Diesel Car Runs Lumpy Until Warmed Up

GunJack

Been going round in circles looking for possible solutions to this one…..

2011 Ford CMax 1.6 diesel, when cold and you first start it up, it doesn't like ticking over smoothly and drives a bit hesitant until it's been running for a couple of minutes (not even up to normal temp) then it's fine. I've had many diesels over the years but have never had this issue before…

Been looking around online, various forums, etc. and people have suggested a glow plug on the way out, an injector leaking air, various valves sticking, a vacuum leak and other bits that cvould be causing it.

Anyone on here got any pointers as to what may be causing it, before I resort to my local trusted garage and the possibility of part-swapping???

paul_c123

I would first suggest scanning for codes. That will give useful direction, but bear in mind there's an interpretation needed on the results, and its not idiot proof.

It may be an injector but it WON'T be leaking air.

Ectophile

My experience of dead glow plugs is that they make the car hard to start on a cold morning. But they only run for a few seconds to start the car. Once started, the cylinder with a dead plug very quickly gets warm enough to run normally. Not minutes.

Iceweasel

In many modern diesels the glow-plugs can play an active part until the engine is filly up to temperature.

Could take 5 to 10 miles for that.

Goudy

There is a whole host of things that can cause these symptoms.

The main things to look out for first is a fuel/air imbalance. This could be anything from a leaking air intake hose after the MAF, sticking EGR valve, clogged fuel or air filter, leaks of the fuel system (not just outward leaks but air leaking into the fuel system), iffy MAF. (does it run better with the MAf unplugged?)

Next up would be the glow plugs. It's true a modern diesel will continue to use them after a cold start, but if the car is cold starting cleaning then they are generally working okay. If it really labours to start first thing in the morning then you have got a problem.

There's not a lot you can check yourself with the fuel system apart from outward leaks. You really need diagnostic software to read rail pressures etc or other specialist equipment to measure injector spill off and things like that.

It could be an injector is spilling off too much fuel and causing a lower rail pressure. At cold start it will normally fire the injectors with a fairly low rail pressure compared to hot starting as it knows the fuel is cold and slow to move. If the rail pressure is too low the engine will stumble when cold. When it warms up it will generally drive okay until fuel demand is really high, like wide open throttle up a hill.

I had a 2.0 TDCi that did this, one injector was spilling off a bit too much and the engine stumbled at cold start until it warmed up properly.

Years ago it was usual for a clear bit of pipe to be fitted just before the HP pump so you could see if the fuel system was drawing in air, they don't tend to do this anymore which is a shame.

Have you had any work done recently like a service? I know from experience some Fords don't like aftermarket fuel filters. Are the connectors to the fuel filter seated and the right way around?

As you are only mentioning this being a cold running issue, there is another problem with these and that's the PCM.

The PCM will have different fuelling strategies for cold and hot running and they have what is known as a pilot learn as the engine starts to warm up. It's basically learning what needs to be injected as it warms up and it does tend to effect cold idle when it goes wrong.

My best advise would be to find a local diesel specialist and not your common or garden garage and set aside for money for some diagnostics to be ran.

A local garage might just try replacing expensive parts in hope as they tend to see a problem in the system but can misdiagnose a part as it's not always that part at fault, it's just having a problem because of something else.

GunJack

Thanks for the detailed reply @Goudy , sounds like it's a how longs a piece of string? job ☹️

Bit more info...it had full service about 5k ago, but the issue was present before & after, so no change there. It pulls up hills just fine, drives well all round and averages 57mpg on mixed driving, and it starts first time every time. It's only lumpy for first 3-6 miles and is soo annoying.

Currently looking for local diesel specialists to get it checked over, any idea how much I'm looking at for diagnostics? (North Wales/Cheshire border)

Goudy

You should just pay an hourly rate for diagnostics and how long will depend on how far they need to go.

Electronically they can flag up things with trouble codes, if it's flagged them that is. You can also log other perimeters via the onboard diagnostic port but you need to know what you are actually looking at.

Then of course there are some physical checks and tests, but they should be set up to run these with ease.

You'll likely have to leave it with them until it's cold if it's a cold running issue.

Hopefully a decent diesel specialist will have a good diagnostic routine but it always worries me when garages want to start to change parts wholesale, like the entire fuel system. You'd only consider that if the high pressure pump has started to break up and swarf has contaminated everything else.

Mildly_Miffed

Don't guess. Read fault codes. Ask the car.

Glow plugs are much less relevant on cold start with a common rail diesel than they used to be - they're mostly used for emission purposes now, especially in the current weather.

If just one cylinder is misfiring cold, I'd be thinking injector or compression before glows.

Bigwheels1111

My 5008 diesel runs sweet.

In the very cold weather it hesitates just a touch, so I use Mannol 500ml Super Diesel Cetane Plus Cetan Diesel Fuel Additive. Car drives smoothly in -10 weather, have you tried a fuel cleaner and a good spanking.

When was the fuel filter last changed.

GunJack

https://forums.moneysavingexpert.com/discussion/comment/82078326#Comment_82078326

Thanks, will try that...as per earlier posts fuel filter changed 5k ago on the service but the issue was there before and after ☹️

Goudy

I was talking to someone more familiar with this engine yesterday and it's not unheard of for the connectors to the fuel injectors to rattle loose.

It's not the plastic connectors becoming loose but the connector's pins between the looms socket and the injector it's self can work loose and cause a misfire. Some have had to nudge the pins over a little to make a better connection.

I would have thought this would cause a misfire all the time but the metal pins might be expanding when they heat up as the engine warms.