C220 CDI - Loss of Low End Power

colonel

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Okay, here goes....was out driving yesterday and the car went into limp home mode with revs not exceeding 3000rpm. I drove the car to my mate's garage where he connected it to a launch machine and no codes were present on the ECU.

Restarted the car and was able to rev up to 3750 revs whilst stationary which i think is the safety limit whilst stood still.

My mate suggested that the ECU could have picked up an unbalanced pulse and kicked in to limp home mode.

Drove the car home with no problems...was able to hit 4k revs no problems and was able to get good speeds but the car was very unresponsive at low speeds.

In other words, you put your foot down and it takes a good few seconds to respond etc.

At first, I thought MAS sensors but surely, the ECU would kick into safe mode again ? This has not happened as I am able to get it up to speed...eventually !

I did fill up at tesco two days ago and the tank had about a quarter of a tank...could this be low quality fuel ? I always fill up at tesco with no previous problems etc....

Please help ;)

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rf065

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The same thing happened to mine, went into limp mode once with no fault codes & after a restart was working fine, except, the auto box began changeing down a gear every time the accelerator was pressed, but there was a second or two delay before it even did that and then began to accelerate.

Only thing I could find was the gearbox oil level was low, MB had renewed the gearbox oil & filter a few weeks before. Took it back & the oil was topped up & it has been fine ever since. Worth a check of auto box oil level anyway?

Russ
 
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colonel

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The box is 6 speed manual.

MB, I will get the car hooked up to the Bosch....would a problem with the MAF filter generate a fault code on the ECU ? I ask because when the car when into limp mode, we connected it to a launch handheld and no codes were present ?
 

MB TECH WARRINGTON

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The box is 6 speed manual.

MB, I will get the car hooked up to the Bosch....would a problem with the MAF filter generate a fault code on the ECU ? I ask because when the car when into limp mode, we connected it to a launch handheld and no codes were present ?

NO, not always, you need to get someone who can analyse the live data.

Or try an airmass, make sure its genuine though
 

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On most cars it can be unplugged,,the idle may be lousy or poor but the top end power could be OK,,that would prove the point
 
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colonel

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Okay, I have connected the car to a Bosch laptop....and whilst I am getting a few different codes...the main one affecting the cars performance is P1470 Boost Pressure Control.

In order to troubleshoot, I cleared the codes and disconnected the MAF sensor. Hence, the MAF fault code came up which indicates the MAF is working correctly.

I cleaned the contacts to the Boost Pressure Control and the same lack of power occured. The car no longer goes into limp mode...instead, there is a constant lack of low end power.

My indie says it needs a new Boost Pressure Control unit...but I am not convinced...

What is the next step ?
 

Alex Crow

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i have read your posts and it does not seem clear to me how you know the maf sensor is definately ok.

if it were, the next step would be checking out all the intake system, especially the hoses and INTERCOOLER! then check for blocked exhaust. then the wastegate vacuum modulator on the o/s inner wing and egr system - depending on the model you have.

what model do you have exactly? first six numbers of the vin would be good.
 
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colonel

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I disconnected the MAF sensor and drove it....the car went straight into limp home mode.

I then connected it back up again and cleared the error code and drove it again and I was able to go above 3000 revs but still have low end power...

Would that not rule out any problems with the MAF ?
 
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colonel

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The model is a W203 C220 CDI 2001 (Y)
 

Cole@MBS

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Sounds like a leak on the vacuum side of the transducer to me, seeing a lot of these the last few weeks!!
 
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colonel

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Is this expensive !

This thread (http://forums.mercedesclub.org.uk/showthread.php?t=27230) sounds exactly like my symptoms...however, I can drive it no problems...all it means is I experience a 5 second lag to get to 2k revs...the turbo then kicks in and no probs.....the car drives better through the gears when warm.

I am tempted to change the MAF but want some assurance that disconnection of the MAF sensor would put the car into limp home mode and that the P1470 code would be present ? Surely, the MAF error code would be present ?

I cleaned the connection on the Boost Pressure Control unit. I even ran the engine with the BPC unit disconnected but no change....which would point to the unit being the problem ?

What do you think ?
 

television

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The MAF will not put a fault code up,,its a matter of reading between the lines when you put it on to a test set,,the MAF can shift the O2 sensor from its stored settings,,and normally when you see this you say OK the MAF

Cars behave differently with it disconnected,,it is a cheap way to try
 

Cole@MBS

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We have been here before Malc, a faulty maf CAN throw up a fault code as i have proved before with the print out!

The only way to check is using actual values on star!!
 
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colonel

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By disconnecting the MAF, I can get it to through up a MAF error code.

I guess what you are saying Malc is that a faulty MAF may not throw up a code as being faulty if the sensor gets imbalanced air intake values as the error would show up at the next sensor in the intake system.

I understand the theory however surely, the P1470 fault code would not show as a result of air imbalances.

How can I narrow this down to purely the replacement of the MAF ?
 

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By disconnecting the MAF, I can get it to through up a MAF error code.

I guess what you are saying Malc is that a faulty MAF may not throw up a code as being faulty if the sensor gets imbalanced air intake values as the error would show up at the next sensor in the intake system.

I understand the theory however surely, the P1470 fault code would not show as a result of air imbalances.

How can I narrow this down to purely the replacement of the MAF ?

The MAF can be tested scientifically by reading the voltages on the sensor pin,,but a break out box is needed to get to it .

What often happens is the MAF gives the wrong info and the upstream O2 sensor alter the fueling to compensate, and this is why it seldom shows up
 
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colonel

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Okay, so assuming that the MAF is the issue, do you think replace of the MAF sensor will suffice or should I go with replacement of the whole MAF ?

Or should I attempt the MAF clean to see if it improves power temporarily ? At least then if the power returns for a short period, I will be more confident that the MAF is the issue !
 

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Okay, so assuming that the MAF is the issue, do you think replace of the MAF sensor will suffice or should I go with replacement of the whole MAF ?

Or should I attempt the MAF clean to see if it improves power temporarily ? At least then if the power returns for a short period, I will be more confident that the MAF is the issue !

I am one of those that does not have much faith in the cleaning on them,,though saying this it does work better on diesels than on petrols
 
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colonel

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Okay, I will attempt a clean tomorrow...hopefully that will produce some sort of low end performance gain.

Is this an easy job...also, I know on here somewhere I have seen someone post how to do a clean....do you know what member produced that post ? It shows photo by photo... ?
 

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Okay, I will attempt a clean tomorrow...hopefully that will produce some sort of low end performance gain.

Is this an easy job...also, I know on here somewhere I have seen someone post how to do a clean....do you know what member produced that post ? It shows photo by photo... ?

It is in the DIY section by Parrot of Doom
 

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