Backfire and loss of power.

[MGB]

Hi..Can anyone give me a little advice. I have a C200 auto (1999) and changed the plugs last week after 3 years after detecting slight 'pinking'. Had used some injector cleaner and octane boost a week before that. I dis-connected the negative earth to do the plugs. Anyway, on first start up the engine backfired and ran rough but then settled down. Now on first start up from cold it backfires and splutters so I turn it off and start it again and all is fine. It is ok on hot start. Also it reaches 70 mph and then struggles to go faster and also struggles up long hills. Then it will surge and pick up. Runs ok apart from these symptoms. Any ideas. I am thinking fuel starvation or plugs not connected correctly. They are the right plugs. Any help would be really appreciated.

 

[Bolide]

HT leads on wrong plugs (probably not possible), bad connection, bad coil pack or bad HT lead

Or something else entirely. But best to start looking with the last thing changed

Nick Froome
www.w124.co.uk

 

[nickcc101]

Well known workshop manual for the 111/271 engines gives the following advice:- Timing chain incorrectly fitted. Vacuum leak at throttle body, inlet manifold or associated hoses. Blocked injector/fuel injection system fault.
Hope this advice helps.

 

[s and k autos]

try maf sensor any faults codes or engine light on

 

[s and k autos]

take lead off the maf sensor then rev engine if the engine reves ok then put the lead back on maf and then see how the engine reves

 

[MGB]

Hi...thanks for replies. This morning I have re-checked all the fittings with the plugs and air filter and Maf sensor. Started her up and crash,bang, wallop the usual backfire rough idle and coughing. Switched off and restarted and ran sweet as a nut as usual. Took maf sensor off and the engine died (stalled). Put back on and went for short drive with everything fine BUT I know the next cold start will be the same again (coughing and spluttering). Funny how it always does it on a cold start. Does anyone think it could be fuel related. The car is coming up 10 years with old with only 51,000 miles on clock. Everything is kept really clean under bonnet and this only started when I changed the plugs and disconnected the negative earth. Any other thoughts guys. Thanks.

 

[MGB]

UPDATE...Took car to local garage and quick plug-in test diagnosed fault with THROTTLE BODY. Cleared fault and told to drive it for a while but it was still the same and the 'pinking' was worse. Going in to garage on thursday so will give further update after that just for interest.

 

[MGB]

UPDATE...Had maf sensor replaced (part £80) today and on returning home the car seemed alot better. No 'pinking' and had a bit more zip about it. Pushed it up to higher speeds and no stutter or 'limp mode' symptoms. HOWEVER. I noticed on idle that occaisionally the revs jumped up to over 1000 and then dropped down to normal again. This happened a few to times so I will be keeping an eye on this. But for now I am alot happier.

 

[turbopete]

the jump to 1000 rpm is probably to keep the cat free from fuel if its idling for a while or has had the throttle pedal released /been revved up before hand. its a safety feature for the cat. many cars when revved will stop at about 1300rpm till the excess fuel is burnt then drop back to normal idle after a few seconds