TDI75 starting on two cylinders

Proghound

Proghound

Admin Team
United-Kingdom
As you may be aware, I'm currently selling my Cobalt TDI and one thing that's come up as a question from an interested party is, do I know what might be causing it to start on two cylinders from cold? I've mentioned in the advert that I'd floated the subject past Marcus at WOM and he mentioned injector seals as a possibility. In the interest of complete openness, we agreed that I would start this thread to see if the collective wisdom of the forum can come up with any other diagnosis or confirm Marcus' thoughts.

The symptoms are that it's definitely temperature dependent, but not to the extent where glowplugs are involved. In the middle of summer at 25°C plus, it'll fire straight up on all three. On an icy winter's morning, it may take 20-30 seconds for the third pot to wake up. Today at 17°C having not been started since Saturday, it took about 5 seconds, on Saturday at about 13°C also after two days unstarted it was closer to 10 seconds. In my experience 5-10 seconds has been the typical behaviour. It hasn't got any worse that I have noticed in the 18 months I've had the car, and it's never failed to start, almost always firing up on the first try.

Once the third cylinder has chimed in the engine smooths out within a few seconds and runs evenly, without any further misfires. My feeling (although happy to be proved wrong!) is that we can discount the injector loom, which would tend to cause a misfire to come and go depending on the state of the connection in the broken wire(s).

Gentlemen (and ladies :)) your thoughts please?
 
Last edited:
Does start with a cloud of smoke - that would suggest that fuel is getting into the cylinder but it's not being ignited. If it doesn't then it's probably fuel related.
 
depronman said:
Sticking injector
Click to expand...
I'm expecting the low fuel warning in the next few miles. I'll stick a splash and a bottle of injector cleaner in it, although I think I did this before with no difference. For what it's worth, I've always used the standard Shell fuel.
Any further suggestions?
 
Does the car get up to temperate (90 degrees) normally?

if your temperature sensor is not working as it should, it could be “telling” the ECU that the engine is hit when it isn’t and that would under fuel it.
But the guys at WOM know their stuff!!!!!

Steve B
 
Birchall said:
Does the car get up to temperate (90 degrees) normally?

if your temperature sensor is not working as it should, it could be “telling” the ECU that the engine is hit when it isn’t and that would under fuel it.
But the guys at WOM know their stuff!!!!!

Steve B
Click to expand...
Yes, thermostat and temp sensor were both replaced at WOM 18 months ago. It gets to 90 in 5-8 miles and stays there.
 
I have a 6 cylinder 3.0 litre bmw that shakes for 5 seconds or so and coughs a tiny puff of smoke when first started but only when the weather is cold.
I know this to be the glow plug control module which i have yet to get around to replacing, along with the glow plugs themselves but i wonder if your A2 could have the same problem as the symptoms sound very similar?
 
No harm in checking the resistance values for the injector loom from the external plug. How long since the fuel filter has been changed and importantly any water build up drained off. How are the fuel trim values in VCDS especially on initial start? How is the EGR valve? You may have carbon build up in the head or even a loose glow plug.
 
A2Z said:
I have a 6 cylinder 3.0 litre bmw that shakes for 5 seconds or so and coughs a tiny puff of smoke when first started but only when the weather is cold.
I know this to be the glow plug control module which i have yet to get around to replacing, along with the glow plugs themselves but i wonder if your A2 could have the same problem as the symptoms sound very similar?
Click to expand...

The glow plugs wouldn't be in operation at the current daytime temperatures though, would they?
 
audifan said:
No harm in checking the resistance values for the injector loom from the external plug. How long since the fuel filter has been changed and importantly any water build up drained off. How are the fuel trim values in VCDS especially on initial start? How is the EGR valve? You may have carbon build up in the head or even a loose glow plug.
Click to expand...

Fuel filter changed 2000 miles ago (at least, that's what it says on the invoice and I trust the garage I use). I couldn't tell you anything about VCDS values, I don't have any form of code reader. EGR I know is mapped out, I suspect it's also bored out but since I pay for spannering it's basically a closed system to me.
 
A VCDS scan would / could be helpful. Although I have yet to see an injector loom show itself on a VCDS scan. The fuel trim could point you to a particular injector that could have leaking seals bad spray pattern or sticking, some of this can be HELPED with a good injector cleaner. My preferred one is Ecomotive Clean Drive. The water in the fuel does not do any good to the system, so even though it has been recently changed it is worth draining to see if any present. Most of us are using our cars less now so they tend to stand around much more allowing contaminates to build up.
A leaking glow plug can sometimes be heard or by squirting a small amount of soapy water bubbles observed.
 
audifan said:
My preferred one is Ecomotive Clean Drive
Click to expand...
Thanks, I'll try that - ordered one, should arrive Thursday.
The soapy water trick on the glowplugs sounds about my sort of level, I can give that a go too.
If I were to seek a VCDS scan, I presume I would need to do a cold start i.e. it would have to be either here or at my other half's place where we actually live?
 
As you appear to only be having the lazy third cylinder when cold / first start then yes those locations are when to do the scan as those readings are more important. You can have a scan done when the engine is warm but by then the "fault" may have cleared, but still useful as this may give you figures to compare. If the OBDII socket had been placed somewhere safer, I would have suggested connecting everything up and drive the car from a cold start until fully warmed up logging the fuel trim and other values as needed. As the socket is located directly above your feet, while it can be done I do not recommend you do so.
 
Not an expert on this topic, but could it simply be that this pot has lower compression, eg due to valves, head gasket, piston rings leakages?
 
Joga said:
Not an expert on this topic, but could it simply be that this pot has lower compression, eg due to valves, head gasket, piston rings leakages?
Click to expand...
Head gasket and and piston rings can almost certainly be discounted, it uses no coolant, maintains steady temperature and has no crankcase ventilation issues. I'm sure the MOT emissions test would have picked up on a bad exhaust valve, it's been through two tests with the issue that I know of. After the cold start, it simply doesn't run poorly at all, it's perfectly smooth - you'd expect to be able to feel a compression imbalance on a 3-pot engine, surely?
 
Mot test is a waste of time especially if the default value is used

I would remove loom in head and tighten connections
 
You must log in or register to reply here.
Back
Top