Back Firing problem

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headers21

Member
Joined
Mar 1, 2010
Messages
32
Location
Scotland
Car
MB C180 Estate
Please help I changed the spark plugs on my C180 2000 w202 the other day and took i for drive to to make sure everything was ok. The car seemed fine so took it onto local bypass and put the foot down the revs climbed steadily to about 4000 rev and would not go any further it appeared to be backfiring. I tried the kickdown and it just stuck at 4000 revs and would not change gear or go any further. Drove and as long as you dont put the foot down the car drives fine. Brought it and checked over my work and cannot see any probs everything as it should be. I then tried to rev it in park and the same thing happened 4000 revs and it starts to back fire. Changed all the plugs back but the prob is still there.
Has anyone got some ideas on what the prob might be
 
Last edited:
I was hoping someone would give a model specific answer to your question - but not yet!
So back to basics to see if a cure can be found.
Does the backfire you refer to occur in the exhaust, or the inlet?
 
Hi,
The engine reving only to 4,000 in park is normal, the car won,t rev higher than that unless it is in gear, as Olly does sound like a MAF issue, don,t buy the cheap e-bay items, buy Gen MB, or a Bosch one.
 
If the MAF doesn't fix it look at the cat it may be partially blocked.
 
perhaps the car is in limp home mode - you need to have the codes read (by a local Merc specialist) and then deleted.

See what codes come back, if any.
 
Hi guys thanks for the replies :)thought it might be Air mass sensor:crazy: reading my Haynes manual
One other thing I forgot to mention the exhaust blew (back box fell off) and I had to run about for 4 days until I could get a replacment would this block the cats or have impact on the problem how do I clean the cats.
As the car is tiptronic I have tried driving it using the gears and in second i can get it above 4000 revs up to about 5500 third is much the same.

Thanks
 
If you changed plugs you could of crossed 2 wires. Same if you have just changed the dist cap. there can be a crossed wire or you didn't put them back in the same place. Bring the #1 plug up to top dead center on the compression stroke then remove the dist cap & see if the pointer is pointing at the # 1 plug. Check to make sure the wires are in the correct firing order at the cap & trace each wire to the plug that it is suppose to go to. Another reason if you removed the dist from the engine it may not of been put back in in the same place. Worse one is you may have a bent or burnt intake valve. Also look for carbon tracks on inside of cap or a small crack on cap. replace it you see any. You can check the condition of wires/cap at night. Must be dark-start engine & look close at wires & cap.
 
If you changed plugs you could of crossed 2 wires. Same if you have just changed the dist cap. there can be a crossed wire or you didn't put them back in the same place. Bring the #1 plug up to top dead center on the compression stroke then remove the dist cap & see if the pointer is pointing at the # 1 plug. Check to make sure the wires are in the correct firing order at the cap & trace each wire to the plug that it is suppose to go to. Another reason if you removed the dist from the engine it may not of been put back in in the same place. Worse one is you may have a bent or burnt intake valve. Also look for carbon tracks on inside of cap or a small crack on cap. replace it you see any. You can check the condition of wires/cap at night. Must be dark-start engine & look close at wires & cap.
This is an M111 engine and does not have a distributor. The engine will run no matter what leads go on what coil packs. The purists will put the leads on. Cyl 1 to front left, Cyl 2 to rear left, Cyl 3 to rear right and Cyl 4 to front right.
 
Thanks guys yeah its an M111 and I was very carefully to ensure the HT leads went back where they cam efrom wasnt aware that it didnt matter where they went on.
The car is currently going above 4000 revs if drive it using the gears manully but have ordered MAF sensor and will change it at the weekend it there any way to check to see if its faulty
 
Just thought I wuld update this thread manage to change the Air Mass Sensor (bought the Bosch £120) but hey prest car runs like a dream and kickdown working. This might be of interest to someone else with a similar problem
 

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