p0172 and p0175

[HBKJ]

I just rebuilt a 2002 KJ. All new engine internals. All new sensors (o2, map, temp, etc). Keep getting too rich codes I can’t figure out. It doesn’t misfire. The tps is working properly. The o2 sensors are reacting properly. Fuel pressure is 52 psi. I don’t know what else to do. Anyone gave any ideas? I bought the jeep with a blown motor (valve seat blew up piston) so I don’t know if it had this issue prior.

 

[LibertyTC]

Welcome to the forums.
Look for potential vacuum leak causing rich condition.
Spray carb cleaner around intake base to see if rpm changes.
Have you done a full compression test, what are the cylinder psi readings?
Check all spark plugs looking for a sooty or rich condition.
Ensure the correct spark plugs are in there. Use NGK ZFR6F-11G & set gap at .040 inch

 

[HBKJ]

Thanks for the response

I haven’t checked compression yet. I wasn’t leaning towards that being the problem because it was both sides of the engine. And it has new pistons and rings. I’ll check that this weekend and post results.

The reading on the map sensor doesn’t indicate a leak but I will spray around the intake to check. I have only put 100 miles on the newly built motor. I didn’t mention new plugs, coils, injectors also. I know I got NGK but I think I got the platinum ones. I’ll check sat

Thanks again
Bob

 

[Ksat]

Misfires are more likely to happen from a lean condition as opposed to a rich one. Anyway, just because the PCM thinks things are rich, that may not be what's actually happening.

What brand upstream O2 sensors did you use? NTKs are the only ones that should be in there. You said you know the sensors are acting "properly" but how did you come to that conclusion?

 

[HBKJ]

Checked O2 by Viewing the live data and monitoring the voltages. They are NGK.

All cylinders have good compression around 150.

I suspected the intake may be leaking even though engine didn’t react with carb cleaner sprayed around it. I swapped out a manifold from a working engine and so far so good. 40 miles down so far and no codes yet. I suspect a hidden crack or leak where the 2 halves of manifold were bonded together.

 

[HBKJ]

Sorry NTK.

 

[LibertyTC]

Here are the compression specifications:
2002 to 2004 3.7 has 9.1:1 compression ratio.
Cylinder pressure should be between 170psi-225psi with no more then 25% difference.

 

[Ksat]

Upstream O2 sensors are generally tested via propane enrichment to see how they respond. Viewing their voltage switching behavior on a graph tends to not be very conclusive, at least in my experience.

Next time you look for a vac leak, try keeping an eye on the fuel trim values on your scan tool while you're spraying carb clean around. Smaller leaks, or ones in hard to spray areas, often don't change RPMs much, but will affect those trim numbers quite noticeably.

 

[HBKJ]

Upstream O2 sensors are generally tested via propane enrichment to see how they respond. Viewing their voltage switching behavior on a graph tends to not be very conclusive, at least in my experience.

Next time you look for a vac leak, try keeping an eye on the fuel trim values on your scan tool while you're spraying carb clean around. Smaller leaks, or ones in hard to spray areas, often don't change RPMs much, but will affect those trim numbers quite noticeably.

Great info. Thx