Limited power while driving

Long Technician San Jose, California Posted   Latest   Edited  
Question
Driveability
2011 Isuzu NPR 3.0L (4JJ1 150hp)
P20C9 - Reductant Control Module Requested MIL Illumination
P0093 - Fuel System Leak Detected - Large Leak
P2000 - NOx Adsorber Efficiency Below Threshold Bank 1
P2293 - Fuel Pressure Regulator "B" Performance
U2116
Lim Home Mode Operation With Various Mils
Vehicle Reduced Power

Hi Everyone,

This is my first time to post in this forum.

I normally don't work on Isuzu diesel truck due to lack of special diesel tools. When this truck came in the first time (same DTCs set), I've attempted to replace both pri & sec fuel filters, cleared DTCs, test drove OK and truck returned 2 weeks later with the same problem.

Here are some data PIDs I've retrieved by using Autel MaxiSys scanner: Actual rail pressure: 5580 PSI; Desired rail pressure: 5853 PSI; FRP rail pressure: 1.2V; FRP reduction: 540mA; FRP regulated: 1490mA.

There were DTC freeze frames and fail records but fail records had no mileage or time stamped for analysis. I've been using helpful fail record time/mileage stamped from other GM vehicles for determining frequency of circuit/problem failures but that info was not available for this truck. I'm trying to determine the problem of this truck by going after the DTCs caused limp home operation. Here are my questions:

  • Is fail record time/mileage stamped available from Isuzu IDSS or Tech 2 scanner?
  • What Isuzu SW version allow Tech 2 scanner accessing this truck?
  • What is the most likely caused of multiple DTCs

Any suggestions are welcome and thanks for reading my post.

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Richard Mechanic
Chicago, Illinois
Richard Default
 

Need to look at a few things. Look at fuel balancing rates to see if you have a failed overfueling injector. To much fuel will take out DOC an effect DPF efficiency. Also look at regulator on rear of pump. Those go bad and cause p0093 large leak. Also check rubber hoses from filter housing . Factory clamps go bad and air leaks into system . Or primer assembly goes bad.

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Sean Owner/Technician
Santa Ana, California
Sean Default
 

I do not have much to add but it is nice when someone knows their stuff and rings in with the correct answer, i would bet money on the regulator and then proceed with caution, would it be worth it just to get someone with the correct tool to just scan and give you an idea????? If i dont have the scanner, I usually pay someone to get it done for me, that way we both make money instead of client…

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Richard Mechanic
Chicago, Illinois
Richard Default
 

Someone with Isuzu IDSS software is your best bet. You need to look at emissions system and fuel system to get correct diagnosis

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Edwin Mobile Technician
Charleston, South Carolina
Edwin Default
 

Make sure that you have absolutely no leaks in the fuel delivery system from the tank to the pump. I don't jusy mean a liquid leak I mean a loose fuel line that could be drawing in air. Also check your primer pump/fuel water separator for an internal check valve failure. I find these will affect your fuel rail pressure pids as well. Go with IDSS if possible when diagnosing these vehicles.

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Long Technician
San Jose, California
Long Default
 

Thanks everyone for quick replying & suggestions! I will definitely check fuel supply circuit first to cover the basic of troubleshooting.

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Anura Educator
Auckland, New Zealand
Anura Default
 

Hi Long, This 4JJ1-TC engine is fitted with an electronic high-pressure common rail fuel injector system. If either an injector or the pressure control valve leak Fuel(Diesel) to the return line, then P0093 DTC comes on. First what I would do is check for the fuel return quantity of each injector by using 4 equal size see through containers. If any one jar gives a very high leak off reading…

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Long Technician
San Jose, California
Long Default
 

Hi Anura, <<<If any one jar gives a very high leak off reading after 30 seconds at Idle that indicate that PCM dumping fuel to the return line due to an injector/combustion fault, also I would look at the scan tool data of the pressure control valve duty cycle and physical test of the quantity coming out.>>> Thanks for your advising!

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Stanislav Technical Support Specialist
Moscow, Russian Federation
Stanislav Default
 

Hi We have had very similar case and the trouble was in the leakage through Fuel regulator valve, located on the fuel ramp. If problem happens on idle it could be easily caught with the help of scope and scantool in graphic mode. I advise you Gscan 2 or 3 as they are the best for Korean and Japanese commercial vehicles. If trouble happens while driving (I suspect this is the case as regulator B…

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Long Technician
San Jose, California
Long Delay
   

Hi Everyone, I didn't have the right tools and workshop information to get back testing right away after received your responses. I've followed the troubleshooting tree for diagnosing DTC P0093, using scanner and got the results: FRP sensor voltage: 0.5v (spec. 0.4-0.6v) at KOEO; FRP sensor PSI: 4300PSI (spec. …PSI) at normal operating temperature idling. I then proceeded to test the…

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Long Owner/Technician
San Jose, California
Long Default
   

I'm in the process of eliminating problem between the fuel primer pump check valve failing or the FRP reduction valve caused low fuel rail return volume. Do you have any suggestions? I pinched off the fuel supply hose to the high pressure pump inlet and able to build up pressure firmly. There was nothing wrong the primer pump! The FRP reduction valve is part of the fuel rail assembly and not a…

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Anura Educator
Auckland, New Zealand
Anura Default
 

Hi Long, Your pressure/Vacuum test results are perfect, no leak or poor supply from primary (low pressure) side. FRP reduction valve readings are within specs, no need to replace. Now my gut feeling is the wiring for the pressure sensor, check for high resistance and poor connections at both sensor and ECM ends.

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Long Owner/Technician
San Jose, California
Long Default
   

Hi Anura, I went back & rechecked the FRP sensor voltage by measuring voltages at FRP sensor 5v REF, GND & return signal. Both voltmeter & scanner readings were the same. 1.1v At idle on both voltmeter & scanner; 1.9v at 2500 RPM. I've also took a look closer at the engine parameters and noticed "Balancing rate cylinder 3 was high at idle" (2.7 mm3/stroke) by comparing to the…

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Anura Educator
Auckland, New Zealand
Anura Default
 

Hi Long, The 3rd injector is faulty, but not the main issue, any Denso injector having Balancing Rate ( or some scan tools says “ Injector feedback”) more than +1.7 mm3 / stroke at Idle is likely to be an injector, reading of – 1.7 or more is a loss of compression. Remember, always the buddy injector pulled back to negative value, in your case no 3, + 2.7 then no 2 ,-1.5 In your case check…

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Long Owner/Technician
San Jose, California
Long Default
 

Hi Anura, The SCV is a spring loaded solenoid valve with a high precision fit plunger & bore. I've seen the picture of it at other forum with a slightly worn on either plunger or solenoid cylinder wall that could caused binding & fuel delivery problem. The SCV valve winding may electrically tested OK but may fail mechanically. I will current test the valve and take the valve a part for…

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