Running without a MAF - PeachParts Mercedes-Benz Forum

m1tch · #1 04-24-2015, 01:21 PM

Hi all,

I have just fitted a new MAF sensor to the car, it seemed to drive better, however acted poorly after around 50 miles with poor throttle response and the issue where the car would kick down and rev to 4.5k rpm but then just hold it at that if you press the kickdown button.

What does the MAF in my E300TD look after? I know it sorts out the fueling to make it slightly more efficient - does it also affect the shifting as well?

I now have the 'screaming' happening again from light acceleration, this went away when I unplugged the MAF last time, might try it again. I might also reset the transmission again in case its getting confused.

I have checked the throttle cable (to the throttle sensor) and its spot on, but I find that only at 100% does it kick down and accelerate, from around 0-40% there isn't really anything.

I am going to be changing the fuel filter soon, could this be an issue with the engine eg its being starved of fuel? The tank is also full (or near enough full).

I am tempted to just unplug the MAF again and just junk it if its causing issues with the car. The replacement MAF sensor is German, I did see that it did also have an inlet temperature sensor which the original didn't - does this mean its the wrong sort? I am aware that the sensor is common on VWs and Audis and they are slightly different.

m1tch · #2 04-24-2015, 02:17 PM

Ok, just been back outside and unplugged things in different combos:

MAF plugged in + EGR vac line off = better
Unplugged MAF + EGR on = flat but shifted ok
Unplugged MAF + EGR vac line off = more solid but didn't feel it had much power
Replugged in MAF - car then came alive again, seemed to be much happier and I am guessing the boost level was higher.

I still have the annoying whistle/screaming coming from the car on lower boost, I am guessing a vac leak around the EGR side, I guess its more noticeable at lower revs.

It looks like the MAF being reconnected helped, might just have been a lose connection or something but felt better.

I have sprayed the joins in the intercooler pipeing and there weren't any bubbles forming anywhere, seems to be coming from the passenger side which makes me think around the EGR section where I can't easily get access to.

I have checked the turbo for play and there isn't any at all, its 100% solid and rotates freely.

What else should I check out, I was thinking it might be the boost solenoid valve letting off vacuum but thats over on the drivers side.

jay_bob · #3 04-24-2015, 03:39 PM

The vacuum system on this engine is dead simple (at least the U.S. Version)

1 transducer on the left side for the EGR actuator
1 transducer on the right side for the wastegate actuator

And 1 hose from the intake manifold to the MAP sensor in the left rear corner.

So not a lot to check for vacuum/pressure leaks there.

I would have a look underneath and see if the turbo outlet to intercooler and the intercooler to intake hoses are secure. The under cover is kind of a pain to remove but that lets you see everything.

What OBDII codes are you getting?

m1tch · #4 04-24-2015, 04:57 PM

Quote:

Originally Posted by jay_bob

The vacuum system on this engine is dead simple (at least the U.S. Version)

1 transducer on the left side for the EGR actuator
1 transducer on the right side for the wastegate actuator

And 1 hose from the intake manifold to the MAP sensor in the left rear corner.

So not a lot to check for vacuum/pressure leaks there.

I would have a look underneath and see if the turbo outlet to intercooler and the intercooler to intake hoses are secure. The under cover is kind of a pain to remove but that lets you see everything.

What OBDII codes are you getting?

I have found both of the vacuum solenoids, it might be a leak on the EGR side or a split, the rest of the intercooler pipework is air tight.

I will need to get a large 18 pin adaptor to read the codes - there is a blank space where the OBD2 port would be but being a diesel it doesn't have it - think it was added on the later models. It is one of the main things I want to check anyway, will be taking the inlet manifold off soon so I can check any splits on that side - it did look slightly oily making me think there is a leak that side under boost.