2011 Isuzu Npr Ecomax . 3.0L . 4JJ1-TC . P0172

Christopher Technician Saskatoon, Saskatchewan Posted   Latest   Edited  
Heavy Duty
2011 Isuzu NPR 3.0L (4JJ1 150hp)
P0172 - System Too Rich Bank 1

Looking to see if anyone out there has experience working on the Isuzu NPR ECOMAX series with the 3.0L 4JJ1-TC engine..... I have a fair amount of experience working on the Isuzu line but mostly it's always been the 4HK1, 5.2L or the 6HK1, 7.8L series of engines ... This 3.0L has a reoccurring P0172 fault. I though I had it beat with what I will explain shortly , but 9000kms later it has set, unit came in with a CEL and the only fault set is a History P0172, retrieved with IDSS... I have gone thru the IDSS troubleshooting flow chart but the code setting criteria is very vague in description, basically just described all the things that could create a rich condition, ie:. EGR, Turbo, overfueling injector, restricted air intake... 9000kms ago I had a situation where the fault was easily reset within a 40min spirited test drive, and that time I performed function tests on the EGR valve, and Turbo VGT with both checking out good. Injector balance rates are good, all with +/-3 , no smoke from exhaust with it removed pre DPF, and no presence of an missfire, no drivability complaints ever (long term lease, consistent operator) . Checked for a skewed MAF with it being an analog style, showing a smooth trace on a scope moving up and down normally. MAF was replaced in a known good, finding it to make no difference. MAF passes the IDSS self test. Clean air filter. Unrestricted intake (carbon buildup is very minimal, unit has only 190,000kms) ... Wiring was tested at H02S, with heater circuits good. All 4 circuits for HO2S isolated and load tested with 4amp bulb with all good. HO2S was replaced with new OEM part, making no difference. ... Last item in the IDSS was to verify oil reissue in the intercooler and piping had minimal oil residue ( this is a known feature of the 4HK and 6HK engines, and was always considered normal as PCV is closed. But these 4JJ1 engines have an automotive style PCV in the valve cover (there was a prior setting if a P052E for PCV performance) unsure if this oil in the intake is considered normal on these? ... Anyways I removed the intercooler and piping , steam cleaned very well, reset the ECM learned data and after that I was unable to duplicate the fault... The unit drive for the last 9500kms with out fault untill today . . . Seems like this should be a simple fault to diagnose, but the information available even from Isuzu is so vague for code setting criteria it is making it very difficult... Looking to see if anyone out there has much experience on these engines and specifically this fault.. any input will be appreciated . Thanks

Michael Diagnostician
Champaign, Illinois
Michael Default

Does this unit have a air compressor that is oil fed or any other accessories that are oil fed? One of these components might be throwing oil into the intake causing your rich condition. Plus make sure each component can breathe and doesn't have a restriction.

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Christopher Technician
Saskatoon, Saskatchewan
Christopher Default

Sorry so late to reply on this case, it's been a bit crazy .... No air compressor on this unit, and only source of oil to the intake would be failed turbo seals, which both are ok, or the PCV , and still trying to determine to operations as it is unfiltered when reaching the intake side of turbo. So far this looks to simply be a design fault, which I have seen on the earlier 4hk engines, but on…

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Michael Mobile Technician
Clinton, Utah
Michael Default

Christopher, Sure seems like you have covered all your bases. Does the system have a snapshot of when the code sets? With gasoline models you can look at when what the conditions are. RPM, Coolant Temp, Airflow, Ect... If it is available you can get an idea of where to look. Another thought is to check for ECU updates. There may be a software fix for the issue. Using the snapshot try to…

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