R170 MAF issues

[Martin968]

Hi all

Having a strange issue with the mrs SLK320 facelift

I have serviced the car and replaced just about everything I could to make it safe and reliable but have managed to break it

The car is a 2001 SLK320 auto with 71k on the clock, full mb and indie history

I changed all the engine parts filters, oil, plugs and so on, including new belts, the gearbox was a bit jerky so that had a new filter and fluid and the plastic plug replaced

The car has been fine but developed the holding back at 4000 rpm problem, but that would clear if you kept you foot buried

This got worse and worse, tried cleaning the MAF no joy so I bought a cheapo one

This fixed the problem, it drove like a new car, this did not last long, ten days later and the car started almost stalling on take off, real hesitation, checked the codes P0100 circuit A fault

So I got another replacement MAF and that has been fine for 2 weeks, now it’s exactly the same again, hesitating and not pulling away cleanly

And I have the P0100 code back again

I am struggling to work out what I have broken

Any ideas accepted

 

[Martin968]

Hi

I refitted the original MAF yesterday, and the P0100 fault has gone and i now have no error codes, but now its misfiring like crazy and the 3000-4000 flat spot /rev limiter is back,

I will order another cheap MAF as i really dont want to blow up a BOSCH one

 

[ashenfie]

A cheap MAF is generally a no no.

The system works by measure the O2 in the exhaust system and with the MAF data to calc's the correct amount of petrol to inject.

The issue is that if you have a misfire you dump a load of petrol in the exhaust and courses miss reading as no spark = loads on petrol and un burnt o2. That could cause all sorts of errors.

Check the wiring for shorts or breaks. Make sure the MAF sensor is not oiled up and there are no air leaks. The looks at the O2 sensor make sure the wires are good and it's producing error codes. Plus check the plug leads etc as they may be bad or broken.

It's rather complex to check the O2 sensor for correct tracking and might need to be done at a good indie.

 

[Martin968]

Thanks for the explanation, I will grab a cheap second hand genuine one off the bay of fleas and see if that fixes it, if it does then I will bite the bullet and get a Bosch one, I am still struggling to work out how I broke it in the first place

for obvious reasons I don't want to splash out on a new Bosch one to have it go pop in about 2 weeks.

this car is the wifes toy for sunny days, bit of a other end of the shelf to her day to day car, and what makes it worse is she absolutely loves the thing.

I have AA Merctech near me would they be a good choice for an indie

 

[grober]

It sounds as if your MAF may be getting contaminated by oil vapour from the crankcase breathers? If that is the case then any new MAF will work for a short time before becoming contaminated. You could block off the pipework inlet for the breathers to the inlet manifold and allow them to vent temporarily to a suitable catch tank to see if that improves matters?

 

[Martin968]

that is not a bad idea, although i have not seen any oil at all in the airbox or anywhere before the MAF only after it

 

[Martin968]

Hi
Thanks for the suggestions and the second hand genuine MAF seems to have fixed it for now

I will run the car out while the weather is fantastic

Let you know how I get on later