How to start diagnosing crank-no-start on a kubota common rail diesel

[c5vettster]

Hi,
I have a strangely behaving Kubota D1803-T diesel in an air compressor. The engine will crank but will not start under common condition. However, if I put the battery on a charger, it will start every other time with a puff of black smoke. I suspect that I have an issue somewhere within the fuel system whereby a slightly higher voltage helps to open up injector?

I am new to diagnosing the common rail diesel fuel problem. I did basic stuff to make sure that there is a good flow of fuel to the injection pump and the electric fuel pump is doing great job. The internet search suggested that I do injector backflow test, so I ordered the kit from amazon. Am I am on the right track? I am good at troubleshooting the old mechanical fuel injection systems where was a single solenoid on the pump. Here it appears that there are solenoids on the pump, on the fuel rail and then of course the injectors. How does one go about ruling out these before replacing the fuel injectors. On mechanical engines I used to just throw new fuel injectors and then rebuild the pump whenever problems like this showed up. However, it appears that a single injector for this engine is $$$, so I want to be more mindful.

 

[InTheWoods]

I know zero specifics about this, but basic trouble shooting logic allows a couple of observations:

1. Since you describe a condition common to all 3 cylinders, the chance the root cause is 3 bad injectors is pretty dang low.
2. Since the symptom correlates with things battery-related, check carefully its terminals and high current wires. Understand how the grounding system is supposed to work. Replace the battery.
3. Don't rule out simple stuff like air in the system or fuel filter. (I doubt these are the cause, but you need to be certain they aren't.)
4. The battery charger observation is odd. Be sure what you wrote is correct. What is the charger's current rating? What caused you to first try the charger and what exactly did you see when it was connected?

 

[c5vettster]

I know zero specifics about this, but basic trouble shooting logic allows a couple of observations:

1. Since you describe a condition common to all 3 cylinders, the chance the root cause is 3 bad injectors is pretty dang low.
2. Since the symptom correlates with things battery-related, check carefully its terminals and high current wires. Understand how the grounding system is supposed to work. Replace the battery.
3. Don't rule out simple stuff like air in the system or fuel filter. (I doubt these are the cause, but you need to be certain they aren't.)
4. The battery charger observation is odd. Be sure what you wrote is correct. What is the charger's current rating? What caused you to first try the charger and what exactly did you see when it was connected?

This is very weird indeed. The battery is pretty new and shows 12.8V. My charger is 30amp and runs at ~14 volts. The battery has no trouble running the starter alone. However, it will only start if I have the charger on and it starts right up, on the first crank. I am thinking that the slightly higher voltage 14 vs. 12.8 is the key

 

[GreensvilleJay]

thinking out loud...
does it have an electrical solenoid that needs power to allow diesel to flow ?
If the solenoid HAS to be powered to RUN the engine, and the battery is not supplying enough voltage, then no fuel to engine.
Measure the battery when cranking...might only be 8-9 volts ?

 

[c5vettster]

thinking out loud...
does it have an electrical solenoid that needs power to allow diesel to flow ?
If the solenoid HAS to be powered to RUN the engine, and the battery is not supplying enough voltage, then no fuel to engine.
Measure the battery when cranking...might only be 8-9 volts ?

I wish it was that simple. It has several solenoids that I know of one on the pump, one on the common rail and one on each of the injectors. Then it also has crankshaft sensor that is powered by 12V. I wish I could read the codes on the engine

 

[PoTreeBoy]

Is the cranking speed normal? I think I've read that a certain rpm is required before the ECU? will fire the injectors.

 

[c5vettster]

Is the cranking speed normal? I think I've read that a certain rpm is required before the ECU? will fire the injectors.

It cranks very nicely - 300-600 rmp. The battery can crank it for up to a 60 sec w/o any reduction in RPM. However, when it starts, it starts immediately.

 

[North Idaho Wolfman]

The first thing I would do is get the WSM (aka service manual) for the engine.
Sadly that majority of these electronic engines require a computer to read that system and codes.
And that computer is a dealer only item.

 

[c5vettster]

The first thing I would do is get the WSM (aka service manual) for the engine.
Sadly that majority of these electronic engines require a computer to read that system and codes.
And that computer is a dealer only item.

excellent advice. I just downloaded all 3xx pages and will go over it tonight

 

[GreensvilleJay]

focus on whatever STOPS the engine from running when you turn key to 'off'.

 

[c5vettster]

On the unrelated note - are these engines safe to start with the old gas soaked rug in the intake trick? I tried blowing hot air into air intake but given the turbine, it just doesn't heat up enough to make a difference

 

[Sawdust&Shavings]

On the unrelated note - are these engines safe to start with the old gas soaked rug in the intake trick? I tried blowing hot air into air intake but given the turbine, it just doesn't heat up enough to make a difference

“I” would NOT try it.

 

[North Idaho Wolfman]

On the unrelated note - are these engines safe to start with the old gas soaked rug in the intake trick? I tried blowing hot air into air intake but given the turbine, it just doesn't heat up enough to make a difference

NO, absolutely not!
Nothing other than diesel via the injectors.

 

[hodge]

You need to test the battery. What it shows with no load isn't the whole story. If the battery is bad and drops too much when starting, the voltage isn't high enough for the electronics to function. That would be the first place I would look.

 

[c5vettster]

You need to test the battery. What it shows with no load isn't the whole story. If the battery is bad and drops too much when starting, the voltage isn't high enough for the electronics to function. That would be the first place I would look.

I've checked it last night. It gives great cranking current - over 300 rmp. I think there is no easy solution here, I will need to read the manual and start diagnosing step by step

 

[Russell King]

Perhaps you could troubleshoot the voltage drop and see how much voltage is remaining at the wires of the pump and injectors. I guess it would be great to actually know how much is supposed to be there and NOT assume it is going to be 12 volts since they may have changed it for the electronics.

I was goin to suggest using a secondary separate voltage source for the wiring harness but I am not sure that is a good idea since I have read about “fried ECUs” from changing out a battery.

 

[Dustball]

Just to rule out the battery, can you try another known good battery such as one from an operating vehicle? Being able to start when only on a charger is suspect.

 

[c5vettster]

Perhaps you could troubleshoot the voltage drop and see how much voltage is remaining at the wires of the pump and injectors. I guess it would be great to actually know how much is supposed to be there and NOT assume it is going to be 12 volts since they may have changed it for the electronics.

I was goin to suggest using a secondary separate voltage source for the wiring harness but I am not sure that is a good idea since I have read about “fried ECUs” from changing out a battery.

I checked my charger and it is rated for up to 50 amp. So I am pretty sure that the voltage remains stable. I wish I had access to kubota computer to check the pressure in the fuel rail. There are no codes generated in the controller which means that the engine thinks it is ok. Therefore I think the issue maybe in injectors because low fuel pressure in the rail would likely trigger an engine code ? I got the amazon kit for backflow testing and will try it this weekend.

 

[#40Fan]

If you're absolutely sure the battery is good, then I'd be looking for dirty connections that would bring the voltage down during cranking.

 

[RBsingl]

As others suggested, check the voltage while cranking to the ECM 12V feed (and if there is a separate injection control module check there also). The ECM will want to see correct voltage and sufficient rail pressure to fire the injectors. Although a regulated lower voltage should be fed to the fuel rail pressure sensor, it is possible for system voltage to drop low enough to cause loss of regulation. This is important because if you are able to access a Kubota capable scan tool that will display both commanded and actual rail pressure, the sensor may return a false value and send you down an injection pump path when a voltage issue is the true problem.

And check ground connections! If there is a poor connection, then there will be a voltage differential between what the ECM sees and true ground which is exacerbated by high current draw when cranking. When I installed my standby generator a few years ago (Mitsubishi 4 cyl turbo diesel powered), the manufacturer had chosen a poor ground point on an engine shield near the injectors for connecting the ground for the controller assembly and so it was seeing a different voltage and although engine start worked fine, it wouldn't shut down the engine when the auto transfer switch sent the stop command. Fixing the ground cured that little oddity.


Rodger