Car issues, some advise please. Car needed daily (keyworker)

JLT

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Firstly, please let me apologise for my 1st post being a plea for help, but I'm a key worker and need my car daily, but I'm having issues that I need to resolve.

Car is a 2008 W204 C220 CDI with the 646 engine, 5 speed auto, no DPF.

Started about 5 days or so ago. Idle on start was poor, (bouncing around the idle point), almost like rough running, but add revs though, and it feels fine. The throttle response is worse, economy down by about 5-6mpg, but strangely feels faster under acceleration. It is slowly getting worse on start idle and the throttle response is becoming more tempremental.

I've used the great wealth of knowledge here to check for the obvious; no vacuum leaks, no fuel leaks, injectors seem fine - no chuffing or Black Death, air filter is only a month old and still nice and clean. I've plugged in my diagnostic tool, no DTC, but on live data I noticed the MAF is showing airflow that seems quite a bit out of spec (according to google) and the manifold pressure a little high - See pictures and graphs below.

I don't know the CDI engine that well; does 15g/s at idle at 90g/s 2500rpm sound like a faulty MAF and is it as simple as replacing it, or is there other reasons the MAF and MAP can over read?

idle.png load.png graph.png

Any help, advise or thoughts gratefully received, I need to use the car most days and most garages are not open, so hoping to get this resolved.

James
 

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Wearsafoxhat

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Hi,

Does unplugging the MAF, electrical connector, change anything ? That may determine if it is the fault or not.

Difficult time to find faults and parts too.
Worth mentioning your location, town as someone on here may be able to help. All a good bunch.
Hope you manage to get it sorted.


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JLT

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Thanks for the reply, I will unplug tomorrow and see if it drives better without it. I'm sure its just a simple fix, but hate driving the car when it isn't right.

Location, Bradford on Avon, Wilts.
 

LostKiwi

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MAP pressure will be absolute so will be 14.7psi with the engine off making your actual boost about 12psi which I would say is on the low side.
MAF on the other hand is very high so it suggests a boost leak to me.
MAF high means seeing a lot of air in, MAP low saying its not getting to the map sensor = Boost leak.
 
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JLT

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Thank you LostKiwi, that's exactly the sort of info I need as I'm just not knowledgable enough on these things. Will take a look at it tomorrow and see if there is anything obvious.

Does anyone know the most likely culprit area for a boost leak on the CDI engines?
 

ajlsl600

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intercooler hoses. inlet manifold seals/gasket
 

LostKiwi

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Also intercooler - they can get corrosion if dirt gets trapped and eventually rot through.
Most often it's a hose between intercooler and engine. They can split and be very hard to find the split unless you remove the hose.
 

Flyinspanner

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You could try using a paintbrush, & really soapy water and see if you can find a leak. (Bubbles up)
 

umblecumbuz

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When you unplug your Maf for testing, don't be surprised if the engine management light comes on - it will still drive ok.
 

malcolm E53 AMG

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Rough idle can be a symptom of worn injector tips had this on my OM613 engine so if all other checks don’t show anything untoward lift the injectors and do a spray test. Ironically I’m clearing out the garage and came across the old injector tips yesterday and you can visually see the wear on those.

ps. the only symptom with the worn injectors was a rough idle as soon as you increased revs the car ran as normal. It might be a good idea to seek out a local diesel specialist which is what I did at the time
 
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JLT

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An update: Got up early to remove the intercooler pipes. Although the hot side is a little softer, no splits or leaks and on logging the car drive to work this morning, I'm getting 35 absolute psi on WOT, so around 20psi boost, so pretty sure it isn't a boost leak. Logs attached.

I tried driving the car with the MAF unplugged, but there was no throttle response at all, the car simply would not rev above idle? Is this normal?

So, plugged the MAF back in and on my drive seeing figures of up too 161g/s (still 15g/s at idle) and the car economy has got even worse and smells like its heavily over-fueling.

I think I'm either need to just put it into an open garage if I can find one (any recommendations for Merc specialists in the Wilts area) or just order a MAF to rule it out.

Again any advise more than welcomed and thank you for your responses and help so far.

1585822880740.png 1585822899818.png 1585822904545.png IMG_1822.JPG
 
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JLT

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Rough idle can be a symptom of worn injector tips had this on my OM613 engine so if all other checks don’t show anything untoward lift the injectors and do a spray test. Ironically I’m clearing out the garage and came across the old injector tips yesterday and you can visually see the wear on those.

ps. the only symptom with the worn injectors was a rough idle as soon as you increased revs the car ran as normal. It might be a good idea to seek out a local diesel specialist which is what I did at the time

Thanks Malcolm, I agree, time for a specialist I think, whether its fuel or air, something isn't quite right.
 

Wighty

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Steve at Avantgarde Mercedes , Clevedon near Bristol is a top Indy
 

Wighty

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Car booked into Avantgarde on Monday - will update when I know more.
You are in good hands buddy , tell Steve the forum says Hi :D
 
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