MAF Blowing Fuse S320 CDI - Wiring

[GoldorSilver]

Hi,

I have a W220 S320 CDI 51 plate and have got the 7.5A fuse blowing that supplies the 12v to the MAF. Have just replaces the wires direct to the ecu the MAF has been changed and it still pops in about 20 seconds of starting the engine. You know when it has gone as the Coolant warning comes on the dash and it goes into limp mode.

The fuse is in the box left hand side of engine at the rear looking at the engine it is the 6th fuse down 7.5A and I have no fuse diagram or wiring diagram available. Can anyone tell me what else uses this fuse so I can check for a short and has anyone else had this problem or a simialr one.

Thanks.

 

[colechelle]

last time i see that was the inport shut of motor u,s, give me a bit of time and i will check the wiring diagrams to confirm!

 

[television]

Hello and welcome,,Is your car a 220 or 221 please

 

[GoldorSilver]

Hello and welcome,,Is your car a 220 or 221 please

W220.

Thanks.

 

[colechelle]

looking at wis that fuse is correct at 7.5, it does cdi control module and intake manifold heater, still seem to remember a inlet port shut of motor last time!

 

[colechelle]

disconnet the manifold heater and see what happens!

 

[GoldorSilver]

looking at wis that fuse is correct at 7.5, it does cdi control module and intake manifold heater, still seem to remember a inlet port shut of motor last time!

I think you could be right with this inlet port as when the fuse had blown it was one of the errors stored.

Just to follow on if you put the fuse back in and disconnect the MAF then restart and it works although in limp as the MAF is disconnected.

Wierd.

 

[colechelle]

as it would if the inport motor has seized!

 

[GoldorSilver]

It has not been used for about 2 months and now I own it I have just started to use it. Had low power and egr valve and low turbo codes and this ended up being a vac pipe off. Put it back on and it was like a different car.

It has a delay from when you press the accererator pedal at idle to when it starts to rev of about 1 second so thought this may be a maf problem but once on the road or above tick over no problems so I thought this was either "as they are" or something that I would sort later. Just on the way back home the "limp mode" came back on and the coolant low error on the dash appeared. This must use the same fuse. It is odd that if I leave the maf unplugged the error stays away, this is why I have tried a different one and the same happens. So this directed me to the maf wiring, probably on the output side as the fuse would only blow if it is connected. Anyway all this is replaced to the ecu with new wires and I thought this had sorted as it was fine for a while, tried to drive home and coolant error back on and limp mode again, along with a blown fuse.

I don't know what to try next but if the details above help the diagnostic you are now up to speed.

Thanks

 

[colechelle]

the maf picks up it voltage from the engine ecu only, it reads live data and the ecu changes the values to suit the loads asked of the engine, hence 02 sensors to monitor un-burn fuel etc! as for the delay in full throttle from a stand still im sorry to say "thats how they are"!

 

[GoldorSilver]

I can now stop wondering about the delay - thanks.

So the fuse is not linked to the maf so I can stop looking there ? Where do I go with this then, the manifold heater or the inport motor or coolant sensor or are there any other things using that fuse ?

Ta.

 

[colechelle]

for get the coolant warning light,that's not on that fuse, any merc from ABOUT "before anyone corrects me" 2000, as soon as the engine ecu loses its feed it puts the coolant fans on, as it cant see the engine temp, and fires up the coolant warning, as i said that fuse is for the ecu so if its blown than it hits default, i still think (from memory) you have a seized inport shut of motor! hoping olly (blackc55) reads this cause he might remember the job iv got stuck in my head because he was working then in the dealer the said car went into!!

 

[television]

The fan in the ECU box is only for the 210 cdi's up to 01-01 have looked

 

[GoldorSilver]

Many thanks.

Will have a look at the inport motor and the manifold heater tomorrow and report back - is there anything else through that fuse I need to check ?

 

[television]

If Cole runs out of time,,I can look at the wiring diagrams in the morning

 

[GoldorSilver]

If Cole runs out of time,,I can look at the wiring diagrams in the morning

Thank you in advance.

 

[colechelle]

The fan in the ECU box is only for the 210 cdi's up to 01-01 have looked

Well known fault malc and catches a lot of our boys out due to not seeing it for so long, i wasnt talking about the ecu fan, the fault im talking about is the fuse blowning which feeds the main engine ecu, witch in turn puts the main cooling fans on!!

 

[television]

Sorry that I was blowing hot air

 

[colechelle]

Sorry that I was blowing hot air

No problem at all young man, wires crossed!

 

[GoldorSilver]

This only blows the fuse when the maf is connected. If I unplug the maf, put in new fuse, start car it will run albeit max 3000rpm. If this was something else is it because the ecu is not getting any info so is in limp mode and is not trying to change any settings i.e. the inport motor so this is why it does not blow ?

As soon as the maf is connected within 20 seconds the fuse blows.

Malc, have you had a look at the wiring diag. please just to see what else runs through the fuse.

Thanks