Code 172 just won't go away...arrrggghh

spock2001us

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Aug 23, 2005
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I put in new Hpipe (removed cats) and exhaust and got a CEL. Ran codes and among other codes was 172 - too lean bank 1.

CEL is intermittent. Comes on here and there for about 10 seconds, then goes away.

Figured time for a tuneup anyway so I replaced: Plugs, cap, rotor, coil, ECT, MAF, and both O2 sensors. Did not replace wires yet, going to order online.

I've cleared the codes each time I replace something. Remove neg battery cable for 20 mins or so.

All the codes went away except 172. I also smell gas at the right tailpipe. Only thing left is maybe an exhaust leak at the manifold or the wires? Also read about fuel injectors.

What about MIL eliminators?

Any thoughts?
 
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toyman

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MILs aren't required as the O2 sensors are before the cats (or no cats in your case). When the CEL comes on and then off that means whatever triggered the CEL (only emission related) has corrected itself and has fallen back into spec. I would look really hard to find an exhaust leak on bank 1.Is the H-Pipe a O/R pipe without cats? When you say you removed the cats it sounds like they were there and you physically removed them.
 

spock2001us

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I installed a BBK offroad Hpipe after removing the factory cat mid pipe. I will go back under there today loosen and reset the manifold to H pipe flange and see if that helps. Thanks.
 

chaos254

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Jul 27, 2002
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it definitely could be the wires since you have not replaced them yet. I know its frustrating to keep throwing money at it. Maybe swap the all the wires from bank 2 to bank 1 and see if you there is any difference?? Hopefully you'll get a code for the other bank and then you'll know if its the wires.
 

revhead347

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That's usually an exhaust leak right by that O2 sensor. It will suck in air, and give it an incorrect reading. Does the CEL come on as soon as you start the car? You might want to take the H-pipe back off and clean the ball and socket joint to ensure a good seal. Can you hear an exhaust leak?

Kurt
 

spock2001us

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I don't hear an exhaust leak as best I can tell. And I don't see any black soot of any kind at the manifold flange....although I certainly have black on the inside of my tailpipes and they are only 30 days old.

The CEL does not come on for a while. I may drive 20 mins and after the car has heated up, it will come on for maybe 10-20 secs and then go off. I have a 40 min commute to work. It will go off and reappear every 10 mins or so for another 10-20secs and go away. The only code I get is 172

My car seems to run it best in that first 20 mins, then when the CEL light begins it's intermittent flash, my car seems to run not as good.

I have replaced everything except the wires. I read somewhere that a guy finally beat code 172 with new wires, which I have not ordered yet.

Also, I can remove and reset the hpipe to verify the seal, it is just a PITA to have to do all over again..:mad:

I also think I may have an air leak in the MAF housing. A while ago I dropped the housing on the ground and it cracked. I sealed it with duct tape and it has been fine for years. I recently removed the tape and resealed it. Could this be my too much air problem?

I skipped putting on new headers at this time, which may help the seal. I am worried about snapping off bolts in the heads. Is it common to snap the bolts and if I do snap one off, wtf do I do then?
 

toyman

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Any air drawn in after the MAF is a problem as the computer is relying on the MAF to determine the fuel load requirements. That's why vacuum leaks cause problems. An exhaust leak at the flange will often draw air in and cause the O2's to read a lean condition. This in turn prompts the PCM to enrich the fuel load. Bad spark plug wires are more apt to give a rich condition if there is a poor spark and combustion.
 

90mustangGT

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The problem started as soon as you put on the O/R H pipe so it's probably related. I'm betting on that it isn't sealing correctly.
 
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