PO 171 and PO174 codes, 2000 B4000

[steved89]

I'm having an ongoing check engine light problem with these codes. The engine is an OHV model in a 4WD truck. It runs great and I pulled the plugs to check the color which was a light tan so that looked good. I'ved sprayed brake cleaner around the manifold and plenum and all the vacuum lines I can find and can't find a leak.Thats been done when its cold and hot several times. The only bad vac hoses I found were coming off the front hubs which I sealed whin I put on manual hubs. Turned off the light then but it came back on in 120 miles when the truck had been running for about 30 minutes. The O2 sensors ,temp. sensor, and MAP sensor were replaced to try and fix this and nothing worked. Fuel filter is new also. Any thoughts would be welcome as I've run out of ideas. Thanks

 

[Mazda]

Just a thought but I believe there are 4 O2 sensors on that truck did you replace all 4.

But reading post on this and other forums suggest your intake gaskets are bad.

 

[adsm08]

Just a thought but I believe there are 4 O2 sensors on that truck did you replace all 4.

The rear O2 sensors do not figure into this. They are not actually "oxygen sensors" they are "catalyst monitors" and are used to gauge the effectiveness of the cats, not judge the quality of the air/fuel mix by looking at how much oxygen is left over.


Lean codes can be caused by an exhaust leak as well.

I would really try to get a look at the O2 sensor readings and fuel trims if you can get a scanner on it.

 

[steved89]

Thanks for getting back to me. I replaced the 2 upstream O2 sensors only, not the ones after the cat. I haven't heard anything that sounds like an exhaust leak but i will look.

 

[steved89]

These are the O2 readings I got on an actron scanner( truck only rand about 15 minutes from cold start0. o2s11-.080-.750; o2s12-.120; O2S21- .090-.795. Does this mean anything to you? I wonder about the intake gaskets but theres no change in rpm when I spray brake cleaner and the problem doesn't happen all the time. I can clear the code, drive it for several days or weeks before it comes back and during that time there will be no pending ciodes.

 

[modelageek]

I'm having an ongoing check engine light problem with these codes. The engine is an OHV model in a 4WD truck. It runs great and I pulled the plugs to check the color which was a light tan so that looked good. I'ved sprayed brake cleaner around the manifold and plenum and all the vacuum lines I can find and can't find a leak.Thats been done when its cold and hot several times. The only bad vac hoses I found were coming off the front hubs which I sealed whin I put on manual hubs. Turned off the light then but it came back on in 120 miles when the truck had been running for about 30 minutes. The O2 sensors ,temp. sensor, and MAP sensor were replaced to try and fix this and nothing worked. Fuel filter is new also. Any thoughts would be welcome as I've run out of ideas. Thanks

You do not have a MAP sensor.
do you mean you replaced the MAF sensor?

These are the O2 readings I got on an actron scanner( truck only rand about 15 minutes from cold start0. o2s11-.080-.750; o2s12-.120; O2S21- .090-.795. Does this mean anything to you? I wonder about the intake gaskets but theres no change in rpm when I spray brake cleaner and the problem doesn't happen all the time. I can clear the code, drive it for several days or weeks before it comes back and during that time there will be no pending ciodes.

SFDROIDBIONICUT2

 

[Destroyer000]

check the egr tube... right on the bend and check where it goes into the intake.. also check the back of the intake spray carb cleaner around it all.. the 4.0 are very problematic with lower intake leaks. its usually the intake gasket or the fuel rail gasket..

 

[Mazda]

The rear O2 sensors do not figure into this. They are not actually "oxygen sensors" they are "catalyst monitors" and are used to gauge the effectiveness of the cats, not judge the quality of the air/fuel mix by looking at how much oxygen is left over..

Thanks adsm: Didn't exactly know what the downstream O2's were for. As I have only had to endure the cost of replacing only one (a few times) for my 2.3L.

 

[steved89]

It was the mass air flow sensor that was replaced. Also, this truck never had an EGR system. When I couldn't find it I went to the boneyard and located it on other Ford 4.0's but it isnt on mine.

 

[adsm08]

These are the O2 readings I got on an actron scanner( truck only rand about 15 minutes from cold start0. o2s11-.080-.750; o2s12-.120; O2S21- .090-.795. Does this mean anything to you? I wonder about the intake gaskets but theres no change in rpm when I spray brake cleaner and the problem doesn't happen all the time. I can clear the code, drive it for several days or weeks before it comes back and during that time there will be no pending ciodes.

Those are really rich. .9 is about as high as it should ever go. It should be switching around .45 with a range of .2 to .75.

The computer is seeing more air come in that what is really coming in.

 

[steved89]

Are you saying I may not have a vac. leak or lean condition? That something like a faulty sensor may be tricking the computer into thinking that is happening? If so, what should I be looking for now? Thanks for your time and input, Steve.

 

[bigo.spt]

Check evap canister

¤Off like a Terd of Hurtles¤

 

[Dune Runner]

I had this exact same problem on my truck. I spent the better part of a month trying to figure it out. When all was said and done it ended up being the vent line that goes from the back of the fuel tank to the evap canister. The hose was off at the tank. I just popped it back on and no more CEL. It was sucking fresh air in when it was going into purge mode causing it to go lean long enough to trigger the CEL. Ironically my truck doesn't have an EGR either. I don't know if that would make any difference or not. It gave me a lot of frustration before I found it. I had even had it to the dealer and they came up blank. It's worth a look anyway.

 

[steved89]

Won't be able to check that out until this weekend. I'll let you know what I find. Sounds promising and it explains why the vac 'leak' is intermittent. Thanks for the post.

 

[steved89]

Still haven't been able to check it out. The weather has been against me. I will let you know what I find. Thanks again for your input.