MAF - Confirm Diagnosis and Recommend Supplier

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stevesey

MB Enthusiast
Joined
Sep 3, 2007
Messages
2,969
Location
Bristol
Car
Alfa 156 1.8TS
Was thinking the car didn't feel right today - dawned on me that on a couple of prompt pull aways the car seemed to pause at 4000rpm just before I lifted off. Don't know when this started as conditions last week were a bit limiting. Tried nailing the throttle and found car was very slow when and didn't kickdown, if you didn't hit the kickdown switch it acellerated better than if you did. Was wondering gearbox limp mode or engine.

So disconnected MAF, car now revs much better, kickdown works as it should. Reconnected MAF, car sluggish again.

So seems a open and shut case.

Going away at the weekend, so could do with a replacement by then. Anyone reccommend any suppliers Bristol/Swindon or by mail order?

Also anyone have the Bosch part number for a 98 C240 Sport?

TIA
 
Though I'd whipped it off and check the resistances

Pin 1 -> Pin 3 0.8K rising as MAF cools
Pin 1 - > Pin 4 5.4K rising as MAF cools
Pin 3 -> Pin 4 4.5K constant

Just need to check what they should be!

Anyone know what voltages I should see at the plug.
 
Resistances are totally meaningless as it's a complete amplifier circuit.

Pin 1 is probably the temperature sensor, if it's used at all.
Pin2 12v
pin3 Gnd
Pin4 5v
pin5 signal. Expect 2v at idle rising to ~4.8v at full revs.
 
Ah I'll pop out and check.
 
Speak to Nick at Euromerc , he's a member on here , Nick_Mercedes .

Pretty certain he'll have one at a good price . ;)
 
Resistances are totally meaningless as it's a complete amplifier circuit.

Pin 1 is probably the temperature sensor, if it's used at all.
Pin2 12v
pin3 Gnd
Pin4 5v
pin5 signal. Expect 2v at idle rising to ~4.8v at full revs.
Next to no output on pin 5 (I did get 0.2V, hope the thin flying leads I had to wedged in the plug were making contact properly).
 
Got the Bosch part number off the sensor while I was there.

ebay check shows these
 
Anyone else having trouble with eurocarparts at present - getting errors searching for parts.​
 
Bought mine from Eurocarparts, cheaper than anywhere else including internet suppliers. Plus I could just go and collect it rather than waiting for delivery etc.
 
Resistances are totally meaningless as it's a complete amplifier circuit.

Pin 1 is probably the temperature sensor, if it's used at all.
Pin2 12v
pin3 Gnd
Pin4 5v
pin5 signal. Expect 2v at idle rising to ~4.8v at full revs.

Are the pins numbered? I assume V check on pin5 would also require earth to pin3?
 
Numbered on the plug (take the protective cover of first) - I measured accross 3 and 5.

what protective cover? Dont recall one???

Ahhh, I assume you go down the back of the plug with a couple of probes
 
I was thinking of using Batt ground, but didnt know if a circuit had to be completed on the actual MAF itself

Will check mine tomorrow

sorry for hijacking the thread
 
It's best to use body ground in case the lead is faulty.

I'd be very suspicious of a reading of virtually nothing on pin5.
I may re-check in the morning against the body.

I was pondering dodgy wiring, but as the car behaves differently with the MAF disconnected it must be getting some signal on pin 5 (either that or pin 1 is used as a validity check as well).
 

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