Weird w202 c250td power problem

[beany_bot]

Hi,

I have a really weird problem with my 1997 C250 TD.

Basically some journeys I take it goes fine, as you would expect. Then totally randomly other journeys it will feel down on power (especially up-hills).

I had no idea what was going on. It seems totally random but seems quite random and lasts for that whole journey. like good days and bad days. I often drive 14 miles round trip to work and its just "pot luck" whether im going to get "normal car" or "slow car" that journey.

I've recently found that when its in "slow car" mode, if I rev it, in park or neutral it revs up quite slowly and will only rev to 4.5k it also just seems laboured. Whereas in "normal car" mode it will rev spiritedly up to 5.5 or 6k

Very weird indeed. Another thing i think ive noticed is that when its in "slow mode" the exhaust gets very very hot, even right at the tip. im not sure but i dont think it does this when its driving normally.

Once (and only once) it nearly gave up on me. I was driving up a hill and it slowed way down and was totally down on power, i got to about 20mph and it wouldn't rev up or even kick down. i pulled in at the top of the hill and opened the bonnet and there was radiator fluid seeping out of the resivour lid but the weird thing was the car wasnt over-heating, it was fine, also the coolant pipes were really really hard as if the whole system was over pressurised. well i took the lid off the top, released the pressure and put it back. Got back in the car and stared it, revved it up and away I went in "normal car" mode.

Can anyone please tell me what on earth might be going on with my schizophrenia merc!?

p.s. Just there i was driving and pulled in at a petrol station, the car seemed down on power so i reved it up and sure enough it only went to 4.5k and slowly at that (no matter how many times i tried). I stopped the car, put some diesel in and when i got back from paying I tried again, it revved right up to max no problem and away I went in "normal car" mode. How bizzare is that!?!?

p.p.s the turbo seems fine as I had the exhaust off and you can hear it spinning.

 

[JonathanC250]

have you checked the wastegate actuator on the turbo?

sometimes these get stuck because of the carbon build up in them, try getting in there with some carb cleaner or brake cleaner, then moving the rod, then lubricate it, and do the same.

Hopefully this would fix it, or if not, check all the vacuum pipes, one may be leaking to cause the turbo actuator not to work.

I had this happen to me once, i was going up to northampton to pick my amg wheels up, and on the motor way the car just went lazy, as you said, slow to rev and did not go anywhere, because of the air filter fitted to my car, i can hear if the turbo is working, and it sounded like it was spinning, but it was a different sound. so pulled over, tapped the acutator rod a couple of times as it was very stiff, then it eased up, when i got home, i cleaned it then lubricated it. touch wood been fine since.

Hope this helps

Jonathan

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[kwakdonut]

Do these cars have a 'limp home' mode? It certainly sounds similar as everytime you re-start the car, it is ok for a while.

I wouldn't even like to guess what's causing this, but an over-pressurised cooling system could be a sign of head gasket failure

 

[tim.100]

Do these cars have a 'limp home' mode? It certainly sounds similar as everytime you re-start the car, it is ok for a while.

I wouldn't even like to guess what's causing this, but an over-pressurised cooling system could be a sign of head gasket failure

The engine doesn't have an ECU, just an electronic diesel pump control (EDC). So no intentional limp home mode. The gearbox does have an ECU, but that doesn't sound as likely.

 

[SilverSaloon]

sounds like classic fuel filter blockages to me.

replace the main filter and pre-filter. if you still have problems, try the in-tank strainer.

once you've done that and you still have problems explore other areas...

 

[krimat2005]

why would you rev a diesel up to 6k??? I think it makes no good to the engine, as those engines reach power peak at around 4,4k. and as to the power loss it might be blocked EGR valve, worth checking.

 

[s200rey]

Its impossible to rev a 250TD past 5k lol!?...no wonder its driving like a bag of spanners if ur trying to achieve the un achievable out of the poor old girl! :O lol, all the best with that one!!...

 

[Dieselman]

as to the power loss it might be blocked EGR valve, worth checking.

Other way round, more likely EGR valve stuck open. Another possibility is duff MAP sensor.