power loss - Merc C240

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Tue 5 Aug 2003 21:40
power loss - Merc C240 - Puzzled
Car - Merc C240, 91,000 miles. 1998 vintage, automatic 5-speed.

Problem: Round town or city, the car is fine. But on the motorway or dual carriageway it\'s a different story. It will cruise along at 70 fine, no problems, but when I start to overtake it\'s not very energetic. It will change down, and accelerate, but once you hit 4,500 rpm, it runs out of steam. I\'ve managed to get it up to 4,750 rpm or thereabouts, but no more. Car feels as if it\'s struggling to go faster - held back in some way. Kickdown, just the same: it changes down but runs out of go at 4,500 rpm. I thought it might be a clogged air filter, but that seems OK, it looks fairly clean anyway and I cleaned it off before leaving work tonight - no change. It\'s regularly serviced and had an A service about 3,000 miles ago. Nearly all travel is on dual carriageway or motorway.

Any ideas? I\'d value any input.

Richard
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Tue 5 Aug 2003 22:34
power loss - Cheeky
Very odd - My Dad has a C200 on an 'R' plate and has never experienced this.

Could it be a partially blocked fuel inj. system or bad HT/Ignition leads?

Either way, if you've had a full MB service so recently I think you should run it back to them to give it the once over.

Just out of interest, what happens if you drive it as a manual (making the gear shifts yourself) and hold it in gear until 5000-5500 rpm? As well as running out of power is the box changing up too early in kickdown?
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Wed 6 Aug 2003 18:40
power loss - Puzzled
Cheeky,

I hadn't thought about changing manually, but after your post I went out and tried it. In first and second, I could get over 5,000 rpm (couldn't use higher gears because of speed limits).

Hope your dad doesn't have same problem - air mass sensors are expensive!

Richard
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Wed 6 Aug 2003 00:57
power loss - Merc C240 - Dynamic Dave
If it's not got a 'fly by wire' throttle, check to see if the accelerator cable needs adjusting.
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Wed 6 Aug 2003 18:30
power loss - Merc C240 - Puzzled
Update on the power loss issue.

I went to the local independent Merc specialist first thing this morning. They were fully booked up until next week, but asked me to return in a couple of hours, which I did. One of the techs went for a test drive, and said they'd need to hook it up to diagnostic computer. If I left it with them, they'd try to fit it in between jobs. By 6pm they phoned me - car fixed. The cause was that the air mass sensor was on the way out. Fortunately they had one in stock. Impressed by service - they even stayed late to do the fix. Difference in acceleration very noticeable (have to watch the cameras now).

Thanks for input; hopefully this might give someone else a clue if similar symptoms appear (additional symptom which I didn't mention, by the way, was jerky acceleration. In passing,I'd mentioned hesitation / jerky changes to dealer, who couldn't find anything at the last service.

Richard
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Thu 7 Aug 2003 10:18
power loss - Merc C240 - multi
If it is an automatic you will have a sprag clutch which is part of the torque multiplyer if it slips the car will be sluggish to start with until around 3000rpm but if it seizes the pulling away will be fine but you just loose all power at higher speeds this could be the problem maybe
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Thu 7 Aug 2003 12:33
power loss - Merc C240 - Dynamic Dave
multi,

Puzzled has already given the answer to as what was wrong, in the post above yours. \"The cause was that the air mass sensor was on the way out.\"
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