Oxygen Sensors. When the oxygen sensor is bad, the computer will substitue its value. When an oxygen sensor is functioning properly, it will read somewhere between (X) voltage and (Z) voltage, where X is low voltage and Z is high. When the oxygen sensor does not function anymore, the computer will substitute the false readings of the oxygen sensor for a middle value, lets say (Y).

Also, the computer will not read the O2 sensor until it reaches operating temperature (about 600*F) because the O2 sensor will not function properly. So, when you first start your engine and the sensor is cold, your computer will use (Y). After a while, your computer will keep checking the O2 sensor's operation and after a given amount of time, if the O2 sensor still does function properly, the computer will then trip the CEL and keep running on (Y) value. So, if you're driving down the road and after a couple miles you see the light come on, this might be a possibility. Especially since you have 103K on the clock.

 

[Woodsman]

Thanks for the replies

Thanks for the info, i'll check the red and green hard vacuum lines, I looked at them before but didn't go through the trouble of taking all the black plastic off that surrounds them. But I just cleared the light again and went test driving for 2 hours of different conditions(about 50 miles), highway and what not, even hit a few local trails. So far no light.

On the professional thing i hear what your saying but other than ford supported help on the internet,a little better diagnostic tools, and possibly seeing the problem beofre; they probably don't have a whole more to offer. I went to UTI and the BMW factory school after that and have worked as a BMW tech for 3 years at a dealer. There's really no other sensors to test and I like the challenge of a good puzzle.

Anyway so far so good. I don't know why it came back right after the intake package but we'll see. As for now I can say that my truck's never been in a shop and hopefully won't ever have to go.

Thanks again for the quick responses. I'll keep yall posted.

Woodsman

 

[Gotta_gofast]

...maybe you just have a shorted out CEL and it comes on and off as it pleases. hehe

 

[np205]

I would say look at the big egr metal line that hooks up on the drivers side of the upper intake on the front of the motor. Mine had a leak there after replacing the egr and the tube. Just took some high temp silicone to seal it up.

 

[97ranger4x4]

I would say look at the big egr metal line that hooks up on the drivers side of the upper intake on the front of the motor. Mine had a leak there after replacing the egr and the tube. Just took some high temp silicone to seal it up.

I hate that thing with passion. It makes it such a PITA to get the intake plenum off.

 

[jasonl]

Have you sprayed carb cleaner around the intake/vac lines with it running? Check the air filter tube also for cracks or swollen where the PCV tube goes in. Sure sounds like a vac leak to cause both banks to read lean. Do you have a scanner to read the O2 sensors to verify they are reading lean. How does it idle? Usually a vac leak will cause a rough idle and run good with the throttle open.

 

[97fordrunner]

I am very interested in this post to This is exactly the same situation I am having with my '97 4.0

 

[97ranger4x4]

Yeh the reason I suggest going to the dealership or a mechanic is because they have a way of putting a smoke into your vacumme system. It does not harm your truck but it will show where you have a vacume leak. Even after replacing the intake manifold gaskets and many other parts, you could still have a leak. Pay the money to get the problem diagnosed, you will save lots of time and money down the road. Not to mention a huge headache!

 

[Woodsman]

I hear ya on the dealership thing, but something about a good challenge just eggs me on.

Well the light came back on, this time with a 401 code for the egr. I'd seen this code about a year ago, took the egr off and cleaned all the carbon build up off the little shaft. Never came back, untill yesterday.

So I replaced the egr valve($50) and the red and green hard plastic vacuum lines that go to the valve and solenoid. Also from a suggestion on this thread, sealed the connection on the intake from the metal egr pipe. I put RVT around the joint where it spins in the intake. Long story short the light is back with all three faults, 171, 174, and 401.

I've cleared the light a couple of times messing around with it to see when the codes return.

After clearing the codes, i can run my engine for long periods of time without the engine light ever coming on but the PCM still has 171, and 174 stored in the memory(with the CEL off). After shutting off and back on it can idle indefinetly, but when i first torque over the motor such as pulling out of the driveway the CEL will return everytime?(does that indicate something i'm not thinking of???) This time it has the lean codes and the 401 egr code.

I tested the solenoid for egr, clicks over fine. This leads me to think 02 sensors, because they also read the oxygen content to tell if the egr is working properly. And b/c i can't see any reason that the egr is not operating i'm starting to lean towards the 02's. Also since I did the intake package the engine runs and idles like a champ. Called to day 02's are $46 a piece.

I just ordered a better scanner today off ebay that has live data readings, so i think i'll check out the 02 readings before anymore parts go on it.

I've sprayed the entire intake plumbing down with brake cleaner and don't get any idle raise.

I'll update when the scanner arrives.

 

[jasonl]

P401 is probably the DPFE (egr) sensor if the valve is functioning and the little rubber tubes from the egr pipe to the sensor are not cracked or broken. When you get your scanner read the MAF and see if it is in spec also. You can buy MAF cleaner at advance for about $7 a can and try cleaning your MAF. I will be suprised if both upsteram 02's went bad at once. Keep us posted

 

[Woodsman]

yea, i'm thinking the same thing on both 02's bad at one but what else could possible cause both lean faults, but the engine runs and idles great. I don't know, still waiting on scanner for live data.

 

[Twizzler09]

I would say look at the big egr metal line that hooks up on the drivers side of the upper intake on the front of the motor. Mine had a leak there after replacing the egr and the tube. Just took some high temp silicone to seal it up.

Where'd you get the silicone? I need to seal that on mine, and would rather not remove the intake if I can do it with something like that.