Dodge Nitro Forum banner

P0172 help!!!

10K views 53 replies 4 participants last post by  Scar0 
#1 ·
Long story short bought a 3.7l nitro and had a broken valve seat, replace cylinder, timing chain kit and all new gasket, water pump, injectors, coil packs and MAP sensor.

Currently getting only p0172, stumble a bit on idle. I do smell gas and once warmed up long enough it back fire a bit only on idle, While driving no problem at all and has a ton of power.

i have the data from my scanner, if any one can point me in the right direction, it will greatly be appreciated.

38609
38610

38611

38612

38613
38614
 
See less See more
6
#8 ·
wiring diagram says oxygen sensors 1/1 and 1/2 are left side of transmission, sensors 2/1 and 2/2 are right side of tranny, just not sure which 2 are up Stream or down stream
 
  • Like
Reactions: Scar0
#9 · (Edited)
Up stream o2 sensor is before catalytic converter and down stream is in the catalytic converter, so 1/1 is bank 1 sensor 1 which is up stream and 1/2 is bank 1 sensor 2 down stream vise versa with 2/1 and 2/2

Now honestly from the video it confirm I’m running rich with the negative fuel trim, it my first time using the data and seeing all the value, going to see if I can find factory specs and compare and need to do some more learning
 
#10 ·
If you replace one O2 sensor and not the other, on one side, you can also run into issues. Because of this, it is recommended to replace both up and downstream on one side.
 
  • Like
Reactions: Rambo
#13 ·
Ok I would like to update, I replace both upstream o2 sensor and the rich code went away and now only have a misfire in cylinder 2.

when I replaced the passenger side cylinder head and and rebuilt the engine I have 120psi in all 6 cylinder but being that I didn’t know there was a fill port on the water pump housing, the engine didn’t have enough coolant to circulate the coolant and over heated and dropped cylinder 2 exhaust valve seat. Gonna replace that cylinder head and all should be fine
 
#16 · (Edited)
@NitroTech @Scar0
I’ve been playing with the car and monitor the 02 fuel trim and etc. So on cold start I visibly see white smoke from the exhaust and smell gas until the engine is warmed up about 3min or so and smoke is gone and the excessive gas smell is gone.

bank 2 upstream fuel trim is -10 or so does Jump around a lot on idle, while holding 1.5k -2k rpm the fuel trim is positive like its running lean. I can get the fuel trim to behave identically to bank 1 by removing any of the injector on bank 2 and putting it back in, even with the random misfire it will match the fuel trim on bank 1 on idle and revving the engine. I’m stumped and only thing I can think about is the egr valve being that it’s on bank 2 exhaust manifold
 
#17 ·
Disconnect both battery terminals and hold clip them together in some way, leaving them for 5 minutes. This will discharge and clear your PCM memory. Reconnect the terminals to the battery and go for a road test. Once the vehicle is at operating temperature and driving down the highway at about 60mph perform a closed throttle decel. Foot completely off the accelerator pedal. This will relearn your cam/crank numerator and your fuel adaptives will relearn from scratch.

You may also need to replace the downstream. Downstream O2 drives upstream. But perform the procedure above first and let us know.
 
#21 ·
Ok before I head to bed, I checked cylinder 2, 4 and 6 at tdc and no valve leak, also when I removed the negative terminal on the battery while the engine was running and the light were flickering. Probably a bad rectifier causing my issue. Either way will report back in the am
 
#22 ·
Ok, so I just realized that cylinder 1,3 and 5 is on the driver side. I’ve been checking those the whole time. Either way I checked cylinder 2, 4 and 6 on the passenger side and there no valve leak or bottom end leak. I checked for spark in all cylinder and that’s good. I haven’t been able to check injectors. I checked all fuse and swapped relay in the fuse box.

I did notice on cylinder 4 the new spark plug that’s only days old was dark and I read online that from running rich and all the other spark plugs look normal with a little bit of white on them
 
#23 ·
Interesting, usually the Nitro will die if you disconnect the Neg battery terminal.
It is possible the cylinder 4 injector is leaking.
 
#24 · (Edited)
Ok just wanted to update, I replaced the crankshaft sensor and that fixed my hard start issue I had, I just got the misfire on cylinder 2 again and finally I pulled off the valve cover all seem good.

ok I just got back from working on the car. Comparing to bank 1 cylinder, seem like I have an exhaust valve leak
 
#25 · (Edited)
ok so this is what I have tested and found out. I did a leak down test with the valve cover off and all cylinder seem to have a little bit of bottom end leak, on the tester shown here all Cylinder read from 20% to 40%, which mean its good, none of the cylinder had exhaust valve leak
38624


Now cylinder 2 had a little bit of intake valve leak until I put oil in it.

Beside the intake valve leak I found on cylinder 2, the valve and seat looks all good.
38625

38626
38627
38628
 
#26 ·
So I’m still confused why my car is was flooding on start up, I didn’t get a chance to check if that stopped after I replaced the crank sensor. Either way the misfire was still present and still continue to run as usual.

so I know engines that has been flooded may read low compression from the ring not making a seal in the cylinder wall, I’m wondering if that’s my issue with the crankcase leak pass the piston, also the oil don’t look normal for only being a week old. I will take pics. I may pull out cylinder 2 and 4 piston and check the rings and measure the cylinder wall.
 
#28 ·
I was going to replace it. One thing I noticed as well turning the engine is that the passenger side all cylinder leak pass the compression stroke and not the driver side.

I’m going to tested the fuel rail system, going to remove start ignition wire so the engine down crank, going to test ohm on injector and I have a handheld o scope to see the frequency and power to the injector also going to measure the gas from each injectoR somehow.

unless all those rings are worn? Or may be pcm doing some things. I just may replace rings anyway since passenger side is accessible
 
#29 ·
Ok well I’ve been having fun all day taking off the oil pan that was stuck to the gasket/aluminum shield, now I need to replace both. Either way the 4x4 don’t make it easy, I removed both motor mount and loosened the rear A frame bolt and jack the motor up from the transmission oil pan, used some wood to distribute the weight on the pan so it don’t bend.

38635


so here pic of the piston, everything look good imo. That’s cylinder 2 and I removed cylinder 4 as well and it looks good. I also checked the ring in the cylinder wall to see if there any sign of wear leaving a gap in the ring and all seem good.
38636
38637
38638
38639
38640


I’m going to replace the rings for the heck of it and going to have cylinder 2 intake valve replace and the head checked. But once it’s up and running, if I see signs of flooding on start up, going to assume it’s the pcm and replace it and have it programmed.

I’ll report back next weekend
 
#32 ·
Ok rebuilt the passenger side with need piston and rings. Double check timing and replace cylinder 2 intake valve. Still idle like crap.

I’m going to grab a egr valve and ecm for the junkyard and intake temp sensor, I remember someone mentioning it but I kept searching for idle air control valve, I will replace temp sensor first then egr then finally the ecm to accurately diagnose what was causing my issue that way it will help someone down the road, suckS no immediate code come up to pinpoint the issue.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top