Renault Master difficult to start

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Renault Master difficult to start

Postby RYM6746 » Wed May 10, 2017 11:07 pm

Hi all. I have a 2005 Renault Master chassis no VF1UDCWGH34000324. It has an extended crank time due to it taking along time to build pressure in the rail. I have done an injector leak off test and all is good. All are even with a slow fill time (only done 25 000 miles). I have bypassed the fuel filter with a transparent pipe and installed a vacuum guage. There is no air in the fuel and the suction pump is pulling 0.1 bar of negative pressure, 0.5 bar if I clamp the pipe. If I prime it with the hand primer until it goes solid (no leaks) It still has an extended crank time. When it runs it runs with out fault. If you switch engine off an immediately restart the crack time is better but still extended. I have definitely intermittently heard what sounds a lot like an electric fuel pump go off in the tank but not everytime I switch ignition on. But this vehicle has a suction pump on the back of the high pressure pump and a hand primer? ???? Seems strange to me. when I heard what sounds like an electric fuel pump I have not had any rise in pressure in the pre supply system. Has anyone seen this system before. I know for a fact that certain systems on this vehicle definitely have an electric pump but I thought that you wouldn't have a hand primer or even a suction pump on the back of the high pressure pump? If so could you let me know where the fuse or relay for the pump is so I can test further. Or if not what the next best test step is. Thanks for your time and knowledge
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Re: Renault Master difficult to start

Postby RYM6746 » Thu May 11, 2017 2:31 pm

It would take 3.5 seconds for the rail pressure sensor to reach 1 volt (eng start pressure). So I capped off an injector at the fuel rail this instantly brought the time down to 2 seconds. So I capped it off at the back of the pump with a rail pressure sensor that we have in our diesel test kit and that brought the time down to 0.5 seconds. Meaning pre supply system and high pressure pump are all good. Leaving just the injectors (Leak off test was good) or the rail or the high pressure pipes to be at fault, seeing as I didn't have 300 bar of fuel leaking all over the floor when it was running I can only concur that the injectors were leaking internally? I now have no option but to remove them and get them tested unless anyone can think of anything I have missed?
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Re: Renault Master difficult to start

Postby Dcunning35 » Thu May 11, 2017 3:27 pm

Does this have a valve in the injector return line ?if this has and is leaking back your leak off test wouldn't show it.
What fuel system is this ,delphi?
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Re: Renault Master difficult to start

Postby RYM6746 » Thu May 11, 2017 8:17 pm

No valve in injector return line, does have a low pressure bleed off pipe on the end of the rail (I had a bottle on this and literally nothing came out of it). It's a Bosch system. Unbelievably I put it all back together and the very consistent fault had disappeared. Don't you just love inadvertently fixing a fault that you have no idea what the real problem was and how long it is going to stay fixed for :roll:
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Re: Renault Master difficult to start

Postby Dcunning35 » Thu May 11, 2017 9:54 pm

Bosch common rail , so does this have a pressure control valve on the rail or a volume control valve on the pump? .
Im by no means a renault expert but the stuff ive seem with bosch usually doest have a lift pump. Best place to find out is the wiring info.
Checking current draw would be a good test to show mechanical restriction etc.
Capping the injectors and pump yes lower the time for press to build but also reduces the capacity.
Fingers crossed the van stays good without the concern aparent we are as always kicking the brown stuff uphill .
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Re: Renault Master difficult to start

Postby Technician » Thu May 11, 2017 11:03 pm

Just my tuppence worth;

1 / can you check to see if the fuel pressure rises from a cold engine to a normal operating temperature, if it does, then the injectors are not leaking internally!

2 / Have you got a scanner?

3 / if you have, can you go into OBD and use the program there to check item 1 ?
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Re: Renault Master difficult to start

Postby RYM6746 » Fri May 12, 2017 3:11 pm

There is 100 per cent a suction pump on the back of the high pressure pump. Yes I have a decent scanner. How does fuel pressure rising when engine warms up prove that the injectors are ok? Do you mean rail pressure?
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Re: Renault Master difficult to start

Postby Dcunning35 » Sat May 13, 2017 5:37 pm

Yeah im not following that either tech.
Are you saying fuel pressure or temp please can you clarify
Thanks
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Re: Renault Master difficult to start

Postby Technician » Sun May 14, 2017 3:20 pm

I've seen it on VW's, I can't guarantee it will work on other makes but thought it might be worth a look while testing.

The coolant temperature should be minimum 80 degrees C, the rail pressure measured, then while idling allow the engine to continue running for around 10 minutes, the heat soak should see the fuel rail pressure rise, if it does the injectors are not leaking internally. The other point I should make here is that what you can see while testing and measuring might be influenced by the software in the ECM!
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Re: Renault Master difficult to start

Postby Dcunning35 » Sun May 14, 2017 3:38 pm

No disrespect but I cant see that being a concise enough test for the fuel circuit integrity , you can evaluate pressure build up by isolating injector solenoids and making sure imv is forced open either by disconnecting it or forcing it electronically.
This with a leak off measurement is usually sufficient to prove out the hp hardware.
But as we know the hp is reliant on the low pressure , as the original poster states vacuum and flow both good tests.
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