It took a few goes to start my deisel Mazda Bongo this morning. It’s old but always starts ok. But, it then stalled 2 or 3 times over the first few miles.

I realise there could be a whole load of reasons, but if the battery was flat, or at least not 100%, could that cause a stall once the engine was running?

Any other obvious causes with a simple deisel engine? Fuel pump?

Got a multi meter ?

If the batteries shot, replace that first and go from there.

The alternator might not be able to cope with charging a really flat battery and keeping everything above 12v and a bit. So, yes, it could cause issues. Also relying on the alternator to manically charge a dead battery will also kill that.

How ever if the battery is drained because the alternators dead …….. Your replacing the battery for no reason.

Once started the car does not use the battery to continue running – it draws power from the alternator.

Charge the battery stick it back in start the car and start it – stick a multi meter across the terminals – should read about 14volts if alternators good.

12 odd if its bad

Then trace all the alternator wiring and check the earths.

Mines was the voltage rectifier dying which in turn fried the alternator coil.

Sorry, wrong forum.

Yep, got a meter. But does the battery actually do anything once an engine is running?

Depends on the engine. Most modern diesels will need a reasonable electric supply for the glow plugs and fuel pump. If the alternator isn’t working well then there will be a drain on the battery.

What you describe is the classic symptoms of fuel pump seal failure on my Mitsubishi.

So, do I measure the voltage across the battery with the engine running and look for 12v plus? Less than that could indicate an alternator problem maybe?

I think there’s a bit more to it than just checking the voltage from the battery. Don’t Halfords do a free battery health check?

Engine running should see more like 14v

Aye . Personally id do that as an easy check – if it shows good id discount the battery and alternator.

Look at the fuel lines for a leak – both feed and spill lines.

If you have a leak itll take a while to start in the am – as the fuel runs back to the tank when sitting and your priming the system each time and it runs rough as dog usually.

Halfords do nothing free. 😉

http://www.wikihow.com/Check-an-Alternator

Its easy to check if it is your alternator or battery. When the engine is idling get a multi-meter across the battery terminals. It should be reading around 14v. Switch on your lights, heater, heated rear window and all your electrics and the voltage across the battery shouldn’t drop below 12v. If it does your alternator or voltage regulator (usually part of the alternator assembly and can sometimes be replaced separately) is not charging enough. The only way to check a battery is to use one of those devices that shorts across the terminals and tests if it can maintain amp output for a certain number of seconds, but thats not a test you want to repeat regularly as it can damage the battery.

Older generation diesel engines could run fine without a battery – they don’t have an electrical circuit, but modern engines are different with electronic fuel injection and all the mirriads of environmental systems running to ensure emissions are maintained but these all run on low voltage and low current circuits so you’re battery would have to be completely and utterly dead as a doornail before the engine would cut out.

How is it cutting out? Is is as you approach a junction when you depress the clutch? If so it could be something to do with your idle control system like a crank sensor, or a temp sensor for your ECU.

Thanks Wob. Checked, and the alternator is fine. I’m currently charging the battery from the mains anyway.

The van is an automatic. Stalling happened once when pulling away after letting a car out of a junction, then again on accelerating on the upside of a dip in the road, I was probably off the gas/diesel on the downslope. So maybe it was pressing the accelerator than caused the stall.

I had similar problems on a Nissan I had a couple of years ago – hard to start, random stalling, etc. It was the fuel pump on the way out.

If the battery was flat, you would only get the chance to stall it once 😉

Presuming you didn’t jump start it every time, I would say the battery isn’t flat ?

Sounds more fuel related to me, you wouldn’t restart it if the battery was flat. Might sound daft but have you checked the spark plugs & leads? I used to have an astra that used to be a bit on & off like that, after changing the plugs & leads, it seemed to fix it

my deisel Mazda

Might sound daft but have you checked the spark plugs & leads?

🙄

Gotta love the interwebnet.

OP once the car is running its the alternator the does the work, generally if you have a flat battery you jump start car and then keep driving until its charged. The other posters are questioning the alternator as if it’s not working then you won’t have enough juice to keep the car running. One other thought is that diesel engines don’t need much electrical power to keep running (much less than petrol) as such I too suspect you have another issue, eg fuel blockage, dirty fuel, fuel pump etc.

Had similar on an old Citroen C15D – it was a small split in fuel hose along the edge of a clip. Fuel drawn by suction from the tank, so split allowed it to draw in some air.

a petrol will require a good battery but a diesel generally wont – you could remove the battery on my boat and switch off all the electrics and it kept running and had a manual kill switch but it was old

I suspect its the battery as why is it getting flat?
Also worth noting that voltage and cranking amps [ how much power you can draw for starting] drop when it gets cold and you normally discover your battery is fubbared as it starts to get cold

Test that the voltage is higher when running than when not and it is therefore unlikely to be a the alternator

TBH any decent auto electrical place will do a free test for you it takes about a minute to do

What @Junkyard says is definitely true on marine diesels. Had an electrical fire on starting engine, had to cut all electrical connections to battery. Engine ran for 3 hours whilst we sailed/motored back to harbour.

Anyway follow @Junkyard’s advice above.

If its a Turbo my money is on the EGR valve. It does this as its wearing out/getting dirty and may not create any fault codes.

Diesels don’t use battery power other than to start, no spark plug. However thinking about it they are fuel injected so do draw some power but it won’t be more than supplied by the alternator, likely it’ll be a fuel issue, haven’t been filling it with unleaded (wife, kids or GF) have you?

Diesels don’t use battery power other than to start.

on my 87 land rover with mechanical cam driven fuel pump that may be true – but it hasnt been true for many years – especially moreso with jap vehicles.