Whats wrong with my car - engine cuts out under load.

wasc · 17 Jan 2006 at 22:55

Hi everyone,

Got a Merc A Class - the Diesel one (A170).

When it's placed under a heavy load, the engine just cuts out completely, which makes overtaking very erm, interesting

As an example, today on a clear road (40mph) I put the car into 2nd gear at about 15mph, and pressed the accelerator firmly (probably about 3/4 of the way). The car goes from about 1.5k rpm up to about 3.5k (which probably took 2 seconds to do) and then promptly cuts out somewhere between 3.5k - 4k. (And can I say the A class is a right **** to steer into a side road with the power steering cut out due to the engine cutiing out. Need both hands to turn the wheeel lol.

It's not just limited to heavy acceleration. When I was driving back home from uni (i.e had the back of the car loaded up with all my things) the car cut out 11 times on the 1.5hr journey home, one of those times was on the moterway at 60mph.

As some further info, when the engine has cut out, it wont start again for a while. If i turn engine off (i.e turn key all the way to left, put car in neutral, hand brake on, and then turn ingnition on, the engine just turns over. It doesn't catch at all, even if I pump or press the accelerator. Only solution i've found is to give the car 60 - 120 seconds before trying again and it usually starts fine then.

So - any ideas? I only have one light on the dashboard when the engine cuts out - think it says ECU from memory - really should take a note next time. Merc already put a new ECU chip in which hasn't done anything to the car - same fault.

V-Spec · 17 Jan 2006 at 22:58

Could be one of a few things, quite likley to be your air flow meters, fuel pump or ECU problems..

I take it the car idles fine?

wasc · 17 Jan 2006 at 23:01

V-Spec said:
Could be one of a few things, quite likley to be your air flow meters, fuel pump or ECU problems..

I take it the car idles fine?

Thanks for the reply - car runs perfectly - no symptoms whatsoever except seemingly random cutting out under load. Not limited to a certain rpm, speed, or gear. Idles fine.

Forgot to mention, now you mentioned air flow, the car is a Turbo Diesel if that influences anything.

BillytheImpaler · 17 Jan 2006 at 23:02

First thing I'd check is the fuel filter.

Lashout_UK · 17 Jan 2006 at 23:07

sounds like a lack of fuel due to debris in filter/fuel line or an air flow meter problem.

wasc · 17 Jan 2006 at 23:11

Lashout_UK said:
sounds like a lack of fuel due to debris in filter/fuel line or an air flow meter problem.

Any idea if these things are easy to check yourself, or should I take it to a garage to check? You can probably tell I know little about cars

Che · 17 Jan 2006 at 23:11

I know nothing about cars but our Passat used to randomly cut out and turned out it was faulty spark plugs or something.

Bloomin' dangerous it was, the powersteering and assisted breaks cut out half way through going round a corner a few times :eek:

This was after VW said it was fixed by the way lol.

BillytheImpaler · 17 Jan 2006 at 23:19

I don't know about your particular model but the fuel filter in modern cars usually takes some work to expose and replace. The part should be pretty cheap though, so you might want to get one and swap it just to experiment.

How many miles are on it?

Tesla · 17 Jan 2006 at 23:28

Che said:
I know nothing about cars but our Passat used to randomly cut out and turned out it was faulty spark plugs or something.

It wont have any spark plugs so those cannot be at fault

Can Merc read any error codes from the car, saves changing things that are not broken!

geiger · 17 Jan 2006 at 23:28

I had something similar and it was a leak in the air intake manifold. Too much air and the car will idle but not hold a load.

Che · 18 Jan 2006 at 00:11

Tesla said:
It wont have any spark plugs so those cannot be at fault

Well you learn something new everday

Is it because it's a diesel? How does the engine ignite the fuel then?

Ultra_Extreme · 18 Jan 2006 at 00:18

I dont think it would be the fuel filter, the car is in motion momentary lack of fuel would cause power loss but not the engine to cut out completely unless the ECU is designed this way. I personally would go for sensor failure, temp, airflow or lambda.

andi · 18 Jan 2006 at 00:24

Che said:
Well you learn something new everday Is it because it's a diesel? How does the engine ignite the fuel then?

The engine compresses the air in the cylinder, the air gets hot. The diesel is injected in and the hot air ignites it. Whoosh.

BillytheImpaler · 18 Jan 2006 at 00:25

Che said:
Well you learn something new everday Is it because it's a diesel? How does the engine ignite the fuel then?

It raises the pressure in the chamber so high (thus raising the temperature according to Charles' Law)that the air inside burns as soon as the fuel is injected. The fuel is injected at the point in the cycle that a gasoline engine would spark.

EDIT: Beaten to the punch.

Che · 18 Jan 2006 at 00:28

Why doesn't that work with petrols? Is the necessity for high pressure why turbo diesels are the norm?

Hades · 18 Jan 2006 at 00:49

It sounds similar to the problem I once had wth an old Scirocco. Mine turned out to be a faulty fuel pump. In my case the cut-out was signalled by a high pitched whine just before stopping.

Mickey_D · 18 Jan 2006 at 09:08

Ultra_Extreme said:
I dont think it would be the fuel filter, the car is in motion momentary lack of fuel would cause power loss but not the engine to cut out completely unless the ECU is designed this way. I personally would go for sensor failure, temp, airflow or lambda.

A fuel filter IS the most likely suspect. A dirty fuel filter will not just all of a sudden cut the fuel flow off making the car not run at all. It will start by restricting the maximum volume of fuel flow - which is at full throttle. It will get steadily worse as the filter gets more clogged up.

The reason the car takes a while to start back up is that the offending clogging will become smacked so hard against the filter from the pressure, then it takes a while for the low side pressure to slacken to allow the gunk to fall off and let fuel flow again. I've had this happen several times myself (granted not on an oil burner).

It could be several other items, but the most likely is the fuel filter. It's also the cheapest to fix.

wasc · 18 Jan 2006 at 19:11

Mickey_D said:
A fuel filter IS the most likely suspect. A dirty fuel filter will not just all of a sudden cut the fuel flow off making the car not run at all. It will start by restricting the maximum volume of fuel flow - which is at full throttle. It will get steadily worse as the filter gets more clogged up.

The reason the car takes a while to start back up is that the offending clogging will become smacked so hard against the filter from the pressure, then it takes a while for the low side pressure to slacken to allow the gunk to fall off and let fuel flow again. I've had this happen several times myself (granted not on an oil burner).

It could be several other items, but the most likely is the fuel filter. It's also the cheapest to fix.

Thanks, I might phone a few garages around and get a few quotes. Not too good with cars myself so wouldn't want to try it unless if it's fairly easy.

moss · 18 Jan 2006 at 19:12

wasc said:
Thanks, I might phone a few garages around and get a few quotes. Not too good with cars myself so wouldn't want to try it unless if it's fairly easy.

It should be easy, you just usually have to undo the fuel line and put the new filter in place.

Whats wrong with my car - engine cuts out under load.

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