Turns over but wont start 2.5 MN

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Re: Turns over but wont start 2.5 MN

Postby RHKTriton on Sat Jul 11, 2020 10:09 am

Start with the simple stuff before ripping out fuel pumps, injectors, etc.

Limited should be relatively easy to remove and check.

I'd try something like the Moly fuel system cleaner first.

Disconnect the fuel lines and stick them in the container and do a few cycles of cranking the juice through the fuel system. Let it soak a bit and then repeat.

If some contamination is causing your problem, this may help.

Just checked further back. You've checked the SCV valves, but did you checked if any voltage appears at the plug?

From what I understand about the common rail systems, there's always some fuel bleeding back to the tank, it's part of the cooling strategy for the injectors.

The output of the high pressure pump is totally controlled by how much juice the SCV let's into it.

I would have thought an injector stuck open would let some fuel into a cylinder resulting in combustion of some sort.

Life was much simpler back in the carby days. :lol:
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Re: Turns over but wont start 2.5 MN

Postby DibbyDibbyDJ on Sat Jul 11, 2020 1:53 pm

RHKTriton wrote:Start with the simple stuff before ripping out fuel pumps, injectors, etc.

I would have thought an injector stuck open would let some fuel into a cylinder resulting in combustion of some sort.
:lol:


You definatly be getting some smoke
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Re: Turns over but wont start 2.5 MN

Postby aids84 on Sat Jul 11, 2020 1:54 pm

The way CRD injectors work is similar to a quick exhaust valve. Some fuel goes out the pilot which allows fuel pressure to lift up the plunger against spring pressure and inject fuel out the nozzle. If a pilot circuit on just one injector isn't sealing properly the rail pressure won't build to adequate levels to fire the injectors.

Most rail pressure related non-start issues I have seen in the past 10 year working on these things turned out to be a dodgy injector.
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Re: Turns over but wont start 2.5 MN

Postby RHKTriton on Sun Jul 12, 2020 10:43 am

Pity we can't just rip the bastards out like a spark plug. :lol:
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Re: Turns over but wont start 2.5 MN

Postby SLIMaxPower on Sun Jul 12, 2020 6:43 pm

mine did the same thing. took mitsi 2 days. they changed out the ecu amongst other things. ended up being the fuel rail.
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Re: Turns over but wont start 2.5 MN

Postby DibbyDibbyDJ on Mon Jul 13, 2020 6:29 am

aids84 wrote:The way CRD injectors work is similar to a quick exhaust valve. Some fuel goes out the pilot which allows fuel pressure to lift up the plunger against spring pressure and inject fuel out the nozzle. If a pilot circuit on just one injector isn't sealing properly the rail pressure won't build to adequate levels to fire the injectors.

Most rail pressure related non-start issues I have seen in the past 10 year working on these things turned out to be a dodgy injector.


The Electronic injectors on a Triton have a positive fuel pressure behind the needle of between 30 and 200 Mpa. With the fuel pressure being so high, and changeable, the injectors are opened and closed by the solenoid, which uses in excess of 100v with high current to control the fuel delivery. Not relying on fuel pressure to lift plunger and control delivery.

Testing these injectors is very simple , using an oscilloscope with an amp clamp, it would be easy to see a fault injector.

Without proper diagnosis the OP could easily be led down a very long, winding and expensive path to fix this problem
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Re: Turns over but wont start 2.5 MN

Postby aids84 on Mon Jul 13, 2020 9:24 am

DibbyDibbyDJ wrote:The Electronic injectors on a Triton have a positive fuel pressure behind the needle of between 30 and 200 Mpa. With the fuel pressure being so high, and changeable, the injectors are opened and closed by the solenoid, which uses in excess of 100v with high current to control the fuel delivery. Not relying on fuel pressure to lift plunger and control delivery.

Testing these injectors is very simple , using an oscilloscope with an amp clamp, it would be easy to see a fault injector.

Without proper diagnosis the OP could easily be led down a very long, winding and expensive path to fix this problem


A problem with the injector solenoid would show up on an oscilloscope but it wouldn't show a problem like a solenoid valve that wasn't sealing properly. The ECU can account for slight changes in injector operation over time but only up to a point.

The solenoid does not act directly on the injector needle. It releases the pressure from behind the needle which allows the needle to lift up and inject the fuel through the nozzle. This is a very simple explanation but there is plenty of info out there on Denso injectors.

I agree the best path the OP to take is to get a proper diagnosis before ripping apart high pressure pumps and the like.
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Re: Turns over but wont start 2.5 MN

Postby Pinchers on Sun Jul 19, 2020 4:21 am

I was having another look at it today, fuel pressure at stop was 60kpa when cranking it goes up to about 330kpa, decided to disconnect the hi pressure line on the pump going upto the rail and stuck my fingure over it to see if it would build pressure when cranking, well i could keep my fingure over it and hold the fuel back.

Does this mean the fuel pumps internal relief valve is faulty or stuck open?
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Re: Turns over but wont start 2.5 MN

Postby RHKTriton on Sun Jul 19, 2020 8:54 am

Have you checked the HP pump's inlet for blockage?

I recall there is a a microscreen to protect the internals from contamination.
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