brief loss of power or drive at the top of a hill

[moonunit100]

Hi folks!
I have a 2007 C180K SE W203 automatic and a question. Twice now, about a week apart, my car has briefly lost power or maybe drive in the exact same place on my way into work. It results in a sort of 'kangaroo' effect like that of a learner with clutch issues! It was more extreme the first time and only lasts about a quarter of a second. After the first instance if this I'm sure I smelt fuel, but this wasn't the case this morning when it happened again. The car seemed fine before and after the event on both occasions.
Both times this has happened at the top of a hill which is quite steep and about 300 metres long with a small roundabout at the top. For the last 10 metres or so of the hill, I coast towards the small roundabout and then put my foot back on the accelerator as I get halfway round it (turning right). It is at this point the problem occurs.
So basically, I go up a hill for about 15 seconds at about 30 mph, then coast for about 3 seconds before gently accelerating again while turning right, at that moment, the car briefly kangaroos. I havent been able to notice any other details while it's happening as up till now it's been unexpected.
Any ideas? Thanks.

 

[grober]

Sounds a bit like a fuel transfer problem. Possibly a problem with the "saddle bag" tank configuration across the transmission tunnel under the rear seat?

 

[moonunit100]

Thanks Graeme, I'll try to look into that. Any more ideas anyone?

 

[BlackC55]

I would check the codes on a Star firstly.

Does it do it with a full tank?

 

[moonunit100]

Thanks for joining in BlackC55. The first time it happened I can't remember how much fuel I had, the second time it was about 2/3 full. I will get the codes checked, are there likely to be codes even with no warning lights illuminated?

 

[BlackC55]

Yes.

If no codes then fuel pressure needs to be checked when the fault happens. It could be a weak fuel pump.

 

[grober]

These fuel systems are far from simple nowadays and impossible to check some components inside the tank. Hence Olly's suggest to get the fault codes checked. HERE'S AN EXPLANATION.

The fuel delivery module (88) together with the fuel pump (M3) is positioned in the right chamber. A closing plate (89/1) with connection fitting, cable connector, suction spray pump (95), left fuel gage sensor (B4/1) and the fuel tank pressure sensor (B4/3) only are located in the left chamber.

The fuel flows from the 2-stage fuel pump in the delivery module along the line (90) to the left closing plate and on to connection A to the fuel filter with integrated fuel pressure regulator. Excess fuel flows back through
connection B and the suction spray pump (95) and connecting line (91) into the right chamber. A suction effect is produced in the suction spray pump which draws the fuel from the lowest point out of the left fuel tank chamber to the delivery module. This ensures that the left chamber is properly emptied.
The fuel delivery module housing is used as a splash bowl. When cornering with a low level of fuel in the fuel tank, it prevents the fuel pump drawing in air.

Fuel strainers are provided at the bottom of the delivery module and at the inlet to the fuel pump.

Each fuel tank chamber has a fuel gage sensor (lever sensor with potentiometer and sliding contact). The resistances of the two fuel gage sensors are connected electrically
in series (each 100 W).
Fuel tank full: approx. 0 W
Fuel tank empty: approx. 200 W
The fuel tank has no drain. It is drained through the fuel line in the engine compartment.

 

[DrNick]

Although 9 times out of 10 its the obvious solution (ie as suggested, something to do with fuel delivery), occasionally we get another solution hiding in the background. In this case, as it happens at the same physical point, there may be an environmental solution. For example, are there any big radar emitters that come into view as you get to the top of the hill that could lead to electromagnetic interference? Unlikely I know, but lets see if we can dismiss it quickly, and then we can get back to diagnosing the fuel system!
eg http://news.bbc.co.uk/2/hi/uk_news/england/norfolk/6110844.stm

 

[moonunit100]

It's a good point DrNick, the roundabout in question is on Luton airport, so very close to lots of transmitters etc! That's the weird thing, it has only happened twice and both times in the same place. That's why I wondered if if was something to do with the fact I am coasting uphill then turning right just as I accelerate when it has happened. But the electro-magnetic interference theory is an interesting one.

 

[Dieselman]

Does the gearbox have enough ATF in?

 

[moonunit100]

Hi Deiselman, yes it does. I've been keeping my eyes and ears open when on the same bit of road over the last couple of days but the problem hasn't re occured. Maybe it's not a problem at all, just seems a bit weird - a bit of a strange coincidence!