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Common Rail


Guest Ken Park

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Guest Ken Park
I can start my 1998 Fiat 2.5 TDI with a simple turn of the key, even in below zero conditions, whilst a friend who has the same base vehicle has to turn the key half way and wait for the pre - heat orange light to go off. Do I have a 'common rail' motor and not my friend ?
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Guest Clive
I am not an expert on these particular engines BUT what is normal is that DIRECT INJECTION diesel engines fire up easilly when cold. INDIRECT INJECTION diesel engines no not fire up when cold without a pre heater (glow plugs) A few years back all small diesels were indirect injection as the engines are quieter. But as direct injection engines are more fuel efficient technology has advanced at a pace and now they are also quiet. Today most small diesels are direct injection. Common Rail is a method of feeding the injectors with fuel at very high pressure with each injector controlled electronically by the engine management computer. I hope that helps
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Guest Ken Park
Yes, Thankyou. But why does my friend's 1998 Fiat 2.5 tdi cat need to wait to warm up (and the orange light to go off) before staring the engine and mine doesn't have to?
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Guest Derek Uzzell
Ken: No, your motorhome's diesel engine is not 'common rail'. The largest capacity Fiat Ducato motor went from 2.5TDi to 2.8TDi, then, in 2000/2001 to the current 2.8JTD. Only the JTD range of Fiat motors uses common-rail technology. As far as I'm aware, any Fiat diesel motor from the 1998 era will use direct injection, but that doesn't mean there won't be a device of some sort (glow-plugs, fuel pre-heater) to aid cold-starting in extremely cold weather. If your friend's vehicle is exactly the same age as yours I would expect the starting arrangement to be the same. However, if yours and his chassis are of slightly different vintages (I'm referring to when the base-vehicle left the SEVEL factory, not when the motorhome was first registered), it's perfectly possible that the starting systems will differ. If his vehicle has glow-plugs and yours has a fuel pre-heater, the starting procedure would match your description - you just turn the ignition-key, but he has to wait. It should be possible to confirm this by comparing the handbooks or, if you know what to look for, by visually inspecting the motors themselves.
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Guest Clive
"But why does my friend's 1998 Fiat 2.5 tdi cat need to wait to warm up (and the orange light to go off) before staring the engine and mine doesn't have to." Because cats are damaged by unburnt fuel so the manufacturers insist on the heaters (whatever type they may be) being up to temperature before you start your cold engine. This way the smallest amount of unburnt fuel will get into the exhaust system as the engine will fire up the quickest. This is also why you should not jump start a vehicle with a cat.
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Guest Ken Park
Sorry to go on still, but I'm still not fixed. The 1998 handbook I have says that there is a glow plug sysem on all diesel models that involves waiting till the orange light goes out (mine doesn't even come on). So, presumably, my vehicle hasn't got glow plugs but heats up the fuel somehow. Is this instantaneously done then, because even at below zero temperatures it starts with a simple turn of the key? (although it does belch out a bit of smoke in the process).
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Guest Derek Uzzell
Well Ken, there is one possible answer to this apparent conundrum - that the Fiat engines of your motorhome and that of your friend both have glow-plug pre-heating systems, but the "orange light" (or the complete glow-plug system) on yours just isn't working! Direct-injection diesel engines are capable of starting reliably without pre-heating assistance down to very low temperatures, but pre-heating (by glow-plugs or otherwise) helps lessen the load on the battery/starter and assists in reducing immediate smoke emission. The latter feature is a valuable benefit when the vehicle is fitted with a catalytic converter, though on diesel motors 'cats' are far less sophisticated and more tolerant of ill treatment (being primarily particulate traps) than those fitted to petrol-engines. The Ford handbook for my Transit-based diesel-engined motorhome also referred to "glow plugs", but the vehicle in fact had a separate fuel pre-heater that raised a small quantity of fuel to a high temperature before injecting it into the intake manifold when the starter-motor was engaged. Operation of the pre-heater was evidenced by a dashboard light that went out when the fuel had been heated to the correct temperature, at which point one turned the ignition-key to the Start position. I've no idea if this system worked as, even in the coldest weather, the pre-heating light never came on and the motor always started immediately by "a simple turn of the key". Occasionally it used to smoke noticeably when starting, usually if the vehicle hadn't been driven for a while. My recollection of contemporary test reports of motorhomes with Fiat's 2.5 engine was that these motors were renowned for belching smoke at cold start-up and also for diesel-rattle until warmed up. Clearly, without sight of the two vehicles, I can't tell if there are differences between the motors: as I said previously, if you are able to compare the two any significant variations should be apparent. As far as your own vehicle is concerned, it should be evident whether or not glow-plugs are fitted (small spark-plug-like things in the cylinder head near the fuel-injectors). If it has glow-plugs then I would expect a dashboard light to illuminate, but if that's not happening then c'est la vie. Try waiting (say) 20 seconds before turning the ignition-key to the Start position: if the motor starts a bit better and smokes a bit less then your orange light may be duff. If you want genuinely expert advice on this I suggest you ask MMM's "Interchange", but I think you would probably need to provide specific details of both vehicles (VIN numbers & engine numbers) to obtain a comprehensive answer.
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Guest Clive
Connect a volt meter between the top electrical connection of a glow plug and chassis. Expect this to read something like 11.5 volts when the key switch is initially turned to the ON position just before the start position. This voltage should go to zero after 20 seconds or so. If this voltage is present but you don,t have any lights on the dashboard then its probably something as simple as a dash board bulb or a small wire pulled off. If this voltage is not present at all then you need to look further, like the timer relay. At this point you need a vehicle sparky. Hope that helps.
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Guest Ken Park
I'm booked in for Monday the 21st at my local Fiat main dealer for them to check all this out. I'll post a message here afterwards with what they say.
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Guest Derek Uzzell
Ken: I'm sure you are aware of the old maxim "If it ain't broke, don't try to fix it". If I owned a vehicle that started every time 'on the button' whatever the weather, the last thing I'd do is encourage someone to fiddle with it. However, I'll be interested to learn what your Fiat dealer diagnoses.
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Guest Ken Park
As my car has just sprung an oil leak, I've decided to use the appointment for it and (as Derek Uzzell suggests)let sleeping dogs lie as as far as the starting 'non problem' is concerned. Thanks for all the advice everyone.
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Guest Mike P
Ken, Your engine has a small but powerful heater in the inlet manifold (top RHS) adjacent to a small soleniod valve which takes diesel from the injector pump.As soon as you turn the key the heater comes on and heats up very quickly and almost simultaneously diesel is sprayed onto the hot element and drawn into the engine & bingo. Works great until the element fails but you'll notice that immediately. Replacement heater is about £40 from main dealer
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Guest Ken Park
I believe you...... but it's odd that the Fiat manual says to turn the key, then wait till the orange light goes out. My vehicle starts straight away (and no light comes on even at - 10°c) so it seems that the manual is wrong and the MMM forum is right.
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