Hi all. Just got my Explorer from the shop yesterday after having the injectors refurbished and the Sg105 02 sensor replaced. The #1 cylinder was filling with gas and the sensor was bad. Anyway after driving about 50 miles today the check engine light came on anb I'm getting Code 172(Heated Exhaust Oxygen Sensor,HEGO,voltage signal indicates lean, Bank #1). What might cause this or is that sensor possibly going bad? Thanx in advance.

 

After thinking it through a bit more I'm gonna try theses steps. Gonna clean off the MAF sensor, pull out HEGO #2 and clean it off and also replace fuel filter since its probably over due anyway. When Injector #1 leaked and the cylinder started to fill with fuel the vehicle ran very,very rich. I actually had around a half a quart of gas in the oil and a bit of gas exiting through my exhaust. Also had white(mostly)/grey/blue smoke bellowing out of the exhaust. I guess the oxygen in the fuel caused the white smoke. That in turn probaly damaged,coated, fould the sensors. After thinking about it the other sensor I had replaced might of been ok with a good cleaning. Questions I have is what would someone with a bit of knowledge recommend to clean off the MAF and the O2 sensor. Will throttle body cleaner be suffice or should I opt for a can of Electrical Contact Cleaner. If the MAF was reading wrong then that would more than likely set off both sensors instead of the one correct?

 

Is your 172 a continuous memory of KOER code? Does it pass the KOER test?
Cleaning the MAF is a good idea. Personally I use rubbing alcohol and a Qtip. I once went to Rat Shack to buy some electrical contact cleaner, read the label, and it was just isopropyl alcohol. Throttle body cleaner would probably work, too. You just want to use something volatile enough that it isn't going to leave behind a sticky residue that will cause the filament to get dirty quicker.
Beyond that, other things that can cause a lean code:
1) Bad O2 sensor.
2) Bad wiring between the O2 sensor and the computer
3) Exhaust leak upstream of the O2 sensor
4) Bad computer ground
5) low fuel pressure

and I'm sure there are others.

 

I cleaned off the MAF and O2 sensor. MAF didnt look bad but cleaned it anyway. I dont know exactly what to look for in the O2 clean wise but it had a bit of soot on it so I cleaned it down with some Electrical Contact Cleaner and let me tell you, if that stuff gets on your skin it burns like hell. Wife has it now on the road so we'll see what happens. Chances are I'll probably just replace the O2 sensor, they're only $50 anyway for O.E. Wiring looked o.k as far as I could tell. One other POSSIBLE problem of note is a leaky, corrupted head gasket. Boy I hope not but when I had it in the shop the mechanic got a reading of 500 ppm of hydrocarbons in the coolant. I was thinking that with the #1 cyliner filling with gas and the very strong gas fumes coming from the engine that possibly those mixed in with the coolant. I did run the truck about 8 hours when the injector was leaking. But now it seems my fill resevoir is ever so slowly dropping. I'm not a big fan of additives but I used some sodium silica ,aka, liquid glass in an 86' mustang that sealed up a radiator leak and seemed to restore some lost compression. It was hitting arouns 3200 RPM's at 55 but now it's around 2600-2800 RPM's at 55. Any advice on something that might work better to seal a possible gasket leak?

 

It doesn't sound like you're certain which gasket is leaking. One that commonly leaks on the 4.0 OHV is the lower intake manifold gasket. It can cause the engine to run lean, coolant getting into the cylinders (esp. #5), and ping. IF it were me, I'd try tightening the lower intake manifold bolts to see if that helped before introducing a stop leak to the coolant.

 

Ah, Mr.shorty you might of hit the nail. Mechanic said that cylinder #5 was getting a bit moisture in it. Will try that soon.

To answer your other questions Mr.Shorty I was getting the 172 code with Key on and Key off.

 

Well they did seem to be a bit lose. I don't have a torque wrench but I was able to get around a half a turn on them. Out of curiosity does someone know the torque specs for those? I'll run another engine check soon.

 

~15 ft lbs.
That makes your code 172 a continuous memory code as 172 can't be a hard fault code. Just FYI, there are two sets of codes output during the KOEO test: hard fault codes first, then continuous memory codes. Next time, run the KOER test as well. You generally get better diagnoses if you run through the codes in the order KOEO hard faults, KOER codes, and then continuous memory codes last.
And be sure to clear that 172 from continuous memory before running your next battery of tests, so that, if it reappears, you will know that it's recent rather than a hold over from before. (Does that make sense?)

 

Perfect sense. Ran them yesterday after I tightened the bolts. I cleared the codes and also diagnosed with KOER and it didn't show 172. I'll keep an eye on it over the next week. If it get it again I'll replace O2 #2 since #1 was also replaced. I'm more interested in the coolant level and will be watching that like a hawk.

 

Are the lower intake manifold bolts hard to get at? I'm also getting a 172 code.

 

Not at all. They are right below the upper intake. If I remember correctly I think they were 10 mm. Truck is running very good right now(knock on wood) and no KOEO codes are popping up. Coolant level has stabalized completley and show's no signs of dropping. I assume the hydrocarbons the mechanic found in the coolant a while ago were caused by the lower intake.