E220 CDI rpm limit at 3,000...

[IanT]

Help please!

On my way down (even further) South this morning, I became aware that my engine had very little power and pulled in to investigate.

No apparent loss of oil or coolant or anything like that.

It appears that there's a 3k rpm limit in force and even in neutral the engine won't go over that. No engine warning light, although I ought to check that it works. I'd have thought that something would have been displayed on the IC display though.

As a consequence (perhaps?) the gearbox changes up early all the time and the kickdown doesn't function at all.

Turbo works as I can hear it briefly when I blip the throttle in neutral.

Is there any easy way of diagnosing this without taking it to the stealers?

The car is a 2001 W210 with the 611.961 engine and 722.699. 170k miles and a new gearbox was fitted under warranty last February.

Any ideas anyone?

Thanks, Ian.

 

[RichardM]

Mine has done that a few times, it's gone into the limp home mode. Sometime's I have had a warning light come on when it happened, other times not.

Have you tried stopping the car and leaving it for an hour? That may well reset it.

 

[Thmsshaun]

Is it something to do with a feature or something with them?

Only reason I ask is on My 202 if you rev in neutral it limits at a bout 3500-4000.

Why?

Sorry it doesnt help you with your query but could be sensor thinking it isnt in gear. Only a random stab in the dark mind

 

[minyak]

Hi there,

I had an identical problem like yours before, but not so sure whether the cause is the same. Mine is a C220 CDi (W203, just under 100k miles) and at start up it's ok. After 5 minutes say on the motorway and then back on normal roads, the engine will not rev beyond 3000rpm exactly. Everything else seem normal, but at the garage the diagnosis was that the turbo pipe was split, so air was not being rammed (or turboed) into the engine, hence loss of power. So they replace the pipe and now all is well again. Btw, the ECU will not tell you this fault but only a visit to the garage will do! The pipe cost about 20-30 quid, plus 1 hour of labour charge to get it done.

Hope this helps!

 

[IanT]

Thanks, that's very interesting.

I was starting to suspect the air mass meter as it has always run a little smoky, but will investigate the turbo pipework.

I don't see why this would limit the revs though, it definately ought to be able to rev freely even without a functional turbo.

Ian.

 

[RichardM]

Thanks, that's very interesting.

I was starting to suspect the air mass meter as it has always run a little smoky, but will investigate the turbo pipework.

I don't see why this would limit the revs though, it definately ought to be able to rev freely even without a functional turbo.

Ian.

Not if the engine management has detected the fault, it will limit the revs.

 

[Stratman]

Not if the engine management has detected the fault, it will limit the revs.

Then surely the ECU would register this?

 

[Dieselman]

It will but it will only bring the light on if a critical failure is noted.

the car has gone into Limp Home mode.

Check ALL the pressure pipes and the EGR valve function. You should be able to see if the turbo has been released as the wastegate will loose. Also check the wastegate vacuum actuator.

If you really need to check the turbo pressure a simple pressure guage Td into the small bore piping will work.

You can obtain a guide reading from the MAF with a DMM.

 

[GordonTarling]

Most likely cause is the MAF - easy enough to get checked at your dealer.

 

[Dieselman]

Most likely cause is the MAF - easy enough to get checked at your dealer.

Cheaper to buy a new MAF. £44 or so.

 

[IanT]

Sorry, this looks like I'm not interested, I've been away for a few days and dumped the poor car in my garage until I had a better chance to look at it.

Had a quick look around on Sunday, removed the air filter box and the AFM, air ducts etc to the turbo. I didn't have long to do a proper inspection and didn't want to take too much of it to bits without a firm idea of what I am looking for.

But, I have driven it some more. I used it yesterday to travel to Colchester and back, which gained me the knowledge that it isn't always in limp mode. Sometimes it is back to its old self, grunty and willing, other times it changes up and behaves as though I've only just got my foot on the throttle. It also switches in and out of limp mode with no indication on the ICD or any warning lights whatsoever, which puzzles me. It clearly isn't running within its normal design parameters so why not throw up an error telling me to get my wallet out?

I've found nothing wrong with anything so far, I can turn the turbo by hand and it's reasonably free (not totally free, nor stuck). I doubt that the turbo is at fault unless the ECU measures the boost pressure and backs off the throttle if it's not there.

MAF sounds like a reasonable proposition. Do you have the pinout and an idea of what to expect on each pin while the engine is running?

Such a shame I can't get a Tech2 card for the Merc...

Thanks, Ian.

 

[fwb44]

£44 for a MAF sensor?? I paid £190 (to my local independent @ £30/hour at that) for one on our E300 TD a month ago ...

Doesn't disconnecting the battery for a couple of hours have the effect of resetting the ECU?

 

[silverarrow]

maf seems to be a option why not get yours recon see www.bba-reman.co.uk

 

[IanT]

maf seems to be a option why not get yours recon see www.bba-reman.co.uk

Hmmm... my browser tells me I'm not authorised to view that page.

If a new sensor is only £44 I doubt anybody can make any money reconditioning them.

I did take a look at mine, I couldn't say it looked bone dry, possibly has a film of light oil on it - cleaner of some sort?

Are they supposed to be completely dry? Inside the pipework is nice and clean. I could give it a squirt with carb cleaner, or even brake cleaner if they are supposed to be dry.

Disconnecting the battery on a modern car shouldn't lose the codes, usually they are stored in flash EEPROMs and so don't lose their memory when the power fails.

Ian.

 

[Dieselman]

Ian

I think it's the MAF. Pin 5 is the 5v output.

Expect 2v at idle and 4.5V at 5000 Rpm.

 

[IanT]

Great, I'll give that a look tomorrow.

Cheers, Ian.

 

[IanT]

Excellent!

That looks like it might be solved then.

I went outside first thing this morning with my multimeter and a few strands of copper wire. Readings were about 2.5V at idle (1V engine not running) and about 3V at full RPM in Neutral. That would presumably have been more if the engine was under load due to the turbo?

Anyway, seeing as those figures weren't what they were suggested to be, I went down to my local dealer and bought a new MAF, p/n 611 094 00 48. The bill was £61.76 inc VAT and it was fitted in 5 minutes.

Voltages afterwards were approx 1.5V at idle and about 3.8V at full RPM.

I don't want to tempt fate, but I've driven some 15 miles now without any lapses and it feels better. Previously it would have been into and out of limp mode twice over those journeys. Indicated MPG looks better on the ICD too.

Thanks to Dieselman for the info.

Ian.

 

[Dieselman]

Nice one Ian.

Probably the MAF reading being high at idle was telling the ECU that the EGR valve wasn't working, though it probably was, throwing the ECU into limp home after a few minutes driving.

As you noted the turbo will force more air so give a higher reading.

You can do this test whilst driving but make sure you have a passenger as trying to read a multimeter at 120mph isn't ideal.

Regards