Technical Doblo desperation

Currently reading:
Technical Doblo desperation

To inject the fuel at this stage the pump needs to generate huge levels of pressure to overcome any back pressure from the compression of the engine.

I'm sorry but that bit is just pants. Modern common rail diesels inject at up to 2000 bar pressure. That's around 29000 psi!! and engine will generate in the region of just 225 psi.
 
(just jumping in between you guys for a mo) so do you think it's more than likely the injector pump that is faulty? If so would a 'lift pump' help? (that is a question from my pal Mick)
 
(just jumping in between you guys for a mo) so do you think it's more than likely the injector pump that is faulty? If so would a 'lift pump' help? (that is a question from my pal Mick)

When the engine is fully hot and you have switched it off for say 10 minutes, does it start up easily before it starts its cutting out business?
(there are two fuel pumps on your car. An electric one in the fuel tank, and a manual high pressure one driven by the engine. If the pump in the tank has failed, it can cause all sorts of strange occurrences. Some makes of cars, you'd barely notice except that are reluctant to start, especially when cold, others if the tank pump fails the engine just wont run)
 
Ok, so what do you think will happen if you try to inject fuel at 225psi ?
If the pump can't make 225 psi when it should be making around 29000, I would say it's totally fubard. Engine back pressure is a minuscule % of the pumps working pressure and would make an immeasurably small increase in the amount of force required to compress the fuel to the working pressure.
 
Last edited:
If the pump can't make 225 psi when it should be making around 29000, I would say it's totally fubard. Engine back pressure is a minuscule % of the pumps working pressure and would make an immeasurably small increase in the amount of force required to compress the fuel to the working pressure.



You’ve missed my point entirely, and not answered the question I asked.

Why do you think the injection pressure is so high? And what difference do you think it would make if that pressure were to drop even slightly?
 
Hi, and thanks for your reply. I drove 30 miles the other day. Switched off and returned to the vehicle 20 minutes later. It played up again and the only way I got away was to keep the key in turning over position whilst revving the motor to about 3/4000 rpm.
 
Hi - in response to your post (answering my Doblo problem) "check this part out

after 1.9 jtd had the same issue

! discovered a solenoid valve behind EGR, which has 2 vacuum pipes on it, one to the air intake throttle valve or shutoff valve oroverrun valve whatever its called. . Called boost pressure switch, or throttle vacuum solenoid or whatever anyway it wasn't working (12V across the terminal solenoid not clicking and no air flow),so I soaked it in WD40 over night and working great. I refitted it and car is now fully operational again....and has been for a few weeks now"
 
Btw, and this is basic diesel engine stuff;
The reason for that amount of pressure in diesel engines is to atomize the fuel.. You press the fuel throug thin nozzle holes with say 1000 bars and it turns into a mist like spray (atomizing) This again for combustion purposes.
Now a por atomizing can be caused by either por pressure from the pump or por nozzles/injectors.
 
Back
Top