Engine backfire. Please help!

c200_impressor

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W202 C200 1998
Hi. I need some advice...

My C200 1998 W202 (manual) is backfiring intermittently and 'hesitates' under acceleration... especially when accelerating in 3rd gear.

I've put in new spark plugs, new air filter, new ignition leads and new ignition coils but the problem remains.

I've no idea what else could be causing the problem?!

Engine ECU maybe?

Any ideas anyone???
 

Stratman

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Welcome to the forums, sorry it's under such circumstances.

The crankshaft position sensor sound a likely culprit.
 

grober

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Sounds like the mixture is off. So could be the MAFF or maybe the Lambda sensor/s
 
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c200_impressor

c200_impressor

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Thanks for the replies guys.

Will an ECU test tell me if it's the maff/lambda/crankshaft sensors?

Or will I just have to replace them all??
 

BlackC55

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I would say the MAF is at fault. Get the live data and fault codes checked first.
 

BlackC55

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Thanks. How do I go about checking the live data & fault codes?
With a diagnosstic machine. Your local specialist or dealer has such equipment.
 

Dieselman

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You can check the MAF with a voltmeter attached to Pin-5 and Gnd. Expect ~2v at idle rising to ~4.8 at full revs.

The fault does sound like the MAF may be causing a weak mixture so spitting back.
 

horgantrevor

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hi i would also say maf

open bonnet and unplug the maf its located on the pipe from the air box to engine

if you keep driving with a backfire this means your dumping unburned fuel into exhaust and you will reck your cat
 
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c200_impressor

c200_impressor

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Swansea, Wales
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W202 C200 1998
Mega thanks to everyone for the help. Much appreciated!!!!

Looks like it's definately the MAF because when I unplug it the engine runs perfectly and is back to full power. Only problem is it causes the cooling fan to be on permenantly even when cold which is a bit odd. Will source a new MAF asap.

Cheers again people!
 

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