1.6 hdi cranking engine

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thewww
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1.6 hdi cranking engine

Post by thewww »

Hello
can anyone tell me the best was to disable the high pressure diesel supply if I wish to crank the engine over with the injectors removed please .
thanks
John
Goc3k
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Re: 1.6 hdi cranking engine

Post by Goc3k »

If the injectors are out there is no way to prevent fuel leaking from the fuel rail while cranking without plugging the holes in the lines (injection pump is driven mechanically from the engine), normally if you leave the injectors in you can ground their pressure signal out (once sub 230bar the ecu will not allow an injection event), or simply disconnect them. You can also unplug the crank / cam sensor and the ECU will prevent the engine from starting up.

Disconnecting the pre-supply pump will lower the delivery of fuel to the injection pump, this is probably your best bet along with a lot of rags to catch the mess if you need to crank without them.

Why do you need to crank the engine without the injectors installed? Just curious
Bick
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Re: 1.6 hdi cranking engine

Post by Bick »

Goc3k wrote:If the injectors are out there is no way to prevent fuel leaking from the fuel rail while cranking without plugging the holes in the lines (injection pump is driven mechanically from the engine), normally if you leave the injectors in you can ground their pressure signal out (once sub 230bar the ecu will not allow an injection event), or simply disconnect them. You can also unplug the crank / cam sensor and the ECU will prevent the engine from starting up.

Disconnecting the pre-supply pump will lower the delivery of fuel to the injection pump, this is probably your best bet along with a lot of rags to catch the mess if you need to crank without them.

Why do you need to crank the engine without the injectors installed? Just curious
Hi Goc3k - just came across this post and found it interesting - but i was informed that if you unplug the injectors they went into full fuel, i was also told that if you unplug one whan the engine is running because they go into full fuel it can damage that piston. however you are saying if you disconnect an injector they go dead and pass no fuel. To be honest you sound like you know what you are talking about so was i given incorrect information?

many thanks
Goc3k
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Re: 1.6 hdi cranking engine

Post by Goc3k »

I've never worked on any car that has any injectors of any style that are wide open when not powered, even if only as a basic safety precaution (think chafed wires or water damage earthing / shorting the signal for example). Common rail fuel systems especially, injectors remain closed until powered, and then will only allow injection events to occur when signalled by the ECU.

CR injectors are such excellent feats of engineering, allowing multiple injection events of varying quantities to occur in hundredths of a millisecond. To do this while power cycling for each event is (probably) of little feasibility, and is definitely not how the current generation works. If a mechanic told you this I'd probably stop using him. "we need to take the injectors out sir, oh no sorry it's not a quick job...." [-X

Piston damage - no chance. if an injector tip broke off at say, 3.5k RPM while you had your foot mashed to the floor and thus dumped say 5-6% of the fuel rail into that piston within one or two revolutions would probably hydrolock the engine and bend / snap a rod. Allowing an injector to run open at idle would cause a colossal drop in fuel pressure, and then probably cause the ECU to shut down the engine, causing no damage.

That's how I understand it anyway, no personal experience of such a thing happening.
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Re: 1.6 hdi cranking engine

Post by Bick »

Goc3k wrote:I've never worked on any car that has any injectors of any style that are wide open when not powered, even if only as a basic safety precaution (think chafed wires or water damage earthing / shorting the signal for example). Common rail fuel systems especially, injectors remain closed until powered, and then will only allow injection events to occur when signalled by the ECU.

CR injectors are such excellent feats of engineering, allowing multiple injection events of varying quantities to occur in hundredths of a millisecond. To do this while power cycling for each event is (probably) of little feasibility, and is definitely not how the current generation works. If a mechanic told you this I'd probably stop using him. "we need to take the injectors out sir, oh no sorry it's not a quick job...." [-X

Piston damage - no chance. if an injector tip broke off at say, 3.5k RPM while you had your foot mashed to the floor and thus dumped say 5-6% of the fuel rail into that piston within one or two revolutions would probably hydrolock the engine and bend / snap a rod. Allowing an injector to run open at idle would cause a colossal drop in fuel pressure, and then probably cause the ECU to shut down the engine, causing no damage.

That's how I understand it anyway, no personal experience of such a thing happening.

Thanks Goc3k for you excellent reply - the guy that told me was an RAC patrol tec - i know!

The thing is i am myself a qualified motor vehicle engineer but on the truck side but i came off the tools 20 years ago and on to the management side, well before ill health cut me down anyway. My point is you lose touch with things so quickly when you come off the tools and its horrible putting your own vehicle into the hands of other people! The basic stuff im okay with and i even have my own diag kit - none of that around when i was on the spanners it was all ear, common sense and knowledge. Cummins engines was my main stay of work but even these have changed so much.

I have a little Berlingo (had a long line of Citroens) 1.6hdi and its a cracking little engine - Diesels are so quick nowadays!

Anyway thank you so much for explaining things to me and passing on your knowledge.


Many thanks

Bick
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Re: 1.6 hdi cranking engine

Post by Goc3k »

Ah my uncle used to work on lorries years ago. Much the same story escaping to a desk from the backbreaking greasy jobs!

It's funny really, lots of the knowledge of the engineering in an engine seems to have been lost at the average garage - seems they've mostly given up and revert to the classic "it's all computers nowadays" comment. Diesels are still smelly and very simple at least, just the pressures involved and control over injection events is hugely more advanced.

Everyone on the forum seems very helpful - ask away any you'll always get a wide array of responses :)
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