Pinking + poor idle

[mjtray]

Hi,

Help needed. I have an E280 W124 1993 with lowish miles, ie 84000 miles.

I have an ongoing and persistent problem. At a standstill, with the car in drive, the idle will start to hunt, this is especially noticeable when the air-con is on. At a guess I would say that there is an air leak somewhere in the injection system

The car is also pinking like crazy even on a very light throttle. When I took the car for service the last time they cleaned the throttle body and things were much better, but now its getting bad again.

I also discussed this with my local Merc dealer and they mentioned that some E's with the M104 engine had defective throttle bodies fitted to them and that I may need a new replacement.....big £££££'s.

Can anybody confirm this or have they got any ideas's how to diagnose the problem.....would this problem throw up a code in the engine management system for example?

The car is going in for a major service tomorrow, so it would be good if I could try and talk with some knowledge etc etc.

All help appreciated.

 

[p902]

Can you please clarify what 'hunt' and 'pinking' mean? For us non-technical folk.

 

[andy_k]

"hunt" is normally where the revs rise and fall at tickover when the engine should be smooth, it seems like it's hunting for fuel, air etc. In my experience it's caused by too much/too little air getting into the system, a lead/plug that's breaking down or ignition timing is out and can be a pain to rectify as very often it's a case of eliminating the likely suspects one by one.

Pinking is that horrible rattling sound from the engine when the timing is out when the timing is too far advanced.

as for a solution, try running on a higher octane fuel and see if that resolves or eases things. check your distributor cap and rotor arm and all the air/vacuum pipes.

Sorry I can't be more help.

Andy

 

[talbir]

Great advice from Andy.

I had the same problem of hunting at idle once on my 300SE - first thing I did was check the plugs and all 6 of them were oiled up.

Bad valve seals obviosuly and some harsh driving raised oil into the plugs.

Changed the plugs and problem solved.

Changed the valve seals as well of course a little later.


Talbit

 

[mjtray]

I've tried the higher Octane route.....Shell Optimax, but its still pinking like crazy.

It'll be interesting to see if they cure it when it goes in for service tomorrow.

Any other thoughts anyone?

Cheers

 

[Spike]

I disagree with the bit about about the fuel octane rating.

Pinking may originate from glowing combustion chamber deposits, hot spots in the combustion chamber due to poor control of engine heat, cross-firing (electrical induction between spark plug wires), overly advanced timing or the plug heat range is too high for the engine or its operating conditions. Basically something is pre-igniting your mixture. Perhaps you could check your timing, try cooler rated plugs and maybe some redex to clean up the combustion chamber.

Higher octane fuel would only cure detonation (retarded ignition) often caused by a faulty ECU, too lean mixture (has the MOT man leaned it right off as they often do) and/or overly retarded ignition timing.

[EDIT} The more I read about this, the less I am sure....about 50% of sites say that the higher the octane, the slower the burn and about 50% of sites say the opposite.

To me it seems illogical that higher octane fuel burns slower than low octane fuel but there are some seriously technical people producing white papers by companies that should know what they are talking about but strangely there seems to be two schools of thought on the matter. Perhaps I will ask someone whe *really* knows to contribute to this thread.

 

[mjtray]

Update;

Just got the car back from a 84,000 mile service, new plugs, air filter, coolant change etc etc. Garage changed the plugs for a set that run cooler the pinking is still there, although not as bad. Garage have said to run the car for a couple of days and see if it calms down.

They also changed the charcoal filter located in the nearside front wheel arch as this was clogged up.

So question, any other thoughts on how to get rid of this pinking before it damages the engine.


Cheers

 

[Spike]

Does your model have the Advance\Retard switch up near the bulkead on the nearside? My model has a switch which is marked 'S' for use with 98RON or over and 'N' for below that. N will retard the ignition timing and turn your car into a snail but if it doesnt cure the pinking noise, it may not be pinking at all.

I had a similar noise with the engine under load up to about 1500 RPM. It was a horrible noise...almost like an exhaust shield rattling or something - turned out it was the alternator bearing.

Another thing....have you tried the Redex treatment yet?

 

[mjtray]

Spike,

Not sure whether I have that switch or not, I'll have to have a look.

In terms of the alternator, I had that replaced a couple of months ago, as a bearing was on its way out....so its not that unfortunatley.

Secondly, I put some injector cleaner in a couple of weeks ago......could it be this that has caused the pinking????

Am I right in thinking that Redex will clear out carbon deposits....if so can it be used on a Catalised car?

Cheers

 

[Badshot1uk]

hi mjtray

My old 230te was running rough (hunting etc ) this time last year and i changed the rotor arm and dis cap, plugs etc but to no avail.

i tried different plugs - bosch four point plus i think their called.
They compleatly sorted out the problem!

Even now 6000 later it still runs nice and smooth.

Dont know if its worth trying them or not, but i hope you sort your problems out.

Paul

 

[dieselman]

This does sound like an air leak. To test for an air leak try spraying WD40 or Plus Gas around all joint and gaskets in the induction system. You will hear the engine note change when the air leak is found.


Spike.

The higher the octane rating of petrol the slower the burn, hence the more advanced the ignition setting can be. The engine then produces more power because the burn, thus the pressure rise, takes place over a longer time exerting pressure onto the piston and crank for a longer duration.