Ford Focus 1.8TDi - diesel coughs on starting - grumpynd

Focus 1.8 TDi coughs when starting. The colder it is the more it coughs and the longer it takes to start. Main agent diagosed bad battery but a new heavy duty Exide hasn't cured it.
Glow plugs should take a total of 32 Amps. They appear to be taking 80. It suggests they are open circuit. On board (milometer) OBD givesa none amongst a load of hex codes.
I don't know where to go from here. I'd appreciate any ideas especially as the main agent failed.

Once started it runs perfectly and fuel consumption is the same as ever

Ford Focus 1.8TDi - diesel coughs on starting - grumpynd

I meant to say the current suggests that there are not open circuit which I believe is the normal failure mode

Ford Focus 1.8TDi - diesel coughs on starting - mss1tw

Where did you get the 80 amp figure from?

I would expect flames or at minimum a blown fuse with over double the stated design current going down the cables.

Ford Focus 1.8TDi - diesel coughs on starting - Avant

Moved to Technical.

It might help to know whether this is the older TDDI on newer TDCI engine.

Edited by Avant on 27/02/2012 at 20:27

Ford Focus 1.8TDi - diesel coughs on starting - grumpynd

The 80 Amp figure came by using a DC clamp ammeter. I also did a separate check by putting a 0.15 Ohm resistor in series and measuring the voltage across it. They still took 32 Amps and measured about 0.1 Ohms

They are difficult to get at so my measurements are always in the lot in situ

The engine is a Durotorque registration 54.

Ford Focus 1.8TDi - diesel coughs on starting - dieselnut

Glow plugs don't have a constant resistance, they increase in resistance as they warm up just like filament lamps.

Initially they will draw about double the current they draw after about 10 seconds as they warm up. So I dont think there is any problem with the plugs.

Possibly a slight air leak in the fuel supply. Has the fuel filter recently been replaced.

Ford Focus 1.8TDi - diesel coughs on starting - grumpynd

Thanks for replies to everyone

I guessed they might do so but the 80 Amps was the stable current. The meter takes a time to settle and I connected them straight to the battery with jump lead and the meter round that. Nothing has been changed in the way of filters. This simply started happening probably coinciding with the lower winter temperatures. It is kept in a garage so it doesn't see very low temperatures but when I visited my daughter at Christmas it was outside and covered with frost one morning. It spent a lot of time coughing but did start eventually.

Another clue may be that on two occasions it started up in a funny mode. It may have been on two cylinders but sounded more like one. I guess the ecu got screwed up and possibly went into the 2 cylinder mode that it's supposed to when it over heats

Thanks

Ford Focus 1.8TDi - diesel coughs on starting - dieselnut

Glow plugs can start to melt under certain conditions & start to short out.

You would need to test each one individually.

Run a cable direct from the battery to each plug one at a time & check the current with your meter.

Alternatively disconnect three plugs then test one at a time that way, probably be easier.

Edited by dieselnut on 28/02/2012 at 15:03

Ford Focus 1.8TDi - diesel coughs on starting - grumpynd

Thanks that's a useful piece of information and it fits the symptoms reasonably well.

I'd better make the effort to disconnect them but it's not easy to get at them. Straight to the battery means that the meter gets time to settle.

Ford Focus 1.8TDi - diesel coughs on starting - mss1tw
I guess the ecu got screwed up and possibly went into the 2 cylinder mode that it's supposed to when it over heats

First I've heard of any car beside certain Yank V8's doing this!

Ford Focus 1.8TDi - diesel coughs on starting - grumpynd

I think I have proved that it isn't one of the glowplugs having failed.

I've isolated each one, measured it with a Ohmmeter having checked that agains a 1 Ohm resistor. I have meassured the current into each one when connected to the battery.

The current is initially very high and comes down dramatically as expected. I didn't want to burn them out so didn't leave it more that 5 to 10 second

Here are the results for those who like figures for future fault finding

1) 0.5 Ohms and current high falling to 16 Amps

2) 0.4 Ohms starting about 24 Amps and falling. I think this one remained fairly high

3) 0.25 Ohms 29 Amps falling to 13 and continuing to fall slowly

4) 0.1 Ohms 24 Amps falling to 13 and continuing to fall slowly

This car passes out of my hands and into my son's tomorrow which is why I was keen to find a solution. The time between experiments will now be very long and the weather isn't cold enough to be a problem but if we come up with a solution I will post it here. Thanks to all who have made contributions.

 

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